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+Project Gutenberg's The Alphabet of Economic Science, by Philip H. Wicksteed
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever. You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: The Alphabet of Economic Science
+ Elements of the Theory of Value or Worth
+
+Author: Philip H. Wicksteed
+
+Release Date: May 30, 2010 [EBook #32497]
+Most recently updated: June 11, 2021
+
+Language: English
+
+Character set encoding: UTF-8
+
+*** START OF THIS PROJECT GUTENBERG EBOOK THE ALPHABET OF ECONOMIC SCIENCE ***
+
+
+
+
+Produced by Andrew D. Hwang, Frank van Drogen, and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+(This file was produced from scans of public domain works
+at McMaster University's Archive for the History of Economic
+Thought.)
+
+
+
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+% Project Gutenberg's The Alphabet of Economic Science, by Philip H. Wicksteed
+% %
+% This eBook is for the use of anyone anywhere at no cost and with %
+% almost no restrictions whatsoever. You may copy it, give it away or %
+% re-use it under the terms of the Project Gutenberg License included %
+% with this eBook or online at www.gutenberg.org %
+% %
+% %
+% Title: The Alphabet of Economic Science %
+% Elements of the Theory of Value or Worth %
+% %
+% Author: Philip H. Wicksteed %
+% %
+% Release Date: May 30, 2010 [EBook #32497] %
+% Most recently updated: June 11, 2021 %
+% %
+% Language: English %
+% %
+% Character set encoding: UTF-8 %
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+\small
+\begin{PGtext}
+Project Gutenberg's The Alphabet of Economic Science, by Philip H. Wicksteed
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever. You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: The Alphabet of Economic Science
+ Elements of the Theory of Value or Worth
+
+Author: Philip H. Wicksteed
+
+Release Date: May 30, 2010 [EBook #32497]
+Most recently updated: June 11, 2021
+
+Language: English
+
+Character set encoding: UTF-8
+
+*** START OF THIS PROJECT GUTENBERG EBOOK THE ALPHABET OF ECONOMIC SCIENCE ***
+\end{PGtext}
+\end{minipage}
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+
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+
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+\begin{PGtext}
+Produced by Andrew D. Hwang, Frank van Drogen, and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+(This file was produced from scans of public domain works
+at McMaster University's Archive for the History of Economic
+Thought.)
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+% [Blank Page]
+%% -----File: 002.png---Folio v-------
+
+\begin{center}
+\setlength{\TmpLen}{0.2in}%
+\Large THE ALPHABET \\[3\TmpLen]
+\footnotesize OF \\[3\TmpLen]
+\Huge ECONOMIC SCIENCE \\[4\TmpLen]
+\footnotesize BY \\[\TmpLen]
+\normalsize PHILIP H. WICKSTEED \\[5\TmpLen]
+\footnotesize ELEMENTS OF THE THEORY OF VALUE OR WORTH
+\end{center}
+\vfil
+\newpage
+%% -----File: 003.png---Folio vi-------
+\iffalse
+%[** TN: No longer present in page scan]
+London: Macmillan \& Company Ltd., 1888
+\fi
+%% -----File: 004.png---Folio vii-------
+\null
+\vfil
+\selectlanguage{latin}%
+``Est ergo sciendum, quod quædam sunt, quæ nostræ potestati
+minime subjacentia, speculari tantummodo possumus, operari
+autem non, velut Mathematica, Physica, et~Divina. Quædam vero
+sunt quæ nostræ potestati subjacentia, non solum speculari, sed et
+operari possumus; et~in iis non operatio propter speculationem, sed
+hæc propter illam adsumitur, quoniam in talibus operatio est finis.
+Cum ergo materia præsens politica sit, imo fons atque principium
+rectarum politiarum; et~omne politicum nostræ potestati subjaceat;
+manifestum est, quod materia præsens non ad speculationem
+per prius, sed ad operationem ordinatur. Rursus, cum in
+operabilibus principium et causa omnium sit ultimus Finis (movet
+enim primo agentem), consequens est, ut omnis ratio eorum quæ
+sunt ad Finem, ab ipso Fine sumatur: nam alia erit ratio incidendi
+lignum propter domum construendam, et alia propter navim. Illud
+igitur, si quid est, quod sit Finis ultimus Civilitatis humani Generis,
+erit hoc principium, per quod omnia quæ inferius probanda sunt,
+erunt manifesta sufficienter.''---\textsc{Dante.}
+\vfil\vfil
+\newpage
+%% -----File: 005.png---Folio viii-------
+
+\null
+\vfil
+\selectlanguage{english}
+Be it known, then, that there are certain things, in no degree
+subject to our power, which we can make the objects of speculation,
+but not of action. Such are mathematics, physics and theology.
+But there are some which are subject to our power, and to which
+we can direct not only our speculations but our actions. And in
+the case of these, action does not exist for the sake of speculation,
+but we speculate with a view to action; for in such matters action
+is the goal. Since the material of the present treatise, then, is
+political, nay, is the very fount and starting-point of right polities,
+and since all that is political is subject to our power, it is obvious
+that this treatise ultimately concerns conduct rather than speculation.
+Again, since in all things that can be done the final goal is
+the general determining principle and cause (for this it is that first
+stimulates the agent), it follows that the whole rationale of the
+actions directed to the goal depends upon that goal itself. For the
+method of cutting wood to build a house is one, to build a ship
+another. Therefore that thing (and surely there is such a thing)
+which is the final goal of human society will be the principle by
+reference to which all that shall be set forth below must be made
+clear.
+\vfil\vfil
+\newpage
+%% -----File: 006.png---Folio ix-------
+
+
+\Chapter{Preface}
+\pagestyle{fancy}
+
+\First{Dear Reader}---I venture to discard the more stately
+forms of preface which alone are considered suitable for
+a serious work, and to address a few words of direct
+appeal to you.
+
+An enthusiastic but candid friend, to whom I showed
+these pages in proof, dwelt in glowing terms on the
+pleasure and profit that my reader would derive from
+them, ``if only he survived the first cold plunge into
+`functions.'\,'' Another equally candid friend to whom
+I reported the remark exclaimed, ``\emph{Survive} it indeed!
+Why, what on earth is to induce him to \emph{take} it?''
+
+Much counsel was offered me as to the best method
+of inducing him to take this ``cold plunge,'' the substance
+of which counsel may be found at the beginning
+of the poems of Lucretius and Tasso, who have given
+such exquisite expression to the theory of ``sugaring
+the pill'' which their works illustrate. But I am no
+Lucretius, and have no power, even had I the desire
+to disguise the fact that a firm grasp of the elementary
+truths of Political Economy cannot be got without the
+same kind of severe and sustained mental application
+which is necessary in all other serious studies.
+
+At the same time I am aware that forty pages of
+almost unbroken mathematics may seem to many readers
+a most unnecessary introduction to Economics, and it
+is impossible that the beginner should see their bearing
+upon the subject until he has mastered and applied
+%% -----File: 007.png---Folio x-------
+them. Some impatience, therefore, may naturally be
+expected. To remove this impatience, I can but express
+my own profound conviction that the beginner who has
+mastered this mathematical introduction will have solved,
+before he knows that he has even met them, some of the
+most crucial problems of Political Economy on which
+the foremost Economists have disputed unavailingly
+for generations for lack of applying the mathematical
+method. A glance at the ``\hyperref[indexpage]{Index of Illustrations}'' will
+show that my object is to bring Economics down from
+the clouds and make the study throw light on our
+daily doings and experiences, as well as on the great
+commercial and industrial machinery of the world.
+But in order to get this light some mathematical knowledge
+is needed, which it would be difficult to pick out
+of the standard treatises as it is wanted. This knowledge
+I have tried to collect and render accessible to
+those who dropped their mathematics when they left
+school, but are still willing to take the trouble to master
+a plain statement, even if it involves the use of mathematical
+symbols.
+
+The portions of the book printed in the smaller type
+should be omitted on a first reading. They generally
+deal either with difficult portions of the subject that
+are best postponed till the reader has some idea of the
+general drift of what he is doing, or else with objections
+that will probably not present themselves at first, and
+are better not dealt with till they rise naturally.
+
+The student is strongly recommended to consult the
+Summary of Definitions and Propositions on \Pagerange{139}{140}
+at frequent intervals while reading the text.
+
+\begin{flushright}
+P. H. W.\hspace*{2em}
+\end{flushright}
+%% -----File: 008.png---Folio xi-------
+
+\Chapter{Introduction}
+
+\First{On} 1st~June 1860 Stanley Jevons wrote to his brother
+Herbert, ``During the last session I have worked a good
+deal at political economy; in the last few months I
+have fortunately struck out what I have no doubt is \emph{the
+true Theory of Economy}, so thoroughgoing and consistent,
+that I cannot now read other books on the subject
+without indignation.''
+
+Jevons was a student at University College at this
+time, and his new theory failed even to gain him the
+modest distinction of a class-prize at the summer examination.
+He was placed third or fourth in the list, and,
+though much disappointed, comforted himself with the
+prospect of his certain success when in a few months he
+should bring out his work and ``re-establish the science
+on a sensible basis.'' Meanwhile he perceived more
+and more clearly how fruitful his discovery must prove,
+and ``how the want of knowledge of this determining
+principle throws the more complicated discussions of
+economists into confusion.''
+
+It was not till 1862 that Jevons threw the main outlines
+of his theory into the form of a paper, to be read
+before the British Association. He was fully and most
+justly conscious of its importance. ``Although I know
+pretty well the paper is perhaps worth all the others
+that will be read there put together, I cannot pretend to
+say how it will be received.'' When the year had but
+five minutes more to live he wrote of it, ``It has seen
+my theory of economy offered to a learned society~(?)
+%% -----File: 009.png---Folio xii-------
+and received without a word of interest or belief.
+It has convinced me that success in my line of endeavour
+is even a slower achievement than I had thought.''
+
+In 1871, having already secured the respectful attention
+of students and practical men by several important
+essays, Jevons at last brought out his \textit{Theory of Political
+Economy} as a substantive work. It was received in
+England much as his examination papers at college and
+his communication to the British Association had been
+received; but in Italy and in Holland it excited some
+interest and made converts. Presently it appeared that
+Professor Walras of Lausanne had been working on the
+very same lines, and had arrived independently at conclusions
+similar to those of Jevons. Attention being
+now well roused, a variety of neglected essays of a like
+tendency were re-discovered, and served to show that
+many independent minds had from time to time reached
+the principle for which Jevons and Walras were contending;
+and we may now add, what Jevons never
+knew, that in the very year 1871 the Viennese Professor
+Menger was bringing out a work which, in complete
+independence of Jevons and his predecessors, and by a
+wholly different approach, established the identical
+theory at which the English and Swiss scholars were
+likewise labouring.
+
+In 1879 appeared the second edition of Jevons's
+\textit{Theory of Political Economy}, and now it could no longer
+be ignored or ridiculed. Whether or not his guiding
+principle is to win its way to general acceptance and to
+``re-establish the science on a sensible basis,'' it has at
+least to be seriously considered and seriously dealt with.
+
+It is this guiding principle that I have sought to
+illustrate and enforce in this elementary treatise on the
+Theory of Value or Worth. Should it be found to meet
+a want amongst students of economics, I shall hope to
+follow it by similar introductions to other branches of
+the science.
+
+I lay no claim to originality of any kind. Those
+%% -----File: 010.png---Folio xiii-------
+who are acquainted with the works of Jevons, Walras,
+Marshall, and Launhardt, will see that I have not only
+accepted their views, but often made use of their
+terminology and adopted their illustrations without
+specific acknowledgment. But I think they will also
+see that I have copied nothing mechanically, and have
+made every proposition my own before enunciating it.
+
+I have to express my sincere thanks to Mr.\ John
+Bridge, of Hampstead, for valuable advice and assistance
+in the mathematical portions of my work.
+
+I need hardly add that while unable to claim credit
+for any truth or novelty there may be in the opinions
+advocated in these pages, I must accept the undivided
+responsibility for them.
+\medskip
+
+\asterism Beginners will probably find it conducive to the
+comprehension of the argument to omit the small print
+in the first reading.
+
+\begin{Remark}
+\NB---I have frequently given the formulas of the curves
+used in illustration. Not because I attach any value or importance
+to the special forms of the curves, but because I
+have found by experience that it would often be convenient
+to the student to be able to calculate for himself any point
+on the actual curve given in the figures which he may wish
+to determine for the purpose of checking and varying the
+hypotheses of the text.
+
+As a rule I have written with a view to readers guiltless
+of mathematical knowledge (see \Chapref{1}{Preface}). But I have sometimes
+given information in footnotes, without explanation,
+which is intended only for those who have an elementary
+knowledge of the higher mathematics.
+
+In conclusion I must apologise to any mathematicians into
+whose hands this primer may fall for the evidences which they
+will find on every page of my own want of systematic mathematical
+training, but I trust they will detect no errors of
+reasoning or positive blunders.
+\end{Remark}
+%% -----File: 011.png---Folio xiv-------
+% [Blank Page]
+%% -----File: 012.png---Folio xv-------
+
+
+\Chapter{Table of Contents}
+
+\ToCLine{\hfill\scriptsize PAGE}{}
+
+\ToCLine{Preface}{chap:1}% ix %[** TN: N.B. 3rd arg hard-coded]
+
+\ToCLine{Introduction}{chap:2}% xi
+
+\ToCLine{Theory of Value---}{}
+
+% [** TN: Skip chap:3 = this ToC]
+\ToCLine[I.]{Individual}{chap:4}% 1
+
+\ToCLine[II.]{Social}{chap:5}% 68
+
+\ToCLine{Summary---Definitions and Propositions}{chap:6}% 139
+
+\ToCLine{Index of Illustrations}{indexpage}% 141
+
+\vfill
+%% -----File: 013.png---Folio xvi-------
+% [Blank Page]
+%% -----File: 014.png---Folio 1-------
+
+\mainmatter
+\phantomsection
+\pdfbookmark[-1]{Main Matter}{Main Matter}%
+\pagestyle{fancy}
+
+\Chapter[I. Individual]{I}
+
+\Pagelabel{1}%
+\First{It} is the object of this volume in the first place to
+explain the meaning and demonstrate the truth of the
+proposition, that \emph{the value in use and the value in exchange
+of any commodity are two distinct, but connected, functions of
+the quantity of the commodity possessed by the persons or the
+community to whom it is valuable}, and in the second place,
+so to familiarise the reader with some of the methods
+and results that necessarily flow from that proposition
+as to make it impossible for him unconsciously to accept
+arguments and statements which are inconsistent with
+it. In other words, I aim at giving what theologians
+might call a ``saving'' knowledge of the fundamental
+proposition of the Theory of Value; for this, but no more
+than this, is necessary as the first step towards mastering
+the ``alphabet of Economic Science.''
+
+When I speak of a ``function,'' I use the word in the
+mathematical not the physiological sense; and our first
+business is to form a clear conception of what such a
+function is.
+
+\emph{One quantity, or measurable thing~{\upshape($y$)}, is a function of
+another measurable thing~{\upshape($x$)}, if any change in~$x$ will produce
+or ``determine'' a definite corresponding change in~$y$.}
+Thus the sum I pay for a piece of cloth of given quality
+\index{Cloth, price of}%
+is a function of its length, because any alteration in the
+length purchased will cause a definite corresponding
+alteration in the sum I have to pay.
+%% -----File: 015.png---Folio 2-------
+
+\begin{Remark}
+\Pagelabel{2}%
+If I do not stipulate that the cloth shall be of the same
+quality in every case, the sum to be paid will still be a function
+of the length, though not of the length alone, but of the
+quality also. For it remains true that an alteration in the
+length will always produce a definite corresponding alteration
+in the sum to be paid, although a contemporaneous alteration
+in the quality may produce another definite alteration (in the
+same or the opposite sense) at the same time. In this case
+the sum to be paid would be ``a function of two variables''
+(see below). It might still be said, however, without qualification
+or supplement, that ``the sum to be paid is a function
+of the length;'' for the statement, though not complete, would
+be perfectly correct. It asserts that every change of length
+causes a corresponding change in the sum to be paid, and it
+asserts nothing more. It is therefore true without qualification.
+In this book we shall generally confine ourselves to
+the consideration of one variable at a time.
+\end{Remark}
+
+So again, if a heavy body be allowed to drop from a
+\index{Body, falling}%
+\index{Falling@{\textsc{Falling body}}}%
+height, the longer it has been allowed to fall the
+greater the space it has traversed, and any change in
+the time allowed will produce a definite corresponding
+change in the space traversed. Therefore the space
+traversed (say $y$~ft.)\ is a function of the time allowed
+(say $x$~seconds).
+
+Or if a hot iron is plunged into a stream of cold
+\index{Cooling iron}%
+\index{Iron, cooling}%
+water, the longer it is left in the greater will be the fall
+in its temperature. The fall in temperature then (say
+$y$~degrees) is a function of the time of immersion (say $x$~seconds).
+
+The correlative term to ``function'' is ``variable,''
+or, in full, ``independent variable.'' If $y$~is a function
+of~$x$, then $x$ is the variable of that function.
+Thus in the case of the falling body, the time is the
+variable and the space traversed the function. When
+we wish to state that a magnitude is a function of~$x$,
+without specifying what particular function (\ie~when
+we wish to say that the value of~$y$ depends upon the
+value of~$x$, and changes with it, without defining the
+%% -----File: 016.png---Folio 3-------
+nature or law of its dependence), it is usual to represent
+the magnitude in question by the symbol~$f(x)$ or~$\phi(x)$,
+etc. Thus, ``let $y=f(x)$'' would mean ``let $y$~be a
+magnitude which changes when $x$~changes.'' In the
+case of the falling body we know that the space traversed,
+measured in feet, is (approximately) sixteen times
+the square of the number of seconds during which the
+body has fallen. Therefore if $x$~be the number of
+seconds, then $y$~or~$f(x)$ equals~$16x^2$.
+
+\begin{Remark}
+\Pagelabel{3}%
+Since the statement $y=f(x)$ implies a \emph{definite relation}
+between the changes in~$y$ and the changes in~$x$, it follows
+that a change in~$y$ will determine a corresponding change in~$x$,
+as well as \textit{vice versâ}. Hence if $y$ is a function of~$x$ it follows
+that $x$ is also a function of~$y$. In the case of the falling body,
+if $y=16x^2$, then $x=\dfrac{\sqrt{y}}{4}$.\footnote
+ {In the abstract $x=±\dfrac{\sqrt{y}}{4}$. For $-x$ and $x$ will give the same
+ values of $y$ in $f(x)=16x^2=y$; and we shall have $±x=\dfrac{\sqrt{y}}{4}$.}
+It is usual to denote inverse functions
+of this description by the index~$-1$. Thus if $f(x)=y$
+then $f^{-1}(y)=x$. In this case $y=16x^2$, and $f^{-1}(y)$ becomes
+$f^{-1}(16x^2)$. Therefore $f^{-1}(16x^2)=x$. But $x=\dfrac{\sqrt{16x^2}}{4}$. Therefore
+$f^{-1}(16x^2)=\dfrac{\sqrt{16x^2}}{4}$. And $16x^2=y$. Therefore $f^{-1}(y)=\dfrac{\sqrt{y}}{4}$.
+In like manner $f^{-1}(a)=\dfrac{\sqrt{a}}{4}$; and generally $f^{-1}(x)=\dfrac{\sqrt{x}}{4}$,
+whatever $x$ may be.
+\begin{flalign*}
+&\text{\indent Thus } & y&=f(x)=16x^2, && \\
+& & x&=f^{-1}(y)=\dfrac{\sqrt{y}}{4}. &&
+\end{flalign*}
+(See below, \Pageref{11}.)
+\end{Remark}
+
+From the formula $y=f(x)=16x^2$ we can easily
+calculate the successive values of~$f(x)$ as~$x$ increases, \ie\
+the space traversed by the falling body in~one, two,
+three, etc., seconds.
+%% -----File: 017.png---Folio 4-------
+\Pagelabel{4}%
+\begin{align*}
+&\underline{x\quad f(x) = 16x^2} \\
+&0\quad f(0) = 16 × 0^2 = \Z0. \\
+&1\quad f(1) = 16 × 1^2 = \Z16 \quad\text{growth during last second } \Z16\DPtypo{}{.} \\
+&2\quad f(2) = 16 × 2^2 = \Z64 \quad\PadTo{\text{growth during }}{\Ditto}\PadTo{\text{last second }}{\Ditto} \Z48\DPtypo{}{.} \\
+&3\quad f(3) = 16 × 3^2 = 144 \quad\PadTo{\text{growth during }}{\Ditto}\PadTo{\text{last second }}{\Ditto} \Z80\DPtypo{}{.} \\
+&4\quad f(4) = 16 × 4^2 = 256 \quad\PadTo{\text{growth during }}{\Ditto}\PadTo{\text{last second }}{\Ditto} 112\DPtypo{}{.} \\
+&\text{etc.\ etc.} \PadTo{{}=16 × 4^2={}}{\text{etc.}}\text{etc.}\quad\PadTo[r]{growth during last second\quad\;99}{\text{etc.}}
+\end{align*}
+
+In the case of the cooling iron in the stream the
+time allowed is again the variable, but the function,
+which we will denote by~$\phi (x)$, is not such a simple one,
+and we need not draw out the details. Without doing
+so, however, we can readily see that there will be an
+important difference of character between this function
+and the one we have just investigated. For the space
+traversed by the falling body not only grows continually,
+but grows more in each successive second than it
+did in the last, as is shown in the last column of the
+table. Now it is clear that though the cooling iron
+will always go on getting cooler, yet it will not cool
+more during each successive second than it did during
+the last. On the contrary, the fall in temperature of
+the red-hot iron in the first second will be much greater
+than the fall in, say, the hundredth second, when the
+water is only very little colder than the iron; and the
+total fall can never be greater than the total difference
+between the initial temperatures of the iron and the
+water. This is expressed by saying that the one
+function~$f(x)$, \emph{increases without limit} as the variable,~$x$,
+increases, and that the other function~$\phi (x)$ \emph{approaches a
+definite limit} as the variable,~$x$, increases. In either
+case the function is always increased by an increase of
+the variable, but only in the first case can we make the
+function as great as we like by increasing the variable
+sufficiently; for in the second case there is a certain
+fixed limit which the function will never reach, however
+long it continues to increase. If the reader finds this
+conception difficult or paradoxical, let him consider the
+%% -----File: 018.png---Folio 5-------
+series $1 + \frac{1}{2} + \frac{1}{4} + \frac{1}{8} + \frac{1}{16}$, etc., and let $f(x)$ signify the
+sum of $x$~terms of this series. Then we shall have
+\begin{align*}
+&\underline{\PadTo{\text{etc.}}{x}\ f(x)} \\
+&\PadTo{\text{etc.}}{1}\ \PadTo{f(x)}{1.} \\
+&\PadTo{\text{etc.}}{2}\ \PadTo{f(x)}{\frac{3}{2}} \left(\ie\ 1 + \tfrac{1}{2}\right). \\
+&\PadTo{\text{etc.}}{3}\ \PadTo{f(x)}{\frac{7}{4}} \left(\ie\ 1 + \tfrac{1}{2} + \tfrac{1}{4}\right). \\
+&\PadTo{\text{etc.}}{4}\ \PadTo{f(x)}{\frac{15}{8}} \left(\ie\ 1 + \tfrac{1}{2} + \tfrac{1}{4} + \tfrac{1}{8}\right). \\
+&\PadTo{\text{etc.}}{5}\ \PadTo{f(x)}{\frac{31}{16}} \left(\ie\ 1 + \tfrac{1}{2} + \tfrac{1}{4} + \tfrac{1}{8} + \tfrac{1}{16}\right). \\
+&\text{etc.}\ \PadTo{f(x)}{\text{etc.}}
+\end{align*}
+\Pagelabel{5}%
+Here $f(x)$ is always made greater by increasing~$x$, but
+however great we make~$x$ we shall never make~$f(x)$
+quite equal to~$2$. This case furnishes a simple instance
+of a function which always increases as its variable
+increases, but yet never reaches a certain fixed limit.
+The cooling iron presents a more complicated case of
+such a function.
+
+The two functions we have selected for illustration
+differ then in this respect, that as the variable (time)
+increases, the one (space traversed by a falling body)
+increases without limit, while the other (fall of temperature
+in the iron) though always increasing yet approaches
+a fixed limit. But $f(x)$~and~$\phi (x)$ resemble
+each other in this, that they both of them always increase
+(and never decrease) as the variable increases.
+
+There are, however, many functions of which this
+cannot be said. For instance, let a body be projected
+\index{Projectile}%
+vertically upwards, and let the height at which we find
+it at any given moment be regarded as a function of
+the time which has elapsed since its projection. It is
+obvious that at first the body will rise (doing work
+against gravitation), and the function (height) will increase
+as the variable (time) increases. But the initial
+energy of the body cannot hold out and do work against
+gravitation for ever, and after a time the body will rise
+no higher, and will then begin to fall, in obedience to the
+still acting force of gravitation. Then a further increase
+%% -----File: 019.png---Folio 6-------
+of the variable (time) will cause, not an increase, but a
+decrease in the function (height). Thus, as the variable
+increases, the function will at first increase with it, and
+then decrease.
+
+To recapitulate: one thing is a function of another
+if it varies with it, whether increasing as it increases or
+decreasing as it increases, or changing at a certain point
+or points from the one relation to the other.
+\Pagelabel{6}%
+
+We have already reached a point at which we can
+attach a definite meaning to the proposition: \emph{The value-in-use
+of any commodity to an individual is a function of the
+quantity of it he possesses}, and as soon as we attach a
+definite meaning to it, we perceive its truth. For by
+the value-in-use of a commodity to an individual, we
+mean the total worth of that commodity to him, for his
+own purposes, or the sum of the advantages he derives
+immediately from its possession, excluding the advantages
+he anticipates from exchanging it for something else.
+Now it is clear that this sum of advantages is greater
+or less according to the quantity of the commodity the
+man possesses. It is not the same for different quantities.
+The value-in-use of two blankets, that is to say
+\index{Blankets}%
+the total direct service rendered by them, or the sum of
+direct advantages I derive from possessing them, differs
+from the value-in-use of one blanket. If you increase
+or diminish my supply of blankets you increase or
+diminish the sum of direct advantages I derive from
+them. The value-in-use of my blankets, then, is a
+function of the number (or quantity) I possess. Or if
+we take some commodity which we are accustomed to
+think of as acquired and used at a certain rate rather than
+in certain absolute quantities, the same fact still appears.
+The value-in-use of one gallon of water a day, that is to
+say the sum of direct advantages I derive from commanding
+it, differs from the value-in-use of a pint a day
+or of two gallons a day. The sum of direct advantages
+which I derive from half a pound of butcher's meat a
+%% -----File: 020.png---Folio 7-------
+day is something different from that which I should
+derive from either an ounce or a whole carcase per day.
+In other words, \emph{the sum of the advantages I derive from
+the direct use or consumption of a commodity is a function
+of its quantity, and increases or decreases as that quantity
+changes}.
+
+\begin{Remark}
+Two points call for attention here. In the first place,
+there are many commodities which we are not in the habit
+of thinking of as possessed in varying quantities; or at any
+rate, we usually think of the services they render as functions
+of some other variable than their quantity. For instance,
+a watch that is a good time-keeper renders a greater
+sum of services to its possessor than a bad one; but it seems
+an unwarrantable stretch of language to say that the owner
+of a good watch has ``a greater amount or quantity of watch''
+than the owner of a bad one. It is a little more reasonable,
+though still hardly admissible, to say that the one has ``more
+time-keeping apparatus'' than the other. But, as the reader
+will remember, we have already seen that a function may
+depend on two or more variables (\Pageref{2}), and if we consider
+watches of different qualities as one and the same commodity,
+\index{Watches}%
+then we must say that the most important variable is the
+quality of the watch; but it will still be true that two
+watches of the same quality would, as a rule, perform a
+different (and a greater) service for a man than one watch;
+for most men who have only one have experienced temporary
+inconvenience when they have injured it, and would have
+been very glad of another in reserve. Even in this case,
+therefore, the sum of advantages derived from the commodity
+``watches'' is a function of the quantity as well as the quality.
+Moreover, the distinction is of no theoretical importance, for
+the propositions we establish concerning value-in-use as a
+function of quantity will be equally true of it as a function
+of quality; and indeed ``quality'' in the sense of ``excellence,''
+being conceivable as ``more'' or ``less,'' is obviously
+itself a quantity of some kind.
+
+The second consideration is suggested by the frequent use
+of the phrase ``\emph{sum of advantages}'' as a paraphrase of ``\emph{worth}''
+or ``\emph{value-in-use}.'' What are we to consider an ``advantage''?
+%% -----File: 021.png---Folio 8-------
+It is usual to say that in economics everything which a man
+wants must be considered ``useful'' to him, and that the
+word must therefore be emptied of its moral significance.
+In this sense a pint of beer is more ``useful'' than a gimlet
+\index{Beer}%
+\index{Gimlet}%
+to a drunken carpenter. And, in like manner, a wealthier
+person of similar habits would be said to derive a greater
+``sum of advantages'' from drinking two bottles of wine at
+\index{Wine}%
+dinner than from drinking two glasses. In either case, we
+are told, that is ``useful'' which ministers to a desire, and it
+is an ``advantage'' to have our desires gratified. Economics,
+it is said, have nothing to do with ethics, since they
+deal, not with the legitimacy of human desires, but with the
+means of satisfying them by human effort. In answer to
+this I would say that if and in so far as economics have nothing
+to do with ethics, economists must refrain from using ethical
+words; for such epithets as ``useful'' and ``advantageous''
+will, in spite of all definitions, continue to carry with them
+associations which make it both dangerous and misleading to
+apply them to things which are of no real use or advantage.
+I shall endeavour, as far as I can, to avoid, or at least to
+minimise, this danger. I am not aware of any recognised
+word, however, which signifies the quality of being desired.
+``Desirableness'' conveys the idea that the thing not only is
+but deserves to be desired. ``Desiredness'' is not English,
+but I shall nevertheless use it as occasion may require.
+``Gratification'' and ``satisfaction'' are expressions morally
+indifferent, or nearly so, and may be used instead of ``advantage''
+when we wish to denote the result of obtaining a
+thing desired, irrespective of its real effect on the weal or
+woe of him who secures it.\Pagelabel{8}%
+\end{Remark}
+
+Let us now return to the illustration of the body
+\index{Projectile}%
+projected vertically upwards at a given velocity. In
+this case the time allowed is the variable, and the
+height of the body is the function. Taking the
+rough approximation with which we are familiar, which
+gives sixteen feet as the space through which a body
+will fall from rest in the first second, and supposing
+that the velocity with which the body starts is $a$~ft.\
+per~second, we learn by experiment, and might deduce
+%% -----File: 022.png---Folio 9-------
+from more general laws, that we shall have $y=ax-16x^2$,
+where $x$ is the number of seconds allowed, and $y$ is the
+height of the body at the end of $x$~seconds. If $a=128$,
+\ie~if the body starts at a velocity of $128$~ft.\ per~second,
+we shall have
+\[
+y=128x-16x^2.
+\]
+
+\begin{Remark}
+In such an expression the figures $128$~and~$-16$ are called
+the \emph{constants}, because they remain the same throughout the
+investigation, while $x$ and $y$ change. If we wish to indicate
+the general type of the relationship between $x$ and $f(x)$ or $y$
+without determining its details, we may express the constants
+by letters. Thus $y=ax+bx^2$ would determine the general character
+of the function, and by choosing $128$ and~$-16$ as the constants
+we get a definite specimen of the type, which absolutely
+determines the relation between $x$~and~$y$. Thus $y=ax+bx^2$
+is the general formula for the distance traversed in $x$~seconds
+by a body that starts with a given velocity and works directly
+with or against a constant force. If the constant force is
+gravitation, $b$ must equal~$16$; if the body is to work against
+(not with) gravitation the sign of~$b$ must be negative. If
+the initial velocity of the body is $128$~ft.\ per~second, $a$~must
+equal~$128$.
+\end{Remark}
+
+By giving successive values of $1$, $2$, $3$, etc.\ to~$x$ in
+the expression $128x-16x^2$, we find the height at which
+the body will be at the end of the $1$, $2$, $3$, etc.\ seconds.
+\begin{align*}
+&\underline{\PadTo{\text{etc.}}{x}\ f(x) = 128x - 16x^2\qquad} \\
+&\PadTo{\text{etc.}}{0}\ f(0) = 128 × 0 - 16 × 0^2 = 0 \\
+&\PadTo{\text{etc.}}{1}\ f(1) = 128 × 1 - 16 × 1^2 = 112 \\
+&\PadTo{\text{etc.}}{2}\ f(2) = 128 × 2 - 16 × 2^2 = 192 \\
+&\PadTo{\text{etc.}}{3}\ f(3) = 128 × 3 - 16 × 3^2 = 240 \\
+&\text{etc.\quad etc.} \PadTo{{} = 128 × 3 - {}}{\text{etc.}}\PadTo{16 × 3^2 =}{} \text{etc.}\\
+\end{align*}
+
+Now this relation between the function and the
+variable may be represented graphically by the well-known
+method of measuring the \emph{variable} along a base
+line, starting from a given point, and measuring the
+\emph{function} vertically upwards from that line, negative
+%% -----File: 023.png---Folio 10-------
+quantities in either case being measured in the opposite
+direction to that selected for positive quantities. To
+apply this method we must select our unit of length
+and then give it a fixed interpretation in the quantities
+we are dealing with. Suppose we say that a unit
+measured along the base line~$OX$ in \Figref{1} shall represent
+one second, and that a unit measured vertically from~$OX$
+in the direction~$OY$ shall represent $10$~ft. We
+may then represent the connection between the height
+at which the body is to be found and the lapse of time
+since its projection by a curved line. We shall proceed
+thus. Let us suppose a movable button to slip along
+the line~$OX$, bearing with it as it moves along a vertical
+line (parallel to~$OY$) indefinitely extended both upwards
+and downwards. The movement of this button (which
+we may regard as a point, without magnitude, and
+which we may call a ``bearer'') along~$OX$ will represent
+the lapse of time. The lapse of one second, therefore,
+will be represented by the movement of the bearer one
+unit to the right of~$O$. Now by this time the body
+will have risen $112$~ft., which will be represented by
+$11.2$~units, measured upwards on the vertical line
+carried by the bearer. This will bring us to the point
+indicated on \Figref{1} by~$P_1$. Let us mark this point and
+then slip on the bearer through another unit. This will
+represent a total lapse of two seconds, by which time
+the body will have reached a height of $192$~ft., which
+will be represented by $19.2$~units measured on the
+vertical. This will bring us to~$P_2$. In $P_1$ and~$P_2$ we
+have now representations of two points in the history of
+the projectile. $P_1$~is distant one unit from the line~$OY$
+and $11.2$~units from~$OX$, \ie~it represents a movement
+from~$O$ of $1$~unit in the direction~$OX$ (time, or~$x$), and
+of $11.2$~units in the direction of~$OY$ (height, or~$y$). This
+indicates that $11.2$ is the value of~$y$ which corresponds
+to the value~$1$ of~$x$. In like manner the position of~$P_2$
+indicates that $19.2$ is the value of~$y$ that corresponds
+to the value~$2$ of~$x$. Now, instead of finding an
+%% -----File: 024.p n g----------
+%[Blank Page]
+%% -----File: 025.p n g----------
+\begin{figure}[p]
+\Pagelabel{9}%
+ \begin{center}
+ \begin{minipage}[c]{2.25in}
+ \Fig{1}
+ \Input[2.25in]{025a}
+ \end{minipage}\hfil
+ \begin{minipage}[c]{2.25in}
+ \Fig{3}
+ \Input[2.25in]{025b}
+ \end{minipage}
+ \end{center}
+\end{figure}
+%[To face page 11.]
+%% -----File: 026.png---Folio 11-------
+indefinite number of these points, let us suppose that as
+the bearer moves continuously (\ie~without break) along~$OX$
+a pointed pencil is continuously drawn along the
+vertical, keeping exact pace, to scale, with the moving
+body, and therefore always registering its height,---a unit
+of length on the vertical representing $10$~ft. Obviously the
+point of the pencil will trace a continuous curve, the course
+of which will be determined by two factors, the horizontal
+factor representing the lapse of time and the vertical
+factor representing the movement of the body, and if we
+take any point whatever on this curve it will represent
+a point in the history of the projectile; its distance
+from~$OY$ giving a certain point of time and its distance
+from~$OX$ the corresponding height.
+
+Such a curve is represented by \Figref{1}. We have
+seen how it is to be formed; and when formed it is to
+be read thus: If we push the bearer along~$OX$, then for
+every length measured along~$OX$ the curve cuts off a corresponding
+length on the vertical, which we will call the
+``vertical intercept.'' That is to say, for every value of $x$~(time)
+the curve marks a corresponding value of $y$~(height).
+
+$OX$ is called ``the axis of~$x$,'' because $x$ is measured
+along it or in its direction. $OY$~is, for like reason,
+called ``the axis of~$y$.''
+
+\begin{Remark}
+\Pagelabel{11}%
+We have seen that if $y$ is a function of~$x$ then it follows
+that $x$~is also a function of~$y$ (\Pageref{3}). Hence the curve we
+have traced may be regarded as representing $x = f^{-1}(y)$ no
+less than $y = f(x)$. If we move our bearer along~$OY$ to
+represent the height attained, and make it carry a line
+parallel to~$OX$, then the curve will cut off a length indicating
+the time that corresponds to that height. It will be seen
+that there are two such lengths of $x$ corresponding to every
+length of $y$ between $0$~and~$25.6$, one indicating the moment
+at which the body will reach the given height as it ascends,
+and the other the moment at which it returns to the same
+height in its descent.
+
+As an exercise in the notation, let the student follow this
+series of axiomatic identical equations: given $y = f(x)$, then
+%% -----File: 027.png---Folio 12-------
+$xy=f(x)x=f^{-1}(y)f(x)=f^{-1}(y)y$. Also $f^{-1}\left[f(x)\right]=x$ and
+$f\left[f^{-1}(y)\right]=y$.
+\end{Remark}
+
+\Pagelabel{12}%
+It must be carefully noted that the curve \emph{does not
+give us a picture of the course of the projectile}. We have
+supposed the body to be projected vertically upwards,
+and its course will therefore be a straight line, and
+would be marked by the movement of the pencil up and
+down the vertical, taken alone, and not in combination
+with the movement of the vertical itself; just as the
+time would be marked by the movement of the pencil,
+with the bearer, along~$OX$, taken alone. In fact the
+best way to conceive of the curve is to imagine one
+bearer moving along~$OX$ and marking the time, to scale,
+while a second bearer moves along~$OY$ and marks the
+height of the body, to scale, while the pencil point \emph{follows
+the direction and speed of both of them at once}. The
+pencil point, it will be seen, will always be at the intersection
+of the vertical carried by one bearer and the
+horizontal carried by the other. Thus it will be quite
+incorrect and misleading to call the curve ``a curve
+of height,'' and equally but not more so to call it ``a
+curve of time.'' Both height and time are represented
+by straight lines, and the curve is a ``curve
+of height-and-time,'' or ``a curve of time-and-height,''
+that is to say, \emph{a curve which shows the history of the connection
+between height and time}.
+
+And again the scales on which time and height are
+measured are altogether indifferent, as long as we read our
+curve by the same scale on which we construct it. The
+student should accustom himself to draw a curve on a
+number of different scales and observe the wonderful
+changes in its appearance, while its meaning, however
+tested, always remains the same.
+
+All these points are illustrated in \Figref{2}, where the
+very same history of the connection between time and
+height in a body projected vertically upwards at $128$~ft.\
+per~second is traced for four seconds and $256$~ft., but the
+%% -----File: 028.png---Folio 13-------
+height is drawn on the scale $50$~ft.\ $\frac{1}{6}$~in.\ instead of $10$~ft.\
+$\frac{1}{6}$~in. It shows us that the lines representing space
+\Pagelabel{13}%
+and those representing time
+\begin{wrapfigure}[13]{r}{2in}
+ \Fig{2}
+ \Input[2in]{028a}
+\end{wrapfigure}
+enter into the construction of
+the curve on precisely the
+same footing. The curve, if
+drawn, would therefore be
+neither a curve of time nor
+a curve of height, but a curve
+of time-and-height.
+
+The curve then, is not a
+picture of the course of the
+projectile in space, and a
+similar curve might equally
+well represent the history of a phenomenon that has no
+course in space and is independent of time.
+
+For instance, the expansion of a metal bar under
+tension is a function of the degree of tension; and a
+testing machine may register the connection between
+\index{Testing@{\textsc{Testing Machine}}}%
+the tension and expansion upon a curve. The tension
+is the variable~$x$ (measured in tons, per inch cross-section
+of specimen tested, and drawn on axis of~$x$ to
+the scale of, say, seven tons to the inch), and the expansion
+is $f(x)$ or~$y$ (measured in inches, and drawn on
+axis of~$y$, say to the natural scale, $1:1$).\footnote
+ {If we take tension (the variable) along~$y$, and expansion (the
+ function) along~$x$, the theory is of course the same. As a fact,
+ it is usual in testing-machines to regard the tension as measured
+ on the vertical and the expansion on the horizontal. It is only a
+ question of how the paper is held in the hand, and the reader will do
+ well to throw the curve of time-and-height also, on its side, read its
+ $x$ as~$y$ and its $y$ as~$x$, and learn with ease and certainty to read off the
+ same results as before. This will be useful in finally dispelling the
+ illusion (that reasserts itself with some obstinacy) that the figure represents
+ the course of the projectile. The figures may also be varied by
+ being drawn from right to left instead of from left to right,~etc. It is
+ of great importance not to become dependent on any special convention
+ as to the position,~etc.\ of the curves.}
+
+The tension and expansion, then, are indicated by
+straight lines, constantly changing in length, but the
+history of their connection is a curve. It is not a curve
+%% -----File: 029.png---Folio 14-------
+of expansion or a curve of tension, but a curve of tension-and-expansion.
+
+Or again, the pleasurable sensation of sitting in a
+Turkish bath is a function, amongst other things, of
+\index{Turkish bath}%
+the temperature to which the bath is raised. If we
+treat that temperature as the variable, and measure its
+increase by slipping the bearer along the base line~$OX$,
+then the whole body of facts concerning the varying
+degrees of pleasure to be derived from the bath, according
+to its varying degrees of heat, might be represented
+by a curve, which would be in some respects analogous
+to that represented on \Figref{1}; for, as we measure the
+rise of temperature by moving the bearer along our
+base line, we shall, up to a certain point, read our increasing
+sense of luxury on the increasing length of the
+vertical intercepted by a rising curve, after which the
+increasing temperature will be accompanied by a decreasing
+sense of enjoyment, till at last the enjoyment
+will sink to zero, and, if the heat is still raised, will
+become a rapidly increasing negative quantity. Thus:
+
+\emph{If we have a function (of one variable), then whatever
+the nature of the function may be, the connection between the
+function and the variable is theoretically capable of representation
+by a curve.} And since we have seen that the
+total satisfaction we derive from the enjoyment or use
+of any commodity is a function of the quantity we
+possess (\ie~changes in magnitude as the quantity increases
+or decreases), it follows that \emph{a curve must theoretically
+exist which assigns to every conceivable quantity of
+a given commodity the corresponding total satisfaction to be
+derived by a given man from its use or possession}; or, in
+other words, \emph{the connection between the total satisfaction
+derived from the enjoyment of a commodity and the quantity
+of the commodity so enjoyed is theoretically capable of being
+represented by a curve}. Now this ``total satisfaction
+derived'' is what economists call the ``total utility,'' or
+the ``value-in-use'' of a commodity. The conclusion
+we have reached may therefore be stated thus: Since
+%% -----File: 030.png---Folio 15-------
+the value-in-use of a commodity varies with the quantity
+of the commodity used, \emph{the connection between the quantity
+of a commodity possessed and its value-in-use may, theoretically,
+be represented by a curve}.
+
+\begin{Remark}
+\Pagelabel{15}%
+Here an initial difficulty presents itself. To imagine the
+construction of such a curve as even theoretically possible, we
+should have to conceive the theoretical possibility of fixing
+a unit of satisfaction, by which to measure off satisfactions
+two, three, four times as great as the standard unit, on our
+vertical line, just as we measured tens of feet on it in \Figref{1}.
+We shall naturally be led in the course of our inquiry to deal
+with this objection, which is not really formidable (see \Pageref{52});
+and it is only mentioned here to show that it has not been
+overlooked. Meanwhile, it may be observed that since satisfaction
+is certainly capable of being ``more'' or ``less,'' and
+since the mind is capable of estimating one satisfaction as
+``greater than'' or ``equal to'' another, it cannot be theoretically
+impossible to conceive of such a thing as an accurate
+measurement of satisfaction, even though its practical measurement
+should always remain as vague as that of heat was when
+the thermometer was not yet invented.
+\index{Thermometer}%
+\end{Remark}
+
+We may go a step farther, and may say that,
+if curves representing the connection between these
+economic functions (values-in-use) and their variables
+(quantities of commodity) could be actually drawn out,
+they would, at any rate in many cases, present an important
+point of analogy with our curve in \Figref{1}; for
+they would first ascend and then descend, and ultimately
+pass below zero. As the quantity of any commodity in
+our possession increases we gradually approach the point
+at which it has conferred upon us the full satisfaction
+we are capable of deriving from it; after this a larger
+stock is not in any degree desired, and would not add
+anything to our satisfaction. In a word, we have as
+much as we want, and would not take any more at
+a gift. The function has then reached its maximum
+value, corresponding to the highest point on the curve.
+%% -----File: 031.png---Folio 16-------
+If the commodity is still thrust upon us beyond this
+point of complete satisfaction, the further increments
+become, as a rule, \emph{discommodious}, and the excessive
+quantity \emph{diminishes} the total satisfaction we derive from
+possessing the commodity, till at length a point is
+reached at which the inconvenience of the excessive
+supply neutralises the whole of the advantage derived
+from that part which we can enjoy, and we would just
+as soon go without it altogether as have so far too
+much of a good thing. If the supply is still increased,
+the net result is a balance of inconvenience, and (if shut
+up to the alternative of \emph{all} or \emph{none}) we should, on the
+whole, be the gainers if relieved of the advantage and
+disadvantage alike. The heat of a Turkish bath has
+already given us one instance; and for another we may
+take butcher's meat. Most of us derive (or suppose
+\index{Meat@{\textsc{Meat}, butcher's}}%
+ourselves to derive) considerable satisfaction from the
+consumption of fresh meat. The sum of satisfaction
+increases as the amount of meat increases up to a point
+roughly fixed by the popular estimate at half to three-quarters
+of a pound per diem. Then we have enough,
+and if we were required to consume or otherwise personally
+dispose of a larger amount, the inconvenience
+of eating, burying, burning, or otherwise getting rid of
+the surplus, or the unutterable consequences of failing
+to do so, would partially neutralise the pleasure and
+advantage of eating the first half pound, till at some
+point short of a hundredweight of fresh meat per head
+per diem we should (if shut in to the alternative of all
+or none) regretfully embrace vegetarianism as the lesser
+evil. In this case the curve connecting the value-in-use
+of meat with its quantity would rise as the supply of
+meat, measured along the base line, increased until, say
+at half a pound a day, it reached its maximum elevation,
+indicating that up to that point more meat meant more
+satisfaction, after which the curve would begin to descend,
+indicating that additional supplies of meat would
+be worse than useless, and would tend to neutralise the
+%% -----File: 032.png---Folio 17-------
+satisfaction derived from the portion really desired, and
+to reduce the total gratification conferred, till at a
+certain point the curve would cross the base line, indicating
+that so much meat as that (if we were obliged to
+take all or none) would be just as bad as none at all,
+and that if more yet were thrust upon us it would on
+the whole be \emph{worse} than having none.
+
+\begin{Remark}
+Though practically we are almost always concerned with
+commodities our desire for which is not fully satisfied, that
+is to say, with the portions of our curves which are still ascending,
+yet it is highly important, as a matter of theory, to realise
+the fact that curves of quantity-and-value-in-use must always
+\emph{tend} to reach a maximum somewhere, and that as a rule they
+would actually reach that maximum if the variable (measured
+along the axis of~$x$) were made large enough, and would then
+descend if the variable were still further increased; or in
+other words, that there is hardly any commodity of which
+we might not conceivably have enough and too much, and
+even if there be such a commodity its increase would still
+\emph{tend} to produce satiety (compare \Pageref{5}). Some difficulty is
+often felt in fully grasping this very simple and elementary
+fact, because we cannot easily divest our minds in imagination
+of the conditions to which we are practically accustomed.
+Thus we may find that our minds refuse to isolate the \emph{direct}
+use of commodities and to contemplate that alone (though it
+is of this direct use only that we are at present speaking),
+and persist, when we are off our guard, in readmitting the
+idea that we might exchange what we cannot use ourselves
+for something we want. A man will say, for instance, if
+confronted with the illustration of fresh meat which I have
+used above, that he would very gladly receive a hundredweight
+of fresh meat a-day and would still want more,
+because he could sell what he did not need for himself.
+This is of course beside the mark, since our contention is that
+the \emph{direct value-in-use} of an article always tends to reach a
+maximum; but in order to assist the imagination it may be
+well to take a case in which a whole community may suffer
+from having too much of a good thing, so that the confusing
+side-lights of possible exchange may not divert the attention.
+%% -----File: 033.png---Folio 18-------
+\emph{Rain}, in England at least, is an absolute necessary of life,
+but if the rainfall is too heavy we derive less benefit from it
+\index{Rainfall}%
+than if it is normal. Every extra inch of rainfall then
+becomes a very serious discommodity, reducing the total
+utility or satisfaction-derived to something lower than it
+would have been had the rain been less; and it is conceivable
+that in certain districts the rain might produce floods
+that would drown the inhabitants or isolate them, in
+inaccessible islands, till they died of starvation, thus cancelling
+the whole of the advantages it confers and making their
+absolute sum zero.
+
+Another class of objections is, however, sometimes raised.
+We are told that there are some things, notably money, of
+which the ordinary man could never have as much as he
+wanted; and daily experience shows us that so far from an
+increased supply of money tending to satisfy the desire for
+it, the more men have the more they want. This objection
+is based on a loose use of the phrase ``more money.'' Let
+us take any definite sum, say~£1, and ask what effort or
+privation a man will be willing to face in order that he may
+secure it. We shall find, of course, that if a man has a
+hundred thousand a-year he will be willing to make none
+but the very smallest effort in order to get a pound more,
+whereas if the same man only has thirty shillings a-week he
+will do a good deal to get an extra pound. It is true that
+the millionaire may still exert himself to get more money;
+but to induce him to do so the prospect of gain must be
+much greater than was necessary when he was a comparatively
+poor man. He does not want \emph{the same sum of money} as
+much as he did when he was poor, but he sees the possibility
+of getting a very large sum, and wants that as much as he
+used to want a small one. All other objections and apparent
+exceptions will be found to yield in like manner to careful
+and accurate consideration.
+
+It is true, however, that a man may form instinctive
+habits of money-making which are founded on no rational
+principle, and are difficult to include in any rationale of
+action; but even in these cases the action of our law is only
+complicated by combination with others, not really suspended.
+
+It is also true that the very fact of our having a thing
+may develop our taste for it and make us want more; but
+%% -----File: 034.png---Folio 19-------
+this, too, is quite consistent with our theory, and will be
+duly provided for hereafter (\Pageref{63}).
+\end{Remark}
+
+Enough has now been said in initial explanation of
+a curve in general, and specifically a curve that first
+ascends and then descends, as an appropriate means of
+representing the connection between the quantity of a
+commodity and its value-in-use, or the total satisfaction
+it confers.
+
+But if we return once more to \Figref{1}, and recollect
+\index{Projectile}%
+\Pagelabel{19}%
+that the curve there depicted is a curve of time-and-height,
+representing the connection between the elevation
+a body has attained (function) and the time that has
+elapsed since its projection (variable), we are reminded
+that there is another closely-connected function of the
+same variable, with which we are all familiar. We are
+accustomed to ask of a body falling from rest not only
+how far it will have travelled in so many seconds, but
+\emph{at what rate it will be moving} at any given time. And so,
+of a body projected vertically upwards we ask not only
+at what height will it be at the end of $x$~seconds, but
+also \emph{at what rate will it then be rising}. Let us pause for
+a moment to inquire exactly what we mean by saying
+that at a given moment a body, the velocity of which
+is constantly changing, is moving ``at the rate'' of, say,
+$y$~feet per~second. We mean that if, at that moment,
+all causes which \emph{modify} the movement of the body were
+suddenly to become inoperative, and it were to move on
+solely under the impulse already operative, it would then
+move $y$~feet in every second, and, consequently, $ay$~feet
+in $a$~seconds. In the case of \Figref{1} the modifying
+force is the action of gravitation, and what we mean by
+the rate at which the body is moving at any moment is
+the rate at which it would move, from that moment onwards,
+if from that moment the action of gravitation
+ceased to be operative.
+
+As a matter of fact it never moves through any space,
+however small, at the rate we assign, because modifying
+%% -----File: 035.png---Folio 20-------
+causes are at work \emph{continuously} (\ie~without intervals
+and without jerks), so that the velocity is never uniform
+over any fraction of time or space, however small.
+
+When we speak of rate of movement ``at a point,''
+then, we are using an abbreviated expression for the
+rate of movement which would set in at that point if all
+modifying causes abruptly ceased to act thenceforth.
+
+For instance, if we say that a body falling from rest
+has acquired a velocity of $32$~feet per~second when it
+has been falling for one second, we mean that if, after
+acting for one second, terrestrial gravitation should then
+cease to act, the body would thenceforth move $32$~feet
+in every second.
+
+It follows, then, that the departures from this ideal
+rate spring from the continuous action of the modifying
+cause, and will be greater or smaller according as the
+action of that cause has been more or less considerable;
+and since the cause (in this instance) acts uniformly in
+time, it will act more in more time and less in less.
+Hence, the less the time we allow after the close of one
+second the more nearly will the rate at every moment
+throughout that time (and therefore the average rate
+during that time) conform to the rate of $32$~feet per~second.
+And in fact we find that if we calculate (by
+the formula $s=16x^2$) the space traversed between the
+close of the first second and some subsequent point of
+time, then the smaller the time we allow the more
+nearly does the average rate throughout that time
+become $32$~ft.\ per~second. Thus---\\
+\Pagelabel{20}%
+\[
+\begin{array}{c@{ }r@{ }c@{ }l@{ }c@{\quad}cc}
+ & & & &
+ &\settowidth{\TmpLen}{\small Body falls}
+ \parbox[b]{\TmpLen}{\small Body falls}
+ &\settowidth{\TmpLen}{\small Average rate}
+ \parbox[b]{\TmpLen}{\small\centering Average rate\\ per sec.} \\
+\text{Between } &1 &\text{ sec.\ and } &2 & \text{ sec.} & 48 \text{ ft.}&48 \text{ ft.}\\
+\Ditto &1 & \Ditto &1\frac{1}{2} & \Ditto & 20 \Ditto &40 \Ditto\\
+\Ditto &1 & \Ditto &1\frac{1}{4} & \Ditto & \Z9 \Ditto &36 \Ditto\\
+\Ditto &1 & \Ditto &1\frac{1}{8} & \Ditto & \frac{17}{4} \Ditto &34 \Ditto\\
+\Ditto &1 & \Ditto &1\frac{1}{16}& \Ditto & \frac{33}{16} \Ditto &33 \Ditto\\
+\Ditto &1 & \Ditto &1\frac{1}{32}& \Ditto & \frac{65}{64} \Ditto &32\DPtypo{\,}{.}5
+\end{array}
+\]
+%% -----File: 036.png---Folio 21-------
+and the average rate between $1$~second and $1 + \dfrac{1}{z}$~second
+may be made as near $32$~ft.\ a second as we like, by making
+$z$ large enough. This is usually expressed by saying
+that the average rate between $1$~second and $\dfrac{(z+1)}{z}$~seconds
+\Pagelabel{21}%
+becomes $32$~ft.\ per second \emph{in the limit}, as $z$ becomes greater,
+or the time allowed smaller.
+
+We may, therefore, define ``rate at a point'' as
+the ``\emph{limit of the average rate between that point and
+a subsequent point, as the distance between the two points
+decreases}.''
+
+With this explanation we may speak of the rate at
+which the projected body is moving as a function of the
+time that has elapsed since its projection; for obviously
+the rate changes with the time, and that is all that is
+needed to justify us in regarding the time that elapses as
+a variable and the rate of movement as a function of that
+variable. Let us go on then, to consider the relation of
+this new function of the time elapsed to the function we
+have already considered. We will call the first function
+$f(x)$ and the second function~$f'(x)$. Then we shall have
+$x=$~the lapse of time since the projection of the body,
+measured in seconds; $f(x)=$~the height attained by the
+body in $x$~seconds, measured in feet; $f'(x) =$~the rate
+at which the body is rising after $x$~seconds, measured in
+feet per~second.
+
+\begin{Remark}
+It will be observed that $x$~must be positive, for we have
+no data as to the history of the body \emph{before} its projection,
+and if $x$ were negative that would mean that the lapse of
+time since the projection was negative, \ie~that the projection
+was still in the future. On the other hand, $f(x) = 128x-16x^2$
+will become negative as soon as $16x^2$ is greater than~$128x$,
+\ie~as soon as $16x$ is greater than~$128$, or $x$~greater than
+$\frac{128}{16}= 8$; which means that after eight seconds the body will
+not only have passed its greatest height but will already
+have fallen below the point from which it was originally
+%% -----File: 037.png---Folio 22-------
+projected, so that the ``height'' at which it is now found, \ie~$f(x)$,
+will be negative. Again $f'(x)$, or the rate at which the
+body is ``rising,'' will become negative as soon as the maximum
+height is passed, for then the body will be rising
+negatively, \ie~falling.
+\end{Remark}
+
+We have now to examine the connection between
+$f(x)$~and~$f'(x)$. Our common phraseology will help us
+to understand it. Thus: $f(x)$~expresses the height of
+the body at any moment, $f'(x)$~expresses the rate at which
+the body is rising; but the rate at which it is rising is
+\emph{the rate at which its height, or~$f(x)$, is increasing}. That is,
+$f'(x)$~represents the rate which $f(x)$ is increasing. A glance
+at \Figref{1} will suffice to show that this rate is not uniform
+throughout the course of the projectile. At first the
+moving body rises, or increases its height, rapidly, then
+less rapidly, then not at all, then negatively---that is to
+say, it begins to fall. This, as we have seen, may be
+expressed in two ways. We may say $f(x)$ [$={}$the
+height] first increases rapidly, then slowly, then negatively,
+or we may say $f'(x)$ [$={}$the rate of rising] is first
+great, then small, then negative.
+
+Formula: \emph{$f'(x)$~represents the rate at which $f(x)$~grows}.
+
+It is obvious then that some definite relation exists
+between $f(x)$ and~$f'(x)$, and Newton and Leibnitz discovered
+the nature of that relation and established rules
+by which, if any function whatever,~$f(x)$, be given, another
+function~$f'(x)$ may be derived from it which shall
+indicate the rate at which it is growing.
+
+\begin{Remark}
+This second function is called the ``\emph{first derived function},''
+or the ``\emph{differential coefficient}''\footnote{See \Pageref{31}.} of the original function, and if
+the original function is called~$f(x)$, it is usual to represent the
+first derived function by~$f'(x)$. In some cases it is possible
+to perform the reverse operation, and if a function be given,
+say~$\phi(x)$, to find another function such that $\phi(x)$ shall
+%% -----File: 038.png---Folio 23-------
+represent the rate of its increase.\footnote
+ {Such a function always exists, but we cannot always ``find'' it,
+ \ie~express it conveniently in finite algebraical notation.}
+This function is then
+\Pagelabel{23}%
+called the ``\emph{integral}'' of~$\phi(x)$ and is written ${\displaystyle \int_0^x \phi(x)\, dx}$. Thus
+if we start with~$f(x)$, find the function which represents the
+rate of its growth and call it~$f'(x)$, and then starting with~$f'(x)$
+find a function whose rate of growth is~$f'(x)$ and call
+it ${\displaystyle \int_0^x f'(x)\, dx}$, we shall obviously have ${\displaystyle \int_0^x f'(x)\, dx = f(x)}$.
+
+The only flaw in the argument is that it assumes there to
+be only one function of~$x$ which increases at the rate indicated
+by~$f'(x)$, and therefore assumes that if we find \emph{any} function
+${\displaystyle \int_0^x f'(x)\, dx}$ which increases at that rate, it must necessarily be
+the function,~$f(x)$, which we already know does increase at that
+rate. This is not strictly true, and ${\displaystyle \int_0^x f'(x)\, dx}$ is, therefore, an
+indeterminate symbol, which represents~$f(x)$ and also certain
+other functions of~$x$, which resemble~$f(x)$ in all respects save
+one, which one will not in any way affect our inquiries. As
+far as any properties we shall have to consider are concerned,
+we may regard the equation
+\[
+\int_0^x f'(x)\, dx = f(x)
+\]
+as absolute.
+\end{Remark}
+
+In the case we are now considering, $f(x)$ is $128x - 16x^2$,
+and an application of Newton's rules will tell us that
+$f'(x)$ is $128 - 32x$. That is to say, if we are told that
+$x$ being the number of seconds since the projection, the
+height of the body in feet is always $128x - 16x^2$ for all
+values of~$x$, then we know by the rules, without further
+experiment, that the rate at which its height is increasing
+will always be $128 - 32x$ ft.-per-second, for all
+values of~$x$. But the rate at which the height is
+increasing is the rate at which the body is rising, so
+that $128 - 32x$ is the formula which will tell us the
+rate at which the body is rising after the lapse of $x$~seconds.\footnote
+ {See table on \Pageref{24}.---\textit{Trans.}}%[** TN: Added footnote]
+%% -----File: 039.png---Folio 24-------
+\begin{table}[hbt]%[** TN: Floating to avoid noticeably underfull page]
+\Pagelabel{24}%
+\[
+\begin{array}{c@{}l}
+\settowidth{\TmpLen}{\small $x =$ number of seconds}
+\parbox[c]{\TmpLen}{\centering\small $x =$ number of seconds\\ since the projection.}
+ &\quad\settowidth{\TmpLen}{\small Rate at which the}
+ f'(x) = 128 - 32x = \left\{
+ \parbox[c]{\TmpLen}{\centering\small Rate at which the\\ body is rising, in\\ feet-per-second.}\right.\\
+&\\[-12pt]
+\hline
+\Strut
+0 & f'(0) = 128 - 32 × 0 = \PadTo[r]{-128}{128} \\
+1 & f'(1) = 128 - 32 × 1 = \PadTo[r]{-128}{96} \\
+2 & f'(2) = 128 - 32 × 2 = \PadTo[r]{-128}{64} \\
+3 & f'(3) = 128 - 32 × 3 = \PadTo[r]{-128}{32} \\
+4 & f'(4) = 128 - 32 × 4 = \PadTo[r]{-128}{0} \\
+5 & f'(5) = 128 - 32 × 5 = \PadTo[r]{-128}{-32} \\
+6 & f'(6) = 128 - 32 × 6 = \PadTo[r]{-128}{-64} \\
+7 & f'(7) = 128 - 32 × 7 = \PadTo[r]{-128}{-96} \\
+8 & f'(8) = 128 - 32 × 8 = \PadTo[r]{-128}{-128}\\
+\text{etc.} & \ \text{etc.}\PadTo{{}= 128 - 32 × 8 = {}}{\text{etc.}} \;\PadTo[r]{-128}{\text{etc.}}
+\end{array}
+\]
+\end{table}
+
+Now the connection between $f'(x)$~and~$x$ can be
+represented graphically, just as the connection between
+$f(x)$~and~$x$ was. It must be represented by a curve (in
+this case a straight line), which makes the vertical
+intercept $12.8$ (representing $128$~ft.\ per~second), when
+the bearer is at the origin (\ie~when $x$~is~$0$), making it $9.6$
+when the bearer has been moved through one unit to the
+right of the origin (or when $x$~is~$1$), and so forth. It is
+given in \Figref{3} (\Pageref{9}), and registers all the facts drawn out
+in our table, together with all the intermediate facts
+connected with them. If we wish to read this curve,
+and to know at what rate the body will be rising after,
+say, one and a half seconds, we suppose our bearer to
+be pushed half-way between $1$~and~$2$ on our base line,
+and then running our eye up the vertical line it carries
+till it is intercepted by the curve, we find that the
+vertical intercept measures $8$~units. This means that
+the rate at which the body is rising, one and a half
+seconds after its projection, is $80$~ft.\ per~second.
+
+\begin{Remark}
+No attempt will be made here to demonstrate, even in a
+simple case, the algebraical rules by which the derived
+functions are obtained from the original ones; but it may be
+well to show in some little detail, by geometrical methods,
+%% -----File: 040.png---Folio 25-------
+the true nature of the connection between a function and its
+derived function, and the possibility of passing from the one
+to the other.\footnote
+ {The student who finds this note difficult to understand is recommended
+ not to spend much time over it till he has studied the rest of
+ the book.}
+
+Suppose $OP_1P_2P_3$ in \Figref{4} to be a curve representing the
+connection of $f(x)$~and~$x$. We may again suppose $f(x)$ to
+represent the amount of work done against some constant
+force, in which case it will conform to the type $y=f(x)=ax-bx^2$.
+The curve in the figure is drawn to the formula
+\[
+ f(x) = 2x - \frac{x^2}{8}, \text{ where } a=2, b=\tfrac{1}{8}.
+\]
+This will give the following pairs of corresponding values:---
+\[
+\begin{array}{c@{\quad}r@{\;}l@{\;}l@{}c}
+x &f(x)=& 2x-\dfrac{x^2}{8} & =y.
+ &\settowidth{\TmpLen}{\small Growth for last}%
+ \parbox[c]{\TmpLen}{\centering\small Growth for last\\ unit of in-\\crease of~$x$.\medskip} \\
+\hline
+\Strut
+0 &f(0)=& 2 × 0 - \frac{0}{8} &= 0. \\
+1 &f(1)=& 2 × 1 - \frac{1}{8} &= 1\frac{7}{8} &\frac{15}{8} \\
+2 &f(2)=& 2 × 2 - \frac{4}{8} &= 3\frac{1}{2} &\frac{13}{8} \\
+3 &f(3)=& 3 × 2 - \frac{9}{8} &= 4\frac{7}{8} &\frac{11}{8} \\
+4 &f(4)=& 4 × 2 - \frac{16}{8} &= 6 &\frac{9}{8} \\
+5 &f(5)=& 5 × 2 - \frac{25}{8} &= 6\frac{7}{8} &\frac{7}{8} \\
+6 &f(6)=& 6 × 2 - \frac{36}{8} &= 7\frac{1}{2} &\frac{5}{8} \\
+7 &f(7)=& 7 × 2 - \frac{49}{8} &= 7\frac{7}{8} &\frac{3}{8} \\
+8 &f(8)=& 8 × 2 - \frac{64}{8} &= 8 &\frac{1}{8} \\
+9 &f(9)=& 9 × 2 - \frac{81}{8} &= 7\frac{7}{8} &\makebox[0pt][r]{$-$}\frac{1}{8} \\
+\text{etc.} &\text{etc.}\quad &\multicolumn{2}{c}{\PadTo{9 × 2 - \frac{81}{8}= 7\frac{7}{8}}{\text{etc.}}}
+ & \text{etc.}
+\end{array}
+\]
+It is clear from an inspection of the curve and from the
+last column in our table that the rate at which $f(x)$ or~$y$
+increases per unit increase of~$x$ is not uniform throughout its
+history. While $x$~increases from $0$ to~$1$, $y$~grows nearly two
+units, but while $x$~increases from $7$ to~$8$, $y$~only grows one
+eighth of a unit. Now we want to construct a curve on
+which we can read off the rate at which $y$ is growing at any
+point of its history. For instance, if $y$~represents the height
+%% -----File: 041.png---Folio 26-------
+of a body doing work against gravitation (say rising), we want
+to construct a curve which shall tell us at what rate the height
+is increasing at any moment, \ie~at what rate the body is rising.
+
+Now since the increase of the function is represented by
+the rising of the curve, the rate at which the function is
+increasing is the same thing as the rate at which the curve is
+rising, and this is the same thing as the steepness of the curve.
+
+Again, common sense seems to tell us (and I shall presently
+show that it may be rigorously proved) that the steepness of
+the tangent, or line touching the curve, at any point is the
+same thing as the steepness of the curve at that point. Thus
+in \Figref{4}, $R_{1}P_{1}$ (the tangent at~$P_{1}$) is steeper than~$R_{2}P_{2}$
+(the tangent at~$P_{2}$), and that again is steeper than~$R_{3}P_{3}$ (the
+tangent at~$P_{3}$), which last indeed has no steepness at all; and
+obviously the curve too is steeper at~$P_{1}$ than at~$P_{2}$, and
+has no steepness at all at~$P_{3}$.
+
+\Pagelabel{26}%
+But we can go farther than this and can get a precise numerical
+expression for the steepness of the tangent at any point~$P$,
+by measuring how many times the line~$QP$ contains the line~$RQ$
+($Q$~being the point at which the perpendicular from any
+point,~$P$, cuts the axis of~$x$, and~$R$ the point at which
+the tangent to the curve, at the same point~$P$, cuts the same
+axis). For since $QP$ represents the total upward movement
+accomplished by passing from~$R$ to~$P$, while $RQ$ represents
+the total forward movement, obviously $QP:RQ = {}$ratio of upward
+movement to forward movement${}={}$steepness of tangent.
+
+But steepness of tangent at~$P = {}$steepness of curve at~$P = {}$rate
+at which $y$~is growing at~$P$. To find the rate at which
+$y$~is growing at $P_{1}$,~$P_{2}$, $P_{3}$,~etc.\ we must therefore find the
+ratios $\dfrac{Q_{1}P_{1}}{R_{1}Q_{1}}$, $\dfrac{Q_{2}P_{2}}{R_{2}Q_{2}}$, $\dfrac{Q_{3}P_{3}}{R_{3}Q_{3}}$~etc. But if we take $r_{1}$,~$r_{2}$,~$r_{3}$, etc.\
+each one unit to the left of $Q_{1}$,~$Q_{2}$, $Q_{3}$,~etc.\ and draw
+$r_{1}p_{1}$,~$r_{2}p_{2}$, $r_{3}p_{3}$~etc.\ parallel severally to $R_{1}P_{1}$,~$R_{2}P_{2}$, $R_{3}P_{3}$~etc.,
+then by similar triangles we shall have
+\[
+\frac{Q_{1}P_{1}}{R_{1}Q_{1}} = \frac{Q_{1}p_{1}}{r_{1}Q_{1}},\quad
+\frac{Q_{2}P_{2}}{R_{2}Q_{2}} = \frac{Q_{2}p_{2}}{r_{2}Q_{2}},\quad
+\frac{Q_{3}P_{3}}{R_{3}Q_{3}} = \frac{Q_{3}p_{3}}{r_{3}Q_{3}},\ \text{etc.,}
+\]
+but the denominators of the fractions on the right hand of
+the equations are all of them, by hypothesis, unity. Therefore
+the steepness of the curve at the points $P_{1}$,~$P_{2}$, $P_{3}$~etc.\
+is numerically represented by $Q_{1}p_{1}$,~$Q_{2}p_{2}$, $Q_{3}p_{3}$,~etc.
+
+In our figure the points~$P_{1}$, $P_{2}$,~$P_{3}$ correspond to the
+%% -----File: 042.p n g----------
+%[Blank Page]
+%% -----File: 043.p n g----------
+\begin{figure}[p]
+\Pagelabel{25}%
+ \begin{center}
+ \Fig{4}
+ \Input{043a}
+ \vfil
+ \null\hfill\Fig{5}
+ \Input[2.5in]{043b}
+ \end{center}
+\end{figure}
+%[To face page 27.]
+%% -----File: 044.png---Folio 27-------
+values $x=2$, $x=4$, $x=8$, and the lines $Q_{1}p_{1}$, $Q_{2}p_{2}$, $Q_{3}p_{3}$ are
+found on measurement to be $\frac{3}{2}$,~$1$,~$0$.
+
+We may now tabulate the three degrees of steepness of
+the curve (or rates at which the function is increasing), corresponding
+to the three values of~$x$:---
+\[
+\begin{array}{c@{\qquad}c}
+x & \settowidth{\TmpLen}{\small Steepness of curve${}={}$rate}
+\parbox[c]{\TmpLen}
+ {\centering\small Steepness of curve${}={}$rate \\ at which $y$ is growing.\medskip} \\
+\hline
+\Strut
+2 & \frac{3}{2} \\
+4 & 1 \\
+8 & 0
+\end{array}
+\]
+
+By the same method we may find as many more pairs of
+corresponding values as we choose, and it becomes obvious
+that the rate at which $y$ or~$f(x)$ is growing is itself a function
+of~$x$ (since it changes as $x$~changes); and we may indicate this
+function by~$f'(x)$. Then our table gives us pairs of corresponding
+values of $x$~and~$f'(x)$, and we may represent the connection
+between them by a curve, as usual. In this particular
+instance the curve turns out to be a straight line, and it is
+drawn out in \Figref{5}.\footnote
+ {Its formula is $y=2-\frac{x}{4}$.}
+Any vertical intercept on \Figref{5},
+therefore, represents the rate at which the vertical intercept
+for the same value of~$x$ on \Figref{4} is growing.
+
+Thus we see that, given a curve of any variable and
+function, a simple graphical method enables us to find as
+many points as we like upon the curve of the same variable
+and a second function, which second function represents the
+rate at which the first function is growing; \textit{e.g.}, given a
+curve of time-and-height that tells us what the height of a
+body will be after the lapse of any given time, we can construct
+a curve of time-and-rate which will tell us at what rate
+that height is increasing, \ie~at what rate the body is rising,
+at any given time.
+
+It remains for us to show that the common sense notion
+of the steepness of the curve at any point being measured by
+the steepness of the tangent is rigidly accurate. In proving
+this we shall throw further light on the conception of ``rate
+%% -----File: 045.png---Folio 28-------
+of increase at a point'' as applied to a movement, or other
+increase, which is constantly varying.
+
+If I ask what is the average rate of increase of~$y$ between
+the points $P_{2}$~and~$P_{3}$ (\Figref{4}), I mean: If the increase of
+$y$ bore a uniform ratio to the increase of~$x$ between the
+points $P_{2}$~and~$P_{3}$, what would that ratio be? or, if a point
+moved from $P_{2}$ to~$P_{3}$ and if throughout its course its upward
+movement bore a uniform ratio to its forward movement,
+what would that ratio be? The answer obviously is $\dfrac{S_3P_3} {P_2S_3}$.
+Completing the figure as in \Figref{4} we have, by similar
+triangles, average ratio of increase of~$y$ to increase of~$x$
+between the points $P_{2}$ and $P_{3}=\dfrac{S_3P_3}{P_2S_3}=\dfrac{Q_3P_3}{MQ_3}$.
+
+Now, keeping the same construction, we will let $P_{3}$ slip
+along the curve towards~$P_{2}$, making the distance over which
+the average increase is to be taken smaller and smaller.
+Obviously as $P_{3}$~moves, $Q_{3}$,~$S_{3}$, and~$M$ will move also, and
+the ratio $\dfrac{S_3P_3}{P_2S_3}$ will change its value, but the ratio $\dfrac{Q_3P_3}{MQ_3}$ will
+likewise change its value in precisely the same way, and will
+always remain equal to the other. This is indicated by the
+dotted lines and the thin letters in \Figref{4}.
+
+Thus, however near $P_{3}$ comes to $P_{2}$ the average ratio of
+the increase of~$y$ to the increase of~$x$ between $P_2$~and~$P_3$ will
+always be equal to $\dfrac{Q_3P_3}{MQ_3}$. But this ratio, though it changes
+as $P_{3}$ approaches~$P_{2}$, does not change indefinitely, or without
+limit; on the contrary, it is always approaching a definite,
+fixed value, which it can never quite reach as long as $P_{3}$
+remains distinct from~$P_{2}$, but which it can approach within
+any fraction we choose to name, however small, if we make
+$P_{3}$ approach $P_{2}$ near enough. It is easy to see what this
+ratio is. For as $P_{3}$ approaches~$P_{2}$, $S_{3}$ approaches~$P_{2}$, $Q_{3}$ approaches~$Q_{2}$,
+$M$ approaches~$R_{2}$, and therefore the ratio $\dfrac{Q_3P_3}{MQ_3}$
+approaches the ratio $\dfrac{Q_2P_2}{R_2Q_2}$, which is the ratio that measures
+the steepness of the tangent at~$P_{2}$. We must realise exactly
+what is meant by this. The lengths $Q_{2}P_{2}$ and~$R_{2}Q_{2}$ have
+definite magnitudes, which do not change as $P_{3}$ approaches~$P_{2}$,
+whereas the lengths $S_{3}P_{3}$ and $MR_{2}+Q_{2}Q_{3}$, which distinguish
+%% -----File: 046.png---Folio 29-------
+$Q_2P_2$ and $R_2Q_2$ from $Q_3P_3$ and $MQ_3$ respectively,
+may be made as small as we please, and therefore as
+small fractions of the fixed lengths $Q_2P_2$ and $R_2Q_2$ as
+we please. Therefore the numerator and denominator of
+$\dfrac{Q_3P_3}{MQ_3}$ may be made to differ from the numerator and denominator
+of $\dfrac{Q_2P_2}{R_2Q_2}$ by \emph{as small fractions of $Q_2P_2$ and $R_2Q_2$ themselves}
+as we please. That is to say, the former fraction, or
+ratio, may be made to approach the latter without limit.
+But the ratio $\dfrac{S_3P_3}{P_2S_3}$ is always the same as the ratio $\dfrac{Q_3P_3}{MQ_3}$, and
+therefore the ratio $\dfrac{S_3P_3}{P_2S_3}$ (or the average ratio of the increase of~$y$
+to the increase of~$x$ between $P_2$~and~$P_3$) may be made to
+approach the ratio $\dfrac{Q_2P_2}{R_2Q_2}$ without limit. Thus, though $S_3P_3$
+and $P_2S_3$ can be made as small as we please absolutely, neither
+of them can be made as small as we please with reference to
+the other. On the contrary, they tend towards the fixed ratio
+$\dfrac{Q_2P_2}{R_2Q_2}$ as they severally approach zero. This is the limit of
+the average ratio of the increase of~$y$ to the increase of~$x$
+between $P_2$~and~$P_3$, and may be approached as nearly as we
+please by taking that average over a small enough part of the
+curve, that is by taking $P_3$ near enough to~$P_2$. If we take
+the average over no space at all and make $P_3$~coincide with~$P_2$,
+we may if we like say that the ratio of the increase of~$y$
+to the increase of~$x$ \emph{at} the point $P_2$ actually \emph{is} $\dfrac{Q_2P_2}{R_2Q_2}$, or $Q_2p_2$
+per unit. [\NB---Let special note be taken of the conception
+of \emph{rate per unit} as a limit to which a ratio approaches, as
+the related quantities diminish without limit.] But we must
+remember that since neither $y$~nor~$x$ increases at all \emph{at} a
+point, and since $S_3P_3$ and $P_2S_3$ both alike disappear when $P_3$
+coincides with~$P_2$, there is not really any ratio between them
+\emph{at} the limit. But this is exactly in accordance with our
+original definition of the ``rate of growth of~$y$ \emph{at} a given
+point in its history'' (\Pageref{19}), which we discovered to mean
+``the rate at which $y$ would grow if all modifying circumstances
+ceased to operate,'' or ``the limit of the average rate
+of growth of~$y$ between $P_2$~and~$P_3$, as $P_3$ approaches~$P_2$.'' As a
+%% -----File: 047.png---Folio 30-------
+matter of fact $y$ never grows at that rate at all, for as soon as it
+grows ever so little it becomes subject to modifying influence.
+
+We see, then, that as $P_3$ approaches $P_2$ the limiting position
+of the line $P_3P_2M$ is~$P_2R_2$, the tangent at~$P_2$ (as indeed
+is evident to the eye), and the limiting ratio of the increase
+of~$y$ to the increase of~$x$ is $\dfrac{Q_2P_2}{R_2Q_2}$, or the steepness of the
+tangent at~$P_2$. Thus ``the steepness of the tangent at~$P_2$'' is
+the only exact interpretation we can give to ``the steepness
+of the curve at~$P_2$,'' and our common sense notion turns out
+to be rigidly scientific.
+
+We see, then, that by drawing the tangents we can read
+$f'(x)$ as well as~$f(x)$ from \Figref{4}. But this is not easy. On
+the other hand, in \Figref{5}, it is easy to read~$f'(x)$, but not so
+easy to read~$f(x)$. This latter may also be read, however. Let
+the student count the units of area included in the triangle~$OPP_3$
+(\Figref{5}). He will find that they equal the units of
+length in $Q_3P_3$ (\Figref{4}). Or if he take $Q_2$ in \Figref{5}, corresponding
+to $Q_2$ in \Figref{4}, he will find that the area~$OPP_2Q_2$
+(\Figref{5}) contains as many units as the length~$Q_2P_2$ (\Figref{4}).
+Or again, taking $Q_1$~and~$Q_2$, the area $Q_1P_1P_2Q_2$ (\Figref{5}) contains
+as many units as the length~$S_2P_2$ (\Figref{4}), which gives
+the growth of~$y$ between $P_1$~and~$P_2$.
+
+Thus in \Figref{4} the absolute value of~$y$, or~$f(x)$, is indicated
+by \emph{length} and the rate of growth of~$y$, or~$f'(x)$, by \emph{slope} of
+the tangent; whereas in \Figref{5} $f'(x)$ is indicated by \emph{length}
+and $f(x)$ by \emph{area}. In either case the different character of the
+units in which $f(x)$~and~$f'(x)$ are estimated indicates the difference
+in their nature, the one being \emph{space} and the other \emph{rate}.
+
+The reason why the areas in \Figref{5} correspond to the
+lengths in \Figref{4} is not very difficult to understand, for we
+shall find that the units of length in~$S_2P_2$ (\Figref{4}), for example,
+and the units of area in~$Q_1P_1P_2Q_2$ (\Figref{5}) both represent
+exactly the same thing, viz.\ the product of the average
+rate of growth of~$y$ between $P_1$~and~$P_2$ into the period over
+which that average growth is taken, which is obviously equivalent
+to the total actual growth of~$y$ between the two points.
+
+To bring this out, let us call the average rate of growth
+of~$y$, between $P_1$~and~$P_2$, $r$, and the period over which that
+growth is taken,~$t$. Then we shall have $rt={}$average rate of
+growth${}×{}$period of growth${}={}$total growth.
+%% -----File: 048.png---Folio 31-------
+
+Now, in \Figref{4}, taking $OQ_1=x_1$, $OQ_2=x_2$, $Q_1P_1=y_1$, $Q_2P_2=y_2$,
+we shall have $r=\dfrac{P_2S_2}{P_1S_2}=\dfrac{y_2-y_1}{x_2-x_1}$, and $t=Q_1Q_2=x_2-x_1$, and
+$rt = \dfrac{y_2-y_1}{x_2-x_1}(x_2-x_1) = y_2-y_1 = P_2S_2$.
+
+We must now find the representative of~$rt$ in \Figref{5}, and
+to do so we must look for some line that represents~$r$ or
+$\dfrac{y_2-y_1}{x_2-x_1}$ or the average rate of growth of~$y$ between $P_1$~and~$P_2$.
+Now the rate of growth of~$y$ at~$P_1$ is represented by~$y'_1$, and
+its rate of growth at~$P_2$ by~$y'_2$; and an inspection of the
+figure shows that it declines \emph{uniformly} between the two
+points, so that the average rate will be half way between $y'_1$~and~$y'_2$.
+This is represented by the line~$AB$, which equals
+$\dfrac{Q_1P_1+Q_2P_2}{2}$ or $\dfrac{y'_1+y'_2}{2}$. We have then, in \Figref{5}, $r=AB$.
+But $t=x_2-x_1$ or $Q_1Q_2$ as before. Therefore $rt = AB × Q_1Q_2$.
+Again, a glance at \Figref{5} will show that, by equality of
+triangles, the area $AB × Q_1Q_2$ is equal to the area~$Q_1P_1P_2Q_2$.
+Combining our results then, we have
+\[
+Q_1P_1P_2Q_2 \text{ (\Figref{5})} =rt=P_2S_2 \text{ (\Figref{4})}
+\]
+or units of length in $P_2S_2=$ units of area in~$Q_1P_1P_2Q_2$.
+\QED
+
+Had the curve in \Figref{5} not been a straight line, the proof
+would have been the same in principle, though not so simple;
+and the areas would still have corresponded exactly to the
+lengths in the figure of the original function.\footnote
+ {We have seen that the increment of~$y$ (or~$y_2-y_1$) equals the increment
+ of~$x$ (or~$x_2-x_1$) multiplied by $\dfrac{y'_1+y'_2}{2}$ $\left(\text{or } \dfrac{y_2-y_1}{x_2-x_1}\right)$.\Pagelabel{31}%
+
+ Thus: increment of $y={}$increment of $x × \dfrac{y'_1+y'_2}{2}$; and $\dfrac{y'_1+y'_2}{2}=
+ \dfrac{f'(x_1)+f'(x_2)}{2}$; now the increment of~$y$ is the magnitude that differentiates
+ $y_2$ from~$y_1$, and is, therefore, called by Leibnitz the ``quantitas
+ differentialis'' of~$y$, though this term is only applied when $y_1$ and
+ $y_2$ are taken very near together, so that the ``quantitas differentialis''
+ of $y_1$ and $y_2$ bears only a very small ratio to the ``quantitas integralis,''
+ or integral magnitude of $y_1$~itself.
+
+ Thus when $y_2$~and~$x_2$ approach $y_1$~and~$x_1$ very nearly, we have
+ differential of $y_1={}$differential of $x_1 × \dfrac{ f'(x_1)+f'(x_2)}{2}$, and as we approach
+ the limit, and the difference between $f'(x_1)$ and~$f'(x_2)$ becomes not
+ only smaller itself, but a smaller fraction of~$f'(x_1)$, we find that
+ $\dfrac{f'(x_1)+f'(x_2)}{2}$ approaches $\dfrac{f'(x_1)+f'(x_1)}{2}=f'(x_1)$.
+
+ In the limit, then, we have differential of $y_1 ={}$differential of $x_1 × f'(x_1)$;
+ or generally, differential of $y ={}$differential of $x × f'(x)$, where $f'(x)$ is
+ \emph{the coefficient which turns the differential of~$x$ into the differential
+ of~$y$}. Hence $f'(x)$ or~$y'$ is called the ``differential coefficient'' of
+ $f(x)$ or~$y$, and $y$ or~$f(x)$ is called the ``integral'' of $f'(x)$ or~$y'$.
+
+ I insert this explanation in deference to the wish of a friend, who
+ declares that he ``can never properly understand a term scientifically
+ until he understands it etymologically,'' and asks ``why it is a
+ coefficient and why it is differential.'' I believe his state of mind is
+ typical.}
+\end{Remark}
+
+It is essential that the reader should familiarise
+himself perfectly with the precise nature of the relation
+%% -----File: 049.png---Folio 32-------
+subsisting between the two functions we have been investigating,
+and I make no apology, therefore, for dwelling
+on the subject at some length and even risking
+repetitions.
+
+We have seen that $f'(x)$ is the rate at which $f(x)$ is
+increasing, or rate of growth of~$f(x)$. And we measure
+the rate at which a function is increasing by the
+number of units which would be added to the function
+while one unit is being added to the variable if all the
+conditions which determine the relation should remain
+throughout the unit exactly what they were at its commencement.
+
+Again, when we denote a certain function of~$x$ by the
+symbol~$f(x)$, we have~$y=f(x)$, and for $x=a$ $y=f(a)$,
+for $x=1$ $y=f(1)$, for $x=0$ $y=f(0)$, etc. This has been
+fully illustrated in previous tables (compare \Pageref{24}).
+\begin{flalign*}
+&\text{\indent Thus if } & f(x)&=128x-16x^{2}, & \phantom{Thus if} \\
+&\text{then} & f(2)&=[128 × 2-16 × 2^{2}] & \\
+& & &= 192.
+\end{flalign*}
+In \DPtypo{}{the} future, then, we may omit the intermediate stage
+and write at once $f(x)=128x-16x^2$; $f(2)=192$, etc.
+
+We may therefore epitomise the information given us
+\index{Projectile}%
+by the curves in Figs.\ \Figref[]{1}~and~\Figref[]{3} (combined in \Figref{6})\DPtypo{}{.}
+Thus---
+%% -----File: 050.p n g----------
+%[Blank Page]
+%% -----File: 051.p n g----------
+\begin{figure}[p]
+ \begin{center}
+ \Fig{6}
+ \Input[2in]{051a}
+ \end{center}
+\end{figure}
+%
+%[To face page 33.]
+%% -----File: 052.png---Folio 33-------
+%[** TN: Size-dependent hack to get table below to stay on the same page.]
+{\small
+\Pagelabel{33}%
+\[
+\begin{array}{r@{\;}l@{\quad}r@{\;}c}
+f(x) =& 128x - 16x^2 & f'(x) = & 128 - 32x \\
+\hline
+\Strut
+f(0) = & \Z\Z0 & f'(0) = & \PadTo[r]{-128}{128} \\
+f(1) = & 112 & f'(1) = & \PadTo[r]{-128}{96} \\
+f(2) = & 192 & f'(2) = & \PadTo[r]{-128}{64} \\
+f(3) = & 240 & f'(3) = & \PadTo[r]{-128}{32} \\
+f(4) = & 256 & f'(4) = & \PadTo[r]{-128}{0} \\
+f(5) = & 240 & f'(5) = & \PadTo[r]{-128}{-32} \\
+f(6) = & 192 & f'(6) = & \PadTo[r]{-128}{-64} \\
+f(7) = & 112 & f'(7) = & \PadTo[r]{-128}{-96} \\
+f(8) = & \Z\Z0 & f'(8) = & \PadTo[r]{-128}{-128} \\
+\end{array}
+\]}%
+which may be read in \Figref{6} from the lengths cut off
+by the two curves respectively on the vertical carried
+by the bearer as it passes points $0$,~$1$, $2$, $3$,~etc.
+
+This table states the following facts:---At the commencement
+the height of the body~[$f(x)$] is~$0$, but the
+rate at which that height is increasing~[$f'(x)$] is $128$~ft.\ per~second.
+That is to say, the height would increase by $128$~ft.,
+while the time increased by one second, if the conditions
+which regulate the relations between the time that elapses
+and space traversed remained throughout the second
+exactly what they are at the beginning of it. But those
+conditions are continuously changing and never remain
+the same throughout any period of time, however small.
+At the end of the first second then, the height attained
+[$f(x)$] is, not $128$~ft.\ as it would have been had there
+been no change of conditions, but $112$~ft., and the rate
+at which that height is now growing is $96$~ft.\ per~second.
+That is to say, if the conditions which determine the
+relation between the time allowed and the space traversed
+were to remain throughout the second exactly what they
+are at the beginning of it, then the height of the body
+[$f(x)$] would \emph{grow} $96$~ft., while the time grew one second.
+Since these conditions change, however, the height
+grows, not $96$~ft., but $80$~ft.\ during the next second, so
+that after the lapse of two seconds it has reached the
+height of $(112 + 80) = 192$~ft., and is now \emph{growing} at
+the rate of $64$~ft.\ per~second. After the lapse of four
+%% -----File: 053.png---Folio 34-------
+seconds the height of the body is $256$~ft., and that height
+\emph{is not growing at all}. That is to say, if the conditions
+remained exactly what they are at this moment, then
+the lapse of time would not affect the height of the
+body at all. But in this case we realise with peculiar
+vividness the fact that these conditions never do
+remain exactly what they are for any space of time,
+however brief. The movement of the body is the
+resultant of two tendencies, the constant tendency to
+\emph{rise} $128$~ft.\ per~second in virtue of its initial velocity,
+and the growing tendency to \emph{fall} in virtue of the continuous
+action of gravitation. At this moment these
+two tendencies are exactly equal, and \emph{if they remained}
+equal then the body would rise $0$~ft.\ per~second, and
+the lapse of time would not affect its position. But of
+the two tendencies now exactly equal to each other,
+one is continuously increasing while the other remains
+constant. Therefore they will not remain equal during
+any period, however short. Up to this moment
+the body rises, after this moment the body falls.
+There is no period, however short, \emph{during} which it is
+neither rising nor falling, but there is a point of time \emph{at}
+which the conditions are such that if they were continued
+(which they are not) it \emph{would} neither rise nor fall. This
+is expressed by saying that \emph{at} that moment the rate at
+which the height is growing is~$0$. If the reader will
+pause to consider this special case, and then apply the
+like reasoning to other points in the history of the projectile,
+it may serve to fortify his conception of ``rate.''
+After $6$~seconds the height is~$192$, and the rate at
+which it is growing is $-64$~ft.-per-second. That is to
+say, the body is \emph{falling} at the rate of $64$~ft.-per-second.
+At the end of $8$~seconds the height is~$0$, and the rate
+at which the height is growing is $-128$~ft.-per-second.
+
+All this is represented on the table, which may be
+continued indefinitely on the supposition that the body
+is free to fall below the point from which it was
+originally projected.
+%% -----File: 054.png---Folio 35-------
+
+The instance of the vertically projected body must
+be kept for permanent reference in the reader's mind,
+so that if any doubt or confusion as to the relation
+between $f'(x)$ and~$f(x)$ should occur, he may be able
+to use it as a tuning fork: $f'(x)$ is the rate at which
+$f(x)$ is growing, so that if $f(x)$ is the space traversed,
+then $f'(x)$ is the rate of motion, \ie~the rate at which
+the space traversed,~$f(x)$, is being increased.
+
+Now, when we are regarding time solely as a regulator
+of the height of the body, we may without any
+great stretch of language speak of the \emph{effect} of the
+lapse of time in allowing or securing a definite result
+in height. Thus the effect of $1$~second would be
+represented by $112$~ft., the effect of $4$~seconds by $256$~ft.,
+the effect of $7$~seconds by $112$~ft., the effect of
+$8$~seconds by $0$~ft. And to make it clear that we mean
+to register only the net result of the whole lapse of
+time in question, we might call this the ``total effect''
+of so many seconds. In this case $f(x)$ will represent
+the total effect of the lapse of $x$~seconds, regarded as
+a condition affecting the height of the body. What,
+then, will $f'(x)$ signify? It will signify, as always,
+the rate at which $f(x)$ is increasing. That is to say,
+it will signify the rate at which additions to the time
+are at this point increasing the effect, \ie~the rate at
+which the effect is growing. Now, since more time
+must always be added on at the margin of the time
+that has already elapsed, we may say that $f(x)$~represents
+the \emph{total effect} of $x$~seconds of time in giving height
+to the body, and that $f'(x)$~represents the \emph{effectiveness}
+of time, added at the margin of $x$~seconds, in \emph{increasing}
+the height. Or, briefly, $f(x) ={}$total effect, $f'(x) ={}$marginal
+effectiveness.
+
+Here the change of terms from ``effect'' to ``effectiveness''
+may serve to remind us that in the two cases
+we are dealing with two different kinds of magnitude---in
+the one case \emph{space} measured in feet absolutely (effect),
+in the other case \emph{rate} measured in feet-per-second.
+%% -----File: 055.png---Folio 36-------
+
+Before passing on to the economic interpretation of
+all that has been said, we will deal very briefly with
+another scientific illustration, which may serve as a
+transition.
+
+Suppose we have a carbon furnace in which the
+carbon burns at a temperature of $1500°$~centigrade, and
+suppose we are using it to heat a mass of air under
+\begin{figure}[hbt]
+ \begin{center}
+ \Fig{7}
+ \Input[4.5in]{055a}
+ \end{center}
+\end{figure}
+given conditions. Obviously the temperature to which
+we raise the air will be a function of the amount of
+carbon we burn, and will be a function which will
+increase as the variable increases; but not without
+limit, for it can never exceed the temperature of~$1500°$.
+Suppose the conditions are such that the first pound
+%% -----File: 056.png---Folio 37-------
+of carbon burnt raises the temperature of the air from
+\index{Carbon@{\textsc{Carbon Furnace}}}%
+$0°$ to $500°$, \ie~raises it one-third of the way from its
+present temperature to that of the burning carbon, then
+(neglecting certain corrections) the second pound of
+carbon burnt will again raise the temperature one-third
+of the way from its present point ($500°$) to that of
+the carbon ($1500°$). That is to say, it will raise it to
+$833.3°$; and so forth. Measuring the pounds of carbon
+consumed along the axis of~$x$ and the degrees centigrade
+to which the air is raised along the axis of~$y$
+($100°$ to a unit), we may now represent the connection
+between $f(x)$~and~$x$ by a curve.\footnote
+ {The formula will be $y = f(x) = 15 \left\{1-(\frac{2}{3})^x \right\}$}
+Its general
+form may be seen in \Figref{7}, and we shall have the
+total effect of the carbon in raising the temperature
+represented by $f(x)$, and assuming the following values:---
+\begin{align*}
+f(0) &= 0 & f(4) &= 12.04 & f(8) &= 14.42 \\
+f(1) &= 5[ = 500°] & f(5) &= 13.02 & f(9) &= 14.61 \\
+f(2) &= 8.3 & f(6) &= 13.68 & f(10) &= 14.74 \\
+f(3) &= 10.5 & f(7) &= 14.12 & f(11) &= 14.83 \\
+ & & f(12) &= 14.88
+\end{align*}
+
+Now here, as before, we may proceed (either graphically,
+see \Pageref{26}, or by aid of the rules of the calculus)
+to construct a second curve, the curve of $x$~and~$f'(x)$,
+which shall set forth the connection between $x$ and the
+steepness of the first curve, \ie~the connection between
+the value of~$x$ and the rate at which $f(x)$ is growing.\footnote
+ {Its formula will be $15(\frac{2}{3})^x \log_e (\frac{3}{2})$.}
+Again allowing $100°$ to the unit, measured on the axis
+of~$y$, we shall obtain (\Figref{8})---
+\begin{align*}
+f'(0) &= 6.08 & f'(4) &= 1.2 & f'(8) &= .24 \\
+f'(1) &= 4.05 & f'(5) &= \Z.8 & f'(9) &= .16 \\
+f'(2) &= 2.7 & f'(6) &= \Z.53 & f'(10) &= .1 \\
+f'(3) &= 1.8 & f'(7) &= \Z.35 & \rlap{\text{etc.}}\Z &
+\end{align*}
+
+What then will $f'(x)$ represent? Here as always
+%% -----File: 057.png---Folio 38-------
+we have $f'(x) ={}$the rate at which $f(x)$~is growing. But
+$f(x) ={}$the heat to which the air is raised, \ie~the total
+effect of the carbon. Therefore $f'(x)$~is the rate at which
+carbon, added at the margin, will increase the heat, or the
+marginal effectiveness of carbon in raising the heat.
+We have $x ={}$quantity of carbon burnt, $f(x) ={}$total effect
+of~$x$ in raising the heat of the air, $f'(x) ={}$marginal effectiveness
+of additions to~$x$.
+
+Comparing the illustration of the heated air with
+\begin{figure}[hbt]
+ \begin{center}
+ \Fig{8}
+ \Input[3in]{057a}
+ \end{center}
+\end{figure}
+that of the falling body we find that pounds of carbon
+have taken the place of seconds of time as the variable,
+total rise of temperature has taken the place of total
+space traversed as the first function of the variable, rate
+at which additions to carbon are increasing the temperature
+has taken the place of rate at which additions
+to the time allowed are increasing the space traversed,
+as the derived function; but in both cases the derived
+function represents the rate at which the first function
+is growing, in both cases the first function represents
+%% -----File: 058.png---Folio 39-------
+the total efficiency of any given quantity of the variable,
+and the derived function represents its effectiveness at
+any selected margin, so that in both cases the relation
+$f'(x)$~to~$f(x)$ is identical.\Pagelabel{39}%
+
+And now at last we may return to the economic
+interpretation of the curves.
+
+Assuming that \Figref{1} (\Pageref{9}) represents the connection
+between some economic function and its variable, as, for
+example, the connection between the quantity of coal I
+\index{Coal}%
+burn and the sum of advantages or gratifications I
+derive from it, and assuming further that one unit along
+the axis of~$x$ is taken to mean one ton of coal per month,
+we shall have no difficulty in reading \Figref{1} as follows:
+$f(0) = 0$, \ie~if I burn no coal I get no benefit from
+burning it; $f(1) = 11.2$, \ie~the total effect of burning
+one ton of coal per month is represented by $11.2$~units
+of satisfaction; $f(2) = 19.2$, \ie~the total effect of burning
+two tons of coal a month is greater than that of
+burning one ton a month, but not twice as great. The
+difference to my comfort between burning no coal and
+burning a ton a month is greater than the difference
+between burning one and burning two tons. So again,
+$f(4) = 25.6$, \ie~the total effect of four tons of coal per
+month in adding to my comfort is represented by $25.6$~units
+of gratification, and at this point its total effect is
+at its maximum; for now I have as much coal as I
+want, and if I were forced to burn more the total effect
+of that greater quantity would be less than that of a
+smaller quantity, or $f(5)$~is less than~$f(4)$. At last the
+point would arrive at which if I were forced to choose between
+burning, say, eight tons of coal a month and burning
+none at all, I should be quite indifferent in the matter.
+The total effect of eight tons of coal per month as a
+direct instrument of comfort would then be nothing.
+And if more yet were forced upon me at last I should
+prefer the risk of dying of cold to the certainty of
+being burned to death, and $f(x)$ would be a negative
+quantity.
+%% -----File: 059.png---Folio 40-------
+
+\begin{Remark}
+It must be observed that I am not here speaking of the
+\emph{construction} of economic curves, but of their \emph{interpretation} supposing
+we had them (see \Pageref{15}). But it will be seen presently
+that the construction of such curves is quite conceivable
+ideally, and that there is no absurdity involved in speaking
+of so many units of gratification. It is extremely improbable,
+however, that any actual economic curve would coincide with
+that of \Figref{1} (see \Pageref{48}).
+\end{Remark}
+
+Such would be the interpretation of \Figref{1}, $f(x)$~being
+read as the curve of quantity-and-total-effect of coal as
+a producer of comfort under given conditions of consumption.
+What then would be the interpretation of
+\Figref{3} or~$f'(x)$? Obviously $f'(x)$, signifying the rate of
+growth of~$f(x)$, or the ratio of the increase of~$f(x)$ to the
+increase of~$x$ at any point, would mean the rate at which
+an additional supply of coal is increasing my comfort,
+or the marginal effectiveness of coal as a producer of
+comfort to me. This marginal effectiveness of course
+varies with the amount I already enjoy. That is to
+say, $f'(x)$~assumes different values as $x$~changes. When
+I have no coal, the marginal effectiveness is very high.
+That is to say, increments of coal would add to my comfort
+at a great rate, $f'(0)= 12.8$. When I already command
+a ton a month further increments of coal would
+add to my comfort at a less rapid rate, $f'(1) = 9.6$;
+when I have four tons a month further increments would
+not add to my comfort at all, $f'(4) = 0$, after that yet
+further increments would detract from my comfort,
+$f'(5)=-32$.
+
+In thus interpreting Figs.\ \Figref[]{1}~and~\Figref[]{3} we have substituted
+consumption of coal per month (measured in
+tons), for lapse of time (measured in seconds), as our
+variable; sum of advantages derived from consuming
+the coal, for space traversed by the projectile, as $f(x)$,
+or the total effect of the variable; and rate per unit
+at which coal is increasing comfort, for rate per unit
+at which time is increasing the space traversed, as
+$f'(x)$, or the marginal effectiveness of the variable.
+%% -----File: 060.png---Folio 41-------
+
+If we call $f(x)$ the ``total utility'' of $x$~tons of coal
+per month, we might call $f'(x)$ the ``marginal usefulness''
+of coal when the supply is $x$~tons per month.
+
+The reader should now turn back to \Pageref{33}, and
+read the table of successive values of $f(x)$ and~$f'(x)$
+with the subsequent comments and interpretations,
+substituting the economic meanings of $x$, $f(x)$, and
+$f'(x)$ for the physical ones throughout.
+
+A similar re-reading of Figs.\ \Figref[]{7}~and~\Figref[]{8} will also be
+instructive.
+
+Before going on to the further consideration of the
+total effect and marginal effectiveness of a commodity
+as functions of the quantity possessed, it will be well
+to point out a method of reading $f'(x)$ which will bring
+it more nearly within the range of our ordinary experiences,
+and make it stand for something more definitely
+realisable by the practical intellect than can be the
+case with the abstract idea of rate.\Pagelabel{41}%
+
+Reverting to our first interpretation of \Figref{3}, we
+remember that $f'(2)=64$ means that after the lapse
+of $2$~seconds the body will be rising \emph{at the rate} of
+$64$~ft.\ per~second; but it is entirely untrue that it will
+actually rise $64$~ft.\ during the next following second.
+We see by \Figref{1} that it will only rise $48$~ft.\ in that
+second. This is because the rate, which was $64$~ft.\
+per~second at the beginning of the second, has constantly
+changed during the lapse of the second itself.
+But the rate of $64$~ft.\ per~second is the same thing as the
+rate of $6.4$~ft.\ per~tenth of a second (or per $.1$~second),
+and this again is the same as the rate $.64$~ft.\ per $.01$~second,
+or $.000064$~ft.\ per $.000001$~second, and I may
+therefore read \Figref{3} thus: $f'(2)=64$, \ie~after the lapse
+of $2$~seconds the body will be rising at the rate of
+$64$~millionths of a foot per millionth of a second. Now,
+we should have to allow many millionths of a second
+to elapse before the rate of movement materially
+altered, and therefore we may with a very close approximation
+to the truth say that the rate of motion will
+%% -----File: 061.png---Folio 42-------
+be the same at the end as it was at the beginning
+of the first millionth of a second, \ie\ $64$~millionths
+of a foot per millionth of a second. Hence it will
+be approximately true to say that during the next
+millionth of a second the body will actually rise $64$~millionths
+of a foot (compare \Pageref{20}).\Pagelabel{42}\footnote
+ {It would be [assuming the formula to be absolutely true]
+ $63.999984$ millionths of a foot. The error, therefore, would be
+ $\frac{16}{1000000}$ or $\frac{1}{62500}$ in~$64$.}
+But a rise of
+$64$~millionths of a foot would be a concrete \emph{effect; hence
+if we translate the \textsc{effectiveness} of the variable into terms
+of a small enough unit, it tells us within any degree of
+accuracy we may demand the actual \textsc{effect} of the next small
+increment of the variable}. This is expressed by saying
+that ``in the limit'' each small increment actually produces
+this effect; which means that by making the
+increments small enough we may make the proposition
+as nearly true as we like.
+
+Thus [assuming the ordinary formula $y=16x^2$ to
+be absolutely correct] it is nearly true to say that when
+a body has been falling $2$~seconds it will fall $64$~millionths
+of a foot in the next millionth of a second,
+$128$~millionths of a foot in the next $2$~millionths of a
+second, $64n$~millionths of a foot in the next $n$~millionths
+of a second, so long as $n$~is an insignificant
+number in comparison to one million. What is nearly
+true when the unit is small and more and more nearly
+true as the unit grows smaller is said to be ``true in
+the limit, as the unit decreases.''
+
+Marginal \emph{effectiveness} of the variable, then, may always
+be read as marginal \emph{effect} per unit of very small units
+of increment. And in this sense we shall generally
+understand it. Total effect and unitary marginal effect
+will then be magnitudes of the same nature or character;
+and indeed the unitary marginal effect will itself
+be a total effect in a certain sense, the total effect
+namely of one small unit, added at that particular place.
+Even when we are not dealing with small units we
+%% -----File: 062.png---Folio 43-------
+may still speak of the marginal effect of a unit of the
+commodity, but in that case the effect of a unit of the
+commodity at the margin of~$x$ will no longer correspond
+closely to the marginal effectiveness of the commodity
+at~$x$. It will correspond to the \emph{average} marginal effectiveness
+of the commodity between~$x$, at which its
+application begins, and $x + 1$, at which it ends. And if
+the effect of the next unit after the~$a$\textsuperscript{th} is~$z$, it will probably
+not be true (as it is in the case of small units)
+that the effect of the next two units will be nearly~$2z$.
+A reference to Figs.~\Figref[]{1}, \Figref[]{3}, \Figref[]{7},~\Figref[]{8}, and a comparison of
+the last column and the last but one in the table of
+\Pageref{4}, will sufficiently illustrate this point; and the
+economic illustration of the next paragraph will furnish
+an instance of the correspondence, in the limit, between
+the effectiveness of the commodity and the effect of a
+small unit.
+
+\begin{Remark}
+Reverting to Figs.\ \Figref[]{4}~and~\Figref[]{5} (\Pageref{25}) we have $Q_1 p_1$ in \Figref{4}
+$= Q_1 P_1$ in \Figref{5}. But we have seen that if we start from $P_1$ in
+\Figref{4} and move a very little way along the curve, the ratio of
+the increment of~$x$ to the increment of~$y$ will be very nearly
+$\dfrac{r_1 Q_1}{Q_ 1p_1}$; or in the limit $\dfrac{\text{increment of } x}{\text{increment of } y} = \dfrac{r_1 Q_1}{Q_1p_1}$. But $r_1 Q_1 = 1$,
+therefore in the limit $\dfrac{\text{increment of } x}{\text{increment of } y} = \dfrac{1}{\DPtypo{Q}{Q_1} p_1}$ (\Figref{4}) $= \dfrac{1}{Q_1 P_1}$ (\Figref{5}),
+or, in the limit, $Q_1 P_1 × \text{ increment of } x = \text{increment of } y$.
+Now in \Figref{5} increments of~$x$ are measured along~$OX$, and
+therefore (if we follow the ordinary system of interpretation)
+we shall regard $Q_1 P_1 × \text{ increment of } x$, as an area, and it will
+be seen that as $x$ decreases the area in question approximates
+to a thin slice cut vertically from the triangle~$Q_1 P_1 P_3$. But we
+have seen that areas cut in vertical slices out of this triangle
+correspond to lengths in \Figref{4}, or portions of the total effect
+of the variable. Thus if a small unit is taken, the \emph{effect} of
+units of a commodity applied at any margin (\Figref{4}) is approximately
+represented by the \emph{effectiveness} of the commodity
+at that margin (\Figref{5}) multiplied by the number of units.
+And in the limit this relation is said to hold absolutely
+(compare pp.~\Pageref[]{21},~\Pageref[]{42}).
+\end{Remark}
+%% -----File: 063.png---Folio 44-------
+
+The method of reading curves of quantity-and-marginal-effectiveness
+as though they were curves of
+quantity-and-marginal-effect may be illustrated by the
+following example.
+
+\Figref{9} represents part of the curve of quantity-and-marginal-effectiveness
+\Pagelabel{44}%
+of wheat in Great Britain, based
+\index{Wheat}%
+upon a celebrated estimate made about the beginning of
+the eighteenth century.\footnote
+ {The estimate is generally known as ``Gregory King's,'' and its
+ formula is
+ \[
+ 60y = 1500 - 374x + 33x^2 - x^3.
+ \]
+ }
+In the figure the unit of~$x$ is
+(roughly speaking) about $20$~millions of bushels; and if
+\begin{figure}[hbt]
+ \begin{center}
+ \Fig{9}
+ \Input[4.5in]{063a}
+ \end{center}
+\end{figure}
+we place our quantity-index eleven units from the origin,
+that will mean that we suppose the supply of wheat in
+Great Britain to be $220$~millions of bushels per annum.
+Our curve asserts that when we have that supply
+additions of wheat will have an ``effectiveness'' in supplying
+our wants represented by $.8$~per $20$~million
+bushels; but we cannot translate the ``effectiveness''
+into the actual ``effect'' which $20$~millions of bushels
+%% -----File: 064.png---Folio 45-------
+would have; because the ``effectiveness'' would not continue
+the same if so large an addition were made to our
+supply. On the contrary it would drop from $.8$ to~$.6$.
+But $.8$~per $20,000,000$ bushels is $.00000008$~per $2$~bushels
+and $.00000004$ per~bushel, and since the addition
+of another bushel to the $220$~millions already
+possessed will not materially affect the usefulness or
+effectiveness of wheat at the margin, we may say that
+that effectiveness remains constant during the consumption
+of the bushel of wheat, and therefore, given
+a supply of $20,000,000$ bushels a year, not only is the
+``marginal effectiveness'' of wheat $.8$~per $20,000,000$
+bushels or $.0000004$ per~bushel, but the ``marginal
+effect'' of a bushel is~$.00000004$. Thus, if we had two
+commodities, $W$~and~$V$, and curves of their quantity-and-marginal-usefulness
+or effectiveness similar to that in
+\Figref{9}, the vertical intercepts on the quantity-indices
+would indicate the marginal usefulness per unit of the
+two commodities, and if we then selected ``small'' units
+of each commodity bearing in each case the same proportion
+(say $1 : z$) to the unit to which the curve of the
+commodity was drawn, we should then have the marginal
+utility or effect of the small units of the two commodities
+proportional to the length of the vertical intercepts, and
+calling the small unit of~$W$, $w$, and the small unit of~$V$, $v$,
+and the ratio of the marginal usefulness of~$W$ to that of~$V$,
+$r$, we should have
+\begin{align*}
+\text{marginal utility of }
+ w &= \Z r × \text{marginal utility of } v \\
+\PadTo{\text{marginal}}{\Ditto} \PadTo{\text{utility of}}{\Ditto}
+ 2w &= 2r × \text{marginal utility of } v. \\
+\PadTo{\text{marginal utility of }}{\text{etc.}}
+ & \PadTo{2r × \text{marginal utility of } v}
+ {\text{etc.}\ \makebox[0pt][l]{\text{(compare \Pageref{56})}}}
+\end{align*}
+
+We shall make it a convention henceforth to use
+Roman capitals $A$,~$X$, $W$,~etc., to signify commodities,
+italic minuscules $a$,~$x$, $w$,~etc., to signify units of these
+commodities (generally ``small'' units in the sense explained),
+and italic capitals, \Person{A}, \Person{B}, etc., to signify persons.
+Thus we shall speak of the marginal \emph{usefulness} or \emph{effectiveness}
+of $A$,~$W$,~etc., and the marginal \emph{utility} or \emph{effect} of
+$a$,~$w$,~etc.
+%% -----File: 065.png---Folio 46-------
+
+What precise interpretation we are to give to our
+``units of satisfaction'' or ``utility'' measured on the
+axis of~$y$ is another matter, the consideration of which
+must be reserved for a later stage of our inquiry (see
+pp.~\Pageref[]{52},~\Pageref[]{78}).
+
+\begin{Remark}
+Jevons uses the terms ``total utility'' and ``final degree of
+utility,'' meaning by the latter what I have termed ``marginal
+usefulness'' or ``marginal effectiveness.'' His terminology
+hardly admits of sufficient distinction between ``marginal
+effectiveness,'' \ie~the \emph{rate} per unit at which the commodity is
+satisfying desire, and the ``marginal effect'' of a unit of the
+commodity, \ie~the actual result which it produces when
+applied at the margin. I think this has sometimes confused
+his readers, and I hope that my attempt to preserve the distinction
+will not be found vexatious. Note that the curves
+are always curves of quantity-and-marginal-usefulness, but
+that we can read them with more or less accuracy according
+to the smallness of the supposed increment into curves of
+quantity-and-marginal-utility for small increments.\Pagelabel{46}%
+\end{Remark}
+
+If the reader has now gained a precise idea of the
+total utility or effect and the marginal usefulness of
+commodities, he will see without difficulty that when
+we take a broad general view of life we are chiefly
+concerned with those commodities the total utility of
+which (or their total effect in securing comfort, giving
+pleasure, averting suffering, etc.)\ is high. In considering
+from a general point of view our own material
+welfare or that of a nation, our first inquiries will
+concern the necessaries of life, food, water, clothing,
+shelter, fuel. For these are the things a moderate
+supply of which has the highest total utility. The
+sum of advantages we derive from them collectively
+is, indeed, no other than the advantage of the life they
+support. This is what economists have in view when
+they speak of the ``value in use'' of such a commodity
+as water, and say that nothing is more ``useful'' than
+it. They mean that the total advantage derived from
+%% -----File: 066.p n g----------
+%[Blank Page]
+%% -----File: 067.p n g----------
+\begin{figure}[p]
+\Pagelabel{47}%
+\begin{center}
+ \Fig{10}
+ \Input[4.5in]{067a}
+ \vfil
+%[** TN: Book's graph of 30/(15 + x) - 1 not perfectly accurate]
+ \Fig{11}
+ \Input[3.75in]{067b}
+\end{center}
+\end{figure}
+%To face page 47.
+%% -----File: 068.png---Folio 47-------
+even a small supply of water, the total difference
+\index{Water}%
+between a little water and no water, is enormously
+great. The graphical expression of this would be a
+curve (connecting the total utility of water with its
+quantity) which would rise rapidly and to a great height.
+
+But if it is obvious that when we look upon life as
+a whole, and in the abstract, we are chiefly concerned
+with total utilities, and ask what are the commodities
+we could least afford to dispense with altogether, it is
+equally obvious that in detail and in concrete practice
+we are chiefly concerned not with the total utility but
+the marginal usefulness of things, or rather, their marginal
+utility; and we ask, not what is my whole stock
+of such a commodity worth to me, but how much would
+a little \emph{more} of it \emph{add} to my satisfaction or a little less
+of it detract therefrom. For instance, we do not ask,
+What is the total advantage I derive from all the water
+I can command, but what additional advantage should I
+derive from the extra supply of water for a bath-room,
+\index{Bath-room@{\textsc{Bath-room}}}%
+or for a garden hose? Materfamilias does not ask
+\index{Garden-hose}%
+what advantage she derives from having a kitchen fire,
+\index{Kitchen@{\textsc{Kitchen Fire}}}%
+but she asks, what additional advantage she would
+derive by keeping up her kitchen fire after dinner, by
+heating the oven every day, or by always letting the
+\index{Fire@{Fire in ``practising'' room}}%
+girls have a fire in the room when they are ``practising.''
+Or inversely, we do not ask what disadvantage we
+should incur by ceasing to burn coal, but what disadvantage
+\index{Coal}%
+we should incur by letting our fires go down
+earlier in the day, or having fewer of them. And note
+that this inquiry as to marginal usefulness of a commodity
+is made on its own merits, and wholly without
+reference to the total utilities of the articles in question.
+The fact that I should be much worse off without
+clothes than without books does not make me spend
+fifteen shillings on a new waistcoat instead of on
+\index{Waistcoat@{\textsc{Waistcoat}}}%
+Rossetti's works, if I think that the latter will \emph{add} more
+\index{Rossetti's Works}%
+to my comfort and enjoyment than the former. For
+$f(\text{clothes})$ may be as much bigger than $\phi(\text{books})$ as it
+%% -----File: 069.png---Folio 48-------
+likes, but if $f'(\text{clothes})$ is smaller than~$\phi'(\text{books})$ I shall
+spend the money on the books. So much is this the
+case that we habitually lose sight of the connection
+between $\phi'(\text{books})$ and~$\phi(\text{books})$, between $f'(\text{clothes})$
+and~$f(\text{clothes})$, and do not think, for instance, of
+$\phi'(\text{books})$ as marking the rate at which additional books
+increase the gratification \emph{we derive from books}, but simply
+as marking the rate at which they increase our gratification
+in general.
+
+\Pagelabel{48}%
+Before developing certain consequences of the principles
+we have been examining, let us try to get a
+better representation of our supposed economic functions
+than is supplied by the diagram of a projected body.
+It will be remembered that we saw reason to think
+that a large class of economic functions, representing
+total utilities, would bear an analogy to our \Figref{1} in
+so far as they would first increase and then decrease
+as the variable (\ie~the supply of the commodity)
+increased. But it is highly improbable that any
+economic curve would increase and decrease in the
+symmetrical manner there represented. It is not
+likely, for instance, that the inconvenience of having a
+unit too much of a commodity would be exactly equivalent
+to the inconvenience of having a unit too little.
+As a rule it would be decidedly less. Our economic
+functions, then, will, in many instances, rise more rapidly
+than they fall. The connection of such a function and
+its variable is represented by the upper curve on
+\Figref{10},\footnote
+ {The conditions stated in the text will be complied with by a
+ function of the form $a \log_e {(x + b)} - \log b - x$; and there are some
+ theoretical reasons for thinking that such a function may be a fair approximation
+ to some classes of actual economic functions. The
+ upper curve in \Figref{\DPtypo{9}{10}} is drawn to the formula $y=11 \log_e{(x+1)}-x$.}
+which rises rapidly at first, then rises slowly,
+and then falls more slowly still. Household linen
+\index{Linen}%
+might give a curve something of this character. It is
+not exactly a necessary of life, but the sum of advantages
+conferred by even a small stock is great. The
+rate at which additions to the stock add to its total
+%% -----File: 070.png---Folio 49-------
+utility is at first rapid, but it declines pretty quickly.
+At last we should have as much as we wanted and
+should find it positively inconvenient to stow away any
+more. The excess, however, would have to be very
+great indeed in order to reduce us to a condition as
+deplorable as if we had no linen at all. By way of
+practice in interpreting economic curves, let us suppose
+the unit of household linen, measured along the base
+line, to be such an amount as might be purchased for~£3.
+The curve would then represent the following
+case, which might well be that of a young housekeeper
+\index{Housekeeper}%
+with a four or five roomed cottage, and not much
+space for storage: Household linen (sheets, tablecloths,
+towels, etc.)\ to the amount of some £6~or~£10 worth
+($x = 2$ or~$3\frac{1}{3}$) is little short of a necessity. After this
+additions to the stock, though very acceptable, are not
+so urgently needed, and when the stock has reached
+£18~or~£20 worth ($x = 6$ or~$6\frac{2}{3}$) our housekeeper will
+consider herself very well supplied, and will scarcely
+desire more. Still, if she could get it for nothing, she
+would be glad to find room for it up to, say, £30~worth
+($x = 10$). If after this any one should offer her a present
+of more she would prefer to find a polite excuse for not
+accepting it, but would not be much troubled if she had to
+take it, unless the amount were very large;\footnote
+ {We are supposing throughout that the conditions exclude sale or
+ barter of the unvalued part of the stock.}
+but when
+the total stock had reached, say,~£45 ($x = 15$), the inconvenience
+would become serious, and our heroine, on the
+whole, would be nearly as hard put to it by having £15~worth
+too much as she would have been by having £12~worth
+too little. If her stock were still increased till
+it reached £60~worth ($x = 20$) she would be as badly
+off as if she had only £11~:~8s.\ worth ($x = 3\frac{4}{5}$). At this
+point our ``epic of the hearth'' breaks off.
+
+We may, of course, apply to this curve the process with
+which we are already familiar, and may find the derived
+function which represents the marginal effectiveness or
+%% -----File: 071.png---Folio 50-------
+usefulness of linen, that is to say, the rate at which
+increments of linen are increasing the sum of advantages
+derived from it. This marginal effectiveness or
+usefulness of linen is set forth on the higher curve in
+\Figref{11};\footnote
+ {Its formula is $\dfrac{11}{x + 1} - 1$.}
+on which may be read the facts already
+elaborated in connection with the curve on \Figref{10},
+the only difference being that the specific increase
+between any values of~$x$ is more easily read on \Figref{10},
+and the \emph{rate} of increase at any point more easily read
+on \Figref{11}.
+
+\Pagelabel{50}%
+An analogous pair of curves, with other constants,\footnote
+ {See \Pageref{9}.}
+may be found in the lower lines in Figs.\ \Figref[]{10}~and~\Figref[]{11}.\footnote
+ {They are drawn to the formulæ $y = 30 \log_e (x + 15) - \log_e 15 - x$
+ and $y = \dfrac{30}{x + 15} - 1$ respectively.}
+They might represent respectively the total utility and
+the marginal usefulness of china, for example. In \Figref{10}
+\index{China}%
+the lower curve does not rise so rapidly or so high as
+the other. That is to say, we suppose the total advantage
+derived from as much china as one would care to
+have to be far less than that derived from a similarly
+full supply of household linen. To be totally deprived
+of china (not including coarse crockery in the term)
+would be a less privation than to be totally deprived
+of linen. But we also observe that at a certain point,
+when the curve of linen is rising very slowly, the curve
+of china is rising rather more rapidly. That is to say,
+if our supplies of both linen and china increase \textit{pari
+passu}, unit for unit (£3~worth is the unit we have supposed),
+then there comes a point at which increments of
+china would add to our enjoyment at a greater rate than
+similar increments of linen, although in the mass the
+linen has done much more to make us comfortable than
+the china.
+
+On the curves of \Figref{11} this point is indicated by
+the point at which the curve of the marginal usefulness
+%% -----File: 072.png---Folio 51-------
+of china crosses, and thenceforth runs above, the curve
+of the marginal usefulness of linen.
+
+Now if I possess a certain stock of linen and a
+certain stock of china, and am in doubt as to the
+use to make of an opportunity which presents itself
+for adding in certain proportions to either or both,
+how will the problem present itself to me? I shall
+not concern myself at all with the total utilities,
+but shall simply ask, ``Will the quantity of linen or the
+quantity of china I can now secure \emph{add} most to my
+satisfaction.'' The total gratification I derive from the
+two articles together is made up of their two total utilities
+(represented by two straight lines, viz.\ the vertical intercepts
+made by the two curves on \Figref{10}), and it is
+indifferent to me whether I increase the one already
+greatest or the other, as long as the increase is the
+the same. I therefore ask not which curve is the \emph{highest},
+but which is the \emph{steepest} at the points I have reached on
+them respectively, or since the curves on \Figref{11} represent
+the steepness of those on \Figref{10}, I ask which of
+these is highest. In other words, I examine the~$f'(x)$'s,
+not the~$f(x)$'s; I compare the marginal usefulness and
+not the total utilities of the two commodities. If
+the choice is between one small unit of china and one
+similar unit of linen, I shall ask ``Which of the two has
+the higher marginal utility.'' If my stock of both is
+low, the answer will be ``linen.'' If my stock of both is
+high, it will be ``china.'' If, on the other hand, the
+choice is between one small unit of china and \emph{two} similar
+units of linen, the question will be ``Is the marginal
+effectiveness of china \emph{twice} as great as that of linen,'' if
+not I shall choose the linen, since double the amount at
+anything more than half the effectiveness gives a balance
+of effect over what the other alternative would yield.
+If it seems difficult to imagine the mental process by
+which one thing shall be pronounced exactly \emph{twice} as
+useful as another, we may express the same thing in
+other terms by asking whether half a small unit of china
+%% -----File: 073.png---Folio 52-------
+is as useful to us (or is worth as much to us) as one
+small unit of linen, thus transferring the inequality from
+the utilities to the quantities, and the equality from the
+quantities to the utilities.\footnote
+ {Observe that this transfer can only be made in the case of \emph{small}
+ units, for it assumes that half a unit of china is half as useful as a
+ whole unit, which implies that the marginal usefulness of china
+ remains the same throughout the unit.}
+
+\Pagelabel{52}%
+Such considerations as these spontaneously solve the
+problem that suggested itself at the threshold of our
+inquiries (\Pageref{15}) as to the theoretical possibility of fixing
+a unit of utility or satisfaction, and so theoretically
+constructing economic curves. We now see clearly
+enough that though our psychological arithmetic is so
+little developed that the simplest sums in hedonistic
+multiplication or division seem impossible and even
+absurd, yet, as a matter of fact, we are constantly comparing
+and weighing against each other the most heterogeneous
+satisfactions and determining which is the
+greater. The enjoyment of fresh air and friendship, of
+\index{Air, fresh}%
+\index{Friendship}%
+fresh eggs and opportunities of study, all in definite
+\index{Eggs@{\textsc{Eggs}, fresh}}%
+quantities, are weighed against each other when we
+canvass the advantages of residence in London within
+reach of our friends and the British Museum and residence
+\index{Museum, British}%
+in the country with fresh air and fresh eggs.
+Nay, we may even regard space and time as commodities
+each with its varying marginal usefulness. This year I
+eagerly accept a present of books which will occupy a
+\index{Books}%
+great deal of space in my house, but will save me an
+occasional journey to the library; for the marginal
+usefulness of my space and of my time are such that I
+find an advantage in losing space and gaining time
+under given conditions of exchange. Next year my
+space is more contracted, and its marginal usefulness is
+therefore higher; so I decline a similar present, preferring
+the occasional loss of half an hour to the permanent
+cramping of my movements in my own study.
+
+Thus we see that the most absolutely heterogeneous
+%% -----File: 074.png---Folio 53-------
+satisfactions are capable of being practically equated
+against one another, and therefore may be regarded as
+theoretically \emph{reducible to a common measure}, and consequently
+capable of being measured off in lengths, and
+connected by a curve with the lengths representing the
+quantities of commodity to which they correspond.
+We might, for instance, take the effort of doing a given
+amount of work as the standard unit by which to estimate
+the magnitude of satisfaction. Hence the truth of
+the remark, ``Pleasures cannot be measured in feet, and
+they cannot be measured in pounds; but they can be
+measured in foot-pounds'' (Launhardt). If I only had
+\index{Foot-tons}%
+one ton of coal per month, how much lifting work should
+\index{Coal}%
+I be willing to do for a hundredweight of coal? If I
+had two tons a month, how much lifting work would
+I then do for a hundredweight? Definite answers to
+these two questions and other similar ones are conceivable;
+and they would furnish material for a curve
+on which the utility of one, two, three,~etc.\ hundredweight
+of coal per month would be estimated in foot-pounds.
+In academical circles it is not unusual to take an hour of
+correcting examination papers as the standard measure
+\index{Examination papers}%
+of pleasures and pains. A pleasure to secure which a
+man would be willing to correct examination papers for
+six hours (choosing his time and not necessarily working
+continuously) must be regarded as six times as great
+as one for which he would only correct papers for an
+hour. If we wished to reduce satisfactions so estimated
+to the foot-pound standard, we should only have to
+ascertain in the case of each of the university dignitaries
+in question how many foot-pounds of heaving work he
+would undertake in order to escape an hour's work at
+the examination mill. Obviously this change of measure
+would not affect the \emph{relative} magnitudes of the satisfactions
+already estimated on the other scale. It does not,
+then, matter what we suppose the standard unit of satisfaction
+to be, provided we retain it unchanged throughout
+any set of investigations.
+%% -----File: 075.png---Folio 54-------
+
+\begin{Remark}
+It should be noted that to be theoretically accurate we
+must not suppose the quantity of work offered for the same
+quantity of the commodity to change over different parts of
+the curve, but rather the quantity of the commodity for
+which the same fixed quantity of work is offered. For if
+we change the quantity of work, we thereby generally
+change its hedonistic value per unit also, inasmuch as $400$~foot-tons
+\index{Foot-tons}%
+of work, for instance, would generally be more than
+twice as irksome as $200$~foot-tons.
+
+In working out an imaginary example, however, we will
+ignore this fact, and will suppose the hedonistic value of $100$~foot-tons
+to be constant. Let us, then, suppose that a householder
+would be willing to do $3300$ foot-tons of work\footnote
+ {An ordinary day's work is reckoned at $300$~foot-tons; a dock
+ labourer does~$325$ (Mulhall).}
+for a
+certain amount of linen, if he could not get it any other way.
+\index{Linen}%
+We will reckon that amount of linen the unit, and calling~$x$
+the amount of linen and $y$ its total utility, we shall have for
+$x=1$ $y=3300$, or allowing $500$~foot-tons to the unit of~$y$,
+$x=1$ $y=6.6$. Now suppose that having secured one unit,
+our householder would be willing to do $1750$ foot-tons of
+work for a second unit, but not more. This would be represented
+on our scale by~$3.5$, which, added to the previous~$6.6$,
+would give $y=10.1$ for~$x=2$. For yet another unit of linen,
+perhaps no more than $1125$ foot-tons would be offered, represented
+by~$2.2$ on our scale, or $y=12.3$ for~$x=3$, etc. On comparing
+these suppositions with \Figref{10} (\Pageref{47}), it will be found
+that this case would be graphically represented by the upper
+curve of that figure. It will be seen that though we have
+imagined an ideally perfect and exact power of estimating
+what one would be willing to do under given circumstances
+in order to secure a certain object of desire, yet there is
+nothing theoretically absurd in the imaginary process; so
+that the construction of economic curves may henceforth be
+regarded as theoretically possible.
+
+The reader may find it interesting to attempt to construct
+the economic curves that depict the history of some of his
+own wants. Taking some such article as coffee or tobacco,
+let him ask himself how much work he would do for a single
+cup or pipe per week or per day sooner than go entirely
+%% -----File: 076.png---Folio 55-------
+without, how much for a second, etc., and dotting down
+the results, see whether they seem to follow any law and
+form any regular curve. If they do not, it probably shows
+that his imagination is not sufficiently vivid and accurate to
+enable him to realise approximately what he would be willing
+to do under varying circumstances. In any case he will
+probably soon convince himself of the perfect theoretical
+legitimacy of thus supposing actual concrete economic curves
+to be constructed. But even if he cannot tell what amount
+of work he would be willing to do under the varying circumstances,
+obviously \emph{there is} a given amount, which, as a matter
+of fact, he would be willing to do under any given circumstances.
+Thus the curve \emph{really exists}, whether he is able to
+trace it or not.\Pagelabel{55}%
+\end{Remark}
+
+We may now return to our curves with a clear conscience,
+knowing that for any object of desire at any
+moment there actually exists a curve (could we but get
+at it) representing the complete history of the varying
+total utility that would accompany the varying quantity
+possessed. The man who knows most nearly what that
+curve is, in each case, has the most powerful and
+accurate economic imagination, and is best able to predict
+what his expenditure, habits of work, etc.\ would
+be under changed circumstances.
+
+We have now actually constructed some hypothetical
+curves (pp.\ \Pageref[]{48}, \Pageref[]{50}), and have shown that there are certain
+properties, easy to represent, which a large class of
+economic curves must have (pp.~\Pageref[]{15},~\Pageref[]{48}); and we have
+further shown that we are practically engaged, from
+day to day, in considering and comparing the marginal
+utilities of units of heterogeneous articles, that is to say,
+in constructing and comparing fragments of economic
+curves.
+
+We have seen, too, that if I had a chance of getting
+more china or more linen I should not consider the total
+utilities of these commodities, but the marginal utilities
+of the respective quantities between which the option
+lay.
+%% -----File: 077.png---Folio 56-------
+
+And so, too, if I had the opportunity of exchanging a
+\Pagelabel{56}%
+given quantity of china for a given quantity of linen, or the
+\index{China}%
+\index{Linen}%
+reverse, I should consider the marginal utilities of those
+quantities. Thus we see that the \emph{equivalence in worth} to
+me of units of two commodities is measured by their marginal,
+not their total, utilities, and in the limit (\Pageref{44}) is
+directly proportional to their marginal effectiveness or usefulness.
+If, for the stocks I possess, the marginal usefulness of
+linen is twice as great as that of china, \ie~if $f'(\text{linen}) = 2\phi'
+(\text{china})$, then I shall be glad to sacrifice small units of china
+in order to secure similar units of linen at anything up to the
+rate of two to one. But this very process, by decreasing my
+stock of china and increasing my stock of linen, will depress
+the marginal usefulness of the latter and increase that of the
+former, so that now we have
+\[
+f'(\text{linen})<2\phi'(\text{china}).
+\]
+If, however,
+\[
+f'(\text{linen})>\phi'(\text{china})
+\]
+is still true, I shall still wish to sacrifice china for the sake
+of linen, unit for unit, until by the action of the same principle
+we have reached the point at which we have
+\[
+f'(\text{linen})=\phi'(\text{china}).
+\]
+After this I shall not be willing to sacrifice china for the
+sake of obtaining linen unless I can obtain a unit of linen by
+foregoing \emph{less} than a unit of china. All this may be represented
+very simply and clearly on our diagrams. Drawing
+out separately, for convenience, the curves given in \Figref{11},
+and making any assumptions we choose as to quantities of
+linen and china possessed, we may read at once (\Figref{12}) the
+\emph{equivalents in worth} (to the possessor) of linen and china. Thus
+if I have eight units of china [$\phi'(\text{china})=.3$] and four units
+of linen [$f'(\text{linen})=1.2$]; then in the limit one small unit
+of linen at the margin is equivalent in worth to four small
+units of china at the margin. If I have seven units of linen
+and two of china, then one small unit of china at the margin is
+equivalent in worth to two small units of linen at the margin.
+
+Hitherto we have spoken of foot-tons, or generally of
+work, merely as a standard by which to measure a man's
+%% -----File: 078.png---Folio 57-------
+estimate of the various objects of his desire; but we
+know, as a matter of fact, that work is often a \emph{means of
+securing} these objects, and it by no means follows that
+\begin{figure}[htbp]
+ \begin{center}
+ \Fig{12}
+ \Input[3.5in]{078a} \\
+ \Input[4.5in]{078b}
+ \end{center}
+\end{figure}
+the precise amount of work a man would be willing to do
+rather than go without a thing is also the precise amount
+of work he will have to do in order to make it. Indeed
+there is no reason in general why a man should have to
+%% -----File: 079.png---Folio 58-------
+do either more or less work for the first unit of a commodity
+with its high utility than for the last with its
+comparatively low utility. The question then arises:
+On what principle will a man distribute his work
+between two objects of desire? In other words, If a
+man can make two different things which he wants, in
+what proportions will he make them?
+
+\Pagelabel{58}%
+We must begin by drawing out the curves of quantity-and-marginal-usefulness
+of the two commodities, and we
+will select as the unit on the axis of~$x$ in each case that
+quantity of the commodity that can be made or got by
+an hour's work. Suppose Robinson Crusoe\footnote
+ {``Political economists have always been addicted to Robinsoniads''
+ (Marx).}
+\index{Robinson Crusoe}%
+\index{Root-digging}%
+\index{Rush-gathering}%
+has provided
+himself with the absolute necessaries of life, but
+finds that he can vary his diet by digging for esculent
+roots, and can add to the comfort and beauty of his hut
+by gathering fresh rushes to strew on the floor two or
+three times a week. Adopting any arbitrary standard
+unit of satisfaction, let us suppose that the marginal
+usefulness of the roots begins at six and would be extinguished
+(for the week, let us say) when eight hours'
+work had been done. That is to say, the quantity
+which Robinson could dig in eight hours would absolutely
+satisfy him for a week, so that he would not care
+for more even if he could get them for nothing. In like
+manner let the marginal usefulness of rushes begin at
+four and be extinguished (for the week) by five hours'
+work; and let the other data be such as are depicted on
+the two curves in \Figref{13}.\footnote
+ {They are drawn to the formulæ---
+ \[
+ y=\frac{24-3x}{4+x} \text{ and } y=\frac{40-8x}{10+7x} \text{ respectively}.
+ \]}
+Now suppose further that
+Robinson can give seven hours a week to the two tasks
+together. How will he distribute his labour between
+them? If he gives four hours' work to digging for roots
+and three to gathering rushes, the marginal usefulness
+of the two articles will be measured by the vertical
+intercepts on $a$~and~$a'$ respectively. Clearly there has
+%% -----File: 080.png---Folio 59-------
+been waste, for the latter portions of the time devoted
+to rush-gathering have been devoted to producing a
+thing less urgently needed than a further supply of roots.
+Again, if six hours be given to digging and one to rush-gathering,
+the marginal usefulness will be measured by
+the vertical intercepts on $b$~and~$b'$, and again there
+has been waste, this time from excessive root digging.
+But if five hours are given to digging for roots and two
+to rush-gathering, the usefulness will be measured
+by the vertical intercepts on $c$~and~$c'$, and there is no
+loss, for obviously any labour subtracted from either
+\begin{figure}[hbt]
+ \begin{center}
+ \Fig{13}
+ \Input{080a}
+ \end{center}
+\end{figure}
+occupation and added to the other would result in the
+sacrifice of a greater satisfaction than the one it secured.
+
+It is obvious that for any given time, such as three
+hours or two hours, there is a similar ideal distribution
+between the two occupations which secures the maximum
+result in gratification of desires; and the method
+of distribution may be represented by a very simple and
+beautiful graphic device, exemplified in \Figref{14}.
+
+First draw the two curves one within the other,\footnote
+ {If the curves should cross, as in \Figref{10}, the principle is entirely
+ unaffected.}
+then add them together sideways, so as to make a
+%% -----File: 081.png---Folio 60-------
+third curve (dotted in figure), after the following fashion:
+For $y=1$ the corresponding value of~$x$ for the inner
+curve is~$2$, and that for the outer curve~$5$. Adding
+these two together we obtain~$7$; and for our new curve
+we shall have
+\[
+y=1 \qquad x=7.
+\]
+Every other point of the new curve may be found in
+the same way, and we shall then have a dotted curve such
+that if any line~$pp_{1}p_{2}p_{3}$ be drawn parallel to the axis
+of~$x$, and cutting the three curves, the line~$p_{2}p_{3}$ shall
+be equal to the line~$pp_{1}$. We shall then have $pp_{3}=pp_{1}+pp_{2}$;\footnote
+ {If the curves are drawn to the formulæ $y=f(x)$ and $y=\phi(x)$ we
+ may express them also as $x=f^{-1}(y)$ and $x=\phi^{-1}(y)$. It is obvious
+ that our new curve will then be $x=f'^{-1}(y)+\phi^{-1}(y)$, which in this
+ case will give $x=\dfrac{312+146y-38y^{2}}{24+29y+7y^{2}}$ to which formula the curve is drawn
+ between the values $y=4$ and $y=0$.}
+and if we desire to see how Robinson will
+\begin{figure}[hbt]
+\Pagelabel{60}%
+ \begin{center}
+ \Fig{14}
+ \Input[4in]{081a}
+ \end{center}
+\end{figure}
+apportion any quantity of time~$Oq_{3}$ between the two
+\index{Time, distribution of}%
+occupations we shall simply have to erect a perpendicular
+at~$q_{3}$, and where it cuts the dotted curve draw a parallel
+to the axis of~$x$, cutting the other curves at $p_{2}$~and~$p_{1}$.
+We shall then have divided the whole time of~$Oq_{3}$ into
+%% -----File: 082.png---Folio 61-------
+two parts, $Oq_{1}$~and~$Oq_{2}$ ($=pp_{1}$~and~$pp_{2}$), such that if $Oq_{1}$
+is devoted to the one occupation and $Oq_{2}$ to the other
+the maximum satisfaction will be secured.
+
+If we take $Oq_{3}=7$ we shall find we get $Oq_{1}=2$, $Oq_{2}=5$,
+as above.\footnote
+ {Note that when the hours of work have been distributed between
+ the two occupations they pass into concrete results in the shape of
+ commodity. Thus, strictly speaking, we measure \emph{hours} along the axis
+ of~$x$ when dealing with the dotted curve, but \emph{hour-results} in commodity
+ when we come to the other curves. If $Oq_{3}=7$, then, whereas
+ $Oq_{3}=7 \text{\emph{ hours}}$, $Oq_{1}$~and~$Oq_{2}$ represent respectively $2$~and~$5$~\emph{units of
+ commodity}, each unit being the result of an hour's work.}
+
+\begin{Remark}
+This is a principle of the utmost importance, applicable to
+a great variety of problems, such as the most advantageous
+distribution of a given quantity of any commodity between
+two or more different uses. It is particularly important in
+the pure theory of the currency. It need hardly be pointed
+out that these diagrams do not pretend to assist any one in
+practically determining how to divide his time. They are
+merely intended to throw light on the process by which he
+effects the distribution. In any concrete investigation we
+should have direct access to the result but not to the conditions
+of want and estimated satisfaction which determine
+it; so that the actual distributions would be our data and
+the preceding conditions of desire, etc.~our quæsita.\Pagelabel{61}%
+\end{Remark}
+
+We have now reached a stage of our investigations
+at which it will be useful to recapitulate and expand
+our conclusions as to the marginal usefulness of commodities.
+In doing so we must bear in mind especially
+what has been said as to the nature of our diagrammatic
+curves (\Pageref{12}). The law of a curve is the law of the
+connection between the corresponding pairs of values of
+two varying quantities, one of which is a function of the
+other. The curve on \Figref{7}, for instance, is not the
+``curve of the heat produced by given quantities of
+carbon in a furnace,'' nor yet the ``curve of the quantities
+of carbon which effect given degrees of heat in a
+furnace,'' but ``the curve of the connection between
+varying quantities of carbon burned and varying degrees
+%% -----File: 083.png---Folio 62-------
+of heat produced,'' each of which magnitudes severally is
+always measured by a vertical or horizontal straight line.
+
+\Pagelabel{62}%
+In like manner, the first curve in \Figref{13} is not ``the
+curve of the varying marginal usefulness of esculent
+roots to Robinson at given margins,'' nor ``the curve
+of the varying quantities of esculent roots which
+correspond to given marginal usefulnesses,'' but ``the
+curve of the connection between the quantity of roots
+Robinson possesses and the marginal usefulness of roots
+to him.''
+
+When this fact is fully grasped it will become obvious
+that there are only two things which can conceivably
+alter the marginal usefulness of a commodity to me:
+either the quantity I possess must change, or the law
+must change which connects that quantity and the
+marginal usefulness of the commodity. If \emph{both} these
+remain the same, obviously the marginal utility must
+remain the same. Or, in symbols, if $y=f(x)$\footnote
+ {Note that the symbol $f(x)$ is perfectly general, and signifies any
+ kind of function of~$x$. It therefore includes and may properly represent
+ the class of functions we have hitherto represented by letters with
+ a dash, $f'(x)$, $\phi'(x)$, etc.}
+the value
+of~$y$ can only be altered by changing the value of~$x$, or
+by changing the function signified by~$f$. The necessity
+for insisting upon this axiomatic truth will become
+evident as we proceed. Meanwhile,
+\begin{center}
+\begin{tabular}{l}
+One charge, one sovereign charge I press,\\
+And stamp it with reiterate stress,
+\end{tabular}
+\end{center}
+viz.~to bear in mind, so as to recognise it under all disguises,
+the fundamental and self-evident truth, that the
+marginal usefulness of a commodity always depends
+upon the quantity of the commodity possessed [$y=f(x)$],
+and that if the \emph{nature of the dependence} [the form of
+the function~$f$] and the quantity of the commodity
+possessed [the value of~$x$] remain the same, then the
+marginal usefulness of the commodity [the value of~$y$]
+likewise remains unchanged. Whatever changes it must
+%% -----File: 084.png---Folio 63-------
+do so either by changing the nature of its dependence
+upon the quantity possessed or by changing that quantity
+itself; nothing which cannot change either of
+these can change the marginal usefulness; and whatever
+changes the marginal usefulness does so by means
+of changing one of these. The length of the vertical
+intercept cannot change unless \emph{either} the course of the
+curve changes \emph{or} the position of the bearer is shifted.
+
+These remarks, of course, apply to total utility as
+well as to marginal usefulness.
+
+Now, hitherto we have considered changes in the
+quantity possessed only; and have supposed the nature
+of the connection between the quantity and the total
+utility or marginal usefulness to remain constant, \ie~we
+have shifted our bearers, but have supposed our
+curves to remain fixed in their forms. But obviously
+\Pagelabel{63}%
+in practical life it is quite as important to consider the
+shifting of the curve as the shifting of the bearer and
+the quantity-index. To revert to our first example.
+The law that connects the quantity of coal I burn with
+\index{Coal}%
+the sum of advantages I derive from its consumption is
+not the same in winter and in summer, or in the house
+I now live in and the house I left ten years ago. And
+in other cases, where there is a less obvious external
+cause of change, a man's tastes and desires are nevertheless
+perpetually varying. The state of his health, the
+state of his affections, the nature of his studies, and a
+thousand other causes change the amount of enjoyment
+or advantage he can derive from a given quantity of a
+given commodity; and if we wish to have an adequate
+conception of the real economic conditions of life we
+must not only imagine what we have called the ``bearer,''
+that carries the vertical or quantity-index moving freely
+along the axis of~$x$, but we must also imagine the form
+of the curve to be perpetually flowing and changing.
+
+\begin{Remark}
+The obvious impossibility of adequately representing on
+diagrams the flux and change of the curves presents a great
+%% -----File: 085.png---Folio 64-------
+difficulty to the demonstrator. Some attempt will here be
+made to convey to the reader an elementary conception of
+the nature of these changes.
+
+We will take the simplest case, that of the straight line,
+as an illustration. Suppose (a not very probable supposition)
+that the quantity-and-marginal-usefulness curve of a certain
+commodity for a certain man at a certain time is represented
+by
+\[
+y=12-2x.
+\]
+By giving successive values to~$x$ we shall find the corresponding
+\begin{figure}[hbt]
+ \begin{center}
+ \Fig{15}
+ \Input{085a}
+ \end{center}
+\end{figure}
+values of~$y$, and shall see that the curve is the
+highest of the straight lines represented on \Figref{15}~(\textit{a}). Now
+suppose that, owing to some cause or other, the man comes
+to need the commodity less, so that its marginal utility,
+while still decreasing by the same law as before, shall now
+begin at ten instead of twelve. The formula of the curve
+will then be $y=10-2x$, and the curve will be the second
+straight line in \Figref{15}~(\textit{a}). By taking the formula, $y=8-2x$,
+we may obtain yet another line, and so on indefinitely.
+%% -----File: 086.png---Folio 65-------
+
+What we have now been doing may be represented by the
+formula
+\[
+y=f(z,x)=z-2x,
+\]
+where $y$ is a function of two variables, namely $z$~and~$x$, and
+we proceed by giving $z$ successive values, and then for each
+several value of~$z$ giving $x$ successive values. If instead of
+taking the values $12$, $10$, $8$ for~$z$, we suppose it to pass continuously
+through all values, it is obvious that we should
+have a system of parallel straight lines, one of which would
+pass through any given point on the axis of $x$ or~$y$.
+
+But we have supposed the modifications in the position of
+the line always to be of one perfectly simple character;
+whereas it is easy to imagine that the man whose wants we
+are considering might find that for some reason he needed a
+smaller and smaller quantity of the commodity in question
+completely to satisfy his wants, whereas his initial desire
+remained as keen as ever. Such a case would be represented
+by
+\[
+y=f(z,x)=12-zx,
+\]
+in which we may give $z$ the values of $2$, $3$, $4$, $6$ successively,
+and then trace the lines in \Figref{15}~(\textit{b}) by making $x$~pass
+through all values from $0$ to~$\dfrac{12}{z}$, after which the values of~$y$
+would be negative.
+
+But again we might suppose that while the quantity of
+the commodity needed completely to sate a man remained
+the same, the eagerness of his initial desire might abate.
+This case might be represented by
+\[
+y=f(z,x)=z-\frac{z}{6}x,
+\]
+where by making $z$ successively equal to $12$, $10$, $8$, $6$,~etc.,
+we shall get a system of lines such as those in \Figref{15}~(\textit{c}).
+
+This is very far from exhausting the different modifications
+our curve might undergo while still remaining a straight
+line. For instance we might have a series of lines, one of
+which should run from $12$ on the axis of~$y$ to $6$ on the axis
+of~$x$, as before, while another ran from $8$ on the axis of~$y$
+to $12$ on the axis of~$x$, and so on. This would indicate that
+two independent causes were at work to modify the man's
+want for the commodity.
+
+Passing on to a case rather less simple, we may take the
+first curve of \Figref{13}, which was drawn to the formula
+\[
+y=f(x)=\frac{24-3x}{4+x},
+\]
+%% -----File: 087.png---Folio 66-------
+and confining ourselves to a single modification, may regard
+it as
+\[
+y=f(z,x)=\frac{24-3x}{z+x},
+\]
+when, by making $z$ successively equal $4$, $6$, $8$, and $12$, we
+shall get the four curves of \Figref{16}.
+
+If we suppose that $z$~and~$x$ are both changing at the same
+time, \ie~that the quantity of the commodity \emph{and} the nature
+of the dependence of its marginal usefulness upon its quantity
+are changing together, then the effect of the two changes
+may be that each will intensify the other, or it may be that
+\begin{figure}[hbt]
+ \begin{center}
+ \Fig{16}
+ \Input[2.5in]{087a}
+ \end{center}
+\end{figure}
+they will counteract each other. Thus in $y=f(z,x)=
+\dfrac{24-3x}{z+x}$, if $x$~is first~$5$ and then~$3$, while $z$ at the same time
+passes from $4$ to~$12$, we shall have for the two values of~$y$
+$\dfrac{24 - 3×5}{4+5}$ and $\dfrac{24 - 3×3}{12+3}$, and in either case $y=1$. This is
+shown on the figure by the lines at $a$~and~$b$.
+
+We must remember, then, that two things, and only two,
+can alter the marginal usefulness of a commodity, viz.\ (i)~a
+change in its quantity and (ii)~a change in the connection
+between its quantity and its marginal usefulness. In the
+diagrams these are represented by (i)~a movement of the
+``bearer'' carrying the vertical to and fro on the base line,
+and (ii)~a change in the form or position of the curve. In
+%% -----File: 088.png---Folio 67-------
+symbols they are represented (i)~by a change in the value of~$x$,
+and (ii)~by a change in the meaning of~$f$. Anything that
+changes the value of~$y$ must do so \emph{by} changing one of these.
+Generally speaking the causes that affect the nature of the
+function (\ie~the shape and position of the curve), so far as
+they lend themselves to investigation, must be studied under
+the ``theory of consumption;'' while an examination of the
+causes which affect the magnitude of~$x$ (\ie~the position of the
+``quantity-index'') will include, together with other things,
+the ``theory of production.''
+\Pagelabel{67}%
+\end{Remark}
+%% -----File: 089.png---Folio 68-------
+
+
+\Chapter[II. Social]{II}
+
+\Pagelabel{68}%
+We have seen that the most varied and heterogeneous
+wants and desires that exist \emph{in one mind} or ``subject''
+may be reduced to a common measure and compared
+one with another; but there is another truth which must
+never be lost sight of on peril of a total misconception of
+all the results we may arrive at in our investigations;
+and that is, that by no possibility can desires or wants,
+even for one and the same thing, which exist \emph{in different
+minds}, be measured against one another or reduced to a
+common measure. If $x$,~$y$, and~$z$ are all of them objects
+\Pagelabel{69}% [** TN: Attempted to locate as closely as possible]
+of desire to~\Person{A}, we can tell by his actions which of them
+he desires most, but if \Person{A},~\Person{B}, and~\Person{C} all desire~$x$ no possible
+process can determine which of them desires it
+most. For any method of investigation is open to the
+fatal objection that it must use as a standard of measurement
+something that may not mean the same in
+the different minds to be compared. Lady Jane Grey
+\index{Lady@{\textsc{Lady Jane Grey}}}%
+studies Plato while her companions ride in Bradgate
+\index{Bradgate Park}%
+\index{Plato}%
+Park, whence we learn that an hour's study was more
+than an equivalent to the ride to Lady Jane and less
+than its equivalent to the others. But who is to tell
+us whether Greek gave \emph{her} more pleasure than hunting
+gave \emph{them}? Lady Jane fancied it did, but she may
+have been mistaken. My account-book, intelligently
+\index{Account-book@{\textsc{Account-book}}}%
+studied, may tell you a good deal as to the equivalence
+of various pleasures and comforts to me, but it can
+establish no kind of equation between the amount of
+pleasure which I derive from a certain article and the
+%% -----File: 090.p n g----------
+%[Blank Page]
+%% -----File: 091.p n g----------
+\begin{figure}[hbtp]
+\Pagelabel{70}% [** TN: Attempted to locate as closely as possible]
+ \begin{center}
+ \Fig{17}
+ \Input{091a}
+ \end{center}
+\end{figure}
+% [To face page 69.]
+%% -----File: 092.png---Folio 69-------
+amount of pleasure you would derive from it. \Person{B}~wears his
+black coats out to the bitter end and goes shabby three
+\index{Coats}%
+months in every year in order to get a few pounds
+worth of books per annum. \Person{A}~would never think of
+\index{Books}%
+doing so---but whether because he values books less or
+a genteel appearance more than~\Person{B} does not appear.
+Nay, it is even possible he values books more, but
+that his sensitiveness in the matter of clothing exceeds
+\Person{B}'s in a still higher degree. \Person{C}~may be willing
+to wait three hours at the door of a theatre to get a
+place, whereas \Person{D} will not wait more than ten minutes;
+but this does not show that \Person{C}~wants to witness the
+representation more than \Person{D}~does; it may be that \Person{D} has
+less physical endurance than~\Person{C}, and would suffer severely
+from the exhaustion of long waiting; or it may be that
+\index{Theatre, waiting}%
+\index{Waiting@{Waiting (at theatre)}}%
+\Person{C}~has nothing particular to do with his time and so
+does not value it as much as \Person{D} does his.
+
+Look at it how we will, then, it is impossible to
+establish any scientific comparison between the wants
+and desires of two or more separate individuals. Yet
+it is obvious that almost the whole field of economic
+investigation is concerned with collective wants and
+desires; and we shall constantly have to speak of the
+relative intensity of the demand for different articles or
+commodities not on the part of this or that individual,
+but on the part of society in general. In like manner
+we shall speak of the marginal usefulness and utility
+of such and such an article, not for the individual but
+for the community at large. What right have we to use
+such language, and what must we take it to mean?
+
+To answer this question satisfactorily we must make
+the relative intensity of the desires and wants of the
+individual our starting-point. Let us suppose that \Person{A}
+possesses stocks of $U$,~$V$, $W$,~$X$, $Y$,~$Z$, the marginal utility
+to him of the customary unit (pound, yard, piece, bushel,
+hundredweight, or whatever it may be) of each of
+these articles being such that, calling a unit of~$U$, $u$,
+a unit of~$V$, $v$,~etc., we shall have $3u$ or $10v$ or $4w$ or
+%% -----File: 093.png---Folio 70-------
+$\dfrac{x}{4}$ or~$\dfrac{3y}{2}$, applied at the margin, just equivalent to~$z$ (\ie~one
+unit of~$Z$) at the margin. Portions of arbitrary
+curves illustrating the supposed cases of $U$,~$X$, and~$Z$
+are given in \Figref{17}~(\Person{A}). The curves represent the marginal
+usefulness per unit of~$U$ as being one-third as great
+as that of~$Z$. That is to say, if $u$ is but a very small
+fraction of \Person{A}'s whole stock of~$U$, then, in the limit, $3u=z$.
+In like manner $\dfrac{x}{4}=z$, in the limit. Now let us take
+another man,~\Person{B}. We may find that he does not possess
+(and possibly is not aware of definitely desiring) any $V$,~$W$,
+or~$Y$ at all; but we will suppose that he possesses
+stocks of $U$,~$X$, and~$Z$. In this case (neglecting the
+practically very important element of friction) we shall
+find that the units of $U$,~$X$, and~$Z$ stand in exactly the
+same \emph{relative} positions for him as they do for~\Person{A}; that is
+to say, we shall find that for~\Person{B}, as for~\Person{A}, $3u$ or~$\dfrac{x}{4}$ is exactly
+equivalent to~$z$. For were it otherwise the conditions
+for a mutually advantageous exchange would
+obviously be present.
+
+Suppose, for instance, we have
+\[
+\frac{x}{3} \text{ equivalent to~$2u$\qquad for~\Person{B}},
+\]
+as represented in Fig~17~(\Person{B}), while
+\[
+\frac{x}{4} \text{ is equivalent to~$3u$\qquad for~\Person{A}},
+\]
+as before. Then, reducing to more convenient forms,\footnote
+ {This process is legitimate if $x$~and~$u$ are ``small'' units of $X$~and~$U$,
+ so that the marginal usefulness of~$U$ remains sensibly constant
+ throughout the consumption of $3u$,~etc.}
+we shall have
+\begin{align*}
+ 6u \text{ equivalent to~$x$} & \qquad \text{for~\Person{B}}, \\
+12u \text{ equivalent to~$x$} & \qquad \text{for~\Person{A}}.
+\end{align*}
+
+\begin{Remark}
+Observe that though we may suppose there will frequently
+be some general similarity of form between the curves that
+%% -----File: 094.png---Folio 71-------
+connect the quantity of~$U$ with its marginal usefulness in
+the cases of \Person{A}~and~\Person{B} respectively, yet we have no right
+whatever to assume any close resemblance between these
+curves.
+\end{Remark}
+
+Now since six units of~$U$ are equivalent to a unit of~$X$
+for~\Person{B}, he will evidently be glad to receive anything
+\emph{more than six} units of~$U$ in exchange for a unit of~$X$;
+whereas \Person{A}~will be glad to give \emph{anything less than twelve}
+units of~$U$ for a unit of~$X$. The precise terms on which
+we may expect the exchange to take place will not be
+investigated here, but it is obvious that there is a wide
+margin for an arrangement by which \Person{A} can give~$U$ in
+exchange for~$X$ from~\Person{B}, to the mutual advantage of the
+two parties. The result of such an exchange will be to
+change the quantities and make the quantity indices
+move in the directions indicated by the arrow heads;
+\Person{A}'s~stock of~$U$ decreasing and his stock of~$X$ increasing,
+while \Person{B}'s~stock of~$U$ increases and his stock of~$X$
+decreases. But this very process tends to bring the
+ratio $\dfrac{\text{marginal usefulness of~$U$}}{\text{marginal usefulness of~$X$}}$ or $\dfrac{\text{marginal utility of~$u$}}{\text{marginal utility of~$x$}}$
+nearer to unity (\ie~increase it) for~\Person{A}, for whom it
+is now~$\frac{1}{12}$, and to remove it farther from unity
+(\ie~decrease it) for~\Person{B}, to whom it is now~$\frac{1}{6}$. This
+is obvious from a glance at the figures or a moment's
+reflection on what they represent. Using $\dfrac{u}{x}$ as a
+symbol of $\dfrac{\text{marginal utility of~$u$}}{\text{marginal utility of~$x$}}$ we may, therefore, say
+that the ratio~$\dfrac{u}{x}$ will increase for~\Person{A}, to whom it is now
+lowest, and decrease for~\Person{B}, to whom it is now highest.
+If this movement continues long enough,\footnote
+ {Compare below, \Pageref{73} and the note.}
+there must
+come a point at which $\dfrac{u}{x}$ will be the same for \Person{A}~and~\Person{B}.
+Now until this point is reached the causes which produce
+%% -----File: 095.png---Folio 72-------
+the motion towards it continue to be operative, for it is
+always possible to imagine a ratio of exchange~$\dfrac{u}{x}$ which
+shall be greater than \Person{A}'s~$\dfrac{u}{x}$ and less than \Person{B}'s~$\dfrac{u}{x}$, and shall
+therefore be advantageous to both. But when \Person{A}'s~$\dfrac{u}{x}$
+and \Person{B}'s~$\dfrac{u}{x}$ have met there will be equilibrium. Hence
+if the \emph{relative} worth, at the margin, of units of any two
+commodities $U$~and~$X$ should not be identical for two
+persons \Person{A}~and~\Person{B}, the conditions of a profitable exchange
+between them exist, and continue to exist, until the
+resultant changes have brought about a state of equilibrium,
+in which the relative worths, at the margin, of
+units of the two commodities are identical for the two
+individuals.
+
+This proposition is of such crucial and fundamental
+importance that we will repeat the demonstration with a
+more sparing use of symbols, and without reference to
+the figures.\Pagelabel{71}% [** TN: Attempted to locate as closely as possible.]
+
+\Person{B}, who is glad to get anything more than~$6u$ for~$x$,
+and \Person{A},~who is glad to give anything short of~$12u$ for~$x$,
+exchange $U$~and~$X$ to their mutual advantage, \Person{B}~getting
+$U$ and giving~$X$, while \Person{A}~gets $X$ and gives~$U$.
+
+But by this very act of exchange \Person{B}'s~stock of~$X$ is
+decreased and his stock of~$U$ increased, and thereby the
+marginal usefulness of~$X$ is raised and that of~$U$ lowered,
+so that \Person{B}~will now find $6u$~less than the equivalent
+of~$x$; or in other words, the interval between the worth
+of a unit of~$X$ and that of a unit of~$U$ is increasing,
+and at the same time \Person{A}'s~stock of~$X$ is increasing and
+his stock of~$U$ diminishing, whereby the marginal usefulness
+of~$U$ increases and that of~$X$ diminishes, so that
+now less than twelve units of~$U$ are needed to make an
+equivalent to one unit of~$X$; or in other words, the
+interval between the worths at the margin of a unit of~$U$
+and a unit of~$X$ is diminishing. To begin with, then,
+%% -----File: 096.png---Folio 73-------
+$u$~and~$x$ differ less in worth, at the margin, to~\Person{B} than
+they do to~\Person{A}, but the difference in worth to~\Person{B} is constantly
+increasing and that to~\Person{A} constantly diminishing
+as the exchange goes on. There must, therefore,
+come a point at which the expanding smaller difference
+and the contracting greater difference will coincide.\footnote
+ {Unless, indeed, the whole stock of \Person{A}'s~$X$ or of \Person{B}'s~$U$ is exhausted
+ before equilibrium is reached. See \Pageref{82}.}
+The conditions for a profitable exchange will then cease
+\Pagelabel{73}%
+to exist; but at the same moment the marginal worths
+of $u$~and~$x$ will come to stand in precisely the same ratio
+for~\Person{A} and for~\Person{B}. Wherever, then, articles possessed in
+common by \Person{A} and~\Person{B} differ in the ratio of their unitary
+marginal utilities as estimated by \Person{A} and~\Person{B}, the conditions
+of a profitable exchange exist, and this exchange itself
+tends to remove the difference which gives rise to it.
+We may take it, then, that in a state of equilibrium the
+ratios of the unitary marginal utilities of any articles, $X$,~$Y$,
+$Z$,~etc., possessed in common by \Person{A},~\Person{B}, \Person{C},~etc., taken
+two by two, viz.\ $x : y$, $x : z$, $y : z$,~etc., \emph{are severally identical
+for all the possessors}. Any departure from this state of
+equilibrium tends to correct itself by giving rise to
+exchanges that restore the equilibrium on the same or
+another basis.
+
+To give precision and firmness to this conception, we
+may work it out a little farther. Let us call such a
+table as the one given on pp.~\Pageref[]{69},~\Pageref[]{70} a ``scale of the relative
+unitary marginal utilities to~\Person{A} of the commodities he
+possesses,'' or briefly, ``\Person{A}'s~relative scale.'' How shall
+we bring the relative scales of~\Person{B}, \Person{C},~etc.\ into the form
+most convenient for comparison with~\Person{A}'s? In \Person{A}'s~relative
+scale the unitary marginal utilities of all the articles,
+that is to say, $u$,~$v$, $w$,~$x$, $y$,~$z$, were expressed in terms of
+the unitary marginal utility of~$Z$, that is to say,~$z$. And
+in like manner \Person{B}'s~relative scale expressed $u$~and~$x$ in terms
+of~$z$. But now suppose \Person{C}~possesses $S$,~$T$, $V$,~$X$, and~$Y$,
+but no $U$,~$W$, or~$Z$. It is obvious that, in so far as he
+possesses the same commodities as \Person{A}~and~\Person{B}, his relative
+%% -----File: 097.png---Folio 74-------
+scale, when there is equilibrium, must coincide with
+theirs. But when we attempt to draw out that scale by
+direct reference to \Person{B}'s~wants, we find ourselves unable
+to express the unitary marginal utilities of his commodities
+in terms of the unitary marginal utility of~$Z$, for
+since he has no~$Z$ (and perhaps does not want any) we
+cannot ask him to estimate its marginal usefulness to
+him.\footnote
+ {We shall see presently (\Pageref{82}) that the estimate must positively
+ be made in terms of a commodity possessed, and that even if \Person{B} wants~$Z$,
+ and knows exactly how much he wants a first unit of it, that want
+ will not serve as the standard unit of desire unless he actually possesses
+ some quantity of~$Z$.}
+But it is obvious that \Person{A}'s~scale fixes the relative
+marginal utilities of the units $v$,~$x$, and~$y$ in terms
+of each other as well as in terms of~$z$, and unless they
+are the same to~\Person{C} that they are to~\Person{A} the conditions
+of an advantageous exchange between \Person{A}~and~\Person{C} will
+arise and will continue till $v$,~$x$,~$y$ coincide on the
+two relative scales. In like manner \Person{B}'s~scale expresses
+the marginal utilities of the units $s$~and~$t$ in terms
+of each other, and \Person{C}'s~scale must, when there is
+equilibrium, coincide with~\Person{B}'s in respect of these two
+units. Now, even though \Person{C} not only possesses no~$Z$,
+but does not even desire any, there is nothing to prevent
+him, for convenience of transactions with \Person{A}~and~\Person{B},
+from estimating $s$,~$t$, $v$,~$x$, and~$y$ not in terms of each
+other, but in terms of~$z$, placing it hypothetically in his
+own scale in the same place relatively to the other units
+which it occupies for \Person{A}~and~\Person{B}. Thus he may express
+his desire for the commodities he has or wants to have,
+in terms of a desire to which he is himself a stranger,
+but the relative strength of which in other men's minds
+he has been able to ascertain.
+
+Lastly, if \Person{C} knows that he can at any time get $S$~and~$T$
+from~\Person{B}, and $V$,~$X$ and~$Y$ from~\Person{A}, in exchange for~$Z$,
+on definite terms of exchange, then, although he may
+not want~$Z$ for himself, and may have no possible use
+for it, yet he will be glad to get it, though only as representing
+the things he does want, and for which he
+%% -----File: 098.png---Folio 75-------
+will immediately exchange it, unless indeed he finds it
+more convenient to keep a stock of~$Z$ on hand ready to
+exchange for~$S$, $T$,~etc.\ as he wants them for actual
+consumption than to keep those commodities themselves
+in any large quantities.
+
+All this is exactly what really takes place. Gold
+(in England) is the~$Z$ adopted for purposes of reference
+(and also, though less exclusively, as a vehicle of
+exchange). Gold is valuable for many purposes in
+the arts and sciences, and, therefore, there are always
+a number of persons who want gold to use, and
+will give other things in exchange for it. Most of
+us possess, and use in a very direct manner, a small
+quantity of gold which we could not dispense with
+without great immediate suffering and the risk of serious
+ultimate detriment to our health, viz., the gold stoppings
+\index{Gold stoppings in teeth}%
+of some of our teeth. There is a constant demand for
+gold for this use. Lettering and ornamenting the backs
+of books is another use of gold in which vast numbers
+of persons have an immediate interest as consumers.
+Plate and ornaments are a more obvious if not more
+important means of employing gold for the direct
+gratification of human desires or supply of human wants.
+In short, there are a great number of well-known and
+easily accessible persons who, for one purpose or another
+of direct use or enjoyment, desire gold, and since these
+persons desire many other things also, their wants
+furnish a scale on which the unitary marginal utilities
+of a great variety of articles are registered in terms of
+the unitary marginal utility of gold, and if the relative
+scales of any two of these gold-and-other-commodities-desiring
+individuals differ, then exchanges will be made
+until they coincide. Other persons who have no direct
+desire or use for gold desire a number of the other commodities
+which find a place in the scale of the gold-desiring
+persons, and can, therefore, compare the
+relative positions they occupy in their own scale of
+desires with that which is assigned them in the scale of
+%% -----File: 099.png---Folio 76-------
+the gold-desiring people, and if these relative positions
+vary exchanges may advantageously be made until they
+coincide. Thus the non-gold-desiring people may find
+it convenient to express their desires in terms of the
+gold-desire to which they are themselves strangers, and
+seeing that the gold-desiring people are accessible and
+numerous, even those who have no real personal gold-desire
+will always value gold, because they can always
+get what they want in exchange for it from the gold-desiring
+people. Indeed, as soon as this fact is generally
+known and realised, people will generally find it convenient
+to keep a certain portion of their possessions not
+in the form of anything they really want, but in the
+form of gold.
+
+We may, therefore, measure all concrete utilities in
+terms of gold, and so compare them one with another.
+Only we must remember that by this means we reach
+a purely objective and material scale of equivalence, and
+that the fact that I can get a sovereign for either of
+two articles does not prove, or in any way tend to prove,
+that the two articles really confer equivalent benefits,
+\emph{unless it is the same man who is willing to give a sovereign
+for either}.
+
+\Person{A}'s and \Person{B}'s desires for $U$~and~$W$, when measured in
+their respective desires for~$Z$, are indeed equivalent;
+but the \emph{measure itself} may mean to the two men things
+severed by a hell-wide chasm; for \Person{A}'s desire for~$U$, $W$,
+and~$Z$ alike may be satisfied almost to the point of
+satiety, so that an extra unit of~$Z$ would hardly confer
+any perceptible gratification upon him; whereas \Person{B} may
+be in extreme need alike of~$U$, $W$, and~$Z$, so that an
+extra unit of~$Z$ would minister to an almost unendurable
+craving.
+
+Or again, \Person{A} may possess certain commodities, $V$, $X$,
+$Y$, which \Person{B} does not possess, and is not conscious of
+wanting at all (say billiard tables, pictures by old
+\index{Billiard-tables}%
+\index{Pictures}%
+masters, and fancy ball costumes), and in like manner
+\index{Fancy ball costumes}%
+\Person{B} may possess $W$~and~$T$ (say corduroy breeches and
+\index{Corduroys}%
+%% -----File: 100.png---Folio 77-------
+tripe), which \Person{A} neither possesses nor desires. Now in
+\index{Tripe}%
+\Person{B}'s scale of marginal utilities we may find that $t=\dfrac{z}{80}$
+(taking $t$ = one cut of tripe, and $z$ = the gold in a
+sovereign),\footnote
+ {These cannot be regarded as ``small'' units in the technical
+ sense, in this case. We are speaking in this example strictly of the
+ values of units at the margin, and they will not coincide even roughly
+ with the ideal ``usefulness'' of the commodity at the margin.}
+whereas in \Person{B}'s scale one $v=50z$. Then
+taking one~$z$ as a purely objective standard, and neglecting
+the difference of its meaning to the two men, and
+regarding \Person{A}~and~\Person{B} as forming a ``community,'' we
+might say that in that community $z=80t$ and $v=50z$,
+or $v=4000t$, \ie~one~$v$ is worth $4000$~times as much as
+one~$t$. By this we should mean that the man in the
+community who wants~$Z$ will give $4000$~times as much
+for a unit of it as you can get out of the man who
+wants~$T$ in exchange for a unit of that. But this does
+not even tend to show that a unit of~$V$ will give the
+man who wants it $4000$~times the pleasure which the
+other man would derive from a unit of~$T$. Nay, it is
+quite possible that the latter satisfaction might be positively
+the greater of the two.\Pagelabel{77}%
+
+\begin{Remark}
+Note, then, that the function of gold, or money, as a
+standard, is to reduce all kinds of services and commodities
+to an objective scale of equivalence; and this constitutes its
+value in commercial affairs, and at the same time explains
+the instinctive dislike of money dealings with friends which
+many men experience. Money is the symbol of the exact
+balancing and setting off one against the other of services
+rendered or goods exchanged; and this balancing can only
+be affected by absolutely renouncing all attempts to arrive at
+a \emph{real} equivalence of effort or sacrifice, and adopting in its
+place an external and mechanical equivalence which has no
+tendency to conform to the real equivalence. It is the
+systematising of the individualistic point of view which says,
+``One unit of~$Z$ may be a very different thing for \Person{A}~or~\Person{B} to
+\Pagelabel{78}%
+\emph{give}, but it is exactly the same thing for me to \emph{get}, wherever
+%% -----File: 101.png---Folio 78-------
+it comes from; and, therefore, I regard it as the same thing
+all the world over, and measure all that I get or give in
+terms of it.'' Where the relations to be regulated are themselves
+prevailingly external and objective, this plan works excellently.
+But amongst friends, and wherever friendship or
+any high degree of conscious and active goodwill enters into
+the relations to be regulated, two things are felt. In the first
+place we do not wish to keep an evenly balanced account, and
+to set services, etc., against each other, but we wish to act on the
+principle of the mutual gratuitousness of services; and in the
+second place, so far as any idea of a rough equivalence enters
+our minds at all, we are not satisfied with anything but a
+real equivalence, an equivalence, that is, of sacrifice or effort;
+and this may depart indefinitely from the objective equivalence
+in gold. This also explains the dislike of money and money
+dealings which characterises such saints as St.~Francis of
+\index{Francis of Assisi}%
+Assisi. Money is the incarnate negation of their principle of
+mutual gratuitousness of service.
+
+Under what circumstances the objective scale might be
+supposed roughly, and taken over a wide area, to coincide
+with the real scale, we shall ask presently. If such circumstances
+were realised, and in as far as they actually are
+realised, it is obvious that the objective scale has a social
+and moral, as well as a commercial, value. (Compare \Pageref{86}.)
+\end{Remark}
+
+In future we may speak of a man's desire or want of
+``gold'' without implying that he has any literal gold-desire
+at all, but using the ``unitary marginal utility of
+gold'' as the standard unit of desire, and expressing
+the (objective) intensity of any man's want of anything
+in terms of that unit. It is abundantly obvious from
+what has gone before in what way we shall reduce to
+this unit the wants of a man who has no real desire for
+gold at all. When we use gold in this extended and representative
+sense we shall indicate the fact by putting it in
+quotation marks: ``gold.'' Thus any one who possesses
+anything at all must to that extent possess ``gold,''
+though he may be entirely without gold.
+
+The result we have now reached is of the utmost
+importance. We have shown that in any catallactic community,\footnote
+ {I mean by a catallactic community one in which the individuals
+ freely exchange commodities one with another, each with a view to
+ making the enjoyment he derives from his possessions a maximum.}
+%% -----File: 102.png---Folio 79-------
+when in the state of equilibrium, the marginal
+utilities of units of all the commodities that enter into the
+circle of exchange will arrange themselves on a certain
+relative scale or table in which any one of them can
+be expressed in terms of any other, and that that scale
+will be general; that is to say, it will accurately translate
+or express, \emph{for each individual in the community}, the
+worth at the margin of a unit of any of the commodities
+he possesses, in terms of any other.
+
+The scope and significance of this result will become
+more and more apparent as we proceed; but we
+can already see that the desiredness at the margin of a
+unit of any commodity, expressed in terms of the desiredness
+at the margin of a unit of any other commodity,
+is the same thing as the \emph{value-in-exchange} (or exchange-value)
+of the first commodity expressed in terms of the
+second.
+
+We have therefore established a precise relation between
+value-in-use and value-in-exchange; for we have
+discovered that the value-in-exchange of an article conforms
+to the place it occupies on the (necessarily coincident)
+relative scales of all the persons in the community
+who possess it. Now to every man the
+marginal utility of an article, that is to say of a unit of
+any commodity, is determined by the average between
+the marginal usefulness of the commodity at the beginning
+and its marginal usefulness at the end of the
+acquisition of that unit; and this marginal usefulness
+itself is the first derived function, or the differential
+coefficient, of the total utility of the stock of the commodity,
+which the man possesses. Or briefly, \emph{the value-in-exchange
+\Pagelabel{79}%
+of a commodity is the differential coefficient of
+the total \DPtypo{utilily}{utility}, to each member of the community, of the stock
+of the commodity he possesses}.
+
+``The things which have the greatest value-in-use
+%% -----File: 103.png---Folio 80-------
+have frequently little or no value-in-exchange; and, on
+the contrary, those which have the greatest value-in-exchange
+have frequently little or no value-in-use. Nothing
+is more useful than water; but it will purchase scarce
+\index{Water}%
+anything; scarce anything can be had in exchange for
+it'' (Adam Smith). Now that we know exchange-value
+to be measured by marginal usefulness, we can well
+understand this fact. For as the total value in use of a
+thing approaches its maximum its exchange-value tends
+to disappear. Were water less abundant its value-in-use
+would be reduced, but its exchange-value would be
+so much increased that there would be ``scarce anything
+that could not be had in exchange for it.'' As it
+is the total effect of water is so near its maximum that
+its effectiveness at the margin is comparatively small.
+
+\Pagelabel{80}%
+Before proceeding farther we will look somewhat
+more closely into this matter of the identity of the
+exchange-value of a unit of any commodity and its
+desiredness at the margin of the stocks of the persons
+who possess it.
+
+%[** TN: Kept pound signs upright on this page; italicized in original.]
+In practical life, if I say that the exchange-value of a
+horse is £31, I am either speaking from the point of view
+\index{Horse}%
+of a buyer, and mean that a horse of a certain quality could
+be got in exchange for $8$~oz.~of gold;\footnote
+ {About $7.97$~oz.~of gold is contained in £31.}
+or I am speaking from
+the point of view of a seller, and mean that a man could
+get $8$~oz.~of gold for the horse; but I cannot mean both,
+for notoriously (if all the conditions remain the same)
+the buying and selling prices are never identical. What
+then do I mean when, speaking as an economist, I suppose,
+without further specification, that the exchange-value
+of a horse in ounces of gold is~$8$? I mean that
+the offer of anything \emph{more} than the $8$~oz.~of gold for
+a horse of the quality specified will \emph{tend to induce} some
+possessor of such a horse to part with him, and the offer
+of such a horse for anything \emph{less} than $8$~oz.~of gold will
+\emph{tend to induce} some possessor of gold to take the horse
+in exchange for some of it; and if I reduce the friction
+%% -----File: 104.png---Folio 81-------
+of exchange (both physical and mental) towards the
+vanishing point, I may say that every man who is
+willing to give \emph{any} more than 8~oz.\ of gold for a horse
+can get him, and every man who is willing to take \emph{any}
+less than 8~oz.\ of gold for a horse can sell him.
+
+The exchange-value of a horse, then, in ounces of gold,
+represents a quantity of gold such that a man can get
+anything short of it for a horse, and can get a horse for
+anything above it. And obviously, if the conditions remain
+the same, every exchange will tend to destroy the
+conditions under which exchanges will take place, for
+after each exchange the number of people who desire to
+exchange on terms which will ``induce business'' tends to
+be reduced by two.
+
+Thus if the exchange value of a horse is 8~oz.\ of
+gold, that means that the ratio ``1 horse to 8~oz.\ gold''
+is a point \emph{on either side of which} exchanges will take
+place, each exchange, however, tending to produce an
+equilibrium on the attainment of which exchange will
+cease.
+
+Now we have shown in detail that the relative scale
+of marginal utilities is a table of precisely such ratios,
+between units of all commodities that enter into the
+circle of exchange. Any departure in the relative scale
+of any individual from these ratios will at once induce
+exchanges that will tend to restore equilibrium. We
+find, then, that the relative scale is, in point of fact, \emph{a
+table of exchange values}, and that the exchange value of
+an article is simply its marginal utility measured in the
+marginal utility of the commodity selected as the standard
+of value. And, after all, this is no more than the
+simplest dictate of common sense and experience; for we
+have seen that the conditions of exchange are that some
+one should be willing, as a matter of business, to give more
+(or take less) than 8~oz.\ of gold for a horse; but what could
+induce that willingness except the fact that the marginal
+utility of a horse is greater, to the man in question, than
+the marginal utility of 8~oz.\ gold? And what should
+%% -----File: 105.png---Folio 82-------
+induce any other man to do business with him except
+the fact that to that other man the marginal utility of a
+horse is \emph{not} greater than that of 8~oz.\ of gold? In other
+words, the conditions of exchange only exist when there
+is a discrepancy in the relative scales of two individuals
+who belong to the same community; and, as we have seen,
+the exchange itself tends to remove this discrepancy.
+
+\Pagelabel{82}%
+Thus, \emph{the function of exchange is to bring the relative
+scales of all the individuals of a catallactic community into
+correspondence}, and the equilibrium-ratio of exchange
+between any two commodities is the ratio which exists
+between their unitary marginal utilities when this correspondence
+has been established. Thus if the machinery
+of exchange were absolutely perfect, then, \emph{given the
+initial possessions of each individual in the community}, there
+would be such a redistribution of them that no two men
+who could derive mutual satisfaction from exchanges
+would fail to find each other out; and so in a certain
+sense the satisfactions of the community would be
+maximised by the flow of all commodities from the
+place in which they were relatively less to the place in
+which they were relatively more valued. But the conformity
+of the net result to any principle of justice or
+of public good \emph{would depend entirely on initial conditions}
+prior to all exchange.
+
+It must never be forgotten that the coincident relative
+scales of the individuals who make up a community
+severally contain the things actually possessed (or commanded)
+only, not all the things \emph{wanted} by the respective
+individuals. If a man's \emph{initial} want of~$X$ relatively to
+his (marginal) want of ``gold'' is not so great as the
+\emph{marginal} want of~$X$ relatively to the (marginal) want of
+gold experienced by the possessors of~$X$, then he will not
+come into the possession of~$X$ at all, and all that we
+shall learn from the fact of his having no~$X$, together
+with an inspection of the position of~$X$ in the relative
+scale of marginal utilities, is that he desires~$X$ with less
+\emph{relative} intensity than its possessors do. But this does
+%% -----File: 106.png---Folio 83-------
+not by any means prove that his actual want of~$X$ is less
+pressing than theirs. It may very well be that he wants
+X far more than they do, but seeing that he has very
+little of anything at all, his want of ``gold'' exceeds
+theirs in a still higher degree. And, again, if one man
+wants~$X$ but does not want~$Y$, and another wants~$Y$ but
+does not want~$X$, and if the man who wants~$X$ wants it
+more, relatively to ``gold,'' than the man who wants~$Y$,
+it does not in the least follow that the one wants~$X$
+absolutely more than the other wants~$Y$, for we have no
+means of comparing the want of ``gold'' in the two
+cases, so that we measure the want of~$X$ and the want
+of~$Y$ in two units that have not been brought into
+any relation with each other. All this is only to
+say that because I cannot ``afford to buy'' a thing it
+does not follow that I have less need of it or less desire
+to have it than another man who can and does afford it.
+
+Obvious as this is, it is constantly overlooked in
+amateur attempts ``to apply the principles of political
+economy to the practical problems of life.'' We are
+told, for instance, that where there is no ``demand'' for
+a thing it shows that no one really wants it. But before
+we can assent to this proposition we must know what is
+meant by ``demand.''
+
+Now if I want a thing that I have not got, there are
+many ways of ``demanding'' it. I may beg for it. I
+may try to make people uncomfortable by forcing the
+extremity of my want upon them. I may try to terrify
+them into giving me what I want. I may attempt to
+seize it. I may offer something for it which stands
+lower than it on the relative scale of marginal utilities
+in my community. I may offer to work for it. All
+these forms of ``demand,'' and many more, the economists
+have with fine, if unconscious, irony classed
+together under one negative description. Not one of
+them constitutes an ``effective'' demand. An ``effective''
+demand (generally described, with the omission of the
+adjective, as ``demand'' simply) is that demand, and
+%% -----File: 107.png---Folio 84-------
+that demand only, which expresses itself in the offer in
+exchange for the thing demanded of something else that
+stands at least as high as it does on the relative scale of
+marginal utilities. No demand which expresses itself in
+any language other than such an offer is recognised as a
+demand at all---it is not ``effective.'' Now this phraseology
+is convenient enough in economic treatises, but
+unhappily the lay disciples of the economists have a
+tendency to adopt their conclusions and then discard
+their definitions. Thus they learn that it is waste of
+effort to produce a commodity or render a service which
+is less wanted than some other commodity or service
+that would demand no greater expenditure (whether of
+money, time, toil, or what not); they learn that what
+men want most they will give most for; and the conclusion
+which seems obvious is announced in such terms
+as these: ``Political economy shows that it is a mistake
+and a waste to produce or provide anything for people
+which they are not willing to pay for at a fair remunerative
+rate;'' or, ``It is false political economy to subsidise
+anything, for if people won't pay for a thing it
+shows they don't want it.'' Of course political economy
+does not really teach any such thing, for if it did it
+would teach that a poor man never ``wants'' food as
+much as a rich one, that a poor man never ``wants'' a
+holiday as much as a rich one; in a word, that a man who
+\index{Holiday}%
+has not much of anything at all has nearly as much of
+everything as he wants---which is shown by his being
+willing to give so very little for some more.
+
+The fallacy, of course, lies in the use made of the
+assertion that ``what men want most they will give most
+for.'' This is true only if we are always speaking of the
+\emph{same men}, or if we have found a measure which can
+determine which of two different men is really giving
+``most.'' Neither of these conditions is fulfilled in the
+case we are dealing with. ``When two men give the
+same thing, it is not the same thing they give,'' and if
+$A$ spends £100 on a continental tour and $B$ half a crown
+%% -----File: 108.png---Folio 85-------
+on a day at the sea-side no one can say, or without
+further examination can even guess, which of them has
+given ``most'' for his holiday.
+\index{Holiday}%
+
+\begin{Remark}
+Again, some confusion may be introduced into our
+thoughts by the fact that desires not immediately backed by
+any ``effective'' demand for gratification sometimes succeed in
+getting themselves indirectly registered by means of secondary
+desires which they beget in the minds of well-disposed
+persons who are in a position to give ``effect'' to them.
+Thus we may suppose that Sarah Bernhardt is charging three
+\index{Sarah@{\textsc{Sarah Bernhardt}}}%
+hundred guineas as her fee for reciting at an evening party,
+and that the three hundred guineas would provide a weeks'
+holiday in the country for six hundred London children. A
+benevolent and fashionable gentleman is in doubt which of
+these two methods of spending the sum in question he shall
+adopt, and after much debate internal makes his selection.
+What do we learn from his decision? We learn whether \emph{his}
+desire to give his friends the treat of hearing the recitation or
+to give the children the benefit of country air is the greater.
+It tells us nothing whatever of the relative intensity of the
+desire of the guests to hear the recitation and of the children
+to breathe the purer air. The primary desires concerned have
+not registered their relative intensities at all, it is only the
+secondary desires which they beget in the benevolent host
+that register themselves; and if the result proclaims the fact
+that the marginal utility of a recitation from the tragic
+actress is just six hundred times as great as the marginal
+utility of a week in the country to a sick child, this does not
+mean that the pleasure or advantage conferred on the company
+by the recitation is (or is expected to be) six hundred
+times as great as that conferred upon each child by the holiday;
+nor does it mean that the company would have estimated
+their pleasure in their own ``gold'' at the same sum
+as that at which the six hundred children would have estimated
+their pleasure in their ``gold,'' but that the host's
+desire to give the pleasure to the company is as great as
+his desire to give the pleasure to the six hundred children.
+And since we have supposed the host's desires to be the
+only ``effective'' ones, they alone are commercially significant.
+No kind of equation---not even an objective one---is established
+%% -----File: 109.png---Folio 86-------
+between the primary desires in question, viz.\ those of
+the guests and of the children respectively.\footnote
+ {It is interesting to note that there are considerable manufactures
+ of things the direct desire for which seldom or never asserts itself at
+ all. There are immense masses of tracts and Bibles produced, for
+\index{Bibles}%
+\index{Tracts}%
+\Pagelabel{86}%
+ instance, which are paid for by persons who do not desire to use them
+ but to give them away to other persons whose desire for them is not
+ in any way an effective factor in the proceeding. And there are
+ numbers of expensive things made expressly to be bought for ``presents,''
+ \index{Presents}%
+ and which no sane person is ever expected to buy for himself.}
+\end{Remark}
+
+The exchange value, then, of any commodity or service
+indicates its position on \emph{its possessors'} relative scale
+of unitary marginal utilities; and if expressed in ``gold''
+it indicates the ratio between the unitary marginal
+desiredness of the commodity and that of ``gold'' upon
+all the (necessarily coincident) relative scales of \emph{all the
+members of the community who possess it}.
+
+\begin{Remark}
+\index{Poor men's wares|(}%
+\index{Rich men's wares|(}%
+I have repeatedly insisted on the fact that we have no
+common measure by which we can compare the necessities,
+wants, or desires of one man with those of another. We
+cannot even say that ``a shilling is worth more to a poor
+man than to a rich one,'' if we mean to enunciate a rule that
+can be safely applied to individual cases. The most we can
+say is, that a shilling is worth more to a man \emph{when he is poor}
+than (\textit{c{\oe}teris paribus}) to \emph{the same man} when he is rich.
+
+But if we take into account the principle of averages, by
+which any purely personal variations may be assumed to
+neutralise each other over any considerable area, then we
+may assert that shillings either are or ought to be worth
+more to poor men than to rich. I say ``either are or ought
+to be;'' for it is obvious that the rich man already has his
+desires gratified to a greater extent than the poor man, and
+if in spite of that they still remain as clamorous for one
+shilling's worth more of satisfaction, it must be because his
+tastes are so much more developed and his sensitiveness to
+gratification has become so much finer that his organism even
+when its most imperative claims are satisfied still remains
+more sensitive to satisfactions of various kinds than the
+other's. But if the poor man owes his comparative freedom
+%% -----File: 110.png---Folio 87-------
+from desires to a low development and blunted powers, then
+the very fact that though he has so few shillings yet one in
+addition would be worth no more to him than to his richer
+neighbour is itself the indication of social pressure and
+inequality. On the assumption, then, that the humanity of
+\Pagelabel{87}%
+all classes of society ought ideally to receive equal development,
+we may say that shillings either are or ought to be
+worth more to poor men than to rich. Thus, if \Person{A}~manufactures
+articles which fetch 1s.~each in the open market and
+are used principally by rich men, and if \Person{B}~produces articles
+which fetch the same price but are principally consumed by
+poor men, then the commercial equivalence of the two wares
+does not indicate a social equivalence, \ie\ it does not indicate
+that the two articles confer an equal benefit or pleasure on
+the community. On the contrary, if the full humanity of
+\Person{B}'s~customers has not been stunted, then his wares are of
+higher social significance than~\Person{A}'s.
+
+It is obvious, too, that if \Person{C}'s wares are such as rich and
+poor consume alike, the different lots which he sells to his
+different customers, though each commercially equivalent to
+the others, perform different services to the opulent and the
+needy respectively.
+
+Now, anything which tends to the more equal distribution
+of wealth tends to remove these discrepancies. Obviously if
+all were equally rich the neutralising, over a wide area, of
+individual variations would take full effect; and if a thousand
+men were willing to give a shilling for \Person{A}'s~article and five
+hundred to give a shilling for~\Person{B}'s, it would be a fair assumption
+that though fewer men wanted \Person{B}'s~wares than~\Person{A}'s, yet
+those who did want them wanted them (at the margin) as
+much; nor would there be any reason to suppose that different
+lots of the same ware ministered, as a rule, to widely
+different intensities of marginal desire; the irreducible variations
+of personal constitution and habit being the only
+source of inequality left.
+
+It is true that the desire for \Person{A}'s~and~\Person{B}'s wares might not
+be equally legitimate, from a moral point of view. I may
+``want'' a shameful and hurtful thing as much as I ``want''
+a beautiful and useful one. The State usually steps in to
+say that certain wants must not be provided for at all---in
+England the ``want'' of gaming tables, for instance---and a
+%% -----File: 111.png---Folio 88-------
+man's own conscience may preclude him from supplying many
+other wants. But on the supposition we are now making
+equal intensity of commercial demand would at least represent
+(what no one can be sure that it represents now) equal
+intensity of desire on the part of the persons respectively
+supplied. If wealth were more equally distributed, therefore,
+it would be nearer the truth than it now is to say that
+when we supply what will sell best we are supplying what is
+wanted most.
+\index{Rich men's wares|)}%
+\index{Poor men's wares|)}%
+
+These considerations are the more important because, in
+general, this index of price is almost the only one we can
+have to guide us as to what really is most wanted. When
+we enter into any extensive relations with men of whom we
+have little personal knowledge it is impossible that we should
+form a satisfactory opinion as to the real ``equivalence'' of
+services between ourselves and them, and it would be an
+immense social and moral amelioration of our civilised life if
+we could have some assurance that a moderate conformity
+existed, over every considerable area, between the price a
+thing would fetch and the intensity of the marginal want of
+it. This would be an ``economic harmony'' of inestimable
+importance. Within the narrower area of close and intimate
+personal relations attempts would still be made, as now, to
+get behind the mere ``averaging'' process and consider the
+personal wants and capacities of the individuals, the ideal
+being for each to ``contribute according to his powers and
+receive according to his needs.'' Thus the different principles
+of conducting the affairs of business and of home would
+remain in force, but instead of their being, as they are now,
+in many respects opposed to each other the principles of
+business would be a first approximation---the closest admitted
+by the nature of the case---to the principles on which
+we deal with family and friends.
+
+Now certain social reformers have imagined an economic
+Utopia in which an equal distribution of wealth, such as we
+have been contemplating, would be brought about as follows:---Certain
+industrial, social and political forces are supposed to
+be at work which will ultimately throw the opportunities of
+acquiring manual and mental skill completely open; and
+skill will then cease to be a monopoly. Seeing, then, that
+there will only be a small number of persons incapable of
+%% -----File: 112.png---Folio 89-------
+doing anything but heaving, it will follow that the greater
+part of the heaving work of the world will be done by persons
+capable of doing skilled work. And hence again it will
+follow that every skilled task may be estimated in the foot-tons,
+which would be regarded by a heaver as its equivalent
+in irksomeness. And if we ask ``What heaver?''\ the answer
+will be ``The man at present engaged in heaving who estimates
+the relative irksomeness of the skilled task most lightly,
+and would therefore be most ready to take it up.'' Then the
+reward, or wages, for doing the task in question will be the
+same as for doing its equivalent (so defined) in foot-tons.
+If more were offered some of the present heavers would
+apply. If less were offered some of those now engaged in
+the skilled work would do heaving instead. To me personally
+heaving may be impossible or highly distasteful, but
+as long as some of my colleagues in my task are capable of
+heaving and some of the heavers capable of doing my task, a
+scale of equivalence will be established at the margin between
+them, and this will fix the scale of remuneration. Thus earnings
+will tend to equality with efforts, estimated in foot-tons.
+
+From this it would follow that inequalities of earnings
+could not well be greater than the natural inequalities of
+mere brute strength; for since foot-tons of labour-power are
+the ultimate measure of all remunerated efforts, he who has
+most foot-tons of labour-power at his disposal is potentially
+the largest earner.
+
+Again, the reformers who look forward to this state of
+things hold that forces are already at work which will ultimately
+dry up all sources of income except earnings, so that
+we shall not only have earnings proportional to efforts, estimated
+in foot-tons, but also incomes proportional to earnings.
+Thus inequalities in the distribution of wealth will be restrained
+within the limits of inequalities of original endowment
+in strength.
+
+The speculative weakness of this Utopia obviously lies in
+its taking no sufficient account of differences of personal
+ability. Throwing open opportunities might level the rank
+and fill up all trades, including skilled craftsmen, artists, and
+heavers; but it would hardly tend to diminish the distance,
+for example, between the mere ``man who can paint'' and
+the great artist.
+%% -----File: 113.png---Folio 90-------
+
+Nevertheless it is interesting to inquire how things would
+go in such a Utopia. In the first place we are obviously as
+far as ever from having established any common measure
+between man and man or any abstract reign of justice; for a
+foot-ton is not the same thing to~\Person{A} and to~\Person{B}, neither is there any
+justice in a strong man having more comforts than a weak one.
+
+Nevertheless there would be greater equality. For the
+number of individual families whose ``means'' in foot-tons of
+labour-power lie near about the average means, is much
+greater than the number of families whose present means in
+``gold'' lie near the average means. As this statement deals
+with a subject on which there is a good deal of loose and inaccurate
+thought, it may be well to expand the conception.
+
+If $\dfrac{a+b+c+d+e}{5}$ remains the same, then the arithmetical
+average of the five quantities remains the same. Suppose
+that average is~$200$. Then we may have $a=b=c=d=e=200$,
+or we may have $a=996$, $b=c=d=e=1$, or $a=394$,
+$b=202$, $c=198$, $d=200$,~$e=6$. In all these cases the
+average is~$200$, but in the second case not one of the several
+quantities lies anywhere near the average. So again, if we
+pass from the case $a=b=c=d=e=200$ to the case $a=997$,
+$b=c=d=e=1$, we shall actually have raised the average,
+but we shall have removed each quantity, severally, immensely
+farther away from that average.
+
+Now if we reflect that the average income of a family of
+five in the United Kingdom is estimated at £175~per annum,
+it is obvious that an enormous number of families have incomes
+a long way below the average. It is held to be self-evident
+that a smaller number of families fall conspicuously
+short of the average means in labour-power.
+
+Further, the extremes evidently lie within less distance of
+the average in the case of labour-power than in the case of
+``gold.'' There are, it is true, some families of extraordinary
+\index{Athletes}%
+athletic power, races of cricketers, oarsmen, runners, and so
+forth, but if we imagine such a family, while still remaining
+an industrial unit, to contain six or seven members each able
+to do the work of a whole average family, we shall probably
+have already exceeded the limit of legitimate speculation,
+and this would give six or seven times the average as the
+upper limit. Whereas the average ``gold'' income (as given
+%% -----File: 114.p n g----------
+%[Blank Page]
+%% -----File: 115.p n g----------
+\begin{figure}[p]
+ \begin{center}
+ \Fig{18}
+ \Input[4.5in]{115a}
+ \end{center}
+\end{figure}
+%[To face page 91.]
+%% -----File: 116.png---Folio 91-------
+above) being £175, we have only to think of the incomes of
+our millionaires to see how much further above the average
+the upper limit of ``gold'' incomes rises than it could possibly
+do in the case of labour-power.
+
+The lower limit being zero in both cases does not lend
+itself to this comparison.
+
+It may be urged, further, that there is no such broad
+distinction between the goods required by the strong (?~skates,
+\index{Skates}%
+bicycles, etc.) and those required by the ``weak'' (?~respirators,
+\index{Bicycles}%
+\index{Respirators}%
+reading-chairs, etc.) as there is between those demanded
+\index{Reading-chairs}%
+by the ``rich'' and those demanded by the ``poor.'' So
+that the analogue of the cases mentioned on \Pageref{87} would
+hardly occur; especially when we take into account the
+balancing effect of the association of strong and weak in the
+same family.
+
+The whole of this inquiry may be epitomised and elucidated
+by a diagramatic illustration.
+
+The unitary marginal utilities of $U$~and~$V$ stand in the
+ratio of~$3:4$ on the relative scale of the community in which
+\Person{A}~and~\Person{B} live. \Person{A}~possesses a considerable supply both of $U$~and~$V$.
+Parts of the curves are given in \Figref{18}~\Person{A}~(i), where
+the ``gold'' standard is supposed to be adopted in measuring
+marginal usefulness and utility. \Person{B}~possesses a little~$V$, but
+no~$U$, and would be willing (as shown on the curves \Figref{18}~\Person{B}~(i\DPtypo{.}{}))
+to give $\dfrac{v}{2}$ for~$u$ ($v$~and~$u$ being small units of $V$~and~$U$),
+but since $u$ is only worth half as much as $v$ to him, he will
+not buy it on higher terms than this. Now we have supposed
+the ratio of utilities of $u$~and~$v$ on the relative scale to
+be~$3:4$. That is to say, if $u$ contains three small units of
+utility then $v$ contains four. Therefore $\dfrac{u}{3}$ has the same value-in-exchange
+or marginal utility as $\dfrac{v}{4}$, and $\dfrac{3u}{3}$, or $u$ has the
+same value-in-exchange as $\dfrac{3v}{4}$; therefore an offer of $\dfrac{3v}{4}$, but
+nothing lower than this, constitutes an ``effective'' demand
+for~$u$; whereas \Person{B} only offers $\dfrac{v}{2}$ or $\dfrac{2v}{4}$ for it. Measuring the
+intensity of a want by the offer of ``gold'' it prompts, we
+should say, that \Person{B} wants $v$ as much as \Person{A} does, but wants $u$
+%% -----File: 117.png---Folio 92-------
+less than \Person{A} does. This, however, is delusive, for we do not
+know how much each of them wants the units of ``gold'' in
+which all his other wants are estimated. Suppose we say,
+``What a man wants he will work for,'' and ascertain that \Person{A}
+would be willing to do half a foot-ton of work for a unit of
+``gold,'' whereas \Person{B} would do one and a half foot-tons for it.
+This would show that, measured in work, the standard unit
+was worth three times as much to \Person{B} as to~\Person{A}. Reducing the
+units on the axis of~$y$ to $\frac{1}{2}$ for~\Person{A}, and raising them to $\frac{3}{2}$ for~\Person{B},
+we shall have the curves of \Figref{18}~\Person{A}~(ii) and \Person{B}~(ii) showing
+the respective ``wants'' of \Person{A}~and~\Person{B} estimated in willingness
+to do work. It will then appear that \Person{B} wants $v$ three
+times as much and $u$ twice as much as \Person{A} does; but his
+demand for~$u$ is still not effective, for he only offers $\dfrac{v}{2}$ or $\dfrac{2v}{4}$
+for it, and its exchange-value is $\dfrac{3v}{4}$. There is only enough
+$U$ to supply those who want a unit of it at least as much as
+they want $\frac{3}{4}$ of a unit of $V$, and \Person{B} is not one of these.
+
+Now if \Person{A} and \Person{B} had both been obliged to earn their
+``gold'' by work, with equal opportunities, then obviously
+the unitary marginal utility of ``gold,'' estimated in foot-tons,
+must have been equally high for both of them, since each
+would go on getting ``gold'' till at the margin it was just
+worth the work it cost to get and no more. And therefore
+the marginal utilities of $u$~and~$v$ (whether measured in foot-tons
+or in ``gold'') must also have stood at the same height
+for \Person{A}~and~\Person{B}. Hence \Person{B} could not have been wholly without
+$U$ while \Person{A} possessed it, unless, measured in foot-tons, its
+marginal usefulness was less to him than to~\Person{A}.
+
+It would remain possible that a foot-ton might represent
+widely different things to the two men; but the contention is
+that this is less probable, and possible only within narrower
+limits, than in the corresponding case of ``gold'' under our
+present system. I need hardly remind the reader that the
+assumptions of \Figref{18} are arbitrary, and might have been
+so made as to yield any result desired. The figure illustrates
+a perhaps rational supposition, and throws light on the
+nature and effects of a change of the standard unit of utility.
+It does not prove anything as to the actual result which
+would follow upon any specified change of the standard.
+%% -----File: 118.png---Folio 93-------
+
+The whole of this note must be regarded as a purely speculative
+examination of the conditions (whether possible of
+approximate realisation or not) under which it might be
+roughly true that ``what men want most they will pay most
+for.''
+\end{Remark}
+
+\Pagelabel{93}%
+We have now gained a distinct conception of what
+is meant by the exchange-value of a commodity. It is
+identical with the marginal utility which a unit of the
+commodity has to every member of the community
+who possesses it, expressed in terms of the marginal
+utility of some concrete unit conventionally agreed
+upon. There is no assignable limit to the divergence
+that may exist in the \emph{absolute} utility of the standard
+unit at the margin to different members of the community,
+but the \emph{relative} marginal utilities of the standard
+unit and a unit of any other article must be identical to
+every member of the community who possesses them, on
+the supposition of perfectly developed frictionless exchange,
+and ``small'' units.
+
+We may now proceed to show the principle on which
+to construct collective or social curves of quantity-possessed-and-marginal-usefulness
+without danger of
+being misled by the equivocal nature of the standard,
+or measure, of usefulness which we shall be obliged to
+employ.
+
+In approaching this problem let us take an artificially
+simple case, deliberately setting aside all the secondary
+considerations and complications that would rise in
+practice.
+
+We will suppose, then, that a man has absolute control
+\index{Mineral spring}%
+of a medicinal spring of unique properties, and that
+its existence and virtues are generally known to the
+medical faculty. We will further suppose that the
+owner is actuated by no consideration except the desire
+to make as much as he can out of his property, without
+exerting himself to conduct the business of bottling and
+disposing of the waters. He determines, therefore, to
+allow people to take the water on whatever terms
+%% -----File: 119.png---Folio 94-------
+prove most profitable to himself, and to concern himself
+no further in the matter.
+
+Now there are from time to time men of enormous
+wealth who would like to try the water, and would give
+many pounds for permission to draw a quart of it, but
+these extreme cases fall under no law. One year the
+owner might have the offer of £50 for a quart, and for
+the next ten years he might never have an offer of more
+than £5, and in neither case would there be any regular
+flow of demand at these fancy prices. He finds that in
+order to strike a broad enough stratum of consumers to
+give him a basis for averaging his sales even over a series
+of years he must let people draw the water at not more
+than ten shillings a quart, at which price he has a small
+but appreciable and tolerably steady demand, which he
+can average with fair certainty at so much a year. This
+means that there is no steady flow of patients to whom
+the marginal utility of a quart of the water is greater
+than that of ten shillings. In other words, the initial
+utility of the water to the community is ten shillings a
+quart. Clearly, then, the curve of quantity-and-marginal-usefulness
+of the water cuts the axis of~$y$ (that is to say,
+begins to exist for our purposes) at a value representing
+ten shillings a quart. If we were to take our unit on $x$ to
+represent a quart and our unit on~$y$ to represent a shilling,
+then we should have the corresponding values $x=0$, $y=10$.
+But since we shall have to deal with large quantities of
+the water, it will be convenient to have a larger unit for
+diagramatic purposes; and since the rate of 10s.~per
+quart is also the rate of £5000 per $10,000$ quarts, we
+may keep our corresponding values $x=0$, $y=10$, while
+interpreting our unit on~$x$ as $10,000$ quarts and our unit
+on~$y$ as £500 ($= 10,000$ shillings). The curve, then,
+cuts the axis of~$y$ at the height~$10$; which is to say that
+the initial \emph{usefulness} of the water to the community is
+£500 per $10,000$ quarts, or ten shillings a quart, which
+latter estimate being made in ``small'' units may be
+converted into the statement that the initial \emph{utility} of a
+%% -----File: 120.png---Folio 95-------
+quart of the water is equal to that of ten shillings, of
+two quarts twenty shillings, etc.\footnote
+ {Whereas it cannot be said that the initial utility of $10,000$ quarts
+ is £500, for the initial usefulness is not sustained throughout
+ the consumption of $10,000$ quarts.}
+
+But at this price customers are few, and the owner
+makes only a few pounds a year. He finds that if he
+lowers the price the increased consumption more than
+compensates him, and as he gradually and experimentally
+lowers the price he finds his revenue steadily rising.
+Even a reduction to nine shillings enables him to sell
+\begin{figure}[hbt]
+\Pagelabel{96}%
+ \begin{center}
+ \Fig{19}
+ \Input{120a}
+ \end{center}
+\end{figure}
+about $1000$ quarts a year, and so to derive a not inconsiderable
+income (£450) from his property. A further
+reduction of a shilling about doubles his sale, and he
+sells $2000$ quarts a year at eight shillings, making £800
+income. When he lowers the price still further to six
+shillings, he sells between $5000$ and $6000$ quarts a year,
+and his income rises to £1500.
+
+Before following him farther we will look at the problem
+%% -----File: 121.png---Folio 96-------
+from the other side. At first no one could get a
+quart of the water unless its marginal utility to him
+was as great as that of ten shillings. Now the issue
+just suffices to supply every one whose marginal want of
+a quart is as high as six shillings. These and these only
+possess the water, and on their relative scales it stands
+as having a marginal utility of six shillings a quart.
+This, then, may be called the marginal utility of the
+water \emph{to the community}; only we must bear in mind that
+we have no reason to suppose that the marginal wants
+of the possessors are \emph{in themselves} either all equal to
+each other or all more urgent than those of the yet unsupplied;
+but relatively to ``gold'' they will be so.
+
+We will now suppose that the owner tries the effect
+of lowering the price further still, and finds that when
+he has come down to four shillings a quart he sells
+$11,000$ quarts a year, so that his revenue is still increasing,
+being now more than £2200 per annum. This means
+that over $11,000$ quarts are needed to supply all those
+members of the community to whom the marginal utility
+of a quart is as great as the marginal utility of four
+shillings. Still the owner lowers the price, and discovers
+at every stage \emph{what quantity of the water it is that has the
+unitary marginal utility to the community corresponding to
+the price he has fixed}. By this means he is tracing the
+curve of price-and-quantity-demanded, and he is doing so
+by giving successive values to~$y$ and ascertaining the
+values of~$x$ that severally correspond to them. \Figref{19}
+shows the supposed result of his experiments, which,
+however, he will not himself carry on much beyond
+$y=1$, which gives $x=10$,\footnote
+ {In the diagram $y=\dfrac{120-x}{10x+10} - \dfrac{x^2-20x+100}{50}$.}
+and represents an income of
+ten units of area, each unit representing £500, or £5000
+in all. The price is now at the rate of £500 per $10,000$
+quarts, or one shilling per quart, and the annual sales
+amount to $100,000$ quarts. Up to this point we have
+supposed that every reduction of the price has increased
+%% -----File: 122.png---Folio 97-------
+the total pecuniary yield to the owner. But this cannot
+go on for ever, inasmuch as the owner is seeking to
+increase the value of $x × y$ by diminishing $y$ and increasing
+$x$, and since in the nature of the case $x$ cannot be
+indefinitely extended (there being a limit to the quantity
+of the water wanted by the public at all) it follows that
+as $y$ diminishes a point must come at which the increase
+of~$x$ will fail to compensate for the decrease of~$y$, and $xy$
+will become smaller as $y$ decreases. This is obvious from
+the figure. We suppose, then, that when the owner has
+already reduced his price to one shilling a quart he finds
+that further reductions fail to bring in a sufficient increase
+of custom to make up for the decline in price. To make
+the public take $160,000$ quarts a year he would not only
+have to give it away, but would have to pay something
+for having it removed.
+
+We have supposed the owner to fix the price and to
+let the quantity sold fix itself to correspond. That is,
+we have supposed him to say: Any one on whose relative
+scale of marginal utilities a quart of this water
+stands as high as $y$~shillings may have it, and I will see
+how many quarts per annum it will take to meet
+the ``demand'' of all such. Hence he is constructing
+a curve in which the price is the variable and the
+quantity demanded at that price is the function. This
+is a curve of price-and-quantity-demanded. It is usual
+to call it a ``curve of demand'' simply, but this is
+an elliptical, ambiguous, and misleading phrase, which
+should be strictly excluded from elementary treatises.
+We have seen (\Pageref{12}) that a curve is never a curve
+of height, time, quantity, utility, or any other \emph{one} thing,
+but always a curve of connection between some \emph{two}
+things. The amounts of the things themselves are always
+represented by straight lines, and it is the connection of
+the corresponding pairs of these lines that is depicted on
+the curve. If we not only always bear this in mind,
+but always express it, it will be an inestimable safeguard
+against confusion and ambiguity, and we may
+%% -----File: 123.png---Folio 98-------
+make it a convention always to put the magnitude
+which we regard as the variable first. Thus the curve
+we have just traced is a curve of price-and-quantity-demanded.
+
+But it would have been just as easy to suppose our
+owner to fix the quantity issued, and then let the price
+fix itself. The curve itself would, of course, be the
+same (compare pp.~\Pageref[]{3},~\Pageref[]{13}), but we should now regard it as
+a curve of quantity-issued-and-intensity-of-demand. The
+price obtainable always indicating the intensity of the
+demand for more when just so much is issued. From
+this point of view also it might be called a ``curve of
+demand,'' but ``demand'' would then mean intensity of
+demand (the quantity issued being given), and would
+be measured by the price or~$y$. In the other case ``demand''
+would mean quantity demanded (at a given
+price), and would be measured by~$x$.
+
+Now this curve of quantity-issued-and-intensity-of-demand
+is the same thing as the curve of quantity-possessed-(by
+the community)-and-marginal-usefulness,
+or briefly quantity-and-price. Thus if we call the curve
+a curve of price-and-quantity we indicate that we are
+supposing the owner to fix the price and let the
+quantity sold fix itself, whereas if we call it the curve
+of quantity-and-price we are supposing the owner to fix
+the amount he will issue and let the price fix itself. In
+either case we put the variable first, and call it the
+curve of the variable-and-function.
+
+Regarding the curve as one of quantity-and-price
+then, we suppose the owner to say: I will draw $x$~times
+$10,000$ quarts (of course $x$ may be a fraction) from my
+spring every year, and will see how urgent in comparison
+with the want of ``gold'' the want that the last quart
+meets turns out to be. In this case it is obvious that
+as the owner increases the issue the new wants satisfied
+by the larger supply will be less urgent, relatively to
+``gold,'' than the wants supplied before, but still the
+marginal utility of a quart relatively to ``gold'' will be
+%% -----File: 124.png---Folio 99-------
+the same to all the purchasers, and will be greater to
+them than to any of those who do not yet take any.
+Thus as the issue increases the marginal utility to the
+community of a quart steadily sinks on the relative scale
+of the community, and shows itself, as in the case of the
+individual, to be a decreasing function of the quantity
+possessed, each fresh increment meeting a less urgent
+want than the last. But meanwhile the \emph{total} service
+done to the community by the water is increased by
+every additional quart. The man who bought one
+quart a year for ten shillings, and who buys two quarts
+a year when it comes down to eight shillings, and ten
+quarts a year when it is only a shilling, would still be
+willing to give ten shillings for a single quart if he could
+not get it cheaper, and the second and following quarts,
+though not ministering to so urgent a want as the first,
+yet in no way interfere with or lessen the advantage it has
+already conferred, while they add a further advantage of
+their own. Thus from his first quart the man now gets
+for a shilling the full advantage which he estimated at ten
+shillings, and from the second quart the advantage he
+estimated at eight shillings, and so on. It is only the last
+quart from which he derives an advantage no more than
+equivalent to what he gives for it. We may, therefore,
+still preserving the ``gold'' standard, say that the total
+utility of the $q$~quarts which \Person{A} consumes in the year is
+made up of the whole sum he would have given for
+one quart rather than have none, \emph{plus} the whole quantity
+he would have given for a second quart sooner than
+have only one $+ \ldots +$ the whole sum he gives for the
+$q$th~quart sooner than be satisfied with $(q-1)$. In like
+manner the successive quarts, up to~$p$, which \Person{B} adds to
+his yearly consumption as the price comes down, each
+confers a fresh benefit, while leaving the benefits already
+conferred by the others as great as ever. Thus we
+should construct for \Person{A},~\Person{B}, \Person{C}, etc., severally, curves of
+quantity-and-total-utility of the water, on which we
+could read the total benefit derived from any given
+%% -----File: 125.png---Folio 100-------
+quantity of the water by each individual measured in
+terms of the marginal utility to him of the unit of gold.
+And regarding the total utility as a function of the
+quantity possessed, we shall, of course, find that each
+consumer goes on possessing himself of more till the
+first derived function (rate at which more is adding to
+his satisfaction) coincides with the price at which he can
+purchase the water.
+
+In like manner we may, if we choose, add up all the
+utilities of the successive quarts to \Person{A},~\Person{B}, \Person{C}, etc.,
+measured in ``gold,'' as they accrue (neglecting the fact
+that they are not subjectively but only objectively
+commensurate with each other), and may make a curve
+showing the grand total of the utility to the community
+of the whole quantity of water consumed. And this
+curve would of course continue to rise (though at a
+decreasing rate) as long as any one who had anything to
+give in exchange wanted a quart more of the water than
+he had.
+
+Thus we have seen that as the issue increases the
+utility of a quart at the margin to each individual and
+to the whole community continuously falls on the relative
+scale, the exchange value of course (recorded in the
+price) steadily accompanying it; while at the same time
+each extra quart confers a fresh advantage on the
+community without in any way interfering with or
+lessening the advantages already conferred; that is to
+say, the total advantage to the community increases as
+the issue increases, whereas the marginal usefulness constantly
+decreases. The maximum total utility would
+be realised when the issue became free, and every one
+was allowed as much of the water as he wanted, and
+then the marginal utility would sink to nothing, that is
+to say, no one would attach any value to more than he
+already had. This is in precise accordance with the
+results already obtained with reference to a single individual.
+The total effect is at its maximum when the
+marginal effectiveness is zero.
+%% -----File: 126.png---Folio 101-------
+
+But now returning to the owner of the spring, we
+note that his attention is fixed neither upon the total
+nor the marginal utility of the water, but on the total
+price he receives, and we note that that price is represented
+in the diagram by a rectangle, the base of
+which is~$x$, or the quantity sold measured in the unit
+agreed upon, and the height~$y$, the price or rate per unit
+(determined by its marginal usefulness) at which when
+issued in that quantity the commodity sells. The area,
+therefore, is~$xy$. And this brings us to the important
+principle involved in what is known as the ``law of indifference.''
+By this law the owner finds himself obliged to
+sell \emph{all} his wares at the price which \emph{the least urgently needed}
+will fetch, for he cannot as a rule make a separate bargain
+with each customer for each unit, making each pay as
+much for each successive unit as that unit is worth to him;
+since, unless he sold the same quantity at the same price
+to all his customers, those whom he charged high would
+deal with those whom he charged low, instead of directly
+with him. ``There cannot be two prices for the same
+article in the same market.'' Thus we see again, and
+see with ever increasing distinctness, that the exchange
+value of a commodity is regulated by its marginal
+utility, and is independent of the service which that
+particular specimen happens to render to the particular
+individual who purchases it.
+
+Thus (if we bear in mind the purely relative and
+therefore socially equivocal nature of our standard of
+utility) we may now generalise the conclusions we
+reached in the first instance with exclusive reference to
+the individual. From the collective as from the individual
+point of view the marginal utility of a commodity
+is a function of the quantity of it possessed or commanded.
+If the quantity changes, the communal marginal
+utility and therefore the exchange-value changes
+with it; and this altogether irrespective of the nature
+of the causes which produce the change in quantity.
+Whether it is that nature provides so much and no
+%% -----File: 127.png---Folio 102-------
+more, or that some one who has power to control the
+supply chooses, for whatever reason, to issue just so
+much and no more, or that producers think it worth
+while to produce so much and no more---all this, though
+of the utmost consequence in determining whether and
+how the supply can be further changed, is absolutely immaterial
+in the primary determination of the marginal
+utility, and therefore of the exchange-value, so long as
+just so much and no more \emph{is} issued. This amount is
+the variable, and, given a relation between the variable
+and the function (\ie~given the curve), then, when the
+variable is determined, no matter how, why, or by
+whom, the function is thereby determined also (compare
+\Pageref{62}).
+
+\emph{Exchange value, then, is relative marginal value-in-use,
+and is a function of quantity possessed.}\Pagelabel{102}%
+
+\begin{Remark}
+The ``Law of Indifference'' is of fundamental importance
+in economics. Its full significance and bearing cannot be
+grasped till the whole field of economics has been traversed;
+but we may derive both amusement and instruction, at the
+stage we have now reached, from the consideration of the
+various attempts which are made to evade it, and from the light
+which a reference to it throws upon the real nature of many
+familiar transactions.
+
+In the first place, then, sale by auction is often an attempt
+\index{Auction}%
+to escape the law of indifference. The auctioneer has, say,
+ten pictures by a certain master whose work does not often
+come into the market, and his skill consists in getting the
+man who is most keen for a specimen to give his full price
+for the first sold. Then he has to let the second go cheaper,
+because the keenest bidder is no longer competing; but he
+tries to make the next man give \emph{his} outside price; and so on.
+The bidders, on the other hand, if cool enough, try to form a
+rough estimate of the \emph{marginal} utility of the pictures, that is
+to say, of the price which the tenth man will give for a
+picture when the nine keenest bidders are disposed of, and
+they know that if they steadily refuse to go above this point
+there will be one for each of them at the price. When the
+%% -----File: 128.p n g----------
+%[Blank Page]
+%% -----File: 129.p n g----------
+\begin{figure}[p]
+ \begin{center}
+ \Fig{20}
+ \Input[4.5in]{129a}
+ \end{center}
+\end{figure}
+%[To face page 103.]
+%% -----File: 130.png---Folio 103-------
+things on sale are such as can be readily got elsewhere, the
+auctioneer is powerless to evade the law of indifference.
+
+Another instance constantly occurs in the stock markets.
+\index{Stock-broking}%
+A broker wishes to dispose of a large amount of a certain
+stock, which is being taken, say, at~$95$. But he knows that
+only a little can be sold at that price, because a few thousands
+would be enough to meet all demands of the urgency represented
+by that figure. In fact, the stock he has to part with
+would suffice to meet all the wants represented by $93$~and
+upwards, and accordingly the law of indifference would compel
+him to part with the first thousand at that rate just as
+much as the last if he were to offer all he means to sell
+at once. This, in fact, will be the selling price of the
+whole when he has completed his operations. But meanwhile
+he endeavours to hold the law of indifference at bay by
+producing only a small part of his stock and doing business
+at~$95$ till there are no more demands urgent enough to prompt
+an offer of more than~$94\frac{7}{8}$. He then proceeds cautiously to
+meet these wants likewise, obtaining in each case the maximum
+that the other party is willing to give; and so on, till,
+if completely successful, he has let the stock down~$\frac{1}{8}$ at a
+time from $95$ to~$93$. By this time, of course, not only his own
+last batch, but all the others that he has sold, are down at~$93$.
+The law of indifference has been defeated only so far as he is
+concerned, and not in its general operation on the market.
+
+The general principle involved is illustrated, without
+special reference to the cases cited, in \Figref{20}. The law of
+indifference dictates that if the quantity~$Oq_4$ is to be sold,
+then $Oq$, $qq_1$, $q_1q_2$, $q_2q_3$, $q_3q_4$ must all be treated indifferently,
+and therefore sold at the price measured by $Op_4$~($=q_4m_4$).
+This would realise an amount represented by the area~$p_4q_4$.
+But the seller endeavours to mask the fact that $Oq_4$ is to be
+sold, and by issuing separate instalments tries to secure the
+successive areas $pq+s_1q_1+s_2q_2+s_3q_3+s_4q_4$. Obviously the
+``limit'' of this process, under the most favourable possible
+circumstances, is the securing of the whole area bounded by
+the curve, the axes, and the line~$q_nm_n$ (where $q_n$~stands for the
+last of the series $q$,~$q_1$,~etc.)\footnote
+ {If $Op$ or~$q^m$ is~$f(Oq)$, \ie~if $y$ is~$f(x)$, then the area in question
+ will be $\int_0^xf(x)\,dx$ (see pp.~\Pageref[]{23},~\Pageref[]{31}). The meaning of this symbol may
+ now be explained. The sum of all the rectangular areas is $pq+s_1 q_1
+ +s_2 q_2+ \text{etc.}$, or $qm\centerdot Oq+q_1 m_1\centerdot qq_1+q_2 m_2\centerdot q_1q_2+ \text{etc.}$, but $qm$ is
+ $f(Oq)$, $q_1m_1$ is $f(Oq_1)$, $q_2 m_2$ is $f(Oq_2)$, etc. Therefore the sum of the
+ areas is
+ \[
+ f(Oq)\centerdot Oq+f(Oq_1)\centerdot qq_1+f(Oq_2)\centerdot q_1q_2+ \text{etc.}
+ \]
+ But $Oq=qq_1=q_1q_2= \text{etc.}$ We may call this quantity ``the increment
+ of $x$,'' and may write it $\Delta x$. The sum of the rectangular areas will then
+ be
+ \begin{gather*}
+ \{f(Oq)+f(Oq_1)+f(Oq_2) + \text{etc.}\} \Delta x,\\
+ \text{or}\ \operatorname{sum} \{f(Oq)\} \Delta x,\ \text{or}\ \textstyle\sum \{f(Oq)\} \Delta x.
+ \end{gather*}
+ When we wish to indicate the limit of any expression into which
+ $\Delta x$, \ie~an increment of~$x$, enters, as the increment becomes smaller
+ and smaller, it is usual to say that $\Delta x$becomes~$dx$. In the
+ limit then $\sum \{f(Oq)\}\Delta x$ becomes $\int f(Oq)dx$, where $\int$ is simply the
+ letter~\emph{s}, the abbreviation of ``sum.'' The symbol then means, the
+ limit of the sum of the areas of the rectangles as the bases become
+ smaller and the number of the rectangles greater. But we have further
+ to indicate the limits within which we are to perform this summing of
+ the rectangles. If we wished to express the area $q_1m_1m_3q_3$ the limits
+ would be $Oq_1$~and~$Oq_3$. We should wish to sum all the rectangles
+ bounded by~$f(Oq_1)$, \ie~$q_1m_1$, and~$f(Oq_3)$, \ie~$q_3m_3$.
+ This we should
+ indicate thus---
+ \[
+ \int^{O_{q_3}}_{O_{q_1}}f(O_q)\centerdot dx
+ \]
+ And the area~$OPm_nq_n$ will be
+ \[
+ \int_0^{Oq_n}f(Oq)\centerdot dx
+ \]
+ This means that the values successively assumed by~$Oq$ in the expression,
+ $\operatorname{sum} (Oq\centerdot dx)$ are, respectively, all the values between $Oq_1$~and~$Oq_3$,
+ or all the values between $O$~and~$Oq_n$. Finally, since the successive
+ values of~$Oq$ are the successive values of~$x$, and since $Oq_n$ is the
+ last value of~$x$ we are to consider, we may write the expression for
+ $OPm_nq_n$
+ \[
+ \int_0^xf(x)\centerdot dx
+ \]
+ or the expression for $q_1m_1m_nq_n$
+ \[
+ \int_{q_1m_1}^x f(x)\centerdot dx
+ \]
+ remembering the $x$ in~$f(x)$ stands for all the successive values of the
+ variable,~$x$, whereas in, $\int_0^x$ or $\int_{q_1m_1}^x$ or generally $\int_{\text{constant}}^x$ $x$ stands
+ only for the \emph{last} of the values of the variable considered.}
+If the law of indifference takes
+%% -----File: 131.png---Folio 104-------
+full effect the seller is apt to regard the area~$Pp_n m_n$ as a
+territory to be reclaimed. The public, he thinks, has got it
+without paying for it. If the law of indifference is completely
+evaded, the public, in its turn, is apt to think that it
+has been cheated to the extent of this area.
+
+We may now consider some more special cases of attempts
+to escape the action of the law of indifference. The system
+of ``two prices'' in retail dealing is a good instance. It is an
+attempt to isolate two classes of customers and to confine the
+action of the law of indifference to equalising the prices within
+these classes, taken severally. In fact, the principle of ``fixed
+prices in retail trade'' is strictly involved in the frank acceptance
+of the law of indifference; and all evasions or modifications
+of that principle are attempts to escape the action of
+the law. The extent to which ``double prices'' prevail in
+London is perhaps not generally realised. A differential
+charge of a halfpenny or penny a quart on milk, for instance,
+\index{Milkman@{Milkman's prices}}%
+according to the average status (estimated by house rent) of
+%% -----File: 132.png---Folio 105-------
+the inhabitants of each street or neighbourhood, seems to be
+common.
+
+It is clear, too, that when he has established a system of
+differential charges, the tradesman can, if he likes, sell to the
+low-priced customer at a price which would not pay him\footnote
+ {This phrase is used in anticipation, but is perhaps sufficiently
+ clear (see below).}
+if
+charged all round; for the small profit he would make on each
+transaction would not enable him to meet his standing expenses.
+Having met them, however, from the profits of his high-priced
+business, he may now put down any balance of receipts over
+expenses out of pocket on the other business as pure gain. If in
+\Figref{20} the rectangles represent not the actual receipts for the
+respective sales, but the balance of receipts over expenses out of
+pocket on each several transaction, we may suppose that the
+dealer requires to realise an area of~$20$ in order to meet his
+standing expenses and make a living. He can do business
+to the extent of~$Oq_4$ at the (gross)\footnote
+ {\textit{I.e.}~surplus of receipts over expenses out of pocket \emph{on that transaction},
+ all standing expenses being already incurred.}
+rate of profit~$Op_4$, which gives
+him his area of~$20$, \ie~$p_4q_4$. If he did business to the extent
+of~$Oq_n$ at a uniform (gross) profit of~$Op_n$, he would only
+secure an area of~$18$, \ie~$p_nq_n$, and so could not carry on business
+at all. But if he can keep $Oq_4$ at the profit~$Op_4$, and
+%% -----File: 133.png---Folio 106-------
+then without detriment to the other add $q_4q_n$ at a profit
+$Op_n$, he secures $20+8$, \ie~$p_4q_4+s_nq_n$. Nay, it is conceivable
+enough that he could not carry on business at all except on
+the principle of double prices. Suppose, in the case illustrated
+by the figure, that he must realise an area of~$25$ in
+order to go on. It will be found that no rectangle containing
+so large an area can be drawn in the curve. The maximum
+rectangle will be found to correspond to the value of
+nearly $4.5$ for~$x$, which will give an area of only a little more
+than $20$. If the law of indifference, then, takes full effect,
+our tradesman cannot do business at all; but if he can deal
+with $Oq_4$ and $q_4q_n$ separately, he may do very well.
+
+In this case the ``double price'' system is the only possible
+one; and the high-priced customers are not really paying an
+unnaturally high price. For unless \emph{some one} pays as high as
+that the ware cannot be brought into the market at all. But
+it would be easy so to modify our supposition as to make the
+tradesman a kind of commercial Robin Hood, forcing up the
+price for one class of customers above the level at which they
+would naturally be able to obtain their goods, and then
+lowering it for others below the paying line.
+
+The differential charges of railway companies illustrate
+\index{Railway@{\textsc{Railway} charges, differential}}%
+this. A company finds that certain goods~$Oq$ must necessarily
+be sent on their line, whereas $qq_4$ may be equally well
+sent by another line. An average surplus of receipts
+over expenses out of pocket represented by an area of four
+units per unit of~$x$ will pay the company; \ie~$Op_4$ per
+unit, giving $p_4q_4$ or $20$ on the carriage of $Oq_4$ would pay.
+On $Oq$ the company puts a charge which will yield gross
+profits at the rate of~$Op$, and thus secure $pq=14$. They
+then underbid the other company for the carriage of~$qq_4$. $Op_4$
+being the minimum average gross profit that will pay (in
+view of standing expenses), they offer to carry at a gross
+profit of~$Op_n$, for their standing expenses are already incurred,
+and they thus secure an extra gross profit of $qs_n$ ($=8$) which,
+together with the $pq$ ($=14$) they have already secured, gives
+them a total of~$22$, or $2$~more than if they had run at
+uniform prices. Of the ten extra units of area which they
+extracted from the consigners of~$Oq$, they have given eight to
+the consigners of~$qq_4$ in the shape of a deduction from the
+legitimate charge.
+%% -----File: 134.p n g----------
+%[Blank Page]
+%% -----File: 135.p n g----------
+%[** TN: Labels have been transcribed faithfully from the original.]
+\begin{figure}[p]
+ \begin{center}
+ \Fig{21}
+ \Input{135a}
+ \end{center}
+\end{figure}
+% [To face page 107.]
+%% -----File: 136.png---Folio 107-------
+
+Another interesting case is that of a theatre. Here the
+\index{Theatre, pit and stalls}%
+``two (or more) price'' system is disguised by withholding
+from the low-price customers certain conveniences which practically
+cost nothing, but which serve as a badge of distinction
+and enable the high-price customers to pay for the privilege
+of being separated from the rest without offensively parading
+before them that this separation is in fact the privilege for
+which they are paying 8s.~each. The accommodation is
+limited, and the nature of the demand varies according to the
+popularity of the piece. Except under quite exceptional circumstances
+custom fixes the charges for stalls and pit, to which we
+will confine ourselves; and though the manager would rather
+fill his floor with stalls than with benches, yet he is glad of all
+the half-crowns which do not displace half-guineas, since his
+expenses out of pocket for each additional pittite are trivial or
+non-existent. Neglecting the difference of space assigned to
+a sitter in a stall and on a bench, let us suppose the whole
+floor to hold $800$~seats, $400$~of which are made into stalls.
+Representing a hundred theatre-goers by a unit on~$x$, and the
+rate of 1s.~a head, or £5 a 100 by the unit on~$y$, and so
+making each unit of area represent £5 receipts, we may
+read the two curves $a$~and~$a'$ in \Figref{21} thus. There is a
+nightly supply of four hundred theatre-goers who value the
+entertainment, accompanied by the dignity and comfort of a
+stall at not less than 10s.~6d.\ a seat (rate of £52:10s.\ per
+hundred seats.) There are also five hundred more who value
+it, with the discomforts of the pit, at 2s.~6d.\ a seat (rate of
+£12:10s.\ per hundred). There is not accommodation for all
+the latter, since there are but four hundred pit seats, and
+custom prevents the manager from filling his pit at a little
+over 3s.~a place as he might do. So he lets his customers fight
+it out at the door and takes in four hundred at 2s.~6d.\ each
+(area~$p'a'$). His takings are $(10.5× 4+2.5× 4) \text{ times £5}=\text{£260}$,
+since each unit of area represents~£5. The areas
+are $pa$~and~$p'a'$. The former $pa$ is as great as the marginal
+utility of the article offered admits of, but the latter
+$p'a'$ is limited horizontally by the space available and vertically
+by custom.
+
+As the public gets tired of the play the curves $a$~and~$a'$ are
+replaced by $b$~and~$b'$. The manager might fill his stalls by
+going down to 8s., and might almost fill his pit at~2s. But
+%% -----File: 137.png---Folio 108-------
+custom forbids this. His prices are fixed and his issue of tickets
+fixes itself. He has 200~stalls and 300~places in the pit
+taken every night. Area $=pb+p'b'$. Receipts $(10.5× 2+2.5× 3)$
+times £5 = £142:10s.
+
+When the manager puts on a new piece the curves $c$~and~$c'$
+\index{Theatre, waiting}%
+\index{Waiting@{Waiting (at theatre)}}%
+replace $b$~and~$b'$; and finding that he can issue six
+hundred stall tickets per night at 10s.~6d., the manager
+pushes his stalls back and cuts down the pit to two
+hundred places, for which six or seven hundred theatre-goers
+fight; several hundred more, who would gladly have
+paid 2s.~6d.\ each for places, retreating when they find
+that they must wait a few hours and fight with wild
+beasts for ten minutes in addition to paying their half-crowns.
+When the two hundred successful competitors find
+that the manager has not sacrificed £80 a night for the
+sake of keeping the four hundred seats they consider due to
+them and their order, they try to convince him that a pittite
+and peace therewith is better than a stalled ox and contention
+with it. It would be interesting to know in what terms they
+would state their case; but evidently the merely commercial
+principles of ``business'' do not command their loyal assent.
+The areas $pc+p'c'$ are $(10.5× 6+2.5× 2) \text{ times £5}=\text{£340}$.
+
+The case of ``reduced terms'' at boarding schools is very
+\index{Reduced terms at school}%
+like the cases of the railway and the theatre. The reader
+may work it out in detail. As long as the school is not full,
+the ``reduced'' pupils do something towards helping things
+along, if they pay anything more than they actually eat and
+break. At the same time it would be impossible to meet the
+standing expenses and carry on the school if the terms were
+reduced all round. If pupils are taken at reduced terms
+when their places could be filled by paying ones, then the
+master is sacrificing the full amount of the reduction.
+
+These instances, which might be increased almost
+indefinitely, will serve to illustrate the importance of the law
+of indifference and the attempts to escape its action.\Pagelabel{108}%
+\end{Remark}
+
+Having now a sufficiently clear and precise conception
+of the marginal utilities of various commodities \emph{to the
+community}, we may take up again from the general
+point of view the investigation which we have already
+%% -----File: 138.png---Folio 109-------
+entered upon (on \Pageref{58}) with reference to the individual,
+and may inquire what principles will regulate the direction
+taken in an industrial community by the labour
+(and other efforts or sacrifices, if there are any others)
+needful to production.
+
+Strictly speaking, this does not come within the
+scope of our present inquiry. We have already seen
+that the exchange value of an article is a function of the
+quantity possessed, completely independent of the way
+in which that quantity comes to be possessed; and
+any inquiries as to the circumstances that determine, in
+particular cases, the actual quantity produced and therefore
+possessed, fall into the domain of the ``theory of
+production'' or ``making'' rather than into that of the
+``theory of value'' or ``worth.'' But the two subjects
+have been so much confounded, and the connection
+between them is in reality so intimate and so important,
+that even an elementary treatment of the subject of
+``value'' would be incomplete unless it included an
+examination of the simplest case of connection between
+value and what is called cost of production. The consideration
+of any case except the simplest would be out
+of place here.
+
+Suppose \Person{A} can command the efforts and sacrifices
+needed to produce either $U$~or~$V$, and suppose the production
+of either will require the same application of
+these productive agents per unit produced. Obviously~\Person{A},
+if he approaches his problem from the purely mercantile
+side, has simply to ask, ``Which of the two, when
+produced, will be worth most in `gold' to the community?''\
+\ie, he must inquire which of the two has the
+highest relative marginal utility, or stands highest on the
+relative scale. Suppose a unit~$u$ has, at the margin,
+twice the relative utility of the unit~$v$; \Person{A}~will then
+devote himself to the production of~$U$, for by so doing
+he will create a thing having twice the exchange value,
+and will therefore obtain twice as much in exchange, as
+if he took the other course. He will therefore produce
+%% -----File: 139.png---Folio 110-------
+$u$ simply because, when produced, it will exchange for
+more ``gold'' than~$v$. \Person{A}~will not be alone in this preference.
+Other producers, whose productive forces are
+freely disposable, will likewise produce~$U$ in preference
+to~$V$, and the result will be a continual increase in the
+quantity of~$U$. Now we have seen that an increased
+quantity of~$U$ means a decreased marginal usefulness of~$U$
+measured in ``gold,'' so that the production of~$U$ in
+greater and greater quantities means the gradual declension
+on the relative scale of its unitary marginal utility,
+and its gradual approximation to that of~$V$, which will
+cause the exchange values of $u$~and~$v$ to become more
+and more nearly equal. But as long as the marginal
+utility of~$u$ stands at all above that of~$v$ on the relative
+scale, the producers will still devote themselves by preference
+to the production of~$U$, and consequently its
+marginal usefulness will continue to fall on the
+scale until at last it comes down to that of~$V$\@. Then
+the marginal utilities and exchange values of $u$~and~$v$
+will be equal, and as the expenditure of productive
+forces necessary to make them is by hypothesis equal
+also, there will be no reason why producers should
+prefer the one to the other. There will now be equilibrium,
+and if more of \emph{either} is produced, then more of
+\emph{both} will be produced in such proportions as to preserve
+the equilibrium now established. In fact the diagram
+(\Figref{14}, \Pageref{60}) by which we illustrated the principle upon
+which a wise man would distribute his own personal
+labour between two methods of directly supplying his
+own wants, will apply without modification to the
+principles upon which purely mercantile considerations
+tend to distribute the productive forces in a mercantile
+society. But though the diagram is the same there is a
+momentous difference in its signification, for in the one
+case it represents a genuine balancing of desire against
+desire in one and the same mind or ``subject,'' where
+the several desires have a real common measure; in the
+other case it represents a mere mechanical and external
+%% -----File: 140.png---Folio 111-------
+equivalence in the desires gratified arrived at by
+measuring each of them in the corresponding desires for
+``gold'' existing respectively in \emph{different} ``\emph{subjects}.''
+
+It only remains to generalise our conclusions. No
+new principle is introduced by supposing an indefinite
+number of alternatives, instead of only two, to lie before
+the wielders of productive forces. There will always be
+a tendency to turn all freely disposable productive forces
+towards those branches of production in which the
+smallest sum of labour and other necessaries will produce
+a given utility; that is to say, to the production of
+those commodities which have the highest marginal
+utility in proportion to the labour, etc., required to produce
+them; and this rush of productive forces into these
+particular channels will increase the amount of the
+respective commodities, and so reduce their marginal
+usefulness till units of them are no longer of more value
+at the margin than units of other things that can be
+made by the same expenditure of productive forces.
+There will then no longer be any special reason for
+further increasing the supply of them.
+
+The productive forces of the community then, like
+the labour of a self-sufficing industrial unit, will tend to
+distribute themselves in such a way that a given sum of
+productive force will produce equal utilities at the
+margin (measured externally by equivalents in ``gold'')
+wherever applied.
+
+To make this still clearer, we may take a single case
+in detail, and supposing general equilibrium to exist
+amongst the industries, may ask what will regulate the
+extent to which a newly developed industry will be
+taken up? But as a preliminary to this inquiry we
+must define more closely our idea of a general equilibrium
+amongst the industries. On \Pageref{73}~\textit{sqq} we established
+the principle that if commodities $A$~and~$B$ are
+freely exchanged, and commodities $B$~and~$C$ are freely
+exchanged also, then the unitary marginal utilities, and
+thus the exchange values of $a$~and~$c$, may be expressed
+%% -----File: 141.png---Folio 112-------
+each in terms of the other, even though it should happen
+that no owners of~$A$ want~$C$, and no owners of~$C$ want~$A$,
+and in consequence there is no direct exchange between
+them. In like manner the principle of the distribution
+of efforts and sacrifices just established enables us to
+select a single industry as a standard and bring all the
+others into comparison with it. It will be convenient,
+as we took gold for our standard commodity, so to take
+gold-digging as our standard industry; and as we have
+\index{Gold-digging}%
+written ``gold'' as a short expression for ``gold and all the
+commodities in the circle of exchange, expressed in terms
+of gold,'' so we may write ``gold-digging'' as a short expression
+for ``gold-digging and all the industries open to
+producers, in equilibrium with gold-digging,'' and we
+shall mean by one industry being in equilibrium with
+another that the conditions are such that a unit of
+effort-and-sacrifice applied at the margin of either
+industry will produce an equivalent utility.\footnote
+ {To speak of the ``margin'' of an industry again involves an
+ anticipation of matters not dealt with in this volume, but I trust it
+ will create no confusion. It must be taken here simply to mean ``a
+ unit of productive force added to those already employed in a certain
+ industry,'' and the assumption is that all units are employed at the
+ same advantage, the difference in the utility of their yields being due
+ simply to the decreasing marginal utility of the same unit of the commodity
+ as the quantity of the commodity progressively increases.}
+If, then,
+a sufficient number of persons have a practical option
+between gold-digging~($\alpha$) and cattle-breeding~($\beta$), this
+\index{Cattle-breeding}%
+will establish equilibrium between these two occupations
+$\alpha$~and~$\beta$ in accordance with the principle just laid
+down; and if a sufficient number of other persons to
+whom gold-digging is impossible have a practical option
+between cattle-breeding~($\beta$) and corn-growing~($\gamma$), then
+\index{Corn-growing}%
+that will establish equilibrium between $\beta$ and~$\gamma$. But
+since there will always be equilibrium between $\alpha$ and~$\beta$
+as long as sufficient persons have the option between
+them, and since that equilibrium will be restored, whenever
+disturbed, by the forces that first established it, it
+follows that if there is equilibrium between $\beta$ and~$\gamma$
+%% -----File: 142.p n g----------
+%[Blank Page]
+%% -----File: 143.p n g----------
+\begin{figure}[p]
+ \begin{center}
+ \Fig{22}
+ \Input{143a}
+ \end{center}
+\end{figure}
+% [To face page 113.]
+%% -----File: 144.png---Folio 113-------
+there will be equilibrium between $\alpha$ and~$\gamma$ also. We
+may therefore conveniently select $\alpha$~or gold-digging as
+the industry of general reference, and may say that a
+man will prefer $\gamma$~or corn-growing to ``gold-digging'' as
+long as the yield is higher in the former industry,
+although as a matter of fact it is not the yield in gold-digging
+but the yield in cattle-breeding (itself equilibrated
+with gold-digging) with which he directly compares
+his results in corn growing. Industries in equilibrium
+with the same are in equilibrium with each
+other.
+
+We assume, then, that there is a point of equilibrium
+about which all the industries, librated with each other
+directly and indirectly, oscillate; and, neglecting the
+oscillations, we use the yield to a given application of
+productive forces in gold-digging as the representative
+of the equivalent yield in all the other industries in
+equilibrium with it.
+
+Now we imagine a new industry to be proposed, and
+producers who command freely disposable efforts and
+sacrifices to turn their attention to it. Their option is
+between the new industry and ``gold-digging,'' in the
+extended sense just explained. We are justified in
+assuming, for the sake of simplicity, that the whole sum
+of the productive forces under consideration would not
+sensibly affect the marginal usefulness of ``gold'' (in the
+extended sense, observe) if applied to ``gold-digging;''
+that is to say, we assume that in no case will the new
+industry draw to itself so great a volume of effort-and-sacrifice
+as to starve the other industries of the world,
+taken collectively, and make the general want of the things
+they yield perceptibly more keen. Therefore, in examining
+the alternative of ``gold-digging,'' we assume that the
+whole volume of labour and other requisites of production,
+or effort-and-sacrifice, which is in question might
+be applied to ``gold-digging'' without reducing the marginal
+usefulness of ``gold,'' or might be withdrawn from
+it without increasing that usefulness. The yield in
+%% -----File: 145.png---Folio 114-------
+``gold'' of any quantity of labour and other requisites,
+then, would be exactly proportional to that quantity.
+
+Fixing on any arbitrary unit of effort-and-sacrifice
+(say $100,000$ foot-tons), and taking as our standard unit
+of utility the gold that it would produce (say $30$~ounces),
+we may represent the ``gold'' yield of any given amount
+of labour and other requisites by the aid of a straight
+line, drawn parallel to the abscissa at a distance of unity
+from it (\Figref{22}). Thus if $Oq$~effort and sacrifice were
+devoted to ``gold-digging,'' the area~$Gq$ would represent
+the exchange value of the result. Now let the upper
+curve on the figure be the curve of quantity-and-marginal-usefulness
+of the new product, the unit of quantity
+being that amount which the unit of labour and other
+requisites ($100,000$ foot-tons) will produce. And here
+we must make a simplification which would be violent
+if we were studying the theory of production, but which
+is perfectly legitimate for our present purpose. We
+must suppose, namely, that however much or little of
+the new product is secured it is always got under the
+same conditions, so that the yield per unit effort-and-sacrifice
+is the same at every stage of the process. But
+though the \emph{quantity} produced by a unit of productive
+force is always the same its marginal usefulness and
+exchange value will of course descend, according to the
+universal law, as the total quantity of the ware increases.
+In the first instance, then, the commercial mind has
+simply to ask, ``Are there persons to whom such an
+amount of this article as I can produce by applying the
+unit of productive force will be worth more than the
+`gold' I could produce by the same application of force?''
+In other words, ``Will the unit of productive force applied
+to this industry produce more than the unit of utility?''
+Under the conditions represented in the figure the
+answer will be a decisive affirmative, and the producer
+will turn his disposable forces of production into the new
+channel. But as soon as he does so the most importunate
+demands for the new article will be satisfied, and if any
+%% -----File: 146.png---Folio 115-------
+further production is carried on it must be to meet a
+demand of decreasing importunacy, \ie~the marginal
+utility of the article is decreasing, and the exchange
+value of the yield of the unit of productive force in
+the new industry is falling. Production will continue,
+however, as long as there is any advantage in the new
+industry over gold-production, \ie~till the yield of unit
+productive force in the new industry has sunk to unit
+utility.
+
+Thus, if $Oq_1$~effort and sacrifice is devoted to the
+new industry, the marginal usefulness of the product will
+be measured by~$q_1f_1$, and the exchange value of the
+whole output by the rectangle bounded by the dotted
+line and $q_1f_1$,~etc. This is much more than $Gq_1$ the
+alternative ``gold'' yield to the same productive force.
+But there is still an advantage in devoting productive
+forces to the new industry, since $q_1f_1$ is greater than~$q_1g_1$,
+and even if the present producers are unable to
+devote more work to it, or unwilling to do so, because
+it would diminish the area of the rectangle (\Pageref{96}), yet
+there will be others anxious to get a return to their
+work at the rate of~$q_1f_1$ instead of~$q_1g_1$. Obviously,
+then, the new commodity will be produced to the extent
+of~$Oq$ where $qf=qg$, \ie,~the point at which the curve
+cuts the straight line~$Gg$, which is the alternative ``gold''
+curve. If production be carried farther it will be carried
+on at a disadvantage. At~$q_2$, for instance, $q_2f_2$~is less
+than~$q_2g_2$, that is to say, if the supply is already~$Oq_2$,
+then a further supply will meet a demand the importunity
+of which is less than that of the demand for the
+``gold'' which the same productive force would yield.
+This will beget a tendency to desert the industry, and
+will reduce the quantity towards~$Oq$.
+
+We have supposed our units of ``gold'' and the new
+commodity so selected that it requires equal applications
+of productive agencies to secure either, but in practice
+we usually estimate commodities in customary units that
+have no reference to any such equivalence. This of
+%% -----File: 147.png---Folio 116-------
+course does not affect our reasoning. If the unit of~$F$ is
+such that our unit of labour and other necessaries yields
+a hundred units of~$F$ and only one unit of~$G$, then,
+obviously, we shall go on producing~$F$ until, but only
+until, the exchange value of a hundred units of~$F$ (the
+product of unit of labour, etc., in~$F$) becomes equal to the
+exchange value of one unit of~$G$ (the product of unit of
+labour, etc., in~$G$). Or, generally, if it needs $x$~times as
+much effort and sacrifice to produce one unit~$A$ as it
+takes to produce one unit~$B$, then it takes as much to
+produce $x$~units $B$ as to produce one unit~$A$, and there
+will always be an advantage either in producing~$xb$ or
+in producing one~$a$, by preference, unless the exchange
+value of both is the same; that is to say, unless the
+marginal value of~$a$ equals $x$~times that of~$b$. Thus, \emph{if $a$~contains
+$x$~times as much work as~$b$, then there will not be
+equilibrium until $A$ and~$B$ are produced in such amounts as
+to make the exchange value of~$a$ just $x$~times the exchange
+value of~$b$}.
+
+This, then, is the connection between the exchange
+value of an article (that can be produced freely and in
+indefinite quantities) and the amount of work it contains.
+Here as everywhere the quantity possessed
+determines the marginal utility, and with it the exchange
+value; and if the curve is given us we have only
+to look at the quantity-index in order to read the exchange
+value of the commodity (see pp.~\Pageref[]{62},~\Pageref[]{67}). But in
+the practically and theoretically very important case of
+commodities freely producible in indefinite quantities
+we may now note this further fact as to the principle
+by which the position of the quantity-index is in its turn
+fixed---that fluid labour-and-sacrifice tends so to distribute
+itself and so to shift the quantity-indexes as to
+make \emph{the unitary marginal utility of every commodity
+directly proportional to the amount of work it contains}.
+
+\begin{Remark}
+This fact, that the effort-and-sacrifice needed to produce
+two articles is, in a large class of cases (those, namely, in
+%% -----File: 148.png---Folio 117-------
+which production is free and capable of indefinite extension),
+proportional to the exchange values of the articles themselves,
+has led to a strange and persistent delusion not only amongst
+the thoughtless and ignorant but amongst many patient and
+earnest thinkers, who have not realised that the exchange
+value of a commodity is a function of the quantity possessed,
+and may be made to vary indefinitely by regulating
+that quantity. The delusion to which I refer is that it is the
+amount of effort-and-sacrifice or ``labour'' needed to produce
+a commodity which \emph{gives that commodity its value in exchange}.
+A glance at \Figref{22} will remind the reader of the magnitude
+and scope of the error involved in this idea. The commodity,
+on our hypothesis, always contains the same amount
+of effort-and-sacrifice per unit, whether much or little is produced,
+but the fact that only the unit of ``labour'' has been
+put into it does not prevent its exchange value being more
+than unity all the time till it exists in the quantity~$Oq$, nor
+does the fact of its containing a full unit of labour keep its
+exchange value up to unity as soon as it exists in excess of
+the quantity~$Oq$. What gives the commodity its value in
+exchange is the quantity in which it exists and the nature of
+the curve connecting quantity and marginal usefulness; and
+it is no more true and no more sensible to say that the
+quantity of ``labour'' contained in an article determines its
+value than it would be to say that it is the amount of money
+which I give for a thing that makes it useful or beautiful.
+The fact is, of course, precisely the other way. I give so
+much money for the thing because I expect to find it useful
+or think it beautiful; and the producer puts so much
+``labour'' into the making of a thing because when made he
+expects it to have such and such an exchange value. Thus
+one thing is not worth twice as much as another because it
+has twice as much ``labour'' in it, but producers have been
+willing to put twice as much ``labour'' into it because they
+know that when produced it will be worth twice as much,
+because it will be twice as ``useful'' or twice as much
+desired.
+
+This is so obvious that serious thinkers could not have
+fallen into and persisted in the error, and would not be
+perpetually liable to relapse into it, were it not for certain
+considerations which must now be noticed.
+%% -----File: 149.png---Folio 118-------
+
+In the first place, if we have not fully realised and completely
+assimilated the fact that exchange value is a function
+of the quantity possessed, and changes as the quantity-index
+shifts, it seems reasonable to say, ``It is all very well to
+say that because people want~$a$ twice as much as~$b$ they
+will be \emph{willing to do} twice as much to get~$a$ as they will to
+get~$b$, but how does it follow that they will be \emph{able to get} the
+article~$a$ by devoting just twice as much labour to it as to~$b$?
+Surely you cannot maintain that it \emph{always happens} that
+the thing people want twice as much needs exactly twice as
+much ``labour'' to produce as the other? And yet you
+admit yourself that the thing which has twice the exchange
+value always does contain twice the ``labour.'' If it is not
+a chance, then, what is it?'' The answer is obvious, and the
+reader is recommended to write it out for himself as clearly
+and concisely as possible, and then to compare it with the
+following statement: If people want~$a$ just twice as much
+as~$b$, and no more, it does not follow that a producer will
+find $a$ just twice as hard to get, but it does follow that if he
+finds~$a$ is \emph{more} than twice as hard to get (say $x$~times as hard)
+he will not get it at all, but will devote his productive
+energies to making~$b$. Confining ourselves, for the sake
+of simplicity, to these two commodities, we note that other
+producers will, for the like reason, also produce~$B$ in preference
+to~$A$. The result will be an increased supply of~$B$,
+and, therefore, a decreased intensity of the want of it;
+whereas the want of~$A$ remaining the same as it was, the
+utility of~$a$ is now more than twice as great as the (diminished)
+utility of~$b$; and as soon as the want of~$b$ relatively to the
+want of~$a$ has sunk to~$\dfrac{1}{x}$, then one~$a$ is worth $x$~$b$'s, and as it
+needs just $x$~times the effort-and-sacrifice to produce~$a$, there
+is now equilibrium, and $A$ and~$B$ will \emph{both} be made in such
+quantities as to preserve the equilibrium henceforth; but the
+proportion of one utility to the other, and the proportion
+of the ``labour'' contained in one commodity to that
+contained in the other, do not ``happen'' to coincide; they
+have been \emph{made} to coincide by a suitable adjustment of efforts
+so as to secure the maximum satisfaction.
+
+Another source of confusion lurks in the ambiguous use
+of the word ``because''; and behind that in a loose conception
+%% -----File: 150.png---Folio 119-------
+of what is implied and what is involved in one thing being
+the ``cause'' of another.
+
+Thus we sometimes say ``$x$~is true because $y$ is true,''
+when we mean not that $y$ being true is the \emph{cause}, but that it
+is the \emph{evidence} of $x$ being true. For instance, we might say
+``prime beef is less esteemed by the public than prime
+mutton, because the latter sells at~$1$d.\ or~$\frac{1}{2}$d.\ more per pound
+than the former.'' By this we should mean to indicate the
+higher price given for mutton not as the cause of its being
+more esteemed, but as the evidence that it is so.\footnote
+ {Such psychological reactions as the desire to put one dish on the
+ table in preference to another, simply because it is known to be more
+ expensive, do not fall within the scope of this inquiry.}
+So again,
+``Is the House sitting?''---``Yes! because the light on the clock-tower
+\index{House of Commons sitting}%
+is shining.'' This does not mean that the light shining
+causes the House to sit, but that it shows us it is sitting.
+
+In like manner a man may say, ``If I want to know how
+much the exchange value of~$a$ exceeds that of~$b$, I shall look
+into the cost of producing them, and if I find four times as
+much `labour' put into~$a$, I shall say $a$~is worth four times~$b$,
+because I find that producers have put four times the
+`labour' into it;'' and if he means by this that he knows
+the respective values in exchange of $a$~and~$b$ on the evidence
+of the amount of effort-and-sacrifice which he finds producers
+willing to put into them respectively, then we have no fault
+to find with his economics, though he is using language
+dangerously liable to misconception. But if he means that
+it is the effort-and-sacrifice, or ``labour,'' contained in them
+which \emph{gives} them their value in exchange, he is entirely
+wrong. As a matter of fact, the defenders of the erroneous
+theory sometimes make the assertion in the erroneous sense,
+victoriously defend it, when pressed, in the true sense, and
+then retain and apply it in the erroneous sense.
+
+Again, though it is never true that the quantity of
+``labour'' contained in an article \emph{gives} it its value-in-exchange,
+yet it may be and often is true, in a certain sense, that the
+quantity of ``labour'' it contains is the \emph{cause} of its having
+such and such a value in exchange. But if ever we allow
+ourselves to use such language we must exercise ceaseless
+vigilance to prevent its misleading ourselves and others.
+%% -----File: 151.png---Folio 120-------
+For what does it mean? The quantity-index and the curve
+fix the value-in-exchange. But the quantity-index may run
+the whole gamut of the curve, and we have seen that what
+determines the direction of its movement and the point at
+which it rests is, in the case of freely producible articles,
+precisely the quantity of ``labour'' contained in the article.
+This quantity of ``labour'' contained, then, determines the
+amount of the commodity produced, and this again determines
+the value-in-exchange. In this sense the amount of
+``labour'' contained in an article is the cause of its exchange
+value. But this is only in the same sense in which the
+approach of a storm may be called the cause of the storm-signal
+\index{Storm-signal}%
+rising. The approach of the storm causes an intelligent
+agent to pull a string, and the tension on the string causes
+the signal to rise. In this sense the storm is the cause of
+the signal rising. But it would be a woful\DPnote{** [sic] legitimate variant} mistake, which
+might have disastrous consequences, to suppose that there is
+any immediate causal nexus between the brewing of the
+storm and the rising of the ball. And if our mechanics
+were based on the principle that a certain state of the atmosphere
+``gives an upward movement to a storm-signal,'' the
+science would stand in urgent need of revision. So in our
+case: Relative ease of production makes intelligent agents
+produce largely if they can; increasing production results in
+falling marginal utilities and exchange-values; therefore, in a
+certain sense, ease of production causes low marginal utilities
+and exchange-values. But there is no immediate causal
+nexus between ease of production and low exchange-values.
+Exchange values, high and low, are found in things which
+cannot be produced at all; and if (owing to monopolies,
+artificial or natural) the intelligent agents who observe how
+easily a thing is produced are not in a position to produce it
+abundantly, or have reasons for not doing so, the ease of
+production may coexist with a very high marginal utility,
+and consequently with a very high exchange value. In such
+a case the amount of ``labour'' contained in the article will
+be small out of all proportion to its exchange-value; and the
+quantity produced may be regulated by natural causes that
+have no connection with effort and sacrifice, or by the desire
+on the part of a monopolist to secure the maximum gains.
+
+Finally, there are certain phenomena, of not rare occurrence
+%% -----File: 152.png---Folio 121-------
+in the industrial world, which really seem at first
+sight to give countenance to the idea that the exchange-value
+of a commodity is determined, not by its marginal
+desiredness, but by the quantity of ``labour'' it contains.
+These phenomena are for the most part explained by the
+principle of ``discounting,'' or treating as present, a state of
+things which is foreseen as certain to be realised in a near
+future. For instance, suppose a new application of science to
+industry, or the rise into favour of a new sport or game, suddenly
+\index{Games@{\textsc{Games}}}%
+creates a demand for special apparatus, and suppose one
+or two manufacturers are at once prepared to meet it. They
+may, and often do, take advantage of the urgency of the want
+of those who are keenest for the new apparatus, and sell it at its
+full initial exchange-value, only reducing their price as it becomes
+necessary to strike a lower level of desire, and thus
+travelling step by step all down the curve of quantity-and-value-in-exchange
+till the point of equilibrium is at last reached, and
+every one can buy the new apparatus who desires it as much
+as the ``gold'' that the same effort-and-sacrifice would produce.
+But it may also happen that the manufacturers who are
+already on the field foresee that others will very soon be
+ready to compete with them, and that it will require a comparatively
+small quantity of the new apparatus to bring it
+down to its point of equilibrium, inasmuch as it cannot,
+in the nature of the case, be very extensively used. They
+feel, therefore, that they have not much to gain by securing
+high prices for the first specimens, and on the other hand, if
+they ``discount'' or anticipate the fall to the point of equilibrium,
+and at once offer the apparatus on such terms as will
+secure all the orders, they will prevent its being worth while
+for any other manufacturers to enter upon the new industry,
+and will secure the whole of the permanent trade to themselves.
+
+Any intermediate course between these two may likewise
+be adopted; but the discounting or anticipation of the foreseen
+event only disguises and does not change the nature of
+the forces in action.
+
+A more complicated case occurs when a man wants a
+single article made for his special use which will be useless
+to any one else. Let us say he wants a machine to do certain
+work and to fit into a certain place in his shop. The importance
+%% -----File: 153.png---Folio 122-------
+to him of having such a machine is great enough
+to make him willing to give £100 for it sooner than go
+without it. But the ``labour'' (including the skill of the
+designer) needed to produce it would, if applied to making
+other machines, or generally to ``gold-digging,'' only produce
+an article of the exchange-value of £50. ``In this case,'' it
+will be said, ``the marginal utility of the machine is measured
+by £100, yet the manufacturer (if his skill is not a monopoly)
+can only get £50 for making it, because it only contains
+labour and other requisites to production represented by that
+sum. Does not this show conclusively that it is the ``labour''
+contained in an article, not its final utility, which determines
+its exchange-value?'' To judge of the validity of this objection,
+let us begin by asking exactly what our theory would
+lead us to anticipate, and then let us compare it with the
+alleged facts. We have seen that in equilibrium the marginal
+utility of the unit of a commodity must occupy the same
+place on the relative scales of all those who possess it;
+and further, that if ever that marginal utility should be
+higher on \Person{A}'s relative scale than on \Person{B}'s, then (if \Person{B} possesses
+any of the commodity) the conditions for a mutually profitable
+exchange exist, though on what terms that exchange
+will be made remains, as far as our investigations have taken
+us, indeterminate, within certain assignable limits. Now if
+we suppose the machine to be actually made we shall have
+this situation: \Person{A}, on whose relative scale the marginal
+utility of the machine stands at £100 has not got it. \Person{B},
+on whose relative scale it stands at zero, possesses it. The
+conditions of a mutually advantageous exchange therefore
+exist. But the terms on which that exchange will take place
+are indeterminate between 0~and~£100. When a single
+exchange has been made, on whatever terms, then the
+article will stand at zero on every relative scale except
+that of its possessor, and no further exchange will be
+made. \emph{If the machine exists}, therefore, its exchange-value
+will be indeterminate between zero and £100. Now if
+we consistently carry out our system of graphic representation
+this position will be reproduced with faultless accuracy.
+The curve of quantity-possessed-and-marginal usefulness with
+reference to the community being drawn out, the vertical
+intercept on the quantity-index indicates the exchange-value
+%% -----File: 154.png---Folio 123-------
+of the commodity. Now in this instance the curve in question
+consists of the rectangle in \Figref{23}~(\textit{a}), where the unit on
+the axis of~$y$ is £100~per machine, and the unit on the axis
+of~$x$ is one machine. For the usefulness of the first machine
+to the community is at the rate of £100~per machine, and
+the usefulness of all other machines at the rate of $0$~per
+machine. Therefore the curve falls abruptly from $1$ to $0$ \emph{at}
+the value $x=1$. But the quantity possessed by the community
+is one machine. Therefore the quantity index is at
+\begin{figure}[hbtp]
+ \begin{center}
+ \Fig{23}
+ \Input[3.5in]{154a}
+ \end{center}
+\end{figure}
+the distance unity from the origin, \Figref{23}~(\textit{b}). What is the
+length of the intercept? Obviously it is indeterminate between
+$0$ and $1$. This is exactly in accordance with the facts.
+Supposing the machine actually to exist, then, our theory
+vindicates itself entirely. But if the machine does not yet
+exist, what does our theory tell us of the prospect of its being
+made? We have seen that a thing will be made if there is a
+prospect of its exchange-value, when made, being at least as
+great as that of anything else that could be made by the same
+effort-and-sacrifice. Now the exchange-value is determined
+by the intercept on the quantity-index. Before the machine
+is made that intercept is $1$ ($=\text{£100}$), but that does not concern
+the maker, for he wants to know what it \emph{will be} when
+the machine is made, not what it is before. But it will be
+indeterminate, as we have seen, and therefore there is no
+security in making the machine. In order to get the
+machine made, therefore, the man who wants it must remove
+the indeterminateness of the problem by stipulating in
+advance that he will give not less than £50 for it. But
+what he is now doing is not getting the machine (which does
+not exist) in exchange for ``gold.'' It is getting control or
+%% -----File: 155.png---Folio 124-------
+direction of a given application of labour, etc. in exchange
+for ``gold,'' and this being so, it is not to be wondered at
+that the price he pays for this ``labour'' should be proportionate
+to the quantity of it he gets.
+
+This is the general principle of ``tenders'' for specific
+work.
+\end{Remark}
+
+\Pagelabel{124}%
+We may appropriately close our study of exchange
+value by a few reflections and applications suggested
+by the ordinary expenditure of private income, and
+especially shopping and housekeeping.
+
+On \Pageref{58} we considered what would be the most
+sensible way of distributing labour amongst the various
+occupations which might claim it on a desert island.
+There labour was the purchasing power, and the question
+was in what proportions it would be best to exchange it
+for the various things it could secure. We were not
+then able to extend the principle to the more familiar
+case of money as a purchasing power, because we had
+not investigated the phenomena of exchange value and
+price. We may now return to the problem under this
+aspect. The principle obviously remains the same.
+Robinson Crusoe, when industrial equilibrium is established
+\index{Robinson Crusoe}%
+in his island, so distributes his labour that the
+last hour's work devoted to each several task results in
+an equivalent mass or body of satisfaction in every case.
+If the last hour devoted to securing \Person{A} produced less
+satisfaction than the last hour devoted to securing \Person{B},
+Robinson would reduce the former application of labour
+till, his stock of \Person{A} falling and its marginal usefulness
+rising, the last hour devoted to securing it produced a
+satisfaction as great as it could secure if applied otherwise.
+He would then keep his supply at this level, or
+advance the supply of \Person{A} and \Person{B} together in such proportions
+as to maintain this relation. If he lets his stock
+of \Person{A} sink lower he incurs a privation which could be
+removed at the expense of another privation not so
+great; if he makes it greater he gets a smaller gratification
+at a cost which would have secured a greater
+%% -----File: 156.png---Folio 125-------
+one if applied elsewhere. In equilibrium, then, the last
+hour's work applied to each task produces an equal
+gratification, removes an equal discomfort, or gratifies
+an equal volume of desire; which is to say, that Robinson's
+supply of all desired things is kept at such a
+level that the unitary marginal utilities of them all
+are directly proportional to the labour it takes to secure
+them.
+
+In like manner the householder or housewife must
+\index{Housekeeper}%
+\Pagelabel{125}%
+aim at making the last penny (shilling, pound, or whatever,
+in the particular case, is the \textit{minimum sensibile}\footnotemark)
+\footnotetext{\Ie, the smallest thing he can ``feel.'' The importance of this
+ qualification will become apparent presently (see \Pageref{129}).}
+expended on every commodity produce the same gratification.
+If this result is not attained then the money
+is not spent to the best advantage. But how is it to be
+attained? Obviously by so regulating the supplies of
+the several commodities that the marginal utilities of a
+pennyworth of each shall be equal. We take it that the
+demand of the purchaser in question is so small a part
+of the total demand for each commodity as not sensibly
+to affect the position of its quantity-index on the national
+register, and we therefore take the price of each commodity
+as being determined, independently of his
+demand, on the principles already laid down. There is
+enough lump sugar available of a given quality to supply
+\index{Sugar}%
+all people to whom it is worth 3d.\ a pound. Our housewife
+therefore gets lump sugar until the marginal utility
+of one pound is reduced to the level represented by 3d.
+Perhaps this point will be reached when she buys six
+pounds a week. The difference between six pounds and
+seven pounds a week is not worth threepence to her.
+The difference between five pounds and six is. Sooner
+than go without any loaf sugar at all she would perhaps
+pay a shilling a week for one pound. That pound
+secured, a second pound a week would be only worth,
+say, eightpence. Possibly the whole six pounds may
+represent a total utility that would be measured by
+%% -----File: 157.png---Folio 126-------
+$(12\text{d.} + 8\text{d.} + 5\tfrac{1}{2}\text{d.} + 4\text{d.} + 3\tfrac{1}{2}\text{d.}+ 3\text{d.})$ three shillings, or
+an average of sixpence a pound, but the unitary marginal
+utility of a pound is represented by threepence.
+Another housekeeper might be willing to give one and
+sixpence a week for a pound of sugar sooner than go
+without altogether, and to give a shilling a week for
+a second pound, but her demand, though more keen, may
+be also more limited than her neighbour's. She gets a
+third pound a week, worth, say, sevenpence to her, and
+a fourth worth threepence, and there she stops, because
+a fifth pound would be worth less than threepence to
+her, and there is only enough for those who think it
+worth 3d.\ a pound or more. She has purchased for a
+shilling sugar the total utility of which is represented
+by $(18\text{d.} + 12\text{d.} + 7\text{d.}+ 3\text{d.} =)$ 3s.~4d., but the unitary
+marginal utility of a pound is 3d., as in the other case.
+
+So with all other commodities. Each should be purchased
+in such quantities that the marginal utility of one
+pennyworth of it exactly balances the marginal utility of
+one pennyworth of any of the rest; the absolute marginal
+utility of the penny itself changing, of course, with
+circumstances of income, family, and so forth, but the
+relative utilities of pennyworths at the margin always
+being kept equal to each other. The clever housekeeper
+has a delicate sense for marginal utilities, and can
+balance them with great nicety. She is always on the
+alert and free from the slavery of tradition. She follows
+changes of condition closely and quickly, and keeps
+her system of expenditure fluid, so to speak, always
+ready to rise or fall in any one of the innumerable and ever
+shifting, expanding and contracting channels through
+which it is distributed, and so always keeping or
+recovering the same level everywhere. She keeps her
+marginal utilities balanced, and never spends a penny on
+A when it would be more effective if spent on B; and
+combines the maximum of comfort and economy with
+the minimum of ``pinching.''
+
+The clumsy housekeeper spends a great deal too much
+%% -----File: 158.png---Folio 127-------
+on one commodity and a great deal too little on another.
+She does not realise or follow the constant changes of
+condition fast enough to overtake them, and buys
+according to custom and tradition. Her system of
+expenditure is viscous, and cannot change its levels
+so fast as the channels change their bore. She can
+never get her marginal utilities balanced, and therefore,
+though she drives as hard bargains as any one,
+and always seems to ``get her money's worth'' in
+the abstract, yet in comfort and pleasure she does
+not make it go as far as her neighbour does, and
+never has ``a penny in her pocket to give to a boy,''\footnote
+ {The absence of which was lamented by an old Yorkshire woman
+ as the greatest trial incident to poverty and dependence.}
+\index{Penny@{\textsc{Penny} ``to give to a boy''}}%
+a
+fact that she can never clearly understand because she
+has not learned the meaning of the formula, ``My coefficient
+of viscosity is abnormally high.''
+
+\begin{Remark}
+It is rather unfortunate for the advance of economic
+science that the class of persons who study it do not as a rule
+belong to the class in whose daily experience its elementary
+principles receive the sharpest and most emphatic illustrations.
+For example, few students of economics are obliged to
+realise from day to day that a night's lodging, and a supper,
+possess utilities that fluctuate with extraordinary rapidity;
+and the tramps who, towards nightfall, in the possession of
+twopence each, make a rush on suppers, and sleep out, if the
+thermometer is at~$45°$, and make a rush on the beds and go
+\index{Thermometer}%
+supperless if it is at~$30°$, have paid little attention to the
+economic theories which their experience illustrates. As a
+rule it seems easier to train the intellect than to cultivate the
+imagination, and while it is incredibly difficult to make the
+well-to-do householder realise that there are people to whom
+the problem of the marginal utilities of a bed and a bowl of
+\index{Bed@{Bed \textit{versus} supper}}%
+stew is a reality, on the contrary, it is quite easy to demonstrate
+the general theory of value to any housekeeper who
+has been accustomed to keep an eye on the crusts, even
+though she may never have had any economic training. For
+the great practical difficulty in the way of gaining acceptance
+for the true theory is the impression on the part of all but
+%% -----File: 159.png---Folio 128-------
+the very poor or the very careful that it is contradicted by
+experience. In truth our theory demands that no want
+should be completely satisfied as long as the commodity that
+satisfies it costs anything at all; for in equilibrium the
+unitary marginal utilities are all to be proportional to the
+prices, and if any want is completely satisfied then the
+unitary marginal utility of the corresponding commodity
+must be zero, and this cannot be proportional to the price
+unless that is zero too. Again, since all the unitary marginal
+utilities are kept proportional to the prices, it follows
+that though none of them can \emph{reach} zero while the corresponding
+commodity has any price, they must all \emph{approach} zero
+together. Now all this, it is said, is contrary to experience.
+In the first place, we all of us have as much bread and meat
+and potatoes as we want, though they all cost something;
+and in the next place, whereas the marginal utility of these
+things has actually reached zero, the marginal utility of pictures,
+horses, and turtle soup has not even approached it, for
+\index{Turtle soup}%
+we should like much more than we get of them all.
+
+We have only to run this objection down in order to see
+how completely our theory can justify itself; but we must
+begin by reminding ourselves---first, that real commodities
+are not infinitely divisible, and that we are obliged to choose
+between buying a \emph{definite quantity} more or no more at all;
+and second, that our mental and bodily organs are only capable
+of discerning certain definite intervals. There may be
+two tones, not in absolute unison, which no human ear could
+distinguish; two degrees of heat, not absolutely identical, which
+the most highly trained expert could not arrange in their
+order of intensity. With this proviso as to the \emph{minimum
+venale}\footnote
+ {The reply, ``We don't make up ha'poths,'' which damps the
+ purchasing ardour of the youth of Northern England, is constantly
+ made by nature and by man to the economist who tries to apply the
+ doctrine of continuity to the case of individuals.}
+and the \textit{minimum sensibile}, let us examine the supposed
+case in detail. A gentleman has as much bread but not as
+much turtle soup as he would like. This is bad husbandry, for
+he ought to stop short of the complete gratification of his desire
+for bread at the point represented by a usefulness of sixteen-pence
+a quartern (for we assume that he takes the best quality),
+and the surplus which he now wastefully expends on reducing
+%% -----File: 160.png---Folio 129-------
+that usefulness to absolute zero might have been spent on
+turtle soup. But let us see how this would work. We must
+not allow him to adopt the royal precept of eating cake when
+he has no bread, but must suppose him \textit{bona fide} to save on
+his consumption of bread in order to increase his expenditure
+on turtle and on nothing else. Probably he already
+resembles Falstaff in incurring relatively small charges on
+\index{Falstaff}%
+account of bread---say his bill is 3d.~a~day. He has as much
+\Pagelabel{129}%
+as he wants, and therefore the marginal utility is zero, but the
+curve descends rapidly, and if we reduce his allowance by
+one-sixth, and his toast at breakfast, his roll at dinner and
+lunch, and his thin bread-and-butter at tea, or with his white-bait,
+are all of them a little less than he wants, he will find
+that the marginal utility of bread has risen far above 1s.~4d.\
+a quartern, and is more like a shilling an ounce. Taking
+the unit of~$x$ as $1$~ounce, and the unit of~$y$ as 1d., it is a
+delicate operation to arrest the curve for some value between
+$x=2\tfrac{1}{2}$, $y=12$, and $x=3$, $y=0$. But let us suppose
+our householder equal to it. He finds that $x=2\tfrac{3}{4}$ gives
+$y=1$, and accordingly determines to dock himself of $\tfrac{1}{12}$
+of his supply and save $\tfrac{1}{4}$d.~a~day on bread. But now
+arises another difficulty. He wants always to have his bread
+fresh, and the $\tfrac{1}{4}$d.~worth he saves to-day is not suitable
+for his consumption to-morrow. The whole machinery
+of the baking trade and of his establishment is too
+rough to follow his nice discrimination. Its utmost delicacy
+cannot get beyond discerning between $2\tfrac{1}{2}$d.~and~3d., and he
+finds that to be sure of not letting the marginal utility of
+bread down to zero he must generally keep it up immensely
+above 1d.~per ounce. Suppose this difficulty also overcome.
+Then our economist saves $\tfrac{1}{4}$d.~a~day on bread or 6d.\ in twenty-four
+days. In one year and 139~days he has saved enough to
+get an extra pint of turtle soup, which (if it does not reduce its
+marginal utility below 10s.~6d.)\ fully compensates him for
+his loss of bread---but not for the mental wear and tear and the
+unpleasantness in the servants' hall which have accompanied
+his fine distribution of his means amongst the objects of
+his appetite. This is in fact only an elaboration of the principle
+laid down on \Pageref{125}.
+
+As a rule, however, it is by no means true that we all
+have as much bread, meat, and potatoes as we want. Omitting
+%% -----File: 161.png---Folio 130-------
+all consideration of the great numbers who are habitually
+hungry, and confining our attention to the comfortable classes
+who always have enough to eat in a general way, we shall
+nevertheless find that the bread-bill is very carefully watched,
+and that a sensible fall in the price of bread would immediately
+cause a sensible increase in the amount taken.
+For instance, if bread were much cheaper, or if the housekeeping
+\index{Resurrection pudding}%
+allowance were much raised, many a crust would be
+allowed to rest in peace which now reappears in the ``resurrection
+pudding,'' familiar rather than dear to the schoolboy,
+who has given it its name; but also known in villadom,
+where his sister uncomplainingly swallows it without vilifying
+it by theological epithets.
+
+The assertion which for a moment seems to be true of
+bread, though it is not, is obviously false when made concerning
+milk, meat, potatoes, etc. The people who have ``as
+much as they want'' of these things are few; and if in most
+cases a more or less inflexible tradition in our expenditure
+prevents us from quite realising that we save out of potatoes
+to spend on literature or fashion, it is none the less true that
+we do so. Indeed, there are probably many houses in which
+sixpence a week is consciously saved out of bread, milk,
+cheese, etc., for the daily paper during the session, when its
+\index{Daily@{\textsc{Daily Paper}}}%
+marginal utility is relatively high, to be restored to material
+purposes when Parliament adjourns.
+
+Before leaving the subject of domestic expenditure, I
+would again emphasise the important part which tradition
+and viscosity play in it. This is so great that sometimes a
+loss of fortune, which makes it absolutely necessary to break
+\index{Fortune, loss of}%
+up the established system and begin again with the results of
+past experience, but free from enslaving tradition, has been
+found to result in a positive increase of material comfort and
+enjoyment.
+
+One of the benefits of accurate account-keeping consists in
+\index{Account-keeping}%
+the help it is found to give in keeping the distribution of
+funds fluid, and preventing an undue sum being spent on any
+one thing without the administrator realising what he is
+doing.\Pagelabel{130}%
+\end{Remark}
+
+A few miscellaneous notes may be added, in conclusion,
+on points for which no suitable place has been
+%% -----File: 162.png---Folio 131-------
+found in the course of our investigation, but which cannot
+be passed over altogether.
+
+\begin{Remark}
+The reader may have observed a frequent oscillation
+between the conceptions of ``so much a year, a month, a day,
+etc.,'' and ``so much'' absolutely. If a man has one watch,
+he will want a second watch less. But we cannot say that
+if he has one loaf of bread he will want a second loaf less.
+We can only say if he has one loaf of bread \emph{a week} (or a day,
+or some other period) he will want a second less. Our
+curves then do not always mean the same thing. Generally
+the length on the abscissa indicates the breadth of a
+stream of supply which must be regarded as continuously
+flowing, for most of our wants are of such a nature as to
+destroy the things that supply them and to need a perpetual
+renewal of the stores provided to meet them. And in the
+same way the area of the curve of quantity-and-marginal-usefulness
+or the height of the curve of quantity-and-total-utility
+does not indicate an absolute sum of gratification or
+relief from pain, but a rate of enjoyment or relief per week,
+month, year, etc. Thus, strictly speaking, the value of~$y$ in
+one of our quantity-and-marginal-usefulness curves measures
+the rate at which increments in the \emph{rate of supply} are increasing
+the \emph{rate of enjoyment}; but we may, when there is no
+danger of misconception, cancel the two last ``rates'' against
+each other, and speak of the rate at which increments in the
+\emph{supply} increase the \emph{gratification}; for the gratification (area)
+and the supply (base), though rates absolutely, are not rates
+with reference to each other, but the ratio of the increase of
+the one to the increase of the other is a rate with reference
+to the quantities themselves.
+
+We must remember, then, that, as a matter of fact, it is
+generally rates of supply and consumption, not absolute
+quantities possessed, of which we are speaking; and especially
+when we are considering the conditions of the maintenance
+of equilibrium. It will repay us to look into this conception
+more closely than we have hitherto done; and as the problem
+becomes extremely complex, unless we confine ourselves
+to the simplest cases, we will suppose only two persons, \Person{A}~and~\Person{B},
+to constitute the community, and only two articles,
+$V$~and~$W$, to be made and exchanged by them, $V$~being made
+%% -----File: 163.png---Folio 132-------
+exclusively by~\Person{A}, and $W$~exclusively by~\Person{B}. Let the curves on
+\Figref{24} represent \Person{A}'s and \Person{B}'s curves of quantity-and-marginal-utility
+of $V$~and~$W$; and let \Person{A} consume~$V$ at the rate of $q_{av}$~per
+day (or month or other unit of time) and $W$~at the rate of~$q_{aw}$,
+while \Person{B} consumes~$V$ at the rate of~$q_{bv}$, and $W$~at the rate of~$q_{bw}$.
+And let the position of the amount indices in the figure
+represent a position of equilibrium. Let us first inquire how
+many of the data in the figures are arbitrary, and then ask
+what inferences we can draw as to the conditions for maintaining
+equilibrium and the effects of failure to comply with
+those conditions.
+
+Since the quantities $q_{av}$, $q_{aw}$, etc. represent rates of consumption,
+it is evident that if equilibrium is to be preserved
+the rate of production must exactly balance them. Now the
+total rate of consumption, and therefore of production, of~$V$
+is $q_{av}+q_{bv}$, and that of~$W$ is $q_{aw}+q_{bw}$, calling these respectively
+$q_v$ and $q_w$, we have
+\begin{align*}
+\text{(i)\ \ } q_{av} &+ q_{bv} = q_v, \\
+\text{(ii) } q_{aw} &+ q_{bw} = q_w.
+\end{align*}
+
+If we call the ratio of the marginal utility of~$w$ to that of~$v$
+on \Person{A}'s relative scale~$r$, then we shall know, by the general
+law, that in equilibrium the respective marginal utilities
+must bear the same ratio on the relative scale of~\Person{B}; and if \Person{A}'s
+curve of quantity-and-marginal-usefulness in~$V$ be $y=\phi_a(x)$,
+and if $y=\psi_a(x)$, $y=\phi_b(x)$, $y=\psi_b(x)$ be the other three curves
+then we shall have
+\[
+\text{(iii)\ (iv) } \frac{\psi_a(q_{aw})}{\phi_a(q_{av})}=\frac{\psi_b(q_{bw})}{\phi_b(q_{bv})}=r,
+\]
+where $\phi_a(q_{av})$ etc.\ are the vertical intercepts on the figures,
+and where each of the ratios indicated is the ratio of the
+marginal utility of~$w$ to that of~$v$ on the relative scale. And,
+finally, since \Person{B} gets all his~$V$ by giving $W$ in exchange for
+it, getting $r$~units $v$ in exchange for one unit~$w$, and since the
+rate at which he gets it is, on the hypothesis of equilibrium,
+the rate at which he consumes it ($q_{bv}$), and the rate at which
+he gives $W$ is the rate at which \Person{A}~consumes it~($q_{aw}$), we have
+\[
+\text{(v) } q_{bv}=rq_{aw},
+\]
+and we suppose, throughout, that the consumption and production
+%% -----File: 164.p n g----------
+%[Blank Page]
+%% -----File: 165.p n g----------
+\begin{figure}[p]
+ \begin{center}
+ \Fig{24}
+% \Input{165a}
+ \end{center}
+\end{figure}
+%[To face page 133.]
+%% -----File: 166.png---Folio 133-------
+go on continuously, that is to say, not by jerks, so
+that the conditions established are never disturbed.
+
+Here, then, we have eleven quantities,
+\[
+q_v, q_w, q_{av}, q_{aw}, q_{bv}, q_{bw},
+\phi_a(q_{av}), \psi_a(q_{aw}), \phi_b(q_{bv}), \psi_b(q_{bw}), r,
+\]
+and we have five relations between them. It follows that
+we may arbitrarily fix any six of the eleven quantities. Our
+five relations will then determine the other five.
+
+Thus, if in the figures we assume that the four curves are
+known, that is equivalent to assuming that $\phi(q_{av})$, etc. are
+given in terms of $q_{av}$, etc., which reduces the number of our
+unknown quantities to seven, between which we have five
+relations. We may therefore arbitrarily fix two of them.
+Say $q_v=13$, $q_w=7$. We shall then have
+\begin{gather*}
+\text{(i)\ \ }q_{av}+q_{bv}=13, \\
+\text{(ii) }q_{bw}+q_{aw}=7, \\
+\text{(iii)\ (iv) }\frac{\psi_a(q_{aw})}{\phi_a(q_{av})}=\frac{\psi_b(q_{bw})}{\phi_b(q_{bv})}=r, \\
+\text{(v) }q_{bv}=rq_{aw},
+\end{gather*}
+which, if the meaning of $\phi_a(x)$ etc.\ be known, as we have
+supposed, gives us five equations by which to determine five
+unknown quantities. If $\phi_a(x)$ etc.\ were interpreted in accordance
+with the formulæ of the curves in the figure, these
+equations would yield the answers
+\begin{align*}
+q_{av} & = 5, \\
+q_{aw} & = 4, \\
+q_{bv} & = 8, \\
+q_{bw} & = 3, \\
+ r & = 2.
+\end{align*}
+
+I do not give the formulæ, and work out the calculation,
+since such artificial precision tends to withdraw the attention
+from the real importance of the diagrammatic method, which
+consists in the light it throws on the nature of processes, not
+in any power it can have of theoretically anticipating concrete
+industrial phenomena.
+
+Now suppose \Person{A} ceases, for any reason, to produce at the
+rate of~$13$, and henceforth only produces at the rate of~$10$.
+The equilibrium will then be disturbed and must be re-established
+under the changed conditions. We shall have the
+same five equations from which to determine the distribution
+%% -----File: 167.png---Folio 134-------
+of $V$ and~$W$, and the equilibrium exchange value between
+them except that (i)~will be replaced by
+\[
+q_{av}+q_{bv}=10.
+\]
+
+If we wrote out $\phi_a(q_{av})$, etc., in terms of $(q_{av}$,~etc., according
+to the formulæ of the curves, we might obtain definite
+answers giving the values of $(q_{av}$,~etc., and $r$~for equilibrium
+under the new conditions; but without doing so we can
+determine by inspection the general character of the change
+which will take place.
+
+If \Person{A} continues, as before, to consume~$W$ at the rate of~$4$,
+giving $V$ for it at the rate of~$8$, he will only be able to consume~$V$
+at the rate of~$2$ himself, and the marginal utility of~$v$
+will rise to more than half that of~$w$. He will therefore
+find that he is buying his last increments of~$W$ at too high
+a price, and will contract his expenditure on it, \ie,~the quantity
+index of~$(q_{aw}$, will move in the direction indicated by the
+arrow-head. But again, if \Person{A}~continues to consume~$V$ at the full
+present rate of~$5$, he will only be able to use it for purchasing~$W$
+at the rate of (the remaining)~$5$, instead of~$8$ as now, and he
+will therefore get less than~$(q_{aw}$. The marginal utility of~$w$
+will therefore be more than twice that of~$v$, and \Person{A}~will find
+that he is enjoying his last increments of~$V$ at too great a
+sacrifice of~$W$. He will therefore consume less~$V$, and the
+quantity index will move in the direction indicated by the
+arrow-head, \ie, \Person{A}~will consume less~$V$ and less~$W$, and the
+unitary marginal values of both of them will rise.
+
+But since we have seen that \Person{A}~gives less~$V$ to~\Person{B} (and
+receives less~$W$ from him), it follows that~\Person{B}, who cannot
+produce~$V$ himself, must consume it at a slower rate than
+before. This is again indicated by the direction of the
+arrow-head on the quantity-index of~$q_{bv}$. Lastly, since \Person{A}~now
+receives less~$W$ than before there is more left for~\Person{B}, who
+now consumes it at an increased rate; as is again indicated
+by the arrow-head of the quantity-index of~$q_{bw}$.
+
+Now since \Person{B}'s~quantity-indexes are moving in opposite
+directions, and the one is registering a higher and the other
+a lower marginal usefulness, it follows that the new value of~$r$
+will be lower than the old one. \Person{A}'s~quantity-indexes, then,
+must move in such a way that the length intercepted on that
+of~$q_{av}$ shall increase more than the length intercepted on that
+%% -----File: 168.png---Folio 135-------
+of~$q_{aw}$. Whether this will involve the former index actually
+moving farther than the latter depends on the character of
+the curves.
+
+The net result is that though the rate of exchange has
+altered in favour of~\Person{A}, yet he loses part of his enjoyment of
+$V$~and of~$W$ alike, while \Person{B}~loses some of his enjoyment of~$V$,
+but is partly (not wholly) compensated by an increased enjoyment
+of~$W$.
+
+If we begin by representing the marginal usefulness of $V$
+and~$W$ as being not only relatively but absolutely equal for
+\Person{A}~and~\Person{B}, then the deterioration in \Person{A}'s~position relatively to
+\Person{B}'s after the change will be indicated by the final usefulness
+of both articles coming to rest at a higher value for him than
+for~\Person{B}.
+
+The only assumption made in the foregoing argument is
+that all the curves decline as they recede from the origin.
+
+It should be noted---first, that we have investigated the
+conditions with which the new equilibrium must comply
+when reached, and the general character of the forces that
+will lead towards it, but not the precise quantitative relations
+of the actual steps by which it will be reached; and second,
+that since the equations (iii)~and~(iv) involve quadratics (if
+not equations of yet higher order), it must be left undetermined
+in this treatise whether or not there can theoretically
+be two or more points of equilibrium.
+
+The investigation of the same problem with any number
+of producers and articles is similar in character. But if we
+discuss the conditions and motives that determine the amounts
+of each commodity produced by \Person{A},~\Person{B},~etc.\ respectively, we shall
+be trespassing on the theory of production or ``making.''
+
+Now, if we turn from the problem of rates of consumption
+and attempt to deal with \emph{quantities possessed}, in the strict
+sense, without reference to the wearing down or renewal of
+the stocks, we shall find the problem takes the following
+form. Given \Person{A}'s~stock of~$V$, an imperishable article which
+both he and~\Person{B} desire; given \Person{B}'s~stock of~$W$, a similar
+article; and given \Person{A}'s and~\Person{B}'s curves of quantity-and-marginal-desiredness
+for $V$ and~$W$ alike; on what principles and
+in what ratio will \Person{A}~and~\Person{B} exchange parts of their stocks?
+The problem appears to be the same as before, but on closer
+inspection it is found that equation~(v) does not hold; for we
+%% -----File: 169.png---Folio 136-------
+cannot be sure that $V$ and~$W$ will be exchanged at a uniform
+rate up to a certain point, and then not exchanged any more.
+Therefore we cannot say
+\[
+q_{bv}= rq_{aw},
+\]
+for in the case of \emph{rates} of production, of exchange, and of consumption,
+every tentative step is reversible at the next moment.
+By the flow of the commodities the conditions assumed as
+data are being perpetually renewed; and if either of the
+exchangers finds that he can do better than he has done as
+yet, he can try again with his next batch with exactly the same
+advantages as originally, since at every moment he starts fresh
+with his new product; and if the stream of this new product
+flows into channels regulated in any other way than that
+demanded by the conditions of equilibrium we have investigated,
+then ever renewed forces will ceaselessly tend with
+unimpaired vigour to bring it into conformity with those
+conditions, so long as the curves and the quantities produced
+remain constant. But when the stocks are absolute, and
+cannot be replaced, then every partial or tentative exchange
+\emph{alters the conditions}, and is so far irreversible; nor is there
+any recuperative principle at work to restore the former conditions.
+The problem, therefore, is indeterminate, since we
+have not enough equations to find our unknown quantities
+by. The limits within which it is indeterminate cannot be
+examined in an elementary treatise. The student will find
+them discussed in F.~Y. Edgeworth's \textit{Mathematical Psychics}
+(London,~1881).
+
+This problem of absolute quantities possessed is not only
+of much greater difficulty but also of much less importance
+than the problem of \emph{rates} of consumption. For when we
+are considering the economic aspect of such a manufacture
+as that of watches, for instance, though the wares are, relatively
+\index{Watches}%
+speaking, permanent, and we do not talk of the ``rate
+of a man's consumption'' of watches, as we do in the case of
+bread---or umbrellas,---yet the \emph{manufacturer} has to consider the
+rate of consumption of watches per~annum, etc., regarded as a
+stream, not the absolute demand for them considered as a volume.
+Hence the cases are very few in which we have to deal
+with absolute quantities possessed, from the point of view of
+the community and of exchange values. But this does not
+%% -----File: 170.png---Folio 137-------
+absolve us from the necessity of investigating the problem
+with reference to the individual, for he possesses some things
+and consumes others, and has to make equations not only
+between possession and possession, and again between consumption
+and consumption, but also between possession and
+consumption. That is to say, he must ask not only, ``Do I
+prefer to possess a book of Darwin's or a Waterbury watch?''
+\index{Darwin's Works}%
+\index{Watches}%
+and, ``Do I prefer having fish for dinner or having a cigar
+\index{Cigar}%
+\index{Fish for dinner}%
+with my coffee?'' but he must also ask, ``Do I prefer to
+\emph{possess} a valuable picture or to \emph{consume} so much a year in
+\index{Pictures}%
+places at the opera?'' or, in earlier life, ``Is it worth while
+\index{Opera@{\textsc{Opera}}}%
+to give up \emph{consuming} ices till I have saved enough to \emph{possess}
+\index{Ices@{\textsc{Ices}}}%
+a knife?'' But these problems generally resolve themselves
+\index{Knife}%
+into the others. The picture is regarded as yielding a
+revenue of enjoyment, so to speak, and so its possession
+becomes a rate of consumption comparable with another rate
+of consumption; and the abstinence from ices is of definite
+duration and the total enjoyment sacrificed is estimated and
+balanced against the total enjoyment anticipated from the
+possession of the knife. If, however, the enjoyment of the
+knife is regarded as a permanent revenue (subject to risks of
+loss) it becomes difficult to analyse the process of balancing
+which goes on in the boy's mind, for he seems to be comparing
+a \emph{volume} of sacrifice and a \emph{stream} of enjoyment, and
+the stream is to flow for an indefinite period. Mathematically
+the problem must be regarded as the summing of a
+convergent series; but if we are to keep within the
+limits of an elementary treatise, we can only fall back
+upon the fact that, however he arrives at it, the boy
+``wants'' the knife enough to make him incur the privations
+of ``saving up'' for the necessary period. He is balancing
+``desires,'' and whether or not we can get behind them and
+justify their volumes or weights it is clear that, as a matter
+of fact, he can and does equate them.
+
+This will serve as a wholesome reminder that we have
+throughout been dealing with the balancing of \emph{desires} of
+equal weight or volume. I have spoken indifferently of
+``gratification,'' ``relief,'' ``enjoyment,'' ``privation,'' and so
+forth, but since it is only with the \emph{estimated} volumes of all these
+that we have to do the only things really compared are the
+\emph{desires} founded on those estimates. And so too the ``sense
+%% -----File: 171.png---Folio 138-------
+of duty,'' ``love,'' ``integrity,'' and other spiritual motives all
+\index{Duty, sense of}%
+inspire desires which may be greater or less than others, but
+are certainly commensurate with them. This thought, when
+pursued to its consequences, so far from degrading life, will
+help us to clear our minds of a great deal of cant, and to
+substitute true sentiment for empty sentimentality. When
+inclined to say, ``I have a great affection for him, and would
+do anything I could for him, but I cannot give money for I
+have not got it,'' we shall do well to translate the idea into
+the terms, ``My marginal desire to help him is great, but
+relatively to my marginal desire for potatoes, hansom cabs,
+\index{Hansom@{\textsc{Hansom Cabs}}}%
+books, and everything on which I spend my money, it is not
+high enough to establish an `effective' demand for gratification.''
+It may be perfectly right that it should be so; but
+then it is not because ``affection cannot be estimated in
+potatoes;'' it is because the gratification of this particular
+affection, beyond the point to which it is now satisfied, is
+(perhaps rightly) esteemed by us as not worth the potatoes
+it would cost. Rightly looked upon, this sense of the
+unity and continuity of life, by heightening our feelings of
+responsibility in dealing with material things, and showing
+that they are subjectively commensurable with immaterial
+things, will not lower our estimate of affection, but will
+increase our respect for potatoes and for the now no longer
+``dismal'' science that teaches us to understand them in their
+social, and therefore human and spiritual, significance.
+\end{Remark}
+%% -----File: 172.png---Folio 139-------
+
+
+\Chapter[Summary---Definitions and Propositions]{%
+Summary of Important Definitions and Propositions Contained in this Book.}
+\Pagelabel{139}
+
+\hspace*{\parindent}I\@. One quantity is a function of another when any change in the
+latter produces a definite corresponding change in the former (\Pagerange{1}{6}).
+
+II\@. The total utility resulting from the consumption or possession
+of any commodity is a function of the quantity of the commodity
+consumed or possessed (\Pagerange{6}{8}).
+
+III\@. The connection between the quantity of any commodity
+possessed and the resulting total utility to the possessor is theoretically
+capable of being represented by a curve (\Pagerange{8}{15}).
+
+IV\@. Such a curve would, as a rule, attain a maximum height,
+after which it would decline; and in any case it would \emph{tend} to reach
+a maximum height (\Pagerange{15}{19}).
+
+V\@. If such a curve were drawn, it would be possible to derive from
+it a second curve, showing the connection between the quantity of
+the commodity already possessed and the rate at which further increments
+of it add to the total utility derived from its consumption or
+possession; and the height of this derived curve at any point would
+be the differential coefficient of the height of the original curve at
+the same point (\Pagerange{19}{39}).
+
+VI\@. The differential coefficient of the total effect or value-in-use
+of a commodity is its marginal effectiveness or degree of final
+utility; as a rule marginal effectiveness is at its maximum when
+total effect is zero, and marginal effectiveness is zero when total
+effect is at its maximum (\Pagerange{39}{41}).
+
+VII\@. For small increments of commodity marginal \emph{effect} varies,
+in the limit, as marginal effectiveness (\Pagerange{41}{46}).
+
+VIII\@. In practical life we oftener consider marginal effects than
+total effects (\Pagerange{46}{48}).
+
+IX\@. In considering marginal effects we compare, and reduce to a
+common measure, heterogeneous desires and satisfactions (\Pagerange{48}{52}).
+
+X\@. A unit of utility, to which economic curves may be drawn, is
+conceivable (\Pagerange{52}{55}).
+
+XI\@. On such curves we might read the parity or disparity of
+worth of stated increments of different commodities, the proper distribution
+of labour between two or more objects, and all other
+phenomena depending on ratios of equivalence between different
+commodities (\Pagerange{55}{61}).
+
+XII\@. In practice the curves themselves will be in a constant
+state of change and flux, and these changes, together with the
+changes in the quantity of the respective commodities possessed,
+%% -----File: 173.png---Folio 140-------
+exhaust the possible causes of change in marginal effectiveness (\Pagerange{61}{67}).
+
+XIII\@. The absolute intensities of two desires existing in two
+different ``subjects'' cannot be compared with each other; but the
+ratio of \Person{A}'s~desire for~$u$ to \Person{A}'s~desire for~$w$ may be compared with
+the ratio of \Person{B}'s~desire for~$u$ or for~$v$ to \Person{B}'s~desire for~$w$ (\Pagerange{68}{71}).
+
+XIV\@. Thus, though there can be no real subjective common
+measure between the desires of different subjects, yet we may have
+a conventional, objective, standard unit of desire by reference to
+which the desires of different subjects may be reduced to an objective
+common measure (\Pagerange{73}{77}).
+
+XV\@. In a catallactic community there cannot be equilibrium as
+long as any two individuals, \Person{A}~and~\Person{B}, possessing stocks of the same
+two commodities $U$~and~$W$ respectively, desire or esteem $u$~and~$w$
+(at the margin) with unlike relative intensity (\Pagerange{71}{73}).
+
+XVI\@. The function of exchange is to bring about a state of
+equilibrium in which no such divergencies exist in the relative intensity
+with which diverse possessors of commodities severally
+desire or esteem (small) units of them at the margin (\Pagerange{80}{82}).
+
+XVII\@. The relative intensity of desire for a unit of any given
+commodity on the part of one who does \emph{not} possess a stock of it,
+may fall indefinitely below that with which one or more of its possessors
+desire it at the margin without disturbing equilibrium (\Pagerange{82}{86}).
+
+XVIII\@. Hence in every catallactic community there is a general
+relative scale of marginal utilities on which all the commodities in
+the circle of exchange are registered; and if any member of the
+community constructs for himself a relative scale of the marginal
+utilities, to him, of all the articles he possesses, this scale will (on
+the hypothesis of frictionless equilibrium) coincide absolutely, as
+far as it goes, with the corresponding selection of entries on the
+general scale; whereas, if he inserts on his relative scale any article
+he does \emph{not} possess, the entry will rank somewhere below (and may
+rank \emph{anywhere} below) the position that would be assigned to it in
+conformity with the general scale.
+
+And this general relative scale is a table of \emph{exchange values}.
+
+Thus the exchange value of a small unit of commodity is, in the
+limit, measured by the differential coefficient of the total utility, to
+any one member of the community, of the quantity of the commodity
+he possesses; and this measure necessarily yields the same result
+whatever member of the community be selected (\Pagerange{71}{86}).
+
+XIX\@. As a rule exchange value is at its maximum when value-in-use
+is zero, and exchange value is zero when value-in-use is at its
+maximum (pp.~\Pageref[]{79},~\Pageref[]{80}, \Pagerange{93}{102}).
+
+XX\@. If we can indefinitely increase or decrease our supplies of two
+commodities, then we may indefinitely change the ratio between
+the marginal effects to us, of their respective units (\Pagerange{108}{124}).
+
+XXI\@. Labour, money, or other purchasing power, secures the
+maximum of satisfaction to the purchaser when so distributed that
+equal outlays secure equal satisfactions to whichever of the alternative
+margins they are applied (\Pagerange{124}{130}).
+\Pagelabel{140}
+%% -----File: 174.png---Folio 141-------
+
+% INDEX OF ILLUSTRATIONS
+\cleardoublepage%
+\phantomsection\pdfbookmark[0]{Index of Illustrations}{Index}%
+\label{indexpage}%
+\printindex
+
+\iffalse
+Account-book@{\textsc{Account-book}}#Account-book 68
+
+Account-keeping 130
+
+Air, fresh#Air 52
+
+Athletes 90
+
+Auction 102
+
+Bath-room@{\textsc{Bath-room}}#Bath-room 47
+
+Bed@{Bed \textit{versus} supper}#Bed 127
+
+Beer 8
+
+Bibles 86
+
+Bicycles 91
+
+Billiard-tables 76
+
+Blankets 6
+
+Body, falling 2
+
+Books 52, 69
+
+Bradgate Park 68
+
+Carbon@{\textsc{Carbon Furnace}}#Carbon 37
+
+Cattle-breeding 112
+
+China 50, 56
+
+Cigar 137
+
+Cloth, price of#Cloth 1
+
+Coal 39, 47, 53, 63
+
+Coats 69
+
+Cooling iron 2
+
+Corduroys 76
+
+Corn-growing 112
+
+Daily@{\textsc{Daily Paper}}#Daily 130
+
+Darwin's Works 137
+
+Duty, sense of#Duty 138
+
+Eggs@{\textsc{Eggs}, fresh}#Eggs 52
+
+Examination papers 53
+
+Falling@{\textsc{Falling body}}#Falling 2
+
+Falstaff 129
+
+Fancy ball costumes 76
+
+Fire@{Fire in ``practising'' room}#Fire 47
+
+Fish for dinner 137
+
+Foot-tons 53, 54
+
+Fortune, loss of#Fortune 130
+
+Francis of Assisi 78
+
+Friendship 52
+
+Games@{\textsc{Games}}#Games 121
+
+Garden-hose 47
+
+Gimlet 8
+
+Gold-digging 112
+
+Gold stoppings in teeth 75
+
+Hansom@{\textsc{Hansom Cabs}}#Hansom 138
+
+Holiday 84, 85
+
+Horse 80
+
+House of Commons sitting 119
+
+Housekeeper 49, 125
+
+Ices@{\textsc{Ices}}#Ices 137
+
+Iron, cooling#Iron 2
+
+Kitchen@{\textsc{Kitchen Fire}}#Kitchen 47
+
+Knife 137
+
+Lady@{\textsc{Lady Jane Grey}}#Lady 68
+
+Linen 48, 54, 56
+
+Meat@{\textsc{Meat}, butcher's}#Meat 16
+
+Milkman@{Milkman's prices}#Milkman 104
+
+Mineral spring 93
+
+Museum, British 52
+
+Opera@{\textsc{Opera}}#Opera 137
+
+Penny@{\textsc{Penny} ``to give to a boy''}#Penny 127
+%% -----File: 175.png---Folio 142-------
+
+Pictures 76, 137
+
+Plato 68
+
+Poor men's wares 86, 87
+
+Presents 86
+
+Projectile 5, 8, 19, 32
+
+Railway@{\textsc{Railway} charges, differential}#Railway 106
+
+Rainfall 18
+
+Reading-chairs 91
+
+Reduced terms at school 108
+
+Respirators 91
+
+Resurrection pudding 130
+
+Rich men's wares 86, 87
+
+Robinson Crusoe 58, 124
+
+Root-digging 58
+
+Rossetti's Works 47
+
+Rush-gathering 58
+
+Sarah@{\textsc{Sarah Bernhardt}}#Bernhardt 85
+
+Skates 91
+
+Stock-broking 103
+
+Storm-signal 120
+
+Sugar 125
+
+Testing@{\textsc{Testing Machine}}#Testing 13
+
+Theatre, pit and stalls#Theatre 107
+
+Theatre, waiting 69, 108
+
+Thermometer 15, 127
+
+Time, distribution of#Time 60
+
+Tracts 86
+
+Tripe 77
+
+Turkish bath 14
+
+Turtle soup 128
+
+Waistcoat@{\textsc{Waistcoat}}#Waistcoat 47
+
+Waiting@{Waiting (at theatre)}#Waiting 69, 108
+
+Watches 7, 137, 136
+
+Water 47, 80
+
+Wheat 44
+
+Wine 8
+
+THE END
+\fi
+%% -----File: 176.png---Folio 143-------
+
+%[Blank Page]
+
+\backmatter
+\phantomsection
+\pdfbookmark[-1]{Back Matter}{Back Matter}
+
+%%%% LICENSE %%%%
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+% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %
+% %
+% End of the Project Gutenberg EBook of The Alphabet of Economic Science, by
+% Philip H. Wicksteed %
+% %
+% *** END OF THIS PROJECT GUTENBERG EBOOK THE ALPHABET OF ECONOMIC SCIENCE ***
+% %
+% ***** This file should be named 32497-t.tex or 32497-t.zip ***** %
+% This and all associated files of various formats will be found in: %
+% http://www.gutenberg.org/3/2/4/9/32497/ %
+% %
+% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %
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+Project Gutenberg's The Alphabet of Economic Science, by Philip H. Wicksteed
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+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever. You may copy it, give it away or
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+Title: The Alphabet of Economic Science
+ Elements of the Theory of Value or Worth
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+Release Date: May 30, 2010 [EBook #32497]
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+ \footnotesize THE END
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+%%%%%%%%%%%%%%%%%%%%%%%% START OF DOCUMENT %%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\begin{document}
+
+\pagestyle{empty}
+\pagenumbering{alph}
+\phantomsection
+\pdfbookmark[-1]{Front Matter}{Front Matter}
+
+%%%% PG BOILERPLATE %%%%
+\Pagelabel{PGBoilerplate}
+\phantomsection
+\pdfbookmark[0]{PG Boilerplate}{Project Gutenberg Boilerplate}
+
+\begin{center}
+\begin{minipage}{\textwidth}
+\small
+\begin{PGtext}
+Project Gutenberg's The Alphabet of Economic Science, by Philip H. Wicksteed
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever. You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: The Alphabet of Economic Science
+ Elements of the Theory of Value or Worth
+
+Author: Philip H. Wicksteed
+
+Release Date: May 30, 2010 [EBook #32497]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK THE ALPHABET OF ECONOMIC SCIENCE ***
+\end{PGtext}
+\end{minipage}
+\end{center}
+
+\clearpage
+
+
+%%%% Credits and transcriber's note %%%%
+\begin{center}
+\begin{minipage}{\textwidth}
+\begin{PGtext}
+Produced by Andrew D. Hwang, Frank van Drogen, and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+(This file was produced from scans of public domain works
+at McMaster University's Archive for the History of Economic
+Thought.)
+\end{PGtext}
+\end{minipage}
+\end{center}
+\vfill
+
+\begin{minipage}{0.85\textwidth}
+\small
+\pdfbookmark[0]{Transcriber's Note}{Transcriber's Note}
+\subsection*{\centering\normalfont\scshape%
+\normalsize\MakeLowercase{\TransNote}}%
+
+\raggedright
+\TransNoteText
+\end{minipage}
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%% FRONT MATTER %%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\frontmatter
+
+\pagenumbering{roman}
+\pagestyle{empty}
+
+%% -----File: 001.png---Folio iv-------
+% [Blank Page]
+%% -----File: 002.png---Folio v-------
+
+\begin{center}
+\setlength{\TmpLen}{0.2in}%
+\Large THE ALPHABET \\[3\TmpLen]
+\footnotesize OF \\[3\TmpLen]
+\Huge ECONOMIC SCIENCE \\[4\TmpLen]
+\footnotesize BY \\[\TmpLen]
+\normalsize PHILIP H. WICKSTEED \\[5\TmpLen]
+\footnotesize ELEMENTS OF THE THEORY OF VALUE OR WORTH
+\end{center}
+\vfil
+\newpage
+%% -----File: 003.png---Folio vi-------
+\iffalse
+%[** TN: No longer present in page scan]
+London: Macmillan \& Company Ltd., 1888
+\fi
+%% -----File: 004.png---Folio vii-------
+\null
+\vfil
+\selectlanguage{latin}%
+``Est ergo sciendum, quod quædam sunt, quæ nostræ potestati
+minime subjacentia, speculari tantummodo possumus, operari
+autem non, velut Mathematica, Physica, et~Divina. Quædam vero
+sunt quæ nostræ potestati subjacentia, non solum speculari, sed et
+operari possumus; et~in iis non operatio propter speculationem, sed
+hæc propter illam adsumitur, quoniam in talibus operatio est finis.
+Cum ergo materia præsens politica sit, imo fons atque principium
+rectarum politiarum; et~omne politicum nostræ potestati subjaceat;
+manifestum est, quod materia præsens non ad speculationem
+per prius, sed ad operationem ordinatur. Rursus, cum in
+operabilibus principium et causa omnium sit ultimus Finis (movet
+enim primo agentem), consequens est, ut omnis ratio eorum quæ
+sunt ad Finem, ab ipso Fine sumatur: nam alia erit ratio incidendi
+lignum propter domum construendam, et alia propter navim. Illud
+igitur, si quid est, quod sit Finis ultimus Civilitatis humani Generis,
+erit hoc principium, per quod omnia quæ inferius probanda sunt,
+erunt manifesta sufficienter.''---\textsc{Dante.}
+\vfil\vfil
+\newpage
+%% -----File: 005.png---Folio viii-------
+
+\null
+\vfil
+\selectlanguage{english}
+Be it known, then, that there are certain things, in no degree
+subject to our power, which we can make the objects of speculation,
+but not of action. Such are mathematics, physics and theology.
+But there are some which are subject to our power, and to which
+we can direct not only our speculations but our actions. And in
+the case of these, action does not exist for the sake of speculation,
+but we speculate with a view to action; for in such matters action
+is the goal. Since the material of the present treatise, then, is
+political, nay, is the very fount and starting-point of right polities,
+and since all that is political is subject to our power, it is obvious
+that this treatise ultimately concerns conduct rather than speculation.
+Again, since in all things that can be done the final goal is
+the general determining principle and cause (for this it is that first
+stimulates the agent), it follows that the whole rationale of the
+actions directed to the goal depends upon that goal itself. For the
+method of cutting wood to build a house is one, to build a ship
+another. Therefore that thing (and surely there is such a thing)
+which is the final goal of human society will be the principle by
+reference to which all that shall be set forth below must be made
+clear.
+\vfil\vfil
+\newpage
+%% -----File: 006.png---Folio ix-------
+
+
+\Chapter{Preface}
+\pagestyle{fancy}
+
+\First{Dear Reader}---I venture to discard the more stately
+forms of preface which alone are considered suitable for
+a serious work, and to address a few words of direct
+appeal to you.
+
+An enthusiastic but candid friend, to whom I showed
+these pages in proof, dwelt in glowing terms on the
+pleasure and profit that my reader would derive from
+them, ``if only he survived the first cold plunge into
+`functions.'\,'' Another equally candid friend to whom
+I reported the remark exclaimed, ``\emph{Survive} it indeed!
+Why, what on earth is to induce him to \emph{take} it?''
+
+Much counsel was offered me as to the best method
+of inducing him to take this ``cold plunge,'' the substance
+of which counsel may be found at the beginning
+of the poems of Lucretius and Tasso, who have given
+such exquisite expression to the theory of ``sugaring
+the pill'' which their works illustrate. But I am no
+Lucretius, and have no power, even had I the desire
+to disguise the fact that a firm grasp of the elementary
+truths of Political Economy cannot be got without the
+same kind of severe and sustained mental application
+which is necessary in all other serious studies.
+
+At the same time I am aware that forty pages of
+almost unbroken mathematics may seem to many readers
+a most unnecessary introduction to Economics, and it
+is impossible that the beginner should see their bearing
+upon the subject until he has mastered and applied
+%% -----File: 007.png---Folio x-------
+them. Some impatience, therefore, may naturally be
+expected. To remove this impatience, I can but express
+my own profound conviction that the beginner who has
+mastered this mathematical introduction will have solved,
+before he knows that he has even met them, some of the
+most crucial problems of Political Economy on which
+the foremost Economists have disputed unavailingly
+for generations for lack of applying the mathematical
+method. A glance at the ``\hyperref[indexpage]{Index of Illustrations}'' will
+show that my object is to bring Economics down from
+the clouds and make the study throw light on our
+daily doings and experiences, as well as on the great
+commercial and industrial machinery of the world.
+But in order to get this light some mathematical knowledge
+is needed, which it would be difficult to pick out
+of the standard treatises as it is wanted. This knowledge
+I have tried to collect and render accessible to
+those who dropped their mathematics when they left
+school, but are still willing to take the trouble to master
+a plain statement, even if it involves the use of mathematical
+symbols.
+
+The portions of the book printed in the smaller type
+should be omitted on a first reading. They generally
+deal either with difficult portions of the subject that
+are best postponed till the reader has some idea of the
+general drift of what he is doing, or else with objections
+that will probably not present themselves at first, and
+are better not dealt with till they rise naturally.
+
+The student is strongly recommended to consult the
+Summary of Definitions and Propositions on \Pagerange{139}{140}
+at frequent intervals while reading the text.
+
+\begin{flushright}
+P. H. W.\hspace*{2em}
+\end{flushright}
+%% -----File: 008.png---Folio xi-------
+
+\Chapter{Introduction}
+
+\First{On} 1st~June 1860 Stanley Jevons wrote to his brother
+Herbert, ``During the last session I have worked a good
+deal at political economy; in the last few months I
+have fortunately struck out what I have no doubt is \emph{the
+true Theory of Economy}, so thoroughgoing and consistent,
+that I cannot now read other books on the subject
+without indignation.''
+
+Jevons was a student at University College at this
+time, and his new theory failed even to gain him the
+modest distinction of a class-prize at the summer examination.
+He was placed third or fourth in the list, and,
+though much disappointed, comforted himself with the
+prospect of his certain success when in a few months he
+should bring out his work and ``re-establish the science
+on a sensible basis.'' Meanwhile he perceived more
+and more clearly how fruitful his discovery must prove,
+and ``how the want of knowledge of this determining
+principle throws the more complicated discussions of
+economists into confusion.''
+
+It was not till 1862 that Jevons threw the main outlines
+of his theory into the form of a paper, to be read
+before the British Association. He was fully and most
+justly conscious of its importance. ``Although I know
+pretty well the paper is perhaps worth all the others
+that will be read there put together, I cannot pretend to
+say how it will be received.'' When the year had but
+five minutes more to live he wrote of it, ``It has seen
+my theory of economy offered to a learned society~(?)
+%% -----File: 009.png---Folio xii-------
+and received without a word of interest or belief.
+It has convinced me that success in my line of endeavour
+is even a slower achievement than I had thought.''
+
+In 1871, having already secured the respectful attention
+of students and practical men by several important
+essays, Jevons at last brought out his \textit{Theory of Political
+Economy} as a substantive work. It was received in
+England much as his examination papers at college and
+his communication to the British Association had been
+received; but in Italy and in Holland it excited some
+interest and made converts. Presently it appeared that
+Professor Walras of Lausanne had been working on the
+very same lines, and had arrived independently at conclusions
+similar to those of Jevons. Attention being
+now well roused, a variety of neglected essays of a like
+tendency were re-discovered, and served to show that
+many independent minds had from time to time reached
+the principle for which Jevons and Walras were contending;
+and we may now add, what Jevons never
+knew, that in the very year 1871 the Viennese Professor
+Menger was bringing out a work which, in complete
+independence of Jevons and his predecessors, and by a
+wholly different approach, established the identical
+theory at which the English and Swiss scholars were
+likewise labouring.
+
+In 1879 appeared the second edition of Jevons's
+\textit{Theory of Political Economy}, and now it could no longer
+be ignored or ridiculed. Whether or not his guiding
+principle is to win its way to general acceptance and to
+``re-establish the science on a sensible basis,'' it has at
+least to be seriously considered and seriously dealt with.
+
+It is this guiding principle that I have sought to
+illustrate and enforce in this elementary treatise on the
+Theory of Value or Worth. Should it be found to meet
+a want amongst students of economics, I shall hope to
+follow it by similar introductions to other branches of
+the science.
+
+I lay no claim to originality of any kind. Those
+%% -----File: 010.png---Folio xiii-------
+who are acquainted with the works of Jevons, Walras,
+Marshall, and Launhardt, will see that I have not only
+accepted their views, but often made use of their
+terminology and adopted their illustrations without
+specific acknowledgment. But I think they will also
+see that I have copied nothing mechanically, and have
+made every proposition my own before enunciating it.
+
+I have to express my sincere thanks to Mr.\ John
+Bridge, of Hampstead, for valuable advice and assistance
+in the mathematical portions of my work.
+
+I need hardly add that while unable to claim credit
+for any truth or novelty there may be in the opinions
+advocated in these pages, I must accept the undivided
+responsibility for them.
+\medskip
+
+\asterism Beginners will probably find it conducive to the
+comprehension of the argument to omit the small print
+in the first reading.
+
+\begin{Remark}
+\NB---I have frequently given the formulas of the curves
+used in illustration. Not because I attach any value or importance
+to the special forms of the curves, but because I
+have found by experience that it would often be convenient
+to the student to be able to calculate for himself any point
+on the actual curve given in the figures which he may wish
+to determine for the purpose of checking and varying the
+hypotheses of the text.
+
+As a rule I have written with a view to readers guiltless
+of mathematical knowledge (see \Chapref{1}{Preface}). But I have sometimes
+given information in footnotes, without explanation,
+which is intended only for those who have an elementary
+knowledge of the higher mathematics.
+
+In conclusion I must apologise to any mathematicians into
+whose hands this primer may fall for the evidences which they
+will find on every page of my own want of systematic mathematical
+training, but I trust they will detect no errors of
+reasoning or positive blunders.
+\end{Remark}
+%% -----File: 011.png---Folio xiv-------
+% [Blank Page]
+%% -----File: 012.png---Folio xv-------
+
+
+\Chapter{Table of Contents}
+
+\ToCLine{\hfill\scriptsize PAGE}{}
+
+\ToCLine{Preface}{chap:1}% ix %[** TN: N.B. 3rd arg hard-coded]
+
+\ToCLine{Introduction}{chap:2}% xi
+
+\ToCLine{Theory of Value---}{}
+
+% [** TN: Skip chap:3 = this ToC]
+\ToCLine[I.]{Individual}{chap:4}% 1
+
+\ToCLine[II.]{Social}{chap:5}% 68
+
+\ToCLine{Summary---Definitions and Propositions}{chap:6}% 139
+
+\ToCLine{Index of Illustrations}{indexpage}% 141
+
+\vfill
+%% -----File: 013.png---Folio xvi-------
+% [Blank Page]
+%% -----File: 014.png---Folio 1-------
+
+\mainmatter
+\phantomsection
+\pdfbookmark[-1]{Main Matter}{Main Matter}%
+\pagestyle{fancy}
+
+\Chapter[I. Individual]{I}
+
+\Pagelabel{1}%
+\First{It} is the object of this volume in the first place to
+explain the meaning and demonstrate the truth of the
+proposition, that \emph{the value in use and the value in exchange
+of any commodity are two distinct, but connected, functions of
+the quantity of the commodity possessed by the persons or the
+community to whom it is valuable}, and in the second place,
+so to familiarise the reader with some of the methods
+and results that necessarily flow from that proposition
+as to make it impossible for him unconsciously to accept
+arguments and statements which are inconsistent with
+it. In other words, I aim at giving what theologians
+might call a ``saving'' knowledge of the fundamental
+proposition of the Theory of Value; for this, but no more
+than this, is necessary as the first step towards mastering
+the ``alphabet of Economic Science.''
+
+When I speak of a ``function,'' I use the word in the
+mathematical not the physiological sense; and our first
+business is to form a clear conception of what such a
+function is.
+
+\emph{One quantity, or measurable thing~{\upshape($y$)}, is a function of
+another measurable thing~{\upshape($x$)}, if any change in~$x$ will produce
+or ``determine'' a definite corresponding change in~$y$.}
+Thus the sum I pay for a piece of cloth of given quality
+\index{Cloth, price of}%
+is a function of its length, because any alteration in the
+length purchased will cause a definite corresponding
+alteration in the sum I have to pay.
+%% -----File: 015.png---Folio 2-------
+
+\begin{Remark}
+\Pagelabel{2}%
+If I do not stipulate that the cloth shall be of the same
+quality in every case, the sum to be paid will still be a function
+of the length, though not of the length alone, but of the
+quality also. For it remains true that an alteration in the
+length will always produce a definite corresponding alteration
+in the sum to be paid, although a contemporaneous alteration
+in the quality may produce another definite alteration (in the
+same or the opposite sense) at the same time. In this case
+the sum to be paid would be ``a function of two variables''
+(see below). It might still be said, however, without qualification
+or supplement, that ``the sum to be paid is a function
+of the length;'' for the statement, though not complete, would
+be perfectly correct. It asserts that every change of length
+causes a corresponding change in the sum to be paid, and it
+asserts nothing more. It is therefore true without qualification.
+In this book we shall generally confine ourselves to
+the consideration of one variable at a time.
+\end{Remark}
+
+So again, if a heavy body be allowed to drop from a
+\index{Body, falling}%
+\index{Falling@{\textsc{Falling body}}}%
+height, the longer it has been allowed to fall the
+greater the space it has traversed, and any change in
+the time allowed will produce a definite corresponding
+change in the space traversed. Therefore the space
+traversed (say $y$~ft.)\ is a function of the time allowed
+(say $x$~seconds).
+
+Or if a hot iron is plunged into a stream of cold
+\index{Cooling iron}%
+\index{Iron, cooling}%
+water, the longer it is left in the greater will be the fall
+in its temperature. The fall in temperature then (say
+$y$~degrees) is a function of the time of immersion (say $x$~seconds).
+
+The correlative term to ``function'' is ``variable,''
+or, in full, ``independent variable.'' If $y$~is a function
+of~$x$, then $x$ is the variable of that function.
+Thus in the case of the falling body, the time is the
+variable and the space traversed the function. When
+we wish to state that a magnitude is a function of~$x$,
+without specifying what particular function (\ie~when
+we wish to say that the value of~$y$ depends upon the
+value of~$x$, and changes with it, without defining the
+%% -----File: 016.png---Folio 3-------
+nature or law of its dependence), it is usual to represent
+the magnitude in question by the symbol~$f(x)$ or~$\phi(x)$,
+etc. Thus, ``let $y=f(x)$'' would mean ``let $y$~be a
+magnitude which changes when $x$~changes.'' In the
+case of the falling body we know that the space traversed,
+measured in feet, is (approximately) sixteen times
+the square of the number of seconds during which the
+body has fallen. Therefore if $x$~be the number of
+seconds, then $y$~or~$f(x)$ equals~$16x^2$.
+
+\begin{Remark}
+\Pagelabel{3}%
+Since the statement $y=f(x)$ implies a \emph{definite relation}
+between the changes in~$y$ and the changes in~$x$, it follows
+that a change in~$y$ will determine a corresponding change in~$x$,
+as well as \textit{vice versâ}. Hence if $y$ is a function of~$x$ it follows
+that $x$ is also a function of~$y$. In the case of the falling body,
+if $y=16x^2$, then $x=\dfrac{\sqrt{y}}{4}$.\footnote
+ {In the abstract $x=±\dfrac{\sqrt{y}}{4}$. For $-x$ and $x$ will give the same
+ values of $y$ in $f(x)=16x^2=y$; and we shall have $±x=\dfrac{\sqrt{y}}{4}$.}
+It is usual to denote inverse functions
+of this description by the index~$-1$. Thus if $f(x)=y$
+then $f^{-1}(y)=x$. In this case $y=16x^2$, and $f^{-1}(y)$ becomes
+$f^{-1}(16x^2)$. Therefore $f^{-1}(16x^2)=x$. But $x=\dfrac{\sqrt{16x^2}}{4}$. Therefore
+$f^{-1}(16x^2)=\dfrac{\sqrt{16x^2}}{4}$. And $16x^2=y$. Therefore $f^{-1}(y)=\dfrac{\sqrt{y}}{4}$.
+In like manner $f^{-1}(a)=\dfrac{\sqrt{a}}{4}$; and generally $f^{-1}(x)=\dfrac{\sqrt{x}}{4}$,
+whatever $x$ may be.
+\begin{flalign*}
+&\text{\indent Thus } & y&=f(x)=16x^2, && \\
+& & x&=f^{-1}(y)=\dfrac{\sqrt{y}}{4}. &&
+\end{flalign*}
+(See below, \Pageref{11}.)
+\end{Remark}
+
+From the formula $y=f(x)=16x^2$ we can easily
+calculate the successive values of~$f(x)$ as~$x$ increases, \ie\
+the space traversed by the falling body in~one, two,
+three, etc., seconds.
+%% -----File: 017.png---Folio 4-------
+\Pagelabel{4}%
+\begin{align*}
+&\underline{x\quad f(x) = 16x^2} \\
+&0\quad f(0) = 16 × 0^2 = \Z0. \\
+&1\quad f(1) = 16 × 1^2 = \Z16 \quad\text{growth during last second } \Z16\DPtypo{}{.} \\
+&2\quad f(2) = 16 × 2^2 = \Z64 \quad\PadTo{\text{growth during }}{\Ditto}\PadTo{\text{last second }}{\Ditto} \Z48\DPtypo{}{.} \\
+&3\quad f(3) = 16 × 3^2 = 144 \quad\PadTo{\text{growth during }}{\Ditto}\PadTo{\text{last second }}{\Ditto} \Z80\DPtypo{}{.} \\
+&4\quad f(4) = 16 × 4^2 = 256 \quad\PadTo{\text{growth during }}{\Ditto}\PadTo{\text{last second }}{\Ditto} 112\DPtypo{}{.} \\
+&\text{etc.\ etc.} \PadTo{{}=16 × 4^2={}}{\text{etc.}}\text{etc.}\quad\PadTo[r]{growth during last second\quad\;99}{\text{etc.}}
+\end{align*}
+
+In the case of the cooling iron in the stream the
+time allowed is again the variable, but the function,
+which we will denote by~$\phi (x)$, is not such a simple one,
+and we need not draw out the details. Without doing
+so, however, we can readily see that there will be an
+important difference of character between this function
+and the one we have just investigated. For the space
+traversed by the falling body not only grows continually,
+but grows more in each successive second than it
+did in the last, as is shown in the last column of the
+table. Now it is clear that though the cooling iron
+will always go on getting cooler, yet it will not cool
+more during each successive second than it did during
+the last. On the contrary, the fall in temperature of
+the red-hot iron in the first second will be much greater
+than the fall in, say, the hundredth second, when the
+water is only very little colder than the iron; and the
+total fall can never be greater than the total difference
+between the initial temperatures of the iron and the
+water. This is expressed by saying that the one
+function~$f(x)$, \emph{increases without limit} as the variable,~$x$,
+increases, and that the other function~$\phi (x)$ \emph{approaches a
+definite limit} as the variable,~$x$, increases. In either
+case the function is always increased by an increase of
+the variable, but only in the first case can we make the
+function as great as we like by increasing the variable
+sufficiently; for in the second case there is a certain
+fixed limit which the function will never reach, however
+long it continues to increase. If the reader finds this
+conception difficult or paradoxical, let him consider the
+%% -----File: 018.png---Folio 5-------
+series $1 + \frac{1}{2} + \frac{1}{4} + \frac{1}{8} + \frac{1}{16}$, etc., and let $f(x)$ signify the
+sum of $x$~terms of this series. Then we shall have
+\begin{align*}
+&\underline{\PadTo{\text{etc.}}{x}\ f(x)} \\
+&\PadTo{\text{etc.}}{1}\ \PadTo{f(x)}{1.} \\
+&\PadTo{\text{etc.}}{2}\ \PadTo{f(x)}{\frac{3}{2}} \left(\ie\ 1 + \tfrac{1}{2}\right). \\
+&\PadTo{\text{etc.}}{3}\ \PadTo{f(x)}{\frac{7}{4}} \left(\ie\ 1 + \tfrac{1}{2} + \tfrac{1}{4}\right). \\
+&\PadTo{\text{etc.}}{4}\ \PadTo{f(x)}{\frac{15}{8}} \left(\ie\ 1 + \tfrac{1}{2} + \tfrac{1}{4} + \tfrac{1}{8}\right). \\
+&\PadTo{\text{etc.}}{5}\ \PadTo{f(x)}{\frac{31}{16}} \left(\ie\ 1 + \tfrac{1}{2} + \tfrac{1}{4} + \tfrac{1}{8} + \tfrac{1}{16}\right). \\
+&\text{etc.}\ \PadTo{f(x)}{\text{etc.}}
+\end{align*}
+\Pagelabel{5}%
+Here $f(x)$ is always made greater by increasing~$x$, but
+however great we make~$x$ we shall never make~$f(x)$
+quite equal to~$2$. This case furnishes a simple instance
+of a function which always increases as its variable
+increases, but yet never reaches a certain fixed limit.
+The cooling iron presents a more complicated case of
+such a function.
+
+The two functions we have selected for illustration
+differ then in this respect, that as the variable (time)
+increases, the one (space traversed by a falling body)
+increases without limit, while the other (fall of temperature
+in the iron) though always increasing yet approaches
+a fixed limit. But $f(x)$~and~$\phi (x)$ resemble
+each other in this, that they both of them always increase
+(and never decrease) as the variable increases.
+
+There are, however, many functions of which this
+cannot be said. For instance, let a body be projected
+\index{Projectile}%
+vertically upwards, and let the height at which we find
+it at any given moment be regarded as a function of
+the time which has elapsed since its projection. It is
+obvious that at first the body will rise (doing work
+against gravitation), and the function (height) will increase
+as the variable (time) increases. But the initial
+energy of the body cannot hold out and do work against
+gravitation for ever, and after a time the body will rise
+no higher, and will then begin to fall, in obedience to the
+still acting force of gravitation. Then a further increase
+%% -----File: 019.png---Folio 6-------
+of the variable (time) will cause, not an increase, but a
+decrease in the function (height). Thus, as the variable
+increases, the function will at first increase with it, and
+then decrease.
+
+To recapitulate: one thing is a function of another
+if it varies with it, whether increasing as it increases or
+decreasing as it increases, or changing at a certain point
+or points from the one relation to the other.
+\Pagelabel{6}%
+
+We have already reached a point at which we can
+attach a definite meaning to the proposition: \emph{The value-in-use
+of any commodity to an individual is a function of the
+quantity of it he possesses}, and as soon as we attach a
+definite meaning to it, we perceive its truth. For by
+the value-in-use of a commodity to an individual, we
+mean the total worth of that commodity to him, for his
+own purposes, or the sum of the advantages he derives
+immediately from its possession, excluding the advantages
+he anticipates from exchanging it for something else.
+Now it is clear that this sum of advantages is greater
+or less according to the quantity of the commodity the
+man possesses. It is not the same for different quantities.
+The value-in-use of two blankets, that is to say
+\index{Blankets}%
+the total direct service rendered by them, or the sum of
+direct advantages I derive from possessing them, differs
+from the value-in-use of one blanket. If you increase
+or diminish my supply of blankets you increase or
+diminish the sum of direct advantages I derive from
+them. The value-in-use of my blankets, then, is a
+function of the number (or quantity) I possess. Or if
+we take some commodity which we are accustomed to
+think of as acquired and used at a certain rate rather than
+in certain absolute quantities, the same fact still appears.
+The value-in-use of one gallon of water a day, that is to
+say the sum of direct advantages I derive from commanding
+it, differs from the value-in-use of a pint a day
+or of two gallons a day. The sum of direct advantages
+which I derive from half a pound of butcher's meat a
+%% -----File: 020.png---Folio 7-------
+day is something different from that which I should
+derive from either an ounce or a whole carcase per day.
+In other words, \emph{the sum of the advantages I derive from
+the direct use or consumption of a commodity is a function
+of its quantity, and increases or decreases as that quantity
+changes}.
+
+\begin{Remark}
+Two points call for attention here. In the first place,
+there are many commodities which we are not in the habit
+of thinking of as possessed in varying quantities; or at any
+rate, we usually think of the services they render as functions
+of some other variable than their quantity. For instance,
+a watch that is a good time-keeper renders a greater
+sum of services to its possessor than a bad one; but it seems
+an unwarrantable stretch of language to say that the owner
+of a good watch has ``a greater amount or quantity of watch''
+than the owner of a bad one. It is a little more reasonable,
+though still hardly admissible, to say that the one has ``more
+time-keeping apparatus'' than the other. But, as the reader
+will remember, we have already seen that a function may
+depend on two or more variables (\Pageref{2}), and if we consider
+watches of different qualities as one and the same commodity,
+\index{Watches}%
+then we must say that the most important variable is the
+quality of the watch; but it will still be true that two
+watches of the same quality would, as a rule, perform a
+different (and a greater) service for a man than one watch;
+for most men who have only one have experienced temporary
+inconvenience when they have injured it, and would have
+been very glad of another in reserve. Even in this case,
+therefore, the sum of advantages derived from the commodity
+``watches'' is a function of the quantity as well as the quality.
+Moreover, the distinction is of no theoretical importance, for
+the propositions we establish concerning value-in-use as a
+function of quantity will be equally true of it as a function
+of quality; and indeed ``quality'' in the sense of ``excellence,''
+being conceivable as ``more'' or ``less,'' is obviously
+itself a quantity of some kind.
+
+The second consideration is suggested by the frequent use
+of the phrase ``\emph{sum of advantages}'' as a paraphrase of ``\emph{worth}''
+or ``\emph{value-in-use}.'' What are we to consider an ``advantage''?
+%% -----File: 021.png---Folio 8-------
+It is usual to say that in economics everything which a man
+wants must be considered ``useful'' to him, and that the
+word must therefore be emptied of its moral significance.
+In this sense a pint of beer is more ``useful'' than a gimlet
+\index{Beer}%
+\index{Gimlet}%
+to a drunken carpenter. And, in like manner, a wealthier
+person of similar habits would be said to derive a greater
+``sum of advantages'' from drinking two bottles of wine at
+\index{Wine}%
+dinner than from drinking two glasses. In either case, we
+are told, that is ``useful'' which ministers to a desire, and it
+is an ``advantage'' to have our desires gratified. Economics,
+it is said, have nothing to do with ethics, since they
+deal, not with the legitimacy of human desires, but with the
+means of satisfying them by human effort. In answer to
+this I would say that if and in so far as economics have nothing
+to do with ethics, economists must refrain from using ethical
+words; for such epithets as ``useful'' and ``advantageous''
+will, in spite of all definitions, continue to carry with them
+associations which make it both dangerous and misleading to
+apply them to things which are of no real use or advantage.
+I shall endeavour, as far as I can, to avoid, or at least to
+minimise, this danger. I am not aware of any recognised
+word, however, which signifies the quality of being desired.
+``Desirableness'' conveys the idea that the thing not only is
+but deserves to be desired. ``Desiredness'' is not English,
+but I shall nevertheless use it as occasion may require.
+``Gratification'' and ``satisfaction'' are expressions morally
+indifferent, or nearly so, and may be used instead of ``advantage''
+when we wish to denote the result of obtaining a
+thing desired, irrespective of its real effect on the weal or
+woe of him who secures it.\Pagelabel{8}%
+\end{Remark}
+
+Let us now return to the illustration of the body
+\index{Projectile}%
+projected vertically upwards at a given velocity. In
+this case the time allowed is the variable, and the
+height of the body is the function. Taking the
+rough approximation with which we are familiar, which
+gives sixteen feet as the space through which a body
+will fall from rest in the first second, and supposing
+that the velocity with which the body starts is $a$~ft.\
+per~second, we learn by experiment, and might deduce
+%% -----File: 022.png---Folio 9-------
+from more general laws, that we shall have $y=ax-16x^2$,
+where $x$ is the number of seconds allowed, and $y$ is the
+height of the body at the end of $x$~seconds. If $a=128$,
+\ie~if the body starts at a velocity of $128$~ft.\ per~second,
+we shall have
+\[
+y=128x-16x^2.
+\]
+
+\begin{Remark}
+In such an expression the figures $128$~and~$-16$ are called
+the \emph{constants}, because they remain the same throughout the
+investigation, while $x$ and $y$ change. If we wish to indicate
+the general type of the relationship between $x$ and $f(x)$ or $y$
+without determining its details, we may express the constants
+by letters. Thus $y=ax+bx^2$ would determine the general character
+of the function, and by choosing $128$ and~$-16$ as the constants
+we get a definite specimen of the type, which absolutely
+determines the relation between $x$~and~$y$. Thus $y=ax+bx^2$
+is the general formula for the distance traversed in $x$~seconds
+by a body that starts with a given velocity and works directly
+with or against a constant force. If the constant force is
+gravitation, $b$ must equal~$16$; if the body is to work against
+(not with) gravitation the sign of~$b$ must be negative. If
+the initial velocity of the body is $128$~ft.\ per~second, $a$~must
+equal~$128$.
+\end{Remark}
+
+By giving successive values of $1$, $2$, $3$, etc.\ to~$x$ in
+the expression $128x-16x^2$, we find the height at which
+the body will be at the end of the $1$, $2$, $3$, etc.\ seconds.
+\begin{align*}
+&\underline{\PadTo{\text{etc.}}{x}\ f(x) = 128x - 16x^2\qquad} \\
+&\PadTo{\text{etc.}}{0}\ f(0) = 128 × 0 - 16 × 0^2 = 0 \\
+&\PadTo{\text{etc.}}{1}\ f(1) = 128 × 1 - 16 × 1^2 = 112 \\
+&\PadTo{\text{etc.}}{2}\ f(2) = 128 × 2 - 16 × 2^2 = 192 \\
+&\PadTo{\text{etc.}}{3}\ f(3) = 128 × 3 - 16 × 3^2 = 240 \\
+&\text{etc.\quad etc.} \PadTo{{} = 128 × 3 - {}}{\text{etc.}}\PadTo{16 × 3^2 =}{} \text{etc.}\\
+\end{align*}
+
+Now this relation between the function and the
+variable may be represented graphically by the well-known
+method of measuring the \emph{variable} along a base
+line, starting from a given point, and measuring the
+\emph{function} vertically upwards from that line, negative
+%% -----File: 023.png---Folio 10-------
+quantities in either case being measured in the opposite
+direction to that selected for positive quantities. To
+apply this method we must select our unit of length
+and then give it a fixed interpretation in the quantities
+we are dealing with. Suppose we say that a unit
+measured along the base line~$OX$ in \Figref{1} shall represent
+one second, and that a unit measured vertically from~$OX$
+in the direction~$OY$ shall represent $10$~ft. We
+may then represent the connection between the height
+at which the body is to be found and the lapse of time
+since its projection by a curved line. We shall proceed
+thus. Let us suppose a movable button to slip along
+the line~$OX$, bearing with it as it moves along a vertical
+line (parallel to~$OY$) indefinitely extended both upwards
+and downwards. The movement of this button (which
+we may regard as a point, without magnitude, and
+which we may call a ``bearer'') along~$OX$ will represent
+the lapse of time. The lapse of one second, therefore,
+will be represented by the movement of the bearer one
+unit to the right of~$O$. Now by this time the body
+will have risen $112$~ft., which will be represented by
+$11.2$~units, measured upwards on the vertical line
+carried by the bearer. This will bring us to the point
+indicated on \Figref{1} by~$P_1$. Let us mark this point and
+then slip on the bearer through another unit. This will
+represent a total lapse of two seconds, by which time
+the body will have reached a height of $192$~ft., which
+will be represented by $19.2$~units measured on the
+vertical. This will bring us to~$P_2$. In $P_1$ and~$P_2$ we
+have now representations of two points in the history of
+the projectile. $P_1$~is distant one unit from the line~$OY$
+and $11.2$~units from~$OX$, \ie~it represents a movement
+from~$O$ of $1$~unit in the direction~$OX$ (time, or~$x$), and
+of $11.2$~units in the direction of~$OY$ (height, or~$y$). This
+indicates that $11.2$ is the value of~$y$ which corresponds
+to the value~$1$ of~$x$. In like manner the position of~$P_2$
+indicates that $19.2$ is the value of~$y$ that corresponds
+to the value~$2$ of~$x$. Now, instead of finding an
+%% -----File: 024.p n g----------
+%[Blank Page]
+%% -----File: 025.p n g----------
+\begin{figure}[p]
+\Pagelabel{9}%
+ \begin{center}
+ \begin{minipage}[c]{2.25in}
+ \Fig{1}
+ \Input[2.25in]{025a}
+ \end{minipage}\hfil
+ \begin{minipage}[c]{2.25in}
+ \Fig{3}
+ \Input[2.25in]{025b}
+ \end{minipage}
+ \end{center}
+\end{figure}
+%[To face page 11.]
+%% -----File: 026.png---Folio 11-------
+indefinite number of these points, let us suppose that as
+the bearer moves continuously (\ie~without break) along~$OX$
+a pointed pencil is continuously drawn along the
+vertical, keeping exact pace, to scale, with the moving
+body, and therefore always registering its height,---a unit
+of length on the vertical representing $10$~ft. Obviously the
+point of the pencil will trace a continuous curve, the course
+of which will be determined by two factors, the horizontal
+factor representing the lapse of time and the vertical
+factor representing the movement of the body, and if we
+take any point whatever on this curve it will represent
+a point in the history of the projectile; its distance
+from~$OY$ giving a certain point of time and its distance
+from~$OX$ the corresponding height.
+
+Such a curve is represented by \Figref{1}. We have
+seen how it is to be formed; and when formed it is to
+be read thus: If we push the bearer along~$OX$, then for
+every length measured along~$OX$ the curve cuts off a corresponding
+length on the vertical, which we will call the
+``vertical intercept.'' That is to say, for every value of $x$~(time)
+the curve marks a corresponding value of $y$~(height).
+
+$OX$ is called ``the axis of~$x$,'' because $x$ is measured
+along it or in its direction. $OY$~is, for like reason,
+called ``the axis of~$y$.''
+
+\begin{Remark}
+\Pagelabel{11}%
+We have seen that if $y$ is a function of~$x$ then it follows
+that $x$~is also a function of~$y$ (\Pageref{3}). Hence the curve we
+have traced may be regarded as representing $x = f^{-1}(y)$ no
+less than $y = f(x)$. If we move our bearer along~$OY$ to
+represent the height attained, and make it carry a line
+parallel to~$OX$, then the curve will cut off a length indicating
+the time that corresponds to that height. It will be seen
+that there are two such lengths of $x$ corresponding to every
+length of $y$ between $0$~and~$25.6$, one indicating the moment
+at which the body will reach the given height as it ascends,
+and the other the moment at which it returns to the same
+height in its descent.
+
+As an exercise in the notation, let the student follow this
+series of axiomatic identical equations: given $y = f(x)$, then
+%% -----File: 027.png---Folio 12-------
+$xy=f(x)x=f^{-1}(y)f(x)=f^{-1}(y)y$. Also $f^{-1}\left[f(x)\right]=x$ and
+$f\left[f^{-1}(y)\right]=y$.
+\end{Remark}
+
+\Pagelabel{12}%
+It must be carefully noted that the curve \emph{does not
+give us a picture of the course of the projectile}. We have
+supposed the body to be projected vertically upwards,
+and its course will therefore be a straight line, and
+would be marked by the movement of the pencil up and
+down the vertical, taken alone, and not in combination
+with the movement of the vertical itself; just as the
+time would be marked by the movement of the pencil,
+with the bearer, along~$OX$, taken alone. In fact the
+best way to conceive of the curve is to imagine one
+bearer moving along~$OX$ and marking the time, to scale,
+while a second bearer moves along~$OY$ and marks the
+height of the body, to scale, while the pencil point \emph{follows
+the direction and speed of both of them at once}. The
+pencil point, it will be seen, will always be at the intersection
+of the vertical carried by one bearer and the
+horizontal carried by the other. Thus it will be quite
+incorrect and misleading to call the curve ``a curve
+of height,'' and equally but not more so to call it ``a
+curve of time.'' Both height and time are represented
+by straight lines, and the curve is a ``curve
+of height-and-time,'' or ``a curve of time-and-height,''
+that is to say, \emph{a curve which shows the history of the connection
+between height and time}.
+
+And again the scales on which time and height are
+measured are altogether indifferent, as long as we read our
+curve by the same scale on which we construct it. The
+student should accustom himself to draw a curve on a
+number of different scales and observe the wonderful
+changes in its appearance, while its meaning, however
+tested, always remains the same.
+
+All these points are illustrated in \Figref{2}, where the
+very same history of the connection between time and
+height in a body projected vertically upwards at $128$~ft.\
+per~second is traced for four seconds and $256$~ft., but the
+%% -----File: 028.png---Folio 13-------
+height is drawn on the scale $50$~ft.\ $\frac{1}{6}$~in.\ instead of $10$~ft.\
+$\frac{1}{6}$~in. It shows us that the lines representing space
+\Pagelabel{13}%
+and those representing time
+\begin{wrapfigure}[13]{r}{2in}
+ \Fig{2}
+ \Input[2in]{028a}
+\end{wrapfigure}
+enter into the construction of
+the curve on precisely the
+same footing. The curve, if
+drawn, would therefore be
+neither a curve of time nor
+a curve of height, but a curve
+of time-and-height.
+
+The curve then, is not a
+picture of the course of the
+projectile in space, and a
+similar curve might equally
+well represent the history of a phenomenon that has no
+course in space and is independent of time.
+
+For instance, the expansion of a metal bar under
+tension is a function of the degree of tension; and a
+testing machine may register the connection between
+\index{Testing@{\textsc{Testing Machine}}}%
+the tension and expansion upon a curve. The tension
+is the variable~$x$ (measured in tons, per inch cross-section
+of specimen tested, and drawn on axis of~$x$ to
+the scale of, say, seven tons to the inch), and the expansion
+is $f(x)$ or~$y$ (measured in inches, and drawn on
+axis of~$y$, say to the natural scale, $1:1$).\footnote
+ {If we take tension (the variable) along~$y$, and expansion (the
+ function) along~$x$, the theory is of course the same. As a fact,
+ it is usual in testing-machines to regard the tension as measured
+ on the vertical and the expansion on the horizontal. It is only a
+ question of how the paper is held in the hand, and the reader will do
+ well to throw the curve of time-and-height also, on its side, read its
+ $x$ as~$y$ and its $y$ as~$x$, and learn with ease and certainty to read off the
+ same results as before. This will be useful in finally dispelling the
+ illusion (that reasserts itself with some obstinacy) that the figure represents
+ the course of the projectile. The figures may also be varied by
+ being drawn from right to left instead of from left to right,~etc. It is
+ of great importance not to become dependent on any special convention
+ as to the position,~etc.\ of the curves.}
+
+The tension and expansion, then, are indicated by
+straight lines, constantly changing in length, but the
+history of their connection is a curve. It is not a curve
+%% -----File: 029.png---Folio 14-------
+of expansion or a curve of tension, but a curve of tension-and-expansion.
+
+Or again, the pleasurable sensation of sitting in a
+Turkish bath is a function, amongst other things, of
+\index{Turkish bath}%
+the temperature to which the bath is raised. If we
+treat that temperature as the variable, and measure its
+increase by slipping the bearer along the base line~$OX$,
+then the whole body of facts concerning the varying
+degrees of pleasure to be derived from the bath, according
+to its varying degrees of heat, might be represented
+by a curve, which would be in some respects analogous
+to that represented on \Figref{1}; for, as we measure the
+rise of temperature by moving the bearer along our
+base line, we shall, up to a certain point, read our increasing
+sense of luxury on the increasing length of the
+vertical intercepted by a rising curve, after which the
+increasing temperature will be accompanied by a decreasing
+sense of enjoyment, till at last the enjoyment
+will sink to zero, and, if the heat is still raised, will
+become a rapidly increasing negative quantity. Thus:
+
+\emph{If we have a function (of one variable), then whatever
+the nature of the function may be, the connection between the
+function and the variable is theoretically capable of representation
+by a curve.} And since we have seen that the
+total satisfaction we derive from the enjoyment or use
+of any commodity is a function of the quantity we
+possess (\ie~changes in magnitude as the quantity increases
+or decreases), it follows that \emph{a curve must theoretically
+exist which assigns to every conceivable quantity of
+a given commodity the corresponding total satisfaction to be
+derived by a given man from its use or possession}; or, in
+other words, \emph{the connection between the total satisfaction
+derived from the enjoyment of a commodity and the quantity
+of the commodity so enjoyed is theoretically capable of being
+represented by a curve}. Now this ``total satisfaction
+derived'' is what economists call the ``total utility,'' or
+the ``value-in-use'' of a commodity. The conclusion
+we have reached may therefore be stated thus: Since
+%% -----File: 030.png---Folio 15-------
+the value-in-use of a commodity varies with the quantity
+of the commodity used, \emph{the connection between the quantity
+of a commodity possessed and its value-in-use may, theoretically,
+be represented by a curve}.
+
+\begin{Remark}
+\Pagelabel{15}%
+Here an initial difficulty presents itself. To imagine the
+construction of such a curve as even theoretically possible, we
+should have to conceive the theoretical possibility of fixing
+a unit of satisfaction, by which to measure off satisfactions
+two, three, four times as great as the standard unit, on our
+vertical line, just as we measured tens of feet on it in \Figref{1}.
+We shall naturally be led in the course of our inquiry to deal
+with this objection, which is not really formidable (see \Pageref{52});
+and it is only mentioned here to show that it has not been
+overlooked. Meanwhile, it may be observed that since satisfaction
+is certainly capable of being ``more'' or ``less,'' and
+since the mind is capable of estimating one satisfaction as
+``greater than'' or ``equal to'' another, it cannot be theoretically
+impossible to conceive of such a thing as an accurate
+measurement of satisfaction, even though its practical measurement
+should always remain as vague as that of heat was when
+the thermometer was not yet invented.
+\index{Thermometer}%
+\end{Remark}
+
+We may go a step farther, and may say that,
+if curves representing the connection between these
+economic functions (values-in-use) and their variables
+(quantities of commodity) could be actually drawn out,
+they would, at any rate in many cases, present an important
+point of analogy with our curve in \Figref{1}; for
+they would first ascend and then descend, and ultimately
+pass below zero. As the quantity of any commodity in
+our possession increases we gradually approach the point
+at which it has conferred upon us the full satisfaction
+we are capable of deriving from it; after this a larger
+stock is not in any degree desired, and would not add
+anything to our satisfaction. In a word, we have as
+much as we want, and would not take any more at
+a gift. The function has then reached its maximum
+value, corresponding to the highest point on the curve.
+%% -----File: 031.png---Folio 16-------
+If the commodity is still thrust upon us beyond this
+point of complete satisfaction, the further increments
+become, as a rule, \emph{discommodious}, and the excessive
+quantity \emph{diminishes} the total satisfaction we derive from
+possessing the commodity, till at length a point is
+reached at which the inconvenience of the excessive
+supply neutralises the whole of the advantage derived
+from that part which we can enjoy, and we would just
+as soon go without it altogether as have so far too
+much of a good thing. If the supply is still increased,
+the net result is a balance of inconvenience, and (if shut
+up to the alternative of \emph{all} or \emph{none}) we should, on the
+whole, be the gainers if relieved of the advantage and
+disadvantage alike. The heat of a Turkish bath has
+already given us one instance; and for another we may
+take butcher's meat. Most of us derive (or suppose
+\index{Meat@{\textsc{Meat}, butcher's}}%
+ourselves to derive) considerable satisfaction from the
+consumption of fresh meat. The sum of satisfaction
+increases as the amount of meat increases up to a point
+roughly fixed by the popular estimate at half to three-quarters
+of a pound per diem. Then we have enough,
+and if we were required to consume or otherwise personally
+dispose of a larger amount, the inconvenience
+of eating, burying, burning, or otherwise getting rid of
+the surplus, or the unutterable consequences of failing
+to do so, would partially neutralise the pleasure and
+advantage of eating the first half pound, till at some
+point short of a hundredweight of fresh meat per head
+per diem we should (if shut in to the alternative of all
+or none) regretfully embrace vegetarianism as the lesser
+evil. In this case the curve connecting the value-in-use
+of meat with its quantity would rise as the supply of
+meat, measured along the base line, increased until, say
+at half a pound a day, it reached its maximum elevation,
+indicating that up to that point more meat meant more
+satisfaction, after which the curve would begin to descend,
+indicating that additional supplies of meat would
+be worse than useless, and would tend to neutralise the
+%% -----File: 032.png---Folio 17-------
+satisfaction derived from the portion really desired, and
+to reduce the total gratification conferred, till at a
+certain point the curve would cross the base line, indicating
+that so much meat as that (if we were obliged to
+take all or none) would be just as bad as none at all,
+and that if more yet were thrust upon us it would on
+the whole be \emph{worse} than having none.
+
+\begin{Remark}
+Though practically we are almost always concerned with
+commodities our desire for which is not fully satisfied, that
+is to say, with the portions of our curves which are still ascending,
+yet it is highly important, as a matter of theory, to realise
+the fact that curves of quantity-and-value-in-use must always
+\emph{tend} to reach a maximum somewhere, and that as a rule they
+would actually reach that maximum if the variable (measured
+along the axis of~$x$) were made large enough, and would then
+descend if the variable were still further increased; or in
+other words, that there is hardly any commodity of which
+we might not conceivably have enough and too much, and
+even if there be such a commodity its increase would still
+\emph{tend} to produce satiety (compare \Pageref{5}). Some difficulty is
+often felt in fully grasping this very simple and elementary
+fact, because we cannot easily divest our minds in imagination
+of the conditions to which we are practically accustomed.
+Thus we may find that our minds refuse to isolate the \emph{direct}
+use of commodities and to contemplate that alone (though it
+is of this direct use only that we are at present speaking),
+and persist, when we are off our guard, in readmitting the
+idea that we might exchange what we cannot use ourselves
+for something we want. A man will say, for instance, if
+confronted with the illustration of fresh meat which I have
+used above, that he would very gladly receive a hundredweight
+of fresh meat a-day and would still want more,
+because he could sell what he did not need for himself.
+This is of course beside the mark, since our contention is that
+the \emph{direct value-in-use} of an article always tends to reach a
+maximum; but in order to assist the imagination it may be
+well to take a case in which a whole community may suffer
+from having too much of a good thing, so that the confusing
+side-lights of possible exchange may not divert the attention.
+%% -----File: 033.png---Folio 18-------
+\emph{Rain}, in England at least, is an absolute necessary of life,
+but if the rainfall is too heavy we derive less benefit from it
+\index{Rainfall}%
+than if it is normal. Every extra inch of rainfall then
+becomes a very serious discommodity, reducing the total
+utility or satisfaction-derived to something lower than it
+would have been had the rain been less; and it is conceivable
+that in certain districts the rain might produce floods
+that would drown the inhabitants or isolate them, in
+inaccessible islands, till they died of starvation, thus cancelling
+the whole of the advantages it confers and making their
+absolute sum zero.
+
+Another class of objections is, however, sometimes raised.
+We are told that there are some things, notably money, of
+which the ordinary man could never have as much as he
+wanted; and daily experience shows us that so far from an
+increased supply of money tending to satisfy the desire for
+it, the more men have the more they want. This objection
+is based on a loose use of the phrase ``more money.'' Let
+us take any definite sum, say~£1, and ask what effort or
+privation a man will be willing to face in order that he may
+secure it. We shall find, of course, that if a man has a
+hundred thousand a-year he will be willing to make none
+but the very smallest effort in order to get a pound more,
+whereas if the same man only has thirty shillings a-week he
+will do a good deal to get an extra pound. It is true that
+the millionaire may still exert himself to get more money;
+but to induce him to do so the prospect of gain must be
+much greater than was necessary when he was a comparatively
+poor man. He does not want \emph{the same sum of money} as
+much as he did when he was poor, but he sees the possibility
+of getting a very large sum, and wants that as much as he
+used to want a small one. All other objections and apparent
+exceptions will be found to yield in like manner to careful
+and accurate consideration.
+
+It is true, however, that a man may form instinctive
+habits of money-making which are founded on no rational
+principle, and are difficult to include in any rationale of
+action; but even in these cases the action of our law is only
+complicated by combination with others, not really suspended.
+
+It is also true that the very fact of our having a thing
+may develop our taste for it and make us want more; but
+%% -----File: 034.png---Folio 19-------
+this, too, is quite consistent with our theory, and will be
+duly provided for hereafter (\Pageref{63}).
+\end{Remark}
+
+Enough has now been said in initial explanation of
+a curve in general, and specifically a curve that first
+ascends and then descends, as an appropriate means of
+representing the connection between the quantity of a
+commodity and its value-in-use, or the total satisfaction
+it confers.
+
+But if we return once more to \Figref{1}, and recollect
+\index{Projectile}%
+\Pagelabel{19}%
+that the curve there depicted is a curve of time-and-height,
+representing the connection between the elevation
+a body has attained (function) and the time that has
+elapsed since its projection (variable), we are reminded
+that there is another closely-connected function of the
+same variable, with which we are all familiar. We are
+accustomed to ask of a body falling from rest not only
+how far it will have travelled in so many seconds, but
+\emph{at what rate it will be moving} at any given time. And so,
+of a body projected vertically upwards we ask not only
+at what height will it be at the end of $x$~seconds, but
+also \emph{at what rate will it then be rising}. Let us pause for
+a moment to inquire exactly what we mean by saying
+that at a given moment a body, the velocity of which
+is constantly changing, is moving ``at the rate'' of, say,
+$y$~feet per~second. We mean that if, at that moment,
+all causes which \emph{modify} the movement of the body were
+suddenly to become inoperative, and it were to move on
+solely under the impulse already operative, it would then
+move $y$~feet in every second, and, consequently, $ay$~feet
+in $a$~seconds. In the case of \Figref{1} the modifying
+force is the action of gravitation, and what we mean by
+the rate at which the body is moving at any moment is
+the rate at which it would move, from that moment onwards,
+if from that moment the action of gravitation
+ceased to be operative.
+
+As a matter of fact it never moves through any space,
+however small, at the rate we assign, because modifying
+%% -----File: 035.png---Folio 20-------
+causes are at work \emph{continuously} (\ie~without intervals
+and without jerks), so that the velocity is never uniform
+over any fraction of time or space, however small.
+
+When we speak of rate of movement ``at a point,''
+then, we are using an abbreviated expression for the
+rate of movement which would set in at that point if all
+modifying causes abruptly ceased to act thenceforth.
+
+For instance, if we say that a body falling from rest
+has acquired a velocity of $32$~feet per~second when it
+has been falling for one second, we mean that if, after
+acting for one second, terrestrial gravitation should then
+cease to act, the body would thenceforth move $32$~feet
+in every second.
+
+It follows, then, that the departures from this ideal
+rate spring from the continuous action of the modifying
+cause, and will be greater or smaller according as the
+action of that cause has been more or less considerable;
+and since the cause (in this instance) acts uniformly in
+time, it will act more in more time and less in less.
+Hence, the less the time we allow after the close of one
+second the more nearly will the rate at every moment
+throughout that time (and therefore the average rate
+during that time) conform to the rate of $32$~feet per~second.
+And in fact we find that if we calculate (by
+the formula $s=16x^2$) the space traversed between the
+close of the first second and some subsequent point of
+time, then the smaller the time we allow the more
+nearly does the average rate throughout that time
+become $32$~ft.\ per~second. Thus---\\
+\Pagelabel{20}%
+\[
+\begin{array}{c@{ }r@{ }c@{ }l@{ }c@{\quad}cc}
+ & & & &
+ &\settowidth{\TmpLen}{\small Body falls}
+ \parbox[b]{\TmpLen}{\small Body falls}
+ &\settowidth{\TmpLen}{\small Average rate}
+ \parbox[b]{\TmpLen}{\small\centering Average rate\\ per sec.} \\
+\text{Between } &1 &\text{ sec.\ and } &2 & \text{ sec.} & 48 \text{ ft.}&48 \text{ ft.}\\
+\Ditto &1 & \Ditto &1\frac{1}{2} & \Ditto & 20 \Ditto &40 \Ditto\\
+\Ditto &1 & \Ditto &1\frac{1}{4} & \Ditto & \Z9 \Ditto &36 \Ditto\\
+\Ditto &1 & \Ditto &1\frac{1}{8} & \Ditto & \frac{17}{4} \Ditto &34 \Ditto\\
+\Ditto &1 & \Ditto &1\frac{1}{16}& \Ditto & \frac{33}{16} \Ditto &33 \Ditto\\
+\Ditto &1 & \Ditto &1\frac{1}{32}& \Ditto & \frac{65}{64} \Ditto &32\DPtypo{\,}{.}5
+\end{array}
+\]
+%% -----File: 036.png---Folio 21-------
+and the average rate between $1$~second and $1 + \dfrac{1}{z}$~second
+may be made as near $32$~ft.\ a second as we like, by making
+$z$ large enough. This is usually expressed by saying
+that the average rate between $1$~second and $\dfrac{(z+1)}{z}$~seconds
+\Pagelabel{21}%
+becomes $32$~ft.\ per second \emph{in the limit}, as $z$ becomes greater,
+or the time allowed smaller.
+
+We may, therefore, define ``rate at a point'' as
+the ``\emph{limit of the average rate between that point and
+a subsequent point, as the distance between the two points
+decreases}.''
+
+With this explanation we may speak of the rate at
+which the projected body is moving as a function of the
+time that has elapsed since its projection; for obviously
+the rate changes with the time, and that is all that is
+needed to justify us in regarding the time that elapses as
+a variable and the rate of movement as a function of that
+variable. Let us go on then, to consider the relation of
+this new function of the time elapsed to the function we
+have already considered. We will call the first function
+$f(x)$ and the second function~$f'(x)$. Then we shall have
+$x=$~the lapse of time since the projection of the body,
+measured in seconds; $f(x)=$~the height attained by the
+body in $x$~seconds, measured in feet; $f'(x) =$~the rate
+at which the body is rising after $x$~seconds, measured in
+feet per~second.
+
+\begin{Remark}
+It will be observed that $x$~must be positive, for we have
+no data as to the history of the body \emph{before} its projection,
+and if $x$ were negative that would mean that the lapse of
+time since the projection was negative, \ie~that the projection
+was still in the future. On the other hand, $f(x) = 128x-16x^2$
+will become negative as soon as $16x^2$ is greater than~$128x$,
+\ie~as soon as $16x$ is greater than~$128$, or $x$~greater than
+$\frac{128}{16}= 8$; which means that after eight seconds the body will
+not only have passed its greatest height but will already
+have fallen below the point from which it was originally
+%% -----File: 037.png---Folio 22-------
+projected, so that the ``height'' at which it is now found, \ie~$f(x)$,
+will be negative. Again $f'(x)$, or the rate at which the
+body is ``rising,'' will become negative as soon as the maximum
+height is passed, for then the body will be rising
+negatively, \ie~falling.
+\end{Remark}
+
+We have now to examine the connection between
+$f(x)$~and~$f'(x)$. Our common phraseology will help us
+to understand it. Thus: $f(x)$~expresses the height of
+the body at any moment, $f'(x)$~expresses the rate at which
+the body is rising; but the rate at which it is rising is
+\emph{the rate at which its height, or~$f(x)$, is increasing}. That is,
+$f'(x)$~represents the rate which $f(x)$ is increasing. A glance
+at \Figref{1} will suffice to show that this rate is not uniform
+throughout the course of the projectile. At first the
+moving body rises, or increases its height, rapidly, then
+less rapidly, then not at all, then negatively---that is to
+say, it begins to fall. This, as we have seen, may be
+expressed in two ways. We may say $f(x)$ [$={}$the
+height] first increases rapidly, then slowly, then negatively,
+or we may say $f'(x)$ [$={}$the rate of rising] is first
+great, then small, then negative.
+
+Formula: \emph{$f'(x)$~represents the rate at which $f(x)$~grows}.
+
+It is obvious then that some definite relation exists
+between $f(x)$ and~$f'(x)$, and Newton and Leibnitz discovered
+the nature of that relation and established rules
+by which, if any function whatever,~$f(x)$, be given, another
+function~$f'(x)$ may be derived from it which shall
+indicate the rate at which it is growing.
+
+\begin{Remark}
+This second function is called the ``\emph{first derived function},''
+or the ``\emph{differential coefficient}''\footnote{See \Pageref{31}.} of the original function, and if
+the original function is called~$f(x)$, it is usual to represent the
+first derived function by~$f'(x)$. In some cases it is possible
+to perform the reverse operation, and if a function be given,
+say~$\phi(x)$, to find another function such that $\phi(x)$ shall
+%% -----File: 038.png---Folio 23-------
+represent the rate of its increase.\footnote
+ {Such a function always exists, but we cannot always ``find'' it,
+ \ie~express it conveniently in finite algebraical notation.}
+This function is then
+\Pagelabel{23}%
+called the ``\emph{integral}'' of~$\phi(x)$ and is written ${\displaystyle \int_0^x \phi(x)\, dx}$. Thus
+if we start with~$f(x)$, find the function which represents the
+rate of its growth and call it~$f'(x)$, and then starting with~$f'(x)$
+find a function whose rate of growth is~$f'(x)$ and call
+it ${\displaystyle \int_0^x f'(x)\, dx}$, we shall obviously have ${\displaystyle \int_0^x f'(x)\, dx = f(x)}$.
+
+The only flaw in the argument is that it assumes there to
+be only one function of~$x$ which increases at the rate indicated
+by~$f'(x)$, and therefore assumes that if we find \emph{any} function
+${\displaystyle \int_0^x f'(x)\, dx}$ which increases at that rate, it must necessarily be
+the function,~$f(x)$, which we already know does increase at that
+rate. This is not strictly true, and ${\displaystyle \int_0^x f'(x)\, dx}$ is, therefore, an
+indeterminate symbol, which represents~$f(x)$ and also certain
+other functions of~$x$, which resemble~$f(x)$ in all respects save
+one, which one will not in any way affect our inquiries. As
+far as any properties we shall have to consider are concerned,
+we may regard the equation
+\[
+\int_0^x f'(x)\, dx = f(x)
+\]
+as absolute.
+\end{Remark}
+
+In the case we are now considering, $f(x)$ is $128x - 16x^2$,
+and an application of Newton's rules will tell us that
+$f'(x)$ is $128 - 32x$. That is to say, if we are told that
+$x$ being the number of seconds since the projection, the
+height of the body in feet is always $128x - 16x^2$ for all
+values of~$x$, then we know by the rules, without further
+experiment, that the rate at which its height is increasing
+will always be $128 - 32x$ ft.-per-second, for all
+values of~$x$. But the rate at which the height is
+increasing is the rate at which the body is rising, so
+that $128 - 32x$ is the formula which will tell us the
+rate at which the body is rising after the lapse of $x$~seconds.\footnote
+ {See table on \Pageref{24}.---\textit{Trans.}}%[** TN: Added footnote]
+%% -----File: 039.png---Folio 24-------
+\begin{table}[hbt]%[** TN: Floating to avoid noticeably underfull page]
+\Pagelabel{24}%
+\[
+\begin{array}{c@{}l}
+\settowidth{\TmpLen}{\small $x =$ number of seconds}
+\parbox[c]{\TmpLen}{\centering\small $x =$ number of seconds\\ since the projection.}
+ &\quad\settowidth{\TmpLen}{\small Rate at which the}
+ f'(x) = 128 - 32x = \left\{
+ \parbox[c]{\TmpLen}{\centering\small Rate at which the\\ body is rising, in\\ feet-per-second.}\right.\\
+&\\[-12pt]
+\hline
+\Strut
+0 & f'(0) = 128 - 32 × 0 = \PadTo[r]{-128}{128} \\
+1 & f'(1) = 128 - 32 × 1 = \PadTo[r]{-128}{96} \\
+2 & f'(2) = 128 - 32 × 2 = \PadTo[r]{-128}{64} \\
+3 & f'(3) = 128 - 32 × 3 = \PadTo[r]{-128}{32} \\
+4 & f'(4) = 128 - 32 × 4 = \PadTo[r]{-128}{0} \\
+5 & f'(5) = 128 - 32 × 5 = \PadTo[r]{-128}{-32} \\
+6 & f'(6) = 128 - 32 × 6 = \PadTo[r]{-128}{-64} \\
+7 & f'(7) = 128 - 32 × 7 = \PadTo[r]{-128}{-96} \\
+8 & f'(8) = 128 - 32 × 8 = \PadTo[r]{-128}{-128}\\
+\text{etc.} & \ \text{etc.}\PadTo{{}= 128 - 32 × 8 = {}}{\text{etc.}} \;\PadTo[r]{-128}{\text{etc.}}
+\end{array}
+\]
+\end{table}
+
+Now the connection between $f'(x)$~and~$x$ can be
+represented graphically, just as the connection between
+$f(x)$~and~$x$ was. It must be represented by a curve (in
+this case a straight line), which makes the vertical
+intercept $12.8$ (representing $128$~ft.\ per~second), when
+the bearer is at the origin (\ie~when $x$~is~$0$), making it $9.6$
+when the bearer has been moved through one unit to the
+right of the origin (or when $x$~is~$1$), and so forth. It is
+given in \Figref{3} (\Pageref{9}), and registers all the facts drawn out
+in our table, together with all the intermediate facts
+connected with them. If we wish to read this curve,
+and to know at what rate the body will be rising after,
+say, one and a half seconds, we suppose our bearer to
+be pushed half-way between $1$~and~$2$ on our base line,
+and then running our eye up the vertical line it carries
+till it is intercepted by the curve, we find that the
+vertical intercept measures $8$~units. This means that
+the rate at which the body is rising, one and a half
+seconds after its projection, is $80$~ft.\ per~second.
+
+\begin{Remark}
+No attempt will be made here to demonstrate, even in a
+simple case, the algebraical rules by which the derived
+functions are obtained from the original ones; but it may be
+well to show in some little detail, by geometrical methods,
+%% -----File: 040.png---Folio 25-------
+the true nature of the connection between a function and its
+derived function, and the possibility of passing from the one
+to the other.\footnote
+ {The student who finds this note difficult to understand is recommended
+ not to spend much time over it till he has studied the rest of
+ the book.}
+
+Suppose $OP_1P_2P_3$ in \Figref{4} to be a curve representing the
+connection of $f(x)$~and~$x$. We may again suppose $f(x)$ to
+represent the amount of work done against some constant
+force, in which case it will conform to the type $y=f(x)=ax-bx^2$.
+The curve in the figure is drawn to the formula
+\[
+ f(x) = 2x - \frac{x^2}{8}, \text{ where } a=2, b=\tfrac{1}{8}.
+\]
+This will give the following pairs of corresponding values:---
+\[
+\begin{array}{c@{\quad}r@{\;}l@{\;}l@{}c}
+x &f(x)=& 2x-\dfrac{x^2}{8} & =y.
+ &\settowidth{\TmpLen}{\small Growth for last}%
+ \parbox[c]{\TmpLen}{\centering\small Growth for last\\ unit of in-\\crease of~$x$.\medskip} \\
+\hline
+\Strut
+0 &f(0)=& 2 × 0 - \frac{0}{8} &= 0. \\
+1 &f(1)=& 2 × 1 - \frac{1}{8} &= 1\frac{7}{8} &\frac{15}{8} \\
+2 &f(2)=& 2 × 2 - \frac{4}{8} &= 3\frac{1}{2} &\frac{13}{8} \\
+3 &f(3)=& 3 × 2 - \frac{9}{8} &= 4\frac{7}{8} &\frac{11}{8} \\
+4 &f(4)=& 4 × 2 - \frac{16}{8} &= 6 &\frac{9}{8} \\
+5 &f(5)=& 5 × 2 - \frac{25}{8} &= 6\frac{7}{8} &\frac{7}{8} \\
+6 &f(6)=& 6 × 2 - \frac{36}{8} &= 7\frac{1}{2} &\frac{5}{8} \\
+7 &f(7)=& 7 × 2 - \frac{49}{8} &= 7\frac{7}{8} &\frac{3}{8} \\
+8 &f(8)=& 8 × 2 - \frac{64}{8} &= 8 &\frac{1}{8} \\
+9 &f(9)=& 9 × 2 - \frac{81}{8} &= 7\frac{7}{8} &\makebox[0pt][r]{$-$}\frac{1}{8} \\
+\text{etc.} &\text{etc.}\quad &\multicolumn{2}{c}{\PadTo{9 × 2 - \frac{81}{8}= 7\frac{7}{8}}{\text{etc.}}}
+ & \text{etc.}
+\end{array}
+\]
+It is clear from an inspection of the curve and from the
+last column in our table that the rate at which $f(x)$ or~$y$
+increases per unit increase of~$x$ is not uniform throughout its
+history. While $x$~increases from $0$ to~$1$, $y$~grows nearly two
+units, but while $x$~increases from $7$ to~$8$, $y$~only grows one
+eighth of a unit. Now we want to construct a curve on
+which we can read off the rate at which $y$ is growing at any
+point of its history. For instance, if $y$~represents the height
+%% -----File: 041.png---Folio 26-------
+of a body doing work against gravitation (say rising), we want
+to construct a curve which shall tell us at what rate the height
+is increasing at any moment, \ie~at what rate the body is rising.
+
+Now since the increase of the function is represented by
+the rising of the curve, the rate at which the function is
+increasing is the same thing as the rate at which the curve is
+rising, and this is the same thing as the steepness of the curve.
+
+Again, common sense seems to tell us (and I shall presently
+show that it may be rigorously proved) that the steepness of
+the tangent, or line touching the curve, at any point is the
+same thing as the steepness of the curve at that point. Thus
+in \Figref{4}, $R_{1}P_{1}$ (the tangent at~$P_{1}$) is steeper than~$R_{2}P_{2}$
+(the tangent at~$P_{2}$), and that again is steeper than~$R_{3}P_{3}$ (the
+tangent at~$P_{3}$), which last indeed has no steepness at all; and
+obviously the curve too is steeper at~$P_{1}$ than at~$P_{2}$, and
+has no steepness at all at~$P_{3}$.
+
+\Pagelabel{26}%
+But we can go farther than this and can get a precise numerical
+expression for the steepness of the tangent at any point~$P$,
+by measuring how many times the line~$QP$ contains the line~$RQ$
+($Q$~being the point at which the perpendicular from any
+point,~$P$, cuts the axis of~$x$, and~$R$ the point at which
+the tangent to the curve, at the same point~$P$, cuts the same
+axis). For since $QP$ represents the total upward movement
+accomplished by passing from~$R$ to~$P$, while $RQ$ represents
+the total forward movement, obviously $QP:RQ = {}$ratio of upward
+movement to forward movement${}={}$steepness of tangent.
+
+But steepness of tangent at~$P = {}$steepness of curve at~$P = {}$rate
+at which $y$~is growing at~$P$. To find the rate at which
+$y$~is growing at $P_{1}$,~$P_{2}$, $P_{3}$,~etc.\ we must therefore find the
+ratios $\dfrac{Q_{1}P_{1}}{R_{1}Q_{1}}$, $\dfrac{Q_{2}P_{2}}{R_{2}Q_{2}}$, $\dfrac{Q_{3}P_{3}}{R_{3}Q_{3}}$~etc. But if we take $r_{1}$,~$r_{2}$,~$r_{3}$, etc.\
+each one unit to the left of $Q_{1}$,~$Q_{2}$, $Q_{3}$,~etc.\ and draw
+$r_{1}p_{1}$,~$r_{2}p_{2}$, $r_{3}p_{3}$~etc.\ parallel severally to $R_{1}P_{1}$,~$R_{2}P_{2}$, $R_{3}P_{3}$~etc.,
+then by similar triangles we shall have
+\[
+\frac{Q_{1}P_{1}}{R_{1}Q_{1}} = \frac{Q_{1}p_{1}}{r_{1}Q_{1}},\quad
+\frac{Q_{2}P_{2}}{R_{2}Q_{2}} = \frac{Q_{2}p_{2}}{r_{2}Q_{2}},\quad
+\frac{Q_{3}P_{3}}{R_{3}Q_{3}} = \frac{Q_{3}p_{3}}{r_{3}Q_{3}},\ \text{etc.,}
+\]
+but the denominators of the fractions on the right hand of
+the equations are all of them, by hypothesis, unity. Therefore
+the steepness of the curve at the points $P_{1}$,~$P_{2}$, $P_{3}$~etc.\
+is numerically represented by $Q_{1}p_{1}$,~$Q_{2}p_{2}$, $Q_{3}p_{3}$,~etc.
+
+In our figure the points~$P_{1}$, $P_{2}$,~$P_{3}$ correspond to the
+%% -----File: 042.p n g----------
+%[Blank Page]
+%% -----File: 043.p n g----------
+\begin{figure}[p]
+\Pagelabel{25}%
+ \begin{center}
+ \Fig{4}
+ \Input{043a}
+ \vfil
+ \null\hfill\Fig{5}
+ \Input[2.5in]{043b}
+ \end{center}
+\end{figure}
+%[To face page 27.]
+%% -----File: 044.png---Folio 27-------
+values $x=2$, $x=4$, $x=8$, and the lines $Q_{1}p_{1}$, $Q_{2}p_{2}$, $Q_{3}p_{3}$ are
+found on measurement to be $\frac{3}{2}$,~$1$,~$0$.
+
+We may now tabulate the three degrees of steepness of
+the curve (or rates at which the function is increasing), corresponding
+to the three values of~$x$:---
+\[
+\begin{array}{c@{\qquad}c}
+x & \settowidth{\TmpLen}{\small Steepness of curve${}={}$rate}
+\parbox[c]{\TmpLen}
+ {\centering\small Steepness of curve${}={}$rate \\ at which $y$ is growing.\medskip} \\
+\hline
+\Strut
+2 & \frac{3}{2} \\
+4 & 1 \\
+8 & 0
+\end{array}
+\]
+
+By the same method we may find as many more pairs of
+corresponding values as we choose, and it becomes obvious
+that the rate at which $y$ or~$f(x)$ is growing is itself a function
+of~$x$ (since it changes as $x$~changes); and we may indicate this
+function by~$f'(x)$. Then our table gives us pairs of corresponding
+values of $x$~and~$f'(x)$, and we may represent the connection
+between them by a curve, as usual. In this particular
+instance the curve turns out to be a straight line, and it is
+drawn out in \Figref{5}.\footnote
+ {Its formula is $y=2-\frac{x}{4}$.}
+Any vertical intercept on \Figref{5},
+therefore, represents the rate at which the vertical intercept
+for the same value of~$x$ on \Figref{4} is growing.
+
+Thus we see that, given a curve of any variable and
+function, a simple graphical method enables us to find as
+many points as we like upon the curve of the same variable
+and a second function, which second function represents the
+rate at which the first function is growing; \textit{e.g.}, given a
+curve of time-and-height that tells us what the height of a
+body will be after the lapse of any given time, we can construct
+a curve of time-and-rate which will tell us at what rate
+that height is increasing, \ie~at what rate the body is rising,
+at any given time.
+
+It remains for us to show that the common sense notion
+of the steepness of the curve at any point being measured by
+the steepness of the tangent is rigidly accurate. In proving
+this we shall throw further light on the conception of ``rate
+%% -----File: 045.png---Folio 28-------
+of increase at a point'' as applied to a movement, or other
+increase, which is constantly varying.
+
+If I ask what is the average rate of increase of~$y$ between
+the points $P_{2}$~and~$P_{3}$ (\Figref{4}), I mean: If the increase of
+$y$ bore a uniform ratio to the increase of~$x$ between the
+points $P_{2}$~and~$P_{3}$, what would that ratio be? or, if a point
+moved from $P_{2}$ to~$P_{3}$ and if throughout its course its upward
+movement bore a uniform ratio to its forward movement,
+what would that ratio be? The answer obviously is $\dfrac{S_3P_3} {P_2S_3}$.
+Completing the figure as in \Figref{4} we have, by similar
+triangles, average ratio of increase of~$y$ to increase of~$x$
+between the points $P_{2}$ and $P_{3}=\dfrac{S_3P_3}{P_2S_3}=\dfrac{Q_3P_3}{MQ_3}$.
+
+Now, keeping the same construction, we will let $P_{3}$ slip
+along the curve towards~$P_{2}$, making the distance over which
+the average increase is to be taken smaller and smaller.
+Obviously as $P_{3}$~moves, $Q_{3}$,~$S_{3}$, and~$M$ will move also, and
+the ratio $\dfrac{S_3P_3}{P_2S_3}$ will change its value, but the ratio $\dfrac{Q_3P_3}{MQ_3}$ will
+likewise change its value in precisely the same way, and will
+always remain equal to the other. This is indicated by the
+dotted lines and the thin letters in \Figref{4}.
+
+Thus, however near $P_{3}$ comes to $P_{2}$ the average ratio of
+the increase of~$y$ to the increase of~$x$ between $P_2$~and~$P_3$ will
+always be equal to $\dfrac{Q_3P_3}{MQ_3}$. But this ratio, though it changes
+as $P_{3}$ approaches~$P_{2}$, does not change indefinitely, or without
+limit; on the contrary, it is always approaching a definite,
+fixed value, which it can never quite reach as long as $P_{3}$
+remains distinct from~$P_{2}$, but which it can approach within
+any fraction we choose to name, however small, if we make
+$P_{3}$ approach $P_{2}$ near enough. It is easy to see what this
+ratio is. For as $P_{3}$ approaches~$P_{2}$, $S_{3}$ approaches~$P_{2}$, $Q_{3}$ approaches~$Q_{2}$,
+$M$ approaches~$R_{2}$, and therefore the ratio $\dfrac{Q_3P_3}{MQ_3}$
+approaches the ratio $\dfrac{Q_2P_2}{R_2Q_2}$, which is the ratio that measures
+the steepness of the tangent at~$P_{2}$. We must realise exactly
+what is meant by this. The lengths $Q_{2}P_{2}$ and~$R_{2}Q_{2}$ have
+definite magnitudes, which do not change as $P_{3}$ approaches~$P_{2}$,
+whereas the lengths $S_{3}P_{3}$ and $MR_{2}+Q_{2}Q_{3}$, which distinguish
+%% -----File: 046.png---Folio 29-------
+$Q_2P_2$ and $R_2Q_2$ from $Q_3P_3$ and $MQ_3$ respectively,
+may be made as small as we please, and therefore as
+small fractions of the fixed lengths $Q_2P_2$ and $R_2Q_2$ as
+we please. Therefore the numerator and denominator of
+$\dfrac{Q_3P_3}{MQ_3}$ may be made to differ from the numerator and denominator
+of $\dfrac{Q_2P_2}{R_2Q_2}$ by \emph{as small fractions of $Q_2P_2$ and $R_2Q_2$ themselves}
+as we please. That is to say, the former fraction, or
+ratio, may be made to approach the latter without limit.
+But the ratio $\dfrac{S_3P_3}{P_2S_3}$ is always the same as the ratio $\dfrac{Q_3P_3}{MQ_3}$, and
+therefore the ratio $\dfrac{S_3P_3}{P_2S_3}$ (or the average ratio of the increase of~$y$
+to the increase of~$x$ between $P_2$~and~$P_3$) may be made to
+approach the ratio $\dfrac{Q_2P_2}{R_2Q_2}$ without limit. Thus, though $S_3P_3$
+and $P_2S_3$ can be made as small as we please absolutely, neither
+of them can be made as small as we please with reference to
+the other. On the contrary, they tend towards the fixed ratio
+$\dfrac{Q_2P_2}{R_2Q_2}$ as they severally approach zero. This is the limit of
+the average ratio of the increase of~$y$ to the increase of~$x$
+between $P_2$~and~$P_3$, and may be approached as nearly as we
+please by taking that average over a small enough part of the
+curve, that is by taking $P_3$ near enough to~$P_2$. If we take
+the average over no space at all and make $P_3$~coincide with~$P_2$,
+we may if we like say that the ratio of the increase of~$y$
+to the increase of~$x$ \emph{at} the point $P_2$ actually \emph{is} $\dfrac{Q_2P_2}{R_2Q_2}$, or $Q_2p_2$
+per unit. [\NB---Let special note be taken of the conception
+of \emph{rate per unit} as a limit to which a ratio approaches, as
+the related quantities diminish without limit.] But we must
+remember that since neither $y$~nor~$x$ increases at all \emph{at} a
+point, and since $S_3P_3$ and $P_2S_3$ both alike disappear when $P_3$
+coincides with~$P_2$, there is not really any ratio between them
+\emph{at} the limit. But this is exactly in accordance with our
+original definition of the ``rate of growth of~$y$ \emph{at} a given
+point in its history'' (\Pageref{19}), which we discovered to mean
+``the rate at which $y$ would grow if all modifying circumstances
+ceased to operate,'' or ``the limit of the average rate
+of growth of~$y$ between $P_2$~and~$P_3$, as $P_3$ approaches~$P_2$.'' As a
+%% -----File: 047.png---Folio 30-------
+matter of fact $y$ never grows at that rate at all, for as soon as it
+grows ever so little it becomes subject to modifying influence.
+
+We see, then, that as $P_3$ approaches $P_2$ the limiting position
+of the line $P_3P_2M$ is~$P_2R_2$, the tangent at~$P_2$ (as indeed
+is evident to the eye), and the limiting ratio of the increase
+of~$y$ to the increase of~$x$ is $\dfrac{Q_2P_2}{R_2Q_2}$, or the steepness of the
+tangent at~$P_2$. Thus ``the steepness of the tangent at~$P_2$'' is
+the only exact interpretation we can give to ``the steepness
+of the curve at~$P_2$,'' and our common sense notion turns out
+to be rigidly scientific.
+
+We see, then, that by drawing the tangents we can read
+$f'(x)$ as well as~$f(x)$ from \Figref{4}. But this is not easy. On
+the other hand, in \Figref{5}, it is easy to read~$f'(x)$, but not so
+easy to read~$f(x)$. This latter may also be read, however. Let
+the student count the units of area included in the triangle~$OPP_3$
+(\Figref{5}). He will find that they equal the units of
+length in $Q_3P_3$ (\Figref{4}). Or if he take $Q_2$ in \Figref{5}, corresponding
+to $Q_2$ in \Figref{4}, he will find that the area~$OPP_2Q_2$
+(\Figref{5}) contains as many units as the length~$Q_2P_2$ (\Figref{4}).
+Or again, taking $Q_1$~and~$Q_2$, the area $Q_1P_1P_2Q_2$ (\Figref{5}) contains
+as many units as the length~$S_2P_2$ (\Figref{4}), which gives
+the growth of~$y$ between $P_1$~and~$P_2$.
+
+Thus in \Figref{4} the absolute value of~$y$, or~$f(x)$, is indicated
+by \emph{length} and the rate of growth of~$y$, or~$f'(x)$, by \emph{slope} of
+the tangent; whereas in \Figref{5} $f'(x)$ is indicated by \emph{length}
+and $f(x)$ by \emph{area}. In either case the different character of the
+units in which $f(x)$~and~$f'(x)$ are estimated indicates the difference
+in their nature, the one being \emph{space} and the other \emph{rate}.
+
+The reason why the areas in \Figref{5} correspond to the
+lengths in \Figref{4} is not very difficult to understand, for we
+shall find that the units of length in~$S_2P_2$ (\Figref{4}), for example,
+and the units of area in~$Q_1P_1P_2Q_2$ (\Figref{5}) both represent
+exactly the same thing, viz.\ the product of the average
+rate of growth of~$y$ between $P_1$~and~$P_2$ into the period over
+which that average growth is taken, which is obviously equivalent
+to the total actual growth of~$y$ between the two points.
+
+To bring this out, let us call the average rate of growth
+of~$y$, between $P_1$~and~$P_2$, $r$, and the period over which that
+growth is taken,~$t$. Then we shall have $rt={}$average rate of
+growth${}×{}$period of growth${}={}$total growth.
+%% -----File: 048.png---Folio 31-------
+
+Now, in \Figref{4}, taking $OQ_1=x_1$, $OQ_2=x_2$, $Q_1P_1=y_1$, $Q_2P_2=y_2$,
+we shall have $r=\dfrac{P_2S_2}{P_1S_2}=\dfrac{y_2-y_1}{x_2-x_1}$, and $t=Q_1Q_2=x_2-x_1$, and
+$rt = \dfrac{y_2-y_1}{x_2-x_1}(x_2-x_1) = y_2-y_1 = P_2S_2$.
+
+We must now find the representative of~$rt$ in \Figref{5}, and
+to do so we must look for some line that represents~$r$ or
+$\dfrac{y_2-y_1}{x_2-x_1}$ or the average rate of growth of~$y$ between $P_1$~and~$P_2$.
+Now the rate of growth of~$y$ at~$P_1$ is represented by~$y'_1$, and
+its rate of growth at~$P_2$ by~$y'_2$; and an inspection of the
+figure shows that it declines \emph{uniformly} between the two
+points, so that the average rate will be half way between $y'_1$~and~$y'_2$.
+This is represented by the line~$AB$, which equals
+$\dfrac{Q_1P_1+Q_2P_2}{2}$ or $\dfrac{y'_1+y'_2}{2}$. We have then, in \Figref{5}, $r=AB$.
+But $t=x_2-x_1$ or $Q_1Q_2$ as before. Therefore $rt = AB × Q_1Q_2$.
+Again, a glance at \Figref{5} will show that, by equality of
+triangles, the area $AB × Q_1Q_2$ is equal to the area~$Q_1P_1P_2Q_2$.
+Combining our results then, we have
+\[
+Q_1P_1P_2Q_2 \text{ (\Figref{5})} =rt=P_2S_2 \text{ (\Figref{4})}
+\]
+or units of length in $P_2S_2=$ units of area in~$Q_1P_1P_2Q_2$.
+\QED
+
+Had the curve in \Figref{5} not been a straight line, the proof
+would have been the same in principle, though not so simple;
+and the areas would still have corresponded exactly to the
+lengths in the figure of the original function.\footnote
+ {We have seen that the increment of~$y$ (or~$y_2-y_1$) equals the increment
+ of~$x$ (or~$x_2-x_1$) multiplied by $\dfrac{y'_1+y'_2}{2}$ $\left(\text{or } \dfrac{y_2-y_1}{x_2-x_1}\right)$.\Pagelabel{31}%
+
+ Thus: increment of $y={}$increment of $x × \dfrac{y'_1+y'_2}{2}$; and $\dfrac{y'_1+y'_2}{2}=
+ \dfrac{f'(x_1)+f'(x_2)}{2}$; now the increment of~$y$ is the magnitude that differentiates
+ $y_2$ from~$y_1$, and is, therefore, called by Leibnitz the ``quantitas
+ differentialis'' of~$y$, though this term is only applied when $y_1$ and
+ $y_2$ are taken very near together, so that the ``quantitas differentialis''
+ of $y_1$ and $y_2$ bears only a very small ratio to the ``quantitas integralis,''
+ or integral magnitude of $y_1$~itself.
+
+ Thus when $y_2$~and~$x_2$ approach $y_1$~and~$x_1$ very nearly, we have
+ differential of $y_1={}$differential of $x_1 × \dfrac{ f'(x_1)+f'(x_2)}{2}$, and as we approach
+ the limit, and the difference between $f'(x_1)$ and~$f'(x_2)$ becomes not
+ only smaller itself, but a smaller fraction of~$f'(x_1)$, we find that
+ $\dfrac{f'(x_1)+f'(x_2)}{2}$ approaches $\dfrac{f'(x_1)+f'(x_1)}{2}=f'(x_1)$.
+
+ In the limit, then, we have differential of $y_1 ={}$differential of $x_1 × f'(x_1)$;
+ or generally, differential of $y ={}$differential of $x × f'(x)$, where $f'(x)$ is
+ \emph{the coefficient which turns the differential of~$x$ into the differential
+ of~$y$}. Hence $f'(x)$ or~$y'$ is called the ``differential coefficient'' of
+ $f(x)$ or~$y$, and $y$ or~$f(x)$ is called the ``integral'' of $f'(x)$ or~$y'$.
+
+ I insert this explanation in deference to the wish of a friend, who
+ declares that he ``can never properly understand a term scientifically
+ until he understands it etymologically,'' and asks ``why it is a
+ coefficient and why it is differential.'' I believe his state of mind is
+ typical.}
+\end{Remark}
+
+It is essential that the reader should familiarise
+himself perfectly with the precise nature of the relation
+%% -----File: 049.png---Folio 32-------
+subsisting between the two functions we have been investigating,
+and I make no apology, therefore, for dwelling
+on the subject at some length and even risking
+repetitions.
+
+We have seen that $f'(x)$ is the rate at which $f(x)$ is
+increasing, or rate of growth of~$f(x)$. And we measure
+the rate at which a function is increasing by the
+number of units which would be added to the function
+while one unit is being added to the variable if all the
+conditions which determine the relation should remain
+throughout the unit exactly what they were at its commencement.
+
+Again, when we denote a certain function of~$x$ by the
+symbol~$f(x)$, we have~$y=f(x)$, and for $x=a$ $y=f(a)$,
+for $x=1$ $y=f(1)$, for $x=0$ $y=f(0)$, etc. This has been
+fully illustrated in previous tables (compare \Pageref{24}).
+\begin{flalign*}
+&\text{\indent Thus if } & f(x)&=128x-16x^{2}, & \phantom{Thus if} \\
+&\text{then} & f(2)&=[128 × 2-16 × 2^{2}] & \\
+& & &= 192.
+\end{flalign*}
+In \DPtypo{}{the} future, then, we may omit the intermediate stage
+and write at once $f(x)=128x-16x^2$; $f(2)=192$, etc.
+
+We may therefore epitomise the information given us
+\index{Projectile}%
+by the curves in Figs.\ \Figref[]{1}~and~\Figref[]{3} (combined in \Figref{6})\DPtypo{}{.}
+Thus---
+%% -----File: 050.p n g----------
+%[Blank Page]
+%% -----File: 051.p n g----------
+\begin{figure}[p]
+ \begin{center}
+ \Fig{6}
+ \Input[2in]{051a}
+ \end{center}
+\end{figure}
+%
+%[To face page 33.]
+%% -----File: 052.png---Folio 33-------
+%[** TN: Size-dependent hack to get table below to stay on the same page.]
+{\small
+\Pagelabel{33}%
+\[
+\begin{array}{r@{\;}l@{\quad}r@{\;}c}
+f(x) =& 128x - 16x^2 & f'(x) = & 128 - 32x \\
+\hline
+\Strut
+f(0) = & \Z\Z0 & f'(0) = & \PadTo[r]{-128}{128} \\
+f(1) = & 112 & f'(1) = & \PadTo[r]{-128}{96} \\
+f(2) = & 192 & f'(2) = & \PadTo[r]{-128}{64} \\
+f(3) = & 240 & f'(3) = & \PadTo[r]{-128}{32} \\
+f(4) = & 256 & f'(4) = & \PadTo[r]{-128}{0} \\
+f(5) = & 240 & f'(5) = & \PadTo[r]{-128}{-32} \\
+f(6) = & 192 & f'(6) = & \PadTo[r]{-128}{-64} \\
+f(7) = & 112 & f'(7) = & \PadTo[r]{-128}{-96} \\
+f(8) = & \Z\Z0 & f'(8) = & \PadTo[r]{-128}{-128} \\
+\end{array}
+\]}%
+which may be read in \Figref{6} from the lengths cut off
+by the two curves respectively on the vertical carried
+by the bearer as it passes points $0$,~$1$, $2$, $3$,~etc.
+
+This table states the following facts:---At the commencement
+the height of the body~[$f(x)$] is~$0$, but the
+rate at which that height is increasing~[$f'(x)$] is $128$~ft.\ per~second.
+That is to say, the height would increase by $128$~ft.,
+while the time increased by one second, if the conditions
+which regulate the relations between the time that elapses
+and space traversed remained throughout the second
+exactly what they are at the beginning of it. But those
+conditions are continuously changing and never remain
+the same throughout any period of time, however small.
+At the end of the first second then, the height attained
+[$f(x)$] is, not $128$~ft.\ as it would have been had there
+been no change of conditions, but $112$~ft., and the rate
+at which that height is now growing is $96$~ft.\ per~second.
+That is to say, if the conditions which determine the
+relation between the time allowed and the space traversed
+were to remain throughout the second exactly what they
+are at the beginning of it, then the height of the body
+[$f(x)$] would \emph{grow} $96$~ft., while the time grew one second.
+Since these conditions change, however, the height
+grows, not $96$~ft., but $80$~ft.\ during the next second, so
+that after the lapse of two seconds it has reached the
+height of $(112 + 80) = 192$~ft., and is now \emph{growing} at
+the rate of $64$~ft.\ per~second. After the lapse of four
+%% -----File: 053.png---Folio 34-------
+seconds the height of the body is $256$~ft., and that height
+\emph{is not growing at all}. That is to say, if the conditions
+remained exactly what they are at this moment, then
+the lapse of time would not affect the height of the
+body at all. But in this case we realise with peculiar
+vividness the fact that these conditions never do
+remain exactly what they are for any space of time,
+however brief. The movement of the body is the
+resultant of two tendencies, the constant tendency to
+\emph{rise} $128$~ft.\ per~second in virtue of its initial velocity,
+and the growing tendency to \emph{fall} in virtue of the continuous
+action of gravitation. At this moment these
+two tendencies are exactly equal, and \emph{if they remained}
+equal then the body would rise $0$~ft.\ per~second, and
+the lapse of time would not affect its position. But of
+the two tendencies now exactly equal to each other,
+one is continuously increasing while the other remains
+constant. Therefore they will not remain equal during
+any period, however short. Up to this moment
+the body rises, after this moment the body falls.
+There is no period, however short, \emph{during} which it is
+neither rising nor falling, but there is a point of time \emph{at}
+which the conditions are such that if they were continued
+(which they are not) it \emph{would} neither rise nor fall. This
+is expressed by saying that \emph{at} that moment the rate at
+which the height is growing is~$0$. If the reader will
+pause to consider this special case, and then apply the
+like reasoning to other points in the history of the projectile,
+it may serve to fortify his conception of ``rate.''
+After $6$~seconds the height is~$192$, and the rate at
+which it is growing is $-64$~ft.-per-second. That is to
+say, the body is \emph{falling} at the rate of $64$~ft.-per-second.
+At the end of $8$~seconds the height is~$0$, and the rate
+at which the height is growing is $-128$~ft.-per-second.
+
+All this is represented on the table, which may be
+continued indefinitely on the supposition that the body
+is free to fall below the point from which it was
+originally projected.
+%% -----File: 054.png---Folio 35-------
+
+The instance of the vertically projected body must
+be kept for permanent reference in the reader's mind,
+so that if any doubt or confusion as to the relation
+between $f'(x)$ and~$f(x)$ should occur, he may be able
+to use it as a tuning fork: $f'(x)$ is the rate at which
+$f(x)$ is growing, so that if $f(x)$ is the space traversed,
+then $f'(x)$ is the rate of motion, \ie~the rate at which
+the space traversed,~$f(x)$, is being increased.
+
+Now, when we are regarding time solely as a regulator
+of the height of the body, we may without any
+great stretch of language speak of the \emph{effect} of the
+lapse of time in allowing or securing a definite result
+in height. Thus the effect of $1$~second would be
+represented by $112$~ft., the effect of $4$~seconds by $256$~ft.,
+the effect of $7$~seconds by $112$~ft., the effect of
+$8$~seconds by $0$~ft. And to make it clear that we mean
+to register only the net result of the whole lapse of
+time in question, we might call this the ``total effect''
+of so many seconds. In this case $f(x)$ will represent
+the total effect of the lapse of $x$~seconds, regarded as
+a condition affecting the height of the body. What,
+then, will $f'(x)$ signify? It will signify, as always,
+the rate at which $f(x)$ is increasing. That is to say,
+it will signify the rate at which additions to the time
+are at this point increasing the effect, \ie~the rate at
+which the effect is growing. Now, since more time
+must always be added on at the margin of the time
+that has already elapsed, we may say that $f(x)$~represents
+the \emph{total effect} of $x$~seconds of time in giving height
+to the body, and that $f'(x)$~represents the \emph{effectiveness}
+of time, added at the margin of $x$~seconds, in \emph{increasing}
+the height. Or, briefly, $f(x) ={}$total effect, $f'(x) ={}$marginal
+effectiveness.
+
+Here the change of terms from ``effect'' to ``effectiveness''
+may serve to remind us that in the two cases
+we are dealing with two different kinds of magnitude---in
+the one case \emph{space} measured in feet absolutely (effect),
+in the other case \emph{rate} measured in feet-per-second.
+%% -----File: 055.png---Folio 36-------
+
+Before passing on to the economic interpretation of
+all that has been said, we will deal very briefly with
+another scientific illustration, which may serve as a
+transition.
+
+Suppose we have a carbon furnace in which the
+carbon burns at a temperature of $1500°$~centigrade, and
+suppose we are using it to heat a mass of air under
+\begin{figure}[hbt]
+ \begin{center}
+ \Fig{7}
+ \Input[4.5in]{055a}
+ \end{center}
+\end{figure}
+given conditions. Obviously the temperature to which
+we raise the air will be a function of the amount of
+carbon we burn, and will be a function which will
+increase as the variable increases; but not without
+limit, for it can never exceed the temperature of~$1500°$.
+Suppose the conditions are such that the first pound
+%% -----File: 056.png---Folio 37-------
+of carbon burnt raises the temperature of the air from
+\index{Carbon@{\textsc{Carbon Furnace}}}%
+$0°$ to $500°$, \ie~raises it one-third of the way from its
+present temperature to that of the burning carbon, then
+(neglecting certain corrections) the second pound of
+carbon burnt will again raise the temperature one-third
+of the way from its present point ($500°$) to that of
+the carbon ($1500°$). That is to say, it will raise it to
+$833.3°$; and so forth. Measuring the pounds of carbon
+consumed along the axis of~$x$ and the degrees centigrade
+to which the air is raised along the axis of~$y$
+($100°$ to a unit), we may now represent the connection
+between $f(x)$~and~$x$ by a curve.\footnote
+ {The formula will be $y = f(x) = 15 \left\{1-(\frac{2}{3})^x \right\}$}
+Its general
+form may be seen in \Figref{7}, and we shall have the
+total effect of the carbon in raising the temperature
+represented by $f(x)$, and assuming the following values:---
+\begin{align*}
+f(0) &= 0 & f(4) &= 12.04 & f(8) &= 14.42 \\
+f(1) &= 5[ = 500°] & f(5) &= 13.02 & f(9) &= 14.61 \\
+f(2) &= 8.3 & f(6) &= 13.68 & f(10) &= 14.74 \\
+f(3) &= 10.5 & f(7) &= 14.12 & f(11) &= 14.83 \\
+ & & f(12) &= 14.88
+\end{align*}
+
+Now here, as before, we may proceed (either graphically,
+see \Pageref{26}, or by aid of the rules of the calculus)
+to construct a second curve, the curve of $x$~and~$f'(x)$,
+which shall set forth the connection between $x$ and the
+steepness of the first curve, \ie~the connection between
+the value of~$x$ and the rate at which $f(x)$ is growing.\footnote
+ {Its formula will be $15(\frac{2}{3})^x \log_e (\frac{3}{2})$.}
+Again allowing $100°$ to the unit, measured on the axis
+of~$y$, we shall obtain (\Figref{8})---
+\begin{align*}
+f'(0) &= 6.08 & f'(4) &= 1.2 & f'(8) &= .24 \\
+f'(1) &= 4.05 & f'(5) &= \Z.8 & f'(9) &= .16 \\
+f'(2) &= 2.7 & f'(6) &= \Z.53 & f'(10) &= .1 \\
+f'(3) &= 1.8 & f'(7) &= \Z.35 & \rlap{\text{etc.}}\Z &
+\end{align*}
+
+What then will $f'(x)$ represent? Here as always
+%% -----File: 057.png---Folio 38-------
+we have $f'(x) ={}$the rate at which $f(x)$~is growing. But
+$f(x) ={}$the heat to which the air is raised, \ie~the total
+effect of the carbon. Therefore $f'(x)$~is the rate at which
+carbon, added at the margin, will increase the heat, or the
+marginal effectiveness of carbon in raising the heat.
+We have $x ={}$quantity of carbon burnt, $f(x) ={}$total effect
+of~$x$ in raising the heat of the air, $f'(x) ={}$marginal effectiveness
+of additions to~$x$.
+
+Comparing the illustration of the heated air with
+\begin{figure}[hbt]
+ \begin{center}
+ \Fig{8}
+ \Input[3in]{057a}
+ \end{center}
+\end{figure}
+that of the falling body we find that pounds of carbon
+have taken the place of seconds of time as the variable,
+total rise of temperature has taken the place of total
+space traversed as the first function of the variable, rate
+at which additions to carbon are increasing the temperature
+has taken the place of rate at which additions
+to the time allowed are increasing the space traversed,
+as the derived function; but in both cases the derived
+function represents the rate at which the first function
+is growing, in both cases the first function represents
+%% -----File: 058.png---Folio 39-------
+the total efficiency of any given quantity of the variable,
+and the derived function represents its effectiveness at
+any selected margin, so that in both cases the relation
+$f'(x)$~to~$f(x)$ is identical.\Pagelabel{39}%
+
+And now at last we may return to the economic
+interpretation of the curves.
+
+Assuming that \Figref{1} (\Pageref{9}) represents the connection
+between some economic function and its variable, as, for
+example, the connection between the quantity of coal I
+\index{Coal}%
+burn and the sum of advantages or gratifications I
+derive from it, and assuming further that one unit along
+the axis of~$x$ is taken to mean one ton of coal per month,
+we shall have no difficulty in reading \Figref{1} as follows:
+$f(0) = 0$, \ie~if I burn no coal I get no benefit from
+burning it; $f(1) = 11.2$, \ie~the total effect of burning
+one ton of coal per month is represented by $11.2$~units
+of satisfaction; $f(2) = 19.2$, \ie~the total effect of burning
+two tons of coal a month is greater than that of
+burning one ton a month, but not twice as great. The
+difference to my comfort between burning no coal and
+burning a ton a month is greater than the difference
+between burning one and burning two tons. So again,
+$f(4) = 25.6$, \ie~the total effect of four tons of coal per
+month in adding to my comfort is represented by $25.6$~units
+of gratification, and at this point its total effect is
+at its maximum; for now I have as much coal as I
+want, and if I were forced to burn more the total effect
+of that greater quantity would be less than that of a
+smaller quantity, or $f(5)$~is less than~$f(4)$. At last the
+point would arrive at which if I were forced to choose between
+burning, say, eight tons of coal a month and burning
+none at all, I should be quite indifferent in the matter.
+The total effect of eight tons of coal per month as a
+direct instrument of comfort would then be nothing.
+And if more yet were forced upon me at last I should
+prefer the risk of dying of cold to the certainty of
+being burned to death, and $f(x)$ would be a negative
+quantity.
+%% -----File: 059.png---Folio 40-------
+
+\begin{Remark}
+It must be observed that I am not here speaking of the
+\emph{construction} of economic curves, but of their \emph{interpretation} supposing
+we had them (see \Pageref{15}). But it will be seen presently
+that the construction of such curves is quite conceivable
+ideally, and that there is no absurdity involved in speaking
+of so many units of gratification. It is extremely improbable,
+however, that any actual economic curve would coincide with
+that of \Figref{1} (see \Pageref{48}).
+\end{Remark}
+
+Such would be the interpretation of \Figref{1}, $f(x)$~being
+read as the curve of quantity-and-total-effect of coal as
+a producer of comfort under given conditions of consumption.
+What then would be the interpretation of
+\Figref{3} or~$f'(x)$? Obviously $f'(x)$, signifying the rate of
+growth of~$f(x)$, or the ratio of the increase of~$f(x)$ to the
+increase of~$x$ at any point, would mean the rate at which
+an additional supply of coal is increasing my comfort,
+or the marginal effectiveness of coal as a producer of
+comfort to me. This marginal effectiveness of course
+varies with the amount I already enjoy. That is to
+say, $f'(x)$~assumes different values as $x$~changes. When
+I have no coal, the marginal effectiveness is very high.
+That is to say, increments of coal would add to my comfort
+at a great rate, $f'(0)= 12.8$. When I already command
+a ton a month further increments of coal would
+add to my comfort at a less rapid rate, $f'(1) = 9.6$;
+when I have four tons a month further increments would
+not add to my comfort at all, $f'(4) = 0$, after that yet
+further increments would detract from my comfort,
+$f'(5)=-32$.
+
+In thus interpreting Figs.\ \Figref[]{1}~and~\Figref[]{3} we have substituted
+consumption of coal per month (measured in
+tons), for lapse of time (measured in seconds), as our
+variable; sum of advantages derived from consuming
+the coal, for space traversed by the projectile, as $f(x)$,
+or the total effect of the variable; and rate per unit
+at which coal is increasing comfort, for rate per unit
+at which time is increasing the space traversed, as
+$f'(x)$, or the marginal effectiveness of the variable.
+%% -----File: 060.png---Folio 41-------
+
+If we call $f(x)$ the ``total utility'' of $x$~tons of coal
+per month, we might call $f'(x)$ the ``marginal usefulness''
+of coal when the supply is $x$~tons per month.
+
+The reader should now turn back to \Pageref{33}, and
+read the table of successive values of $f(x)$ and~$f'(x)$
+with the subsequent comments and interpretations,
+substituting the economic meanings of $x$, $f(x)$, and
+$f'(x)$ for the physical ones throughout.
+
+A similar re-reading of Figs.\ \Figref[]{7}~and~\Figref[]{8} will also be
+instructive.
+
+Before going on to the further consideration of the
+total effect and marginal effectiveness of a commodity
+as functions of the quantity possessed, it will be well
+to point out a method of reading $f'(x)$ which will bring
+it more nearly within the range of our ordinary experiences,
+and make it stand for something more definitely
+realisable by the practical intellect than can be the
+case with the abstract idea of rate.\Pagelabel{41}%
+
+Reverting to our first interpretation of \Figref{3}, we
+remember that $f'(2)=64$ means that after the lapse
+of $2$~seconds the body will be rising \emph{at the rate} of
+$64$~ft.\ per~second; but it is entirely untrue that it will
+actually rise $64$~ft.\ during the next following second.
+We see by \Figref{1} that it will only rise $48$~ft.\ in that
+second. This is because the rate, which was $64$~ft.\
+per~second at the beginning of the second, has constantly
+changed during the lapse of the second itself.
+But the rate of $64$~ft.\ per~second is the same thing as the
+rate of $6.4$~ft.\ per~tenth of a second (or per $.1$~second),
+and this again is the same as the rate $.64$~ft.\ per $.01$~second,
+or $.000064$~ft.\ per $.000001$~second, and I may
+therefore read \Figref{3} thus: $f'(2)=64$, \ie~after the lapse
+of $2$~seconds the body will be rising at the rate of
+$64$~millionths of a foot per millionth of a second. Now,
+we should have to allow many millionths of a second
+to elapse before the rate of movement materially
+altered, and therefore we may with a very close approximation
+to the truth say that the rate of motion will
+%% -----File: 061.png---Folio 42-------
+be the same at the end as it was at the beginning
+of the first millionth of a second, \ie\ $64$~millionths
+of a foot per millionth of a second. Hence it will
+be approximately true to say that during the next
+millionth of a second the body will actually rise $64$~millionths
+of a foot (compare \Pageref{20}).\Pagelabel{42}\footnote
+ {It would be [assuming the formula to be absolutely true]
+ $63.999984$ millionths of a foot. The error, therefore, would be
+ $\frac{16}{1000000}$ or $\frac{1}{62500}$ in~$64$.}
+But a rise of
+$64$~millionths of a foot would be a concrete \emph{effect; hence
+if we translate the \textsc{effectiveness} of the variable into terms
+of a small enough unit, it tells us within any degree of
+accuracy we may demand the actual \textsc{effect} of the next small
+increment of the variable}. This is expressed by saying
+that ``in the limit'' each small increment actually produces
+this effect; which means that by making the
+increments small enough we may make the proposition
+as nearly true as we like.
+
+Thus [assuming the ordinary formula $y=16x^2$ to
+be absolutely correct] it is nearly true to say that when
+a body has been falling $2$~seconds it will fall $64$~millionths
+of a foot in the next millionth of a second,
+$128$~millionths of a foot in the next $2$~millionths of a
+second, $64n$~millionths of a foot in the next $n$~millionths
+of a second, so long as $n$~is an insignificant
+number in comparison to one million. What is nearly
+true when the unit is small and more and more nearly
+true as the unit grows smaller is said to be ``true in
+the limit, as the unit decreases.''
+
+Marginal \emph{effectiveness} of the variable, then, may always
+be read as marginal \emph{effect} per unit of very small units
+of increment. And in this sense we shall generally
+understand it. Total effect and unitary marginal effect
+will then be magnitudes of the same nature or character;
+and indeed the unitary marginal effect will itself
+be a total effect in a certain sense, the total effect
+namely of one small unit, added at that particular place.
+Even when we are not dealing with small units we
+%% -----File: 062.png---Folio 43-------
+may still speak of the marginal effect of a unit of the
+commodity, but in that case the effect of a unit of the
+commodity at the margin of~$x$ will no longer correspond
+closely to the marginal effectiveness of the commodity
+at~$x$. It will correspond to the \emph{average} marginal effectiveness
+of the commodity between~$x$, at which its
+application begins, and $x + 1$, at which it ends. And if
+the effect of the next unit after the~$a$\textsuperscript{th} is~$z$, it will probably
+not be true (as it is in the case of small units)
+that the effect of the next two units will be nearly~$2z$.
+A reference to Figs.~\Figref[]{1}, \Figref[]{3}, \Figref[]{7},~\Figref[]{8}, and a comparison of
+the last column and the last but one in the table of
+\Pageref{4}, will sufficiently illustrate this point; and the
+economic illustration of the next paragraph will furnish
+an instance of the correspondence, in the limit, between
+the effectiveness of the commodity and the effect of a
+small unit.
+
+\begin{Remark}
+Reverting to Figs.\ \Figref[]{4}~and~\Figref[]{5} (\Pageref{25}) we have $Q_1 p_1$ in \Figref{4}
+$= Q_1 P_1$ in \Figref{5}. But we have seen that if we start from $P_1$ in
+\Figref{4} and move a very little way along the curve, the ratio of
+the increment of~$x$ to the increment of~$y$ will be very nearly
+$\dfrac{r_1 Q_1}{Q_ 1p_1}$; or in the limit $\dfrac{\text{increment of } x}{\text{increment of } y} = \dfrac{r_1 Q_1}{Q_1p_1}$. But $r_1 Q_1 = 1$,
+therefore in the limit $\dfrac{\text{increment of } x}{\text{increment of } y} = \dfrac{1}{\DPtypo{Q}{Q_1} p_1}$ (\Figref{4}) $= \dfrac{1}{Q_1 P_1}$ (\Figref{5}),
+or, in the limit, $Q_1 P_1 × \text{ increment of } x = \text{increment of } y$.
+Now in \Figref{5} increments of~$x$ are measured along~$OX$, and
+therefore (if we follow the ordinary system of interpretation)
+we shall regard $Q_1 P_1 × \text{ increment of } x$, as an area, and it will
+be seen that as $x$ decreases the area in question approximates
+to a thin slice cut vertically from the triangle~$Q_1 P_1 P_3$. But we
+have seen that areas cut in vertical slices out of this triangle
+correspond to lengths in \Figref{4}, or portions of the total effect
+of the variable. Thus if a small unit is taken, the \emph{effect} of
+units of a commodity applied at any margin (\Figref{4}) is approximately
+represented by the \emph{effectiveness} of the commodity
+at that margin (\Figref{5}) multiplied by the number of units.
+And in the limit this relation is said to hold absolutely
+(compare pp.~\Pageref[]{21},~\Pageref[]{42}).
+\end{Remark}
+%% -----File: 063.png---Folio 44-------
+
+The method of reading curves of quantity-and-marginal-effectiveness
+as though they were curves of
+quantity-and-marginal-effect may be illustrated by the
+following example.
+
+\Figref{9} represents part of the curve of quantity-and-marginal-effectiveness
+\Pagelabel{44}%
+of wheat in Great Britain, based
+\index{Wheat}%
+upon a celebrated estimate made about the beginning of
+the eighteenth century.\footnote
+ {The estimate is generally known as ``Gregory King's,'' and its
+ formula is
+ \[
+ 60y = 1500 - 374x + 33x^2 - x^3.
+ \]
+ }
+In the figure the unit of~$x$ is
+(roughly speaking) about $20$~millions of bushels; and if
+\begin{figure}[hbt]
+ \begin{center}
+ \Fig{9}
+ \Input[4.5in]{063a}
+ \end{center}
+\end{figure}
+we place our quantity-index eleven units from the origin,
+that will mean that we suppose the supply of wheat in
+Great Britain to be $220$~millions of bushels per annum.
+Our curve asserts that when we have that supply
+additions of wheat will have an ``effectiveness'' in supplying
+our wants represented by $.8$~per $20$~million
+bushels; but we cannot translate the ``effectiveness''
+into the actual ``effect'' which $20$~millions of bushels
+%% -----File: 064.png---Folio 45-------
+would have; because the ``effectiveness'' would not continue
+the same if so large an addition were made to our
+supply. On the contrary it would drop from $.8$ to~$.6$.
+But $.8$~per $20,000,000$ bushels is $.00000008$~per $2$~bushels
+and $.00000004$ per~bushel, and since the addition
+of another bushel to the $220$~millions already
+possessed will not materially affect the usefulness or
+effectiveness of wheat at the margin, we may say that
+that effectiveness remains constant during the consumption
+of the bushel of wheat, and therefore, given
+a supply of $20,000,000$ bushels a year, not only is the
+``marginal effectiveness'' of wheat $.8$~per $20,000,000$
+bushels or $.0000004$ per~bushel, but the ``marginal
+effect'' of a bushel is~$.00000004$. Thus, if we had two
+commodities, $W$~and~$V$, and curves of their quantity-and-marginal-usefulness
+or effectiveness similar to that in
+\Figref{9}, the vertical intercepts on the quantity-indices
+would indicate the marginal usefulness per unit of the
+two commodities, and if we then selected ``small'' units
+of each commodity bearing in each case the same proportion
+(say $1 : z$) to the unit to which the curve of the
+commodity was drawn, we should then have the marginal
+utility or effect of the small units of the two commodities
+proportional to the length of the vertical intercepts, and
+calling the small unit of~$W$, $w$, and the small unit of~$V$, $v$,
+and the ratio of the marginal usefulness of~$W$ to that of~$V$,
+$r$, we should have
+\begin{align*}
+\text{marginal utility of }
+ w &= \Z r × \text{marginal utility of } v \\
+\PadTo{\text{marginal}}{\Ditto} \PadTo{\text{utility of}}{\Ditto}
+ 2w &= 2r × \text{marginal utility of } v. \\
+\PadTo{\text{marginal utility of }}{\text{etc.}}
+ & \PadTo{2r × \text{marginal utility of } v}
+ {\text{etc.}\ \makebox[0pt][l]{\text{(compare \Pageref{56})}}}
+\end{align*}
+
+We shall make it a convention henceforth to use
+Roman capitals $A$,~$X$, $W$,~etc., to signify commodities,
+italic minuscules $a$,~$x$, $w$,~etc., to signify units of these
+commodities (generally ``small'' units in the sense explained),
+and italic capitals, \Person{A}, \Person{B}, etc., to signify persons.
+Thus we shall speak of the marginal \emph{usefulness} or \emph{effectiveness}
+of $A$,~$W$,~etc., and the marginal \emph{utility} or \emph{effect} of
+$a$,~$w$,~etc.
+%% -----File: 065.png---Folio 46-------
+
+What precise interpretation we are to give to our
+``units of satisfaction'' or ``utility'' measured on the
+axis of~$y$ is another matter, the consideration of which
+must be reserved for a later stage of our inquiry (see
+pp.~\Pageref[]{52},~\Pageref[]{78}).
+
+\begin{Remark}
+Jevons uses the terms ``total utility'' and ``final degree of
+utility,'' meaning by the latter what I have termed ``marginal
+usefulness'' or ``marginal effectiveness.'' His terminology
+hardly admits of sufficient distinction between ``marginal
+effectiveness,'' \ie~the \emph{rate} per unit at which the commodity is
+satisfying desire, and the ``marginal effect'' of a unit of the
+commodity, \ie~the actual result which it produces when
+applied at the margin. I think this has sometimes confused
+his readers, and I hope that my attempt to preserve the distinction
+will not be found vexatious. Note that the curves
+are always curves of quantity-and-marginal-usefulness, but
+that we can read them with more or less accuracy according
+to the smallness of the supposed increment into curves of
+quantity-and-marginal-utility for small increments.\Pagelabel{46}%
+\end{Remark}
+
+If the reader has now gained a precise idea of the
+total utility or effect and the marginal usefulness of
+commodities, he will see without difficulty that when
+we take a broad general view of life we are chiefly
+concerned with those commodities the total utility of
+which (or their total effect in securing comfort, giving
+pleasure, averting suffering, etc.)\ is high. In considering
+from a general point of view our own material
+welfare or that of a nation, our first inquiries will
+concern the necessaries of life, food, water, clothing,
+shelter, fuel. For these are the things a moderate
+supply of which has the highest total utility. The
+sum of advantages we derive from them collectively
+is, indeed, no other than the advantage of the life they
+support. This is what economists have in view when
+they speak of the ``value in use'' of such a commodity
+as water, and say that nothing is more ``useful'' than
+it. They mean that the total advantage derived from
+%% -----File: 066.p n g----------
+%[Blank Page]
+%% -----File: 067.p n g----------
+\begin{figure}[p]
+\Pagelabel{47}%
+\begin{center}
+ \Fig{10}
+ \Input[4.5in]{067a}
+ \vfil
+%[** TN: Book's graph of 30/(15 + x) - 1 not perfectly accurate]
+ \Fig{11}
+ \Input[3.75in]{067b}
+\end{center}
+\end{figure}
+%To face page 47.
+%% -----File: 068.png---Folio 47-------
+even a small supply of water, the total difference
+\index{Water}%
+between a little water and no water, is enormously
+great. The graphical expression of this would be a
+curve (connecting the total utility of water with its
+quantity) which would rise rapidly and to a great height.
+
+But if it is obvious that when we look upon life as
+a whole, and in the abstract, we are chiefly concerned
+with total utilities, and ask what are the commodities
+we could least afford to dispense with altogether, it is
+equally obvious that in detail and in concrete practice
+we are chiefly concerned not with the total utility but
+the marginal usefulness of things, or rather, their marginal
+utility; and we ask, not what is my whole stock
+of such a commodity worth to me, but how much would
+a little \emph{more} of it \emph{add} to my satisfaction or a little less
+of it detract therefrom. For instance, we do not ask,
+What is the total advantage I derive from all the water
+I can command, but what additional advantage should I
+derive from the extra supply of water for a bath-room,
+\index{Bath-room@{\textsc{Bath-room}}}%
+or for a garden hose? Materfamilias does not ask
+\index{Garden-hose}%
+what advantage she derives from having a kitchen fire,
+\index{Kitchen@{\textsc{Kitchen Fire}}}%
+but she asks, what additional advantage she would
+derive by keeping up her kitchen fire after dinner, by
+heating the oven every day, or by always letting the
+\index{Fire@{Fire in ``practising'' room}}%
+girls have a fire in the room when they are ``practising.''
+Or inversely, we do not ask what disadvantage we
+should incur by ceasing to burn coal, but what disadvantage
+\index{Coal}%
+we should incur by letting our fires go down
+earlier in the day, or having fewer of them. And note
+that this inquiry as to marginal usefulness of a commodity
+is made on its own merits, and wholly without
+reference to the total utilities of the articles in question.
+The fact that I should be much worse off without
+clothes than without books does not make me spend
+fifteen shillings on a new waistcoat instead of on
+\index{Waistcoat@{\textsc{Waistcoat}}}%
+Rossetti's works, if I think that the latter will \emph{add} more
+\index{Rossetti's Works}%
+to my comfort and enjoyment than the former. For
+$f(\text{clothes})$ may be as much bigger than $\phi(\text{books})$ as it
+%% -----File: 069.png---Folio 48-------
+likes, but if $f'(\text{clothes})$ is smaller than~$\phi'(\text{books})$ I shall
+spend the money on the books. So much is this the
+case that we habitually lose sight of the connection
+between $\phi'(\text{books})$ and~$\phi(\text{books})$, between $f'(\text{clothes})$
+and~$f(\text{clothes})$, and do not think, for instance, of
+$\phi'(\text{books})$ as marking the rate at which additional books
+increase the gratification \emph{we derive from books}, but simply
+as marking the rate at which they increase our gratification
+in general.
+
+\Pagelabel{48}%
+Before developing certain consequences of the principles
+we have been examining, let us try to get a
+better representation of our supposed economic functions
+than is supplied by the diagram of a projected body.
+It will be remembered that we saw reason to think
+that a large class of economic functions, representing
+total utilities, would bear an analogy to our \Figref{1} in
+so far as they would first increase and then decrease
+as the variable (\ie~the supply of the commodity)
+increased. But it is highly improbable that any
+economic curve would increase and decrease in the
+symmetrical manner there represented. It is not
+likely, for instance, that the inconvenience of having a
+unit too much of a commodity would be exactly equivalent
+to the inconvenience of having a unit too little.
+As a rule it would be decidedly less. Our economic
+functions, then, will, in many instances, rise more rapidly
+than they fall. The connection of such a function and
+its variable is represented by the upper curve on
+\Figref{10},\footnote
+ {The conditions stated in the text will be complied with by a
+ function of the form $a \log_e {(x + b)} - \log b - x$; and there are some
+ theoretical reasons for thinking that such a function may be a fair approximation
+ to some classes of actual economic functions. The
+ upper curve in \Figref{\DPtypo{9}{10}} is drawn to the formula $y=11 \log_e{(x+1)}-x$.}
+which rises rapidly at first, then rises slowly,
+and then falls more slowly still. Household linen
+\index{Linen}%
+might give a curve something of this character. It is
+not exactly a necessary of life, but the sum of advantages
+conferred by even a small stock is great. The
+rate at which additions to the stock add to its total
+%% -----File: 070.png---Folio 49-------
+utility is at first rapid, but it declines pretty quickly.
+At last we should have as much as we wanted and
+should find it positively inconvenient to stow away any
+more. The excess, however, would have to be very
+great indeed in order to reduce us to a condition as
+deplorable as if we had no linen at all. By way of
+practice in interpreting economic curves, let us suppose
+the unit of household linen, measured along the base
+line, to be such an amount as might be purchased for~£3.
+The curve would then represent the following
+case, which might well be that of a young housekeeper
+\index{Housekeeper}%
+with a four or five roomed cottage, and not much
+space for storage: Household linen (sheets, tablecloths,
+towels, etc.)\ to the amount of some £6~or~£10 worth
+($x = 2$ or~$3\frac{1}{3}$) is little short of a necessity. After this
+additions to the stock, though very acceptable, are not
+so urgently needed, and when the stock has reached
+£18~or~£20 worth ($x = 6$ or~$6\frac{2}{3}$) our housekeeper will
+consider herself very well supplied, and will scarcely
+desire more. Still, if she could get it for nothing, she
+would be glad to find room for it up to, say, £30~worth
+($x = 10$). If after this any one should offer her a present
+of more she would prefer to find a polite excuse for not
+accepting it, but would not be much troubled if she had to
+take it, unless the amount were very large;\footnote
+ {We are supposing throughout that the conditions exclude sale or
+ barter of the unvalued part of the stock.}
+but when
+the total stock had reached, say,~£45 ($x = 15$), the inconvenience
+would become serious, and our heroine, on the
+whole, would be nearly as hard put to it by having £15~worth
+too much as she would have been by having £12~worth
+too little. If her stock were still increased till
+it reached £60~worth ($x = 20$) she would be as badly
+off as if she had only £11~:~8s.\ worth ($x = 3\frac{4}{5}$). At this
+point our ``epic of the hearth'' breaks off.
+
+We may, of course, apply to this curve the process with
+which we are already familiar, and may find the derived
+function which represents the marginal effectiveness or
+%% -----File: 071.png---Folio 50-------
+usefulness of linen, that is to say, the rate at which
+increments of linen are increasing the sum of advantages
+derived from it. This marginal effectiveness or
+usefulness of linen is set forth on the higher curve in
+\Figref{11};\footnote
+ {Its formula is $\dfrac{11}{x + 1} - 1$.}
+on which may be read the facts already
+elaborated in connection with the curve on \Figref{10},
+the only difference being that the specific increase
+between any values of~$x$ is more easily read on \Figref{10},
+and the \emph{rate} of increase at any point more easily read
+on \Figref{11}.
+
+\Pagelabel{50}%
+An analogous pair of curves, with other constants,\footnote
+ {See \Pageref{9}.}
+may be found in the lower lines in Figs.\ \Figref[]{10}~and~\Figref[]{11}.\footnote
+ {They are drawn to the formulæ $y = 30 \log_e (x + 15) - \log_e 15 - x$
+ and $y = \dfrac{30}{x + 15} - 1$ respectively.}
+They might represent respectively the total utility and
+the marginal usefulness of china, for example. In \Figref{10}
+\index{China}%
+the lower curve does not rise so rapidly or so high as
+the other. That is to say, we suppose the total advantage
+derived from as much china as one would care to
+have to be far less than that derived from a similarly
+full supply of household linen. To be totally deprived
+of china (not including coarse crockery in the term)
+would be a less privation than to be totally deprived
+of linen. But we also observe that at a certain point,
+when the curve of linen is rising very slowly, the curve
+of china is rising rather more rapidly. That is to say,
+if our supplies of both linen and china increase \textit{pari
+passu}, unit for unit (£3~worth is the unit we have supposed),
+then there comes a point at which increments of
+china would add to our enjoyment at a greater rate than
+similar increments of linen, although in the mass the
+linen has done much more to make us comfortable than
+the china.
+
+On the curves of \Figref{11} this point is indicated by
+the point at which the curve of the marginal usefulness
+%% -----File: 072.png---Folio 51-------
+of china crosses, and thenceforth runs above, the curve
+of the marginal usefulness of linen.
+
+Now if I possess a certain stock of linen and a
+certain stock of china, and am in doubt as to the
+use to make of an opportunity which presents itself
+for adding in certain proportions to either or both,
+how will the problem present itself to me? I shall
+not concern myself at all with the total utilities,
+but shall simply ask, ``Will the quantity of linen or the
+quantity of china I can now secure \emph{add} most to my
+satisfaction.'' The total gratification I derive from the
+two articles together is made up of their two total utilities
+(represented by two straight lines, viz.\ the vertical intercepts
+made by the two curves on \Figref{10}), and it is
+indifferent to me whether I increase the one already
+greatest or the other, as long as the increase is the
+the same. I therefore ask not which curve is the \emph{highest},
+but which is the \emph{steepest} at the points I have reached on
+them respectively, or since the curves on \Figref{11} represent
+the steepness of those on \Figref{10}, I ask which of
+these is highest. In other words, I examine the~$f'(x)$'s,
+not the~$f(x)$'s; I compare the marginal usefulness and
+not the total utilities of the two commodities. If
+the choice is between one small unit of china and one
+similar unit of linen, I shall ask ``Which of the two has
+the higher marginal utility.'' If my stock of both is
+low, the answer will be ``linen.'' If my stock of both is
+high, it will be ``china.'' If, on the other hand, the
+choice is between one small unit of china and \emph{two} similar
+units of linen, the question will be ``Is the marginal
+effectiveness of china \emph{twice} as great as that of linen,'' if
+not I shall choose the linen, since double the amount at
+anything more than half the effectiveness gives a balance
+of effect over what the other alternative would yield.
+If it seems difficult to imagine the mental process by
+which one thing shall be pronounced exactly \emph{twice} as
+useful as another, we may express the same thing in
+other terms by asking whether half a small unit of china
+%% -----File: 073.png---Folio 52-------
+is as useful to us (or is worth as much to us) as one
+small unit of linen, thus transferring the inequality from
+the utilities to the quantities, and the equality from the
+quantities to the utilities.\footnote
+ {Observe that this transfer can only be made in the case of \emph{small}
+ units, for it assumes that half a unit of china is half as useful as a
+ whole unit, which implies that the marginal usefulness of china
+ remains the same throughout the unit.}
+
+\Pagelabel{52}%
+Such considerations as these spontaneously solve the
+problem that suggested itself at the threshold of our
+inquiries (\Pageref{15}) as to the theoretical possibility of fixing
+a unit of utility or satisfaction, and so theoretically
+constructing economic curves. We now see clearly
+enough that though our psychological arithmetic is so
+little developed that the simplest sums in hedonistic
+multiplication or division seem impossible and even
+absurd, yet, as a matter of fact, we are constantly comparing
+and weighing against each other the most heterogeneous
+satisfactions and determining which is the
+greater. The enjoyment of fresh air and friendship, of
+\index{Air, fresh}%
+\index{Friendship}%
+fresh eggs and opportunities of study, all in definite
+\index{Eggs@{\textsc{Eggs}, fresh}}%
+quantities, are weighed against each other when we
+canvass the advantages of residence in London within
+reach of our friends and the British Museum and residence
+\index{Museum, British}%
+in the country with fresh air and fresh eggs.
+Nay, we may even regard space and time as commodities
+each with its varying marginal usefulness. This year I
+eagerly accept a present of books which will occupy a
+\index{Books}%
+great deal of space in my house, but will save me an
+occasional journey to the library; for the marginal
+usefulness of my space and of my time are such that I
+find an advantage in losing space and gaining time
+under given conditions of exchange. Next year my
+space is more contracted, and its marginal usefulness is
+therefore higher; so I decline a similar present, preferring
+the occasional loss of half an hour to the permanent
+cramping of my movements in my own study.
+
+Thus we see that the most absolutely heterogeneous
+%% -----File: 074.png---Folio 53-------
+satisfactions are capable of being practically equated
+against one another, and therefore may be regarded as
+theoretically \emph{reducible to a common measure}, and consequently
+capable of being measured off in lengths, and
+connected by a curve with the lengths representing the
+quantities of commodity to which they correspond.
+We might, for instance, take the effort of doing a given
+amount of work as the standard unit by which to estimate
+the magnitude of satisfaction. Hence the truth of
+the remark, ``Pleasures cannot be measured in feet, and
+they cannot be measured in pounds; but they can be
+measured in foot-pounds'' (Launhardt). If I only had
+\index{Foot-tons}%
+one ton of coal per month, how much lifting work should
+\index{Coal}%
+I be willing to do for a hundredweight of coal? If I
+had two tons a month, how much lifting work would
+I then do for a hundredweight? Definite answers to
+these two questions and other similar ones are conceivable;
+and they would furnish material for a curve
+on which the utility of one, two, three,~etc.\ hundredweight
+of coal per month would be estimated in foot-pounds.
+In academical circles it is not unusual to take an hour of
+correcting examination papers as the standard measure
+\index{Examination papers}%
+of pleasures and pains. A pleasure to secure which a
+man would be willing to correct examination papers for
+six hours (choosing his time and not necessarily working
+continuously) must be regarded as six times as great
+as one for which he would only correct papers for an
+hour. If we wished to reduce satisfactions so estimated
+to the foot-pound standard, we should only have to
+ascertain in the case of each of the university dignitaries
+in question how many foot-pounds of heaving work he
+would undertake in order to escape an hour's work at
+the examination mill. Obviously this change of measure
+would not affect the \emph{relative} magnitudes of the satisfactions
+already estimated on the other scale. It does not,
+then, matter what we suppose the standard unit of satisfaction
+to be, provided we retain it unchanged throughout
+any set of investigations.
+%% -----File: 075.png---Folio 54-------
+
+\begin{Remark}
+It should be noted that to be theoretically accurate we
+must not suppose the quantity of work offered for the same
+quantity of the commodity to change over different parts of
+the curve, but rather the quantity of the commodity for
+which the same fixed quantity of work is offered. For if
+we change the quantity of work, we thereby generally
+change its hedonistic value per unit also, inasmuch as $400$~foot-tons
+\index{Foot-tons}%
+of work, for instance, would generally be more than
+twice as irksome as $200$~foot-tons.
+
+In working out an imaginary example, however, we will
+ignore this fact, and will suppose the hedonistic value of $100$~foot-tons
+to be constant. Let us, then, suppose that a householder
+would be willing to do $3300$ foot-tons of work\footnote
+ {An ordinary day's work is reckoned at $300$~foot-tons; a dock
+ labourer does~$325$ (Mulhall).}
+for a
+certain amount of linen, if he could not get it any other way.
+\index{Linen}%
+We will reckon that amount of linen the unit, and calling~$x$
+the amount of linen and $y$ its total utility, we shall have for
+$x=1$ $y=3300$, or allowing $500$~foot-tons to the unit of~$y$,
+$x=1$ $y=6.6$. Now suppose that having secured one unit,
+our householder would be willing to do $1750$ foot-tons of
+work for a second unit, but not more. This would be represented
+on our scale by~$3.5$, which, added to the previous~$6.6$,
+would give $y=10.1$ for~$x=2$. For yet another unit of linen,
+perhaps no more than $1125$ foot-tons would be offered, represented
+by~$2.2$ on our scale, or $y=12.3$ for~$x=3$, etc. On comparing
+these suppositions with \Figref{10} (\Pageref{47}), it will be found
+that this case would be graphically represented by the upper
+curve of that figure. It will be seen that though we have
+imagined an ideally perfect and exact power of estimating
+what one would be willing to do under given circumstances
+in order to secure a certain object of desire, yet there is
+nothing theoretically absurd in the imaginary process; so
+that the construction of economic curves may henceforth be
+regarded as theoretically possible.
+
+The reader may find it interesting to attempt to construct
+the economic curves that depict the history of some of his
+own wants. Taking some such article as coffee or tobacco,
+let him ask himself how much work he would do for a single
+cup or pipe per week or per day sooner than go entirely
+%% -----File: 076.png---Folio 55-------
+without, how much for a second, etc., and dotting down
+the results, see whether they seem to follow any law and
+form any regular curve. If they do not, it probably shows
+that his imagination is not sufficiently vivid and accurate to
+enable him to realise approximately what he would be willing
+to do under varying circumstances. In any case he will
+probably soon convince himself of the perfect theoretical
+legitimacy of thus supposing actual concrete economic curves
+to be constructed. But even if he cannot tell what amount
+of work he would be willing to do under the varying circumstances,
+obviously \emph{there is} a given amount, which, as a matter
+of fact, he would be willing to do under any given circumstances.
+Thus the curve \emph{really exists}, whether he is able to
+trace it or not.\Pagelabel{55}%
+\end{Remark}
+
+We may now return to our curves with a clear conscience,
+knowing that for any object of desire at any
+moment there actually exists a curve (could we but get
+at it) representing the complete history of the varying
+total utility that would accompany the varying quantity
+possessed. The man who knows most nearly what that
+curve is, in each case, has the most powerful and
+accurate economic imagination, and is best able to predict
+what his expenditure, habits of work, etc.\ would
+be under changed circumstances.
+
+We have now actually constructed some hypothetical
+curves (pp.\ \Pageref[]{48}, \Pageref[]{50}), and have shown that there are certain
+properties, easy to represent, which a large class of
+economic curves must have (pp.~\Pageref[]{15},~\Pageref[]{48}); and we have
+further shown that we are practically engaged, from
+day to day, in considering and comparing the marginal
+utilities of units of heterogeneous articles, that is to say,
+in constructing and comparing fragments of economic
+curves.
+
+We have seen, too, that if I had a chance of getting
+more china or more linen I should not consider the total
+utilities of these commodities, but the marginal utilities
+of the respective quantities between which the option
+lay.
+%% -----File: 077.png---Folio 56-------
+
+And so, too, if I had the opportunity of exchanging a
+\Pagelabel{56}%
+given quantity of china for a given quantity of linen, or the
+\index{China}%
+\index{Linen}%
+reverse, I should consider the marginal utilities of those
+quantities. Thus we see that the \emph{equivalence in worth} to
+me of units of two commodities is measured by their marginal,
+not their total, utilities, and in the limit (\Pageref{44}) is
+directly proportional to their marginal effectiveness or usefulness.
+If, for the stocks I possess, the marginal usefulness of
+linen is twice as great as that of china, \ie~if $f'(\text{linen}) = 2\phi'
+(\text{china})$, then I shall be glad to sacrifice small units of china
+in order to secure similar units of linen at anything up to the
+rate of two to one. But this very process, by decreasing my
+stock of china and increasing my stock of linen, will depress
+the marginal usefulness of the latter and increase that of the
+former, so that now we have
+\[
+f'(\text{linen})<2\phi'(\text{china}).
+\]
+If, however,
+\[
+f'(\text{linen})>\phi'(\text{china})
+\]
+is still true, I shall still wish to sacrifice china for the sake
+of linen, unit for unit, until by the action of the same principle
+we have reached the point at which we have
+\[
+f'(\text{linen})=\phi'(\text{china}).
+\]
+After this I shall not be willing to sacrifice china for the
+sake of obtaining linen unless I can obtain a unit of linen by
+foregoing \emph{less} than a unit of china. All this may be represented
+very simply and clearly on our diagrams. Drawing
+out separately, for convenience, the curves given in \Figref{11},
+and making any assumptions we choose as to quantities of
+linen and china possessed, we may read at once (\Figref{12}) the
+\emph{equivalents in worth} (to the possessor) of linen and china. Thus
+if I have eight units of china [$\phi'(\text{china})=.3$] and four units
+of linen [$f'(\text{linen})=1.2$]; then in the limit one small unit
+of linen at the margin is equivalent in worth to four small
+units of china at the margin. If I have seven units of linen
+and two of china, then one small unit of china at the margin is
+equivalent in worth to two small units of linen at the margin.
+
+Hitherto we have spoken of foot-tons, or generally of
+work, merely as a standard by which to measure a man's
+%% -----File: 078.png---Folio 57-------
+estimate of the various objects of his desire; but we
+know, as a matter of fact, that work is often a \emph{means of
+securing} these objects, and it by no means follows that
+\begin{figure}[htbp]
+ \begin{center}
+ \Fig{12}
+ \Input[3.5in]{078a} \\
+ \Input[4.5in]{078b}
+ \end{center}
+\end{figure}
+the precise amount of work a man would be willing to do
+rather than go without a thing is also the precise amount
+of work he will have to do in order to make it. Indeed
+there is no reason in general why a man should have to
+%% -----File: 079.png---Folio 58-------
+do either more or less work for the first unit of a commodity
+with its high utility than for the last with its
+comparatively low utility. The question then arises:
+On what principle will a man distribute his work
+between two objects of desire? In other words, If a
+man can make two different things which he wants, in
+what proportions will he make them?
+
+\Pagelabel{58}%
+We must begin by drawing out the curves of quantity-and-marginal-usefulness
+of the two commodities, and we
+will select as the unit on the axis of~$x$ in each case that
+quantity of the commodity that can be made or got by
+an hour's work. Suppose Robinson Crusoe\footnote
+ {``Political economists have always been addicted to Robinsoniads''
+ (Marx).}
+\index{Robinson Crusoe}%
+\index{Root-digging}%
+\index{Rush-gathering}%
+has provided
+himself with the absolute necessaries of life, but
+finds that he can vary his diet by digging for esculent
+roots, and can add to the comfort and beauty of his hut
+by gathering fresh rushes to strew on the floor two or
+three times a week. Adopting any arbitrary standard
+unit of satisfaction, let us suppose that the marginal
+usefulness of the roots begins at six and would be extinguished
+(for the week, let us say) when eight hours'
+work had been done. That is to say, the quantity
+which Robinson could dig in eight hours would absolutely
+satisfy him for a week, so that he would not care
+for more even if he could get them for nothing. In like
+manner let the marginal usefulness of rushes begin at
+four and be extinguished (for the week) by five hours'
+work; and let the other data be such as are depicted on
+the two curves in \Figref{13}.\footnote
+ {They are drawn to the formulæ---
+ \[
+ y=\frac{24-3x}{4+x} \text{ and } y=\frac{40-8x}{10+7x} \text{ respectively}.
+ \]}
+Now suppose further that
+Robinson can give seven hours a week to the two tasks
+together. How will he distribute his labour between
+them? If he gives four hours' work to digging for roots
+and three to gathering rushes, the marginal usefulness
+of the two articles will be measured by the vertical
+intercepts on $a$~and~$a'$ respectively. Clearly there has
+%% -----File: 080.png---Folio 59-------
+been waste, for the latter portions of the time devoted
+to rush-gathering have been devoted to producing a
+thing less urgently needed than a further supply of roots.
+Again, if six hours be given to digging and one to rush-gathering,
+the marginal usefulness will be measured by
+the vertical intercepts on $b$~and~$b'$, and again there
+has been waste, this time from excessive root digging.
+But if five hours are given to digging for roots and two
+to rush-gathering, the usefulness will be measured
+by the vertical intercepts on $c$~and~$c'$, and there is no
+loss, for obviously any labour subtracted from either
+\begin{figure}[hbt]
+ \begin{center}
+ \Fig{13}
+ \Input{080a}
+ \end{center}
+\end{figure}
+occupation and added to the other would result in the
+sacrifice of a greater satisfaction than the one it secured.
+
+It is obvious that for any given time, such as three
+hours or two hours, there is a similar ideal distribution
+between the two occupations which secures the maximum
+result in gratification of desires; and the method
+of distribution may be represented by a very simple and
+beautiful graphic device, exemplified in \Figref{14}.
+
+First draw the two curves one within the other,\footnote
+ {If the curves should cross, as in \Figref{10}, the principle is entirely
+ unaffected.}
+then add them together sideways, so as to make a
+%% -----File: 081.png---Folio 60-------
+third curve (dotted in figure), after the following fashion:
+For $y=1$ the corresponding value of~$x$ for the inner
+curve is~$2$, and that for the outer curve~$5$. Adding
+these two together we obtain~$7$; and for our new curve
+we shall have
+\[
+y=1 \qquad x=7.
+\]
+Every other point of the new curve may be found in
+the same way, and we shall then have a dotted curve such
+that if any line~$pp_{1}p_{2}p_{3}$ be drawn parallel to the axis
+of~$x$, and cutting the three curves, the line~$p_{2}p_{3}$ shall
+be equal to the line~$pp_{1}$. We shall then have $pp_{3}=pp_{1}+pp_{2}$;\footnote
+ {If the curves are drawn to the formulæ $y=f(x)$ and $y=\phi(x)$ we
+ may express them also as $x=f^{-1}(y)$ and $x=\phi^{-1}(y)$. It is obvious
+ that our new curve will then be $x=f'^{-1}(y)+\phi^{-1}(y)$, which in this
+ case will give $x=\dfrac{312+146y-38y^{2}}{24+29y+7y^{2}}$ to which formula the curve is drawn
+ between the values $y=4$ and $y=0$.}
+and if we desire to see how Robinson will
+\begin{figure}[hbt]
+\Pagelabel{60}%
+ \begin{center}
+ \Fig{14}
+ \Input[4in]{081a}
+ \end{center}
+\end{figure}
+apportion any quantity of time~$Oq_{3}$ between the two
+\index{Time, distribution of}%
+occupations we shall simply have to erect a perpendicular
+at~$q_{3}$, and where it cuts the dotted curve draw a parallel
+to the axis of~$x$, cutting the other curves at $p_{2}$~and~$p_{1}$.
+We shall then have divided the whole time of~$Oq_{3}$ into
+%% -----File: 082.png---Folio 61-------
+two parts, $Oq_{1}$~and~$Oq_{2}$ ($=pp_{1}$~and~$pp_{2}$), such that if $Oq_{1}$
+is devoted to the one occupation and $Oq_{2}$ to the other
+the maximum satisfaction will be secured.
+
+If we take $Oq_{3}=7$ we shall find we get $Oq_{1}=2$, $Oq_{2}=5$,
+as above.\footnote
+ {Note that when the hours of work have been distributed between
+ the two occupations they pass into concrete results in the shape of
+ commodity. Thus, strictly speaking, we measure \emph{hours} along the axis
+ of~$x$ when dealing with the dotted curve, but \emph{hour-results} in commodity
+ when we come to the other curves. If $Oq_{3}=7$, then, whereas
+ $Oq_{3}=7 \text{\emph{ hours}}$, $Oq_{1}$~and~$Oq_{2}$ represent respectively $2$~and~$5$~\emph{units of
+ commodity}, each unit being the result of an hour's work.}
+
+\begin{Remark}
+This is a principle of the utmost importance, applicable to
+a great variety of problems, such as the most advantageous
+distribution of a given quantity of any commodity between
+two or more different uses. It is particularly important in
+the pure theory of the currency. It need hardly be pointed
+out that these diagrams do not pretend to assist any one in
+practically determining how to divide his time. They are
+merely intended to throw light on the process by which he
+effects the distribution. In any concrete investigation we
+should have direct access to the result but not to the conditions
+of want and estimated satisfaction which determine
+it; so that the actual distributions would be our data and
+the preceding conditions of desire, etc.~our quæsita.\Pagelabel{61}%
+\end{Remark}
+
+We have now reached a stage of our investigations
+at which it will be useful to recapitulate and expand
+our conclusions as to the marginal usefulness of commodities.
+In doing so we must bear in mind especially
+what has been said as to the nature of our diagrammatic
+curves (\Pageref{12}). The law of a curve is the law of the
+connection between the corresponding pairs of values of
+two varying quantities, one of which is a function of the
+other. The curve on \Figref{7}, for instance, is not the
+``curve of the heat produced by given quantities of
+carbon in a furnace,'' nor yet the ``curve of the quantities
+of carbon which effect given degrees of heat in a
+furnace,'' but ``the curve of the connection between
+varying quantities of carbon burned and varying degrees
+%% -----File: 083.png---Folio 62-------
+of heat produced,'' each of which magnitudes severally is
+always measured by a vertical or horizontal straight line.
+
+\Pagelabel{62}%
+In like manner, the first curve in \Figref{13} is not ``the
+curve of the varying marginal usefulness of esculent
+roots to Robinson at given margins,'' nor ``the curve
+of the varying quantities of esculent roots which
+correspond to given marginal usefulnesses,'' but ``the
+curve of the connection between the quantity of roots
+Robinson possesses and the marginal usefulness of roots
+to him.''
+
+When this fact is fully grasped it will become obvious
+that there are only two things which can conceivably
+alter the marginal usefulness of a commodity to me:
+either the quantity I possess must change, or the law
+must change which connects that quantity and the
+marginal usefulness of the commodity. If \emph{both} these
+remain the same, obviously the marginal utility must
+remain the same. Or, in symbols, if $y=f(x)$\footnote
+ {Note that the symbol $f(x)$ is perfectly general, and signifies any
+ kind of function of~$x$. It therefore includes and may properly represent
+ the class of functions we have hitherto represented by letters with
+ a dash, $f'(x)$, $\phi'(x)$, etc.}
+the value
+of~$y$ can only be altered by changing the value of~$x$, or
+by changing the function signified by~$f$. The necessity
+for insisting upon this axiomatic truth will become
+evident as we proceed. Meanwhile,
+\begin{center}
+\begin{tabular}{l}
+One charge, one sovereign charge I press,\\
+And stamp it with reiterate stress,
+\end{tabular}
+\end{center}
+viz.~to bear in mind, so as to recognise it under all disguises,
+the fundamental and self-evident truth, that the
+marginal usefulness of a commodity always depends
+upon the quantity of the commodity possessed [$y=f(x)$],
+and that if the \emph{nature of the dependence} [the form of
+the function~$f$] and the quantity of the commodity
+possessed [the value of~$x$] remain the same, then the
+marginal usefulness of the commodity [the value of~$y$]
+likewise remains unchanged. Whatever changes it must
+%% -----File: 084.png---Folio 63-------
+do so either by changing the nature of its dependence
+upon the quantity possessed or by changing that quantity
+itself; nothing which cannot change either of
+these can change the marginal usefulness; and whatever
+changes the marginal usefulness does so by means
+of changing one of these. The length of the vertical
+intercept cannot change unless \emph{either} the course of the
+curve changes \emph{or} the position of the bearer is shifted.
+
+These remarks, of course, apply to total utility as
+well as to marginal usefulness.
+
+Now, hitherto we have considered changes in the
+quantity possessed only; and have supposed the nature
+of the connection between the quantity and the total
+utility or marginal usefulness to remain constant, \ie~we
+have shifted our bearers, but have supposed our
+curves to remain fixed in their forms. But obviously
+\Pagelabel{63}%
+in practical life it is quite as important to consider the
+shifting of the curve as the shifting of the bearer and
+the quantity-index. To revert to our first example.
+The law that connects the quantity of coal I burn with
+\index{Coal}%
+the sum of advantages I derive from its consumption is
+not the same in winter and in summer, or in the house
+I now live in and the house I left ten years ago. And
+in other cases, where there is a less obvious external
+cause of change, a man's tastes and desires are nevertheless
+perpetually varying. The state of his health, the
+state of his affections, the nature of his studies, and a
+thousand other causes change the amount of enjoyment
+or advantage he can derive from a given quantity of a
+given commodity; and if we wish to have an adequate
+conception of the real economic conditions of life we
+must not only imagine what we have called the ``bearer,''
+that carries the vertical or quantity-index moving freely
+along the axis of~$x$, but we must also imagine the form
+of the curve to be perpetually flowing and changing.
+
+\begin{Remark}
+The obvious impossibility of adequately representing on
+diagrams the flux and change of the curves presents a great
+%% -----File: 085.png---Folio 64-------
+difficulty to the demonstrator. Some attempt will here be
+made to convey to the reader an elementary conception of
+the nature of these changes.
+
+We will take the simplest case, that of the straight line,
+as an illustration. Suppose (a not very probable supposition)
+that the quantity-and-marginal-usefulness curve of a certain
+commodity for a certain man at a certain time is represented
+by
+\[
+y=12-2x.
+\]
+By giving successive values to~$x$ we shall find the corresponding
+\begin{figure}[hbt]
+ \begin{center}
+ \Fig{15}
+ \Input{085a}
+ \end{center}
+\end{figure}
+values of~$y$, and shall see that the curve is the
+highest of the straight lines represented on \Figref{15}~(\textit{a}). Now
+suppose that, owing to some cause or other, the man comes
+to need the commodity less, so that its marginal utility,
+while still decreasing by the same law as before, shall now
+begin at ten instead of twelve. The formula of the curve
+will then be $y=10-2x$, and the curve will be the second
+straight line in \Figref{15}~(\textit{a}). By taking the formula, $y=8-2x$,
+we may obtain yet another line, and so on indefinitely.
+%% -----File: 086.png---Folio 65-------
+
+What we have now been doing may be represented by the
+formula
+\[
+y=f(z,x)=z-2x,
+\]
+where $y$ is a function of two variables, namely $z$~and~$x$, and
+we proceed by giving $z$ successive values, and then for each
+several value of~$z$ giving $x$ successive values. If instead of
+taking the values $12$, $10$, $8$ for~$z$, we suppose it to pass continuously
+through all values, it is obvious that we should
+have a system of parallel straight lines, one of which would
+pass through any given point on the axis of $x$ or~$y$.
+
+But we have supposed the modifications in the position of
+the line always to be of one perfectly simple character;
+whereas it is easy to imagine that the man whose wants we
+are considering might find that for some reason he needed a
+smaller and smaller quantity of the commodity in question
+completely to satisfy his wants, whereas his initial desire
+remained as keen as ever. Such a case would be represented
+by
+\[
+y=f(z,x)=12-zx,
+\]
+in which we may give $z$ the values of $2$, $3$, $4$, $6$ successively,
+and then trace the lines in \Figref{15}~(\textit{b}) by making $x$~pass
+through all values from $0$ to~$\dfrac{12}{z}$, after which the values of~$y$
+would be negative.
+
+But again we might suppose that while the quantity of
+the commodity needed completely to sate a man remained
+the same, the eagerness of his initial desire might abate.
+This case might be represented by
+\[
+y=f(z,x)=z-\frac{z}{6}x,
+\]
+where by making $z$ successively equal to $12$, $10$, $8$, $6$,~etc.,
+we shall get a system of lines such as those in \Figref{15}~(\textit{c}).
+
+This is very far from exhausting the different modifications
+our curve might undergo while still remaining a straight
+line. For instance we might have a series of lines, one of
+which should run from $12$ on the axis of~$y$ to $6$ on the axis
+of~$x$, as before, while another ran from $8$ on the axis of~$y$
+to $12$ on the axis of~$x$, and so on. This would indicate that
+two independent causes were at work to modify the man's
+want for the commodity.
+
+Passing on to a case rather less simple, we may take the
+first curve of \Figref{13}, which was drawn to the formula
+\[
+y=f(x)=\frac{24-3x}{4+x},
+\]
+%% -----File: 087.png---Folio 66-------
+and confining ourselves to a single modification, may regard
+it as
+\[
+y=f(z,x)=\frac{24-3x}{z+x},
+\]
+when, by making $z$ successively equal $4$, $6$, $8$, and $12$, we
+shall get the four curves of \Figref{16}.
+
+If we suppose that $z$~and~$x$ are both changing at the same
+time, \ie~that the quantity of the commodity \emph{and} the nature
+of the dependence of its marginal usefulness upon its quantity
+are changing together, then the effect of the two changes
+may be that each will intensify the other, or it may be that
+\begin{figure}[hbt]
+ \begin{center}
+ \Fig{16}
+ \Input[2.5in]{087a}
+ \end{center}
+\end{figure}
+they will counteract each other. Thus in $y=f(z,x)=
+\dfrac{24-3x}{z+x}$, if $x$~is first~$5$ and then~$3$, while $z$ at the same time
+passes from $4$ to~$12$, we shall have for the two values of~$y$
+$\dfrac{24 - 3×5}{4+5}$ and $\dfrac{24 - 3×3}{12+3}$, and in either case $y=1$. This is
+shown on the figure by the lines at $a$~and~$b$.
+
+We must remember, then, that two things, and only two,
+can alter the marginal usefulness of a commodity, viz.\ (i)~a
+change in its quantity and (ii)~a change in the connection
+between its quantity and its marginal usefulness. In the
+diagrams these are represented by (i)~a movement of the
+``bearer'' carrying the vertical to and fro on the base line,
+and (ii)~a change in the form or position of the curve. In
+%% -----File: 088.png---Folio 67-------
+symbols they are represented (i)~by a change in the value of~$x$,
+and (ii)~by a change in the meaning of~$f$. Anything that
+changes the value of~$y$ must do so \emph{by} changing one of these.
+Generally speaking the causes that affect the nature of the
+function (\ie~the shape and position of the curve), so far as
+they lend themselves to investigation, must be studied under
+the ``theory of consumption;'' while an examination of the
+causes which affect the magnitude of~$x$ (\ie~the position of the
+``quantity-index'') will include, together with other things,
+the ``theory of production.''
+\Pagelabel{67}%
+\end{Remark}
+%% -----File: 089.png---Folio 68-------
+
+
+\Chapter[II. Social]{II}
+
+\Pagelabel{68}%
+We have seen that the most varied and heterogeneous
+wants and desires that exist \emph{in one mind} or ``subject''
+may be reduced to a common measure and compared
+one with another; but there is another truth which must
+never be lost sight of on peril of a total misconception of
+all the results we may arrive at in our investigations;
+and that is, that by no possibility can desires or wants,
+even for one and the same thing, which exist \emph{in different
+minds}, be measured against one another or reduced to a
+common measure. If $x$,~$y$, and~$z$ are all of them objects
+\Pagelabel{69}% [** TN: Attempted to locate as closely as possible]
+of desire to~\Person{A}, we can tell by his actions which of them
+he desires most, but if \Person{A},~\Person{B}, and~\Person{C} all desire~$x$ no possible
+process can determine which of them desires it
+most. For any method of investigation is open to the
+fatal objection that it must use as a standard of measurement
+something that may not mean the same in
+the different minds to be compared. Lady Jane Grey
+\index{Lady@{\textsc{Lady Jane Grey}}}%
+studies Plato while her companions ride in Bradgate
+\index{Bradgate Park}%
+\index{Plato}%
+Park, whence we learn that an hour's study was more
+than an equivalent to the ride to Lady Jane and less
+than its equivalent to the others. But who is to tell
+us whether Greek gave \emph{her} more pleasure than hunting
+gave \emph{them}? Lady Jane fancied it did, but she may
+have been mistaken. My account-book, intelligently
+\index{Account-book@{\textsc{Account-book}}}%
+studied, may tell you a good deal as to the equivalence
+of various pleasures and comforts to me, but it can
+establish no kind of equation between the amount of
+pleasure which I derive from a certain article and the
+%% -----File: 090.p n g----------
+%[Blank Page]
+%% -----File: 091.p n g----------
+\begin{figure}[hbtp]
+\Pagelabel{70}% [** TN: Attempted to locate as closely as possible]
+ \begin{center}
+ \Fig{17}
+ \Input{091a}
+ \end{center}
+\end{figure}
+% [To face page 69.]
+%% -----File: 092.png---Folio 69-------
+amount of pleasure you would derive from it. \Person{B}~wears his
+black coats out to the bitter end and goes shabby three
+\index{Coats}%
+months in every year in order to get a few pounds
+worth of books per annum. \Person{A}~would never think of
+\index{Books}%
+doing so---but whether because he values books less or
+a genteel appearance more than~\Person{B} does not appear.
+Nay, it is even possible he values books more, but
+that his sensitiveness in the matter of clothing exceeds
+\Person{B}'s in a still higher degree. \Person{C}~may be willing
+to wait three hours at the door of a theatre to get a
+place, whereas \Person{D} will not wait more than ten minutes;
+but this does not show that \Person{C}~wants to witness the
+representation more than \Person{D}~does; it may be that \Person{D} has
+less physical endurance than~\Person{C}, and would suffer severely
+from the exhaustion of long waiting; or it may be that
+\index{Theatre, waiting}%
+\index{Waiting@{Waiting (at theatre)}}%
+\Person{C}~has nothing particular to do with his time and so
+does not value it as much as \Person{D} does his.
+
+Look at it how we will, then, it is impossible to
+establish any scientific comparison between the wants
+and desires of two or more separate individuals. Yet
+it is obvious that almost the whole field of economic
+investigation is concerned with collective wants and
+desires; and we shall constantly have to speak of the
+relative intensity of the demand for different articles or
+commodities not on the part of this or that individual,
+but on the part of society in general. In like manner
+we shall speak of the marginal usefulness and utility
+of such and such an article, not for the individual but
+for the community at large. What right have we to use
+such language, and what must we take it to mean?
+
+To answer this question satisfactorily we must make
+the relative intensity of the desires and wants of the
+individual our starting-point. Let us suppose that \Person{A}
+possesses stocks of $U$,~$V$, $W$,~$X$, $Y$,~$Z$, the marginal utility
+to him of the customary unit (pound, yard, piece, bushel,
+hundredweight, or whatever it may be) of each of
+these articles being such that, calling a unit of~$U$, $u$,
+a unit of~$V$, $v$,~etc., we shall have $3u$ or $10v$ or $4w$ or
+%% -----File: 093.png---Folio 70-------
+$\dfrac{x}{4}$ or~$\dfrac{3y}{2}$, applied at the margin, just equivalent to~$z$ (\ie~one
+unit of~$Z$) at the margin. Portions of arbitrary
+curves illustrating the supposed cases of $U$,~$X$, and~$Z$
+are given in \Figref{17}~(\Person{A}). The curves represent the marginal
+usefulness per unit of~$U$ as being one-third as great
+as that of~$Z$. That is to say, if $u$ is but a very small
+fraction of \Person{A}'s whole stock of~$U$, then, in the limit, $3u=z$.
+In like manner $\dfrac{x}{4}=z$, in the limit. Now let us take
+another man,~\Person{B}. We may find that he does not possess
+(and possibly is not aware of definitely desiring) any $V$,~$W$,
+or~$Y$ at all; but we will suppose that he possesses
+stocks of $U$,~$X$, and~$Z$. In this case (neglecting the
+practically very important element of friction) we shall
+find that the units of $U$,~$X$, and~$Z$ stand in exactly the
+same \emph{relative} positions for him as they do for~\Person{A}; that is
+to say, we shall find that for~\Person{B}, as for~\Person{A}, $3u$ or~$\dfrac{x}{4}$ is exactly
+equivalent to~$z$. For were it otherwise the conditions
+for a mutually advantageous exchange would
+obviously be present.
+
+Suppose, for instance, we have
+\[
+\frac{x}{3} \text{ equivalent to~$2u$\qquad for~\Person{B}},
+\]
+as represented in Fig~17~(\Person{B}), while
+\[
+\frac{x}{4} \text{ is equivalent to~$3u$\qquad for~\Person{A}},
+\]
+as before. Then, reducing to more convenient forms,\footnote
+ {This process is legitimate if $x$~and~$u$ are ``small'' units of $X$~and~$U$,
+ so that the marginal usefulness of~$U$ remains sensibly constant
+ throughout the consumption of $3u$,~etc.}
+we shall have
+\begin{align*}
+ 6u \text{ equivalent to~$x$} & \qquad \text{for~\Person{B}}, \\
+12u \text{ equivalent to~$x$} & \qquad \text{for~\Person{A}}.
+\end{align*}
+
+\begin{Remark}
+Observe that though we may suppose there will frequently
+be some general similarity of form between the curves that
+%% -----File: 094.png---Folio 71-------
+connect the quantity of~$U$ with its marginal usefulness in
+the cases of \Person{A}~and~\Person{B} respectively, yet we have no right
+whatever to assume any close resemblance between these
+curves.
+\end{Remark}
+
+Now since six units of~$U$ are equivalent to a unit of~$X$
+for~\Person{B}, he will evidently be glad to receive anything
+\emph{more than six} units of~$U$ in exchange for a unit of~$X$;
+whereas \Person{A}~will be glad to give \emph{anything less than twelve}
+units of~$U$ for a unit of~$X$. The precise terms on which
+we may expect the exchange to take place will not be
+investigated here, but it is obvious that there is a wide
+margin for an arrangement by which \Person{A} can give~$U$ in
+exchange for~$X$ from~\Person{B}, to the mutual advantage of the
+two parties. The result of such an exchange will be to
+change the quantities and make the quantity indices
+move in the directions indicated by the arrow heads;
+\Person{A}'s~stock of~$U$ decreasing and his stock of~$X$ increasing,
+while \Person{B}'s~stock of~$U$ increases and his stock of~$X$
+decreases. But this very process tends to bring the
+ratio $\dfrac{\text{marginal usefulness of~$U$}}{\text{marginal usefulness of~$X$}}$ or $\dfrac{\text{marginal utility of~$u$}}{\text{marginal utility of~$x$}}$
+nearer to unity (\ie~increase it) for~\Person{A}, for whom it
+is now~$\frac{1}{12}$, and to remove it farther from unity
+(\ie~decrease it) for~\Person{B}, to whom it is now~$\frac{1}{6}$. This
+is obvious from a glance at the figures or a moment's
+reflection on what they represent. Using $\dfrac{u}{x}$ as a
+symbol of $\dfrac{\text{marginal utility of~$u$}}{\text{marginal utility of~$x$}}$ we may, therefore, say
+that the ratio~$\dfrac{u}{x}$ will increase for~\Person{A}, to whom it is now
+lowest, and decrease for~\Person{B}, to whom it is now highest.
+If this movement continues long enough,\footnote
+ {Compare below, \Pageref{73} and the note.}
+there must
+come a point at which $\dfrac{u}{x}$ will be the same for \Person{A}~and~\Person{B}.
+Now until this point is reached the causes which produce
+%% -----File: 095.png---Folio 72-------
+the motion towards it continue to be operative, for it is
+always possible to imagine a ratio of exchange~$\dfrac{u}{x}$ which
+shall be greater than \Person{A}'s~$\dfrac{u}{x}$ and less than \Person{B}'s~$\dfrac{u}{x}$, and shall
+therefore be advantageous to both. But when \Person{A}'s~$\dfrac{u}{x}$
+and \Person{B}'s~$\dfrac{u}{x}$ have met there will be equilibrium. Hence
+if the \emph{relative} worth, at the margin, of units of any two
+commodities $U$~and~$X$ should not be identical for two
+persons \Person{A}~and~\Person{B}, the conditions of a profitable exchange
+between them exist, and continue to exist, until the
+resultant changes have brought about a state of equilibrium,
+in which the relative worths, at the margin, of
+units of the two commodities are identical for the two
+individuals.
+
+This proposition is of such crucial and fundamental
+importance that we will repeat the demonstration with a
+more sparing use of symbols, and without reference to
+the figures.\Pagelabel{71}% [** TN: Attempted to locate as closely as possible.]
+
+\Person{B}, who is glad to get anything more than~$6u$ for~$x$,
+and \Person{A},~who is glad to give anything short of~$12u$ for~$x$,
+exchange $U$~and~$X$ to their mutual advantage, \Person{B}~getting
+$U$ and giving~$X$, while \Person{A}~gets $X$ and gives~$U$.
+
+But by this very act of exchange \Person{B}'s~stock of~$X$ is
+decreased and his stock of~$U$ increased, and thereby the
+marginal usefulness of~$X$ is raised and that of~$U$ lowered,
+so that \Person{B}~will now find $6u$~less than the equivalent
+of~$x$; or in other words, the interval between the worth
+of a unit of~$X$ and that of a unit of~$U$ is increasing,
+and at the same time \Person{A}'s~stock of~$X$ is increasing and
+his stock of~$U$ diminishing, whereby the marginal usefulness
+of~$U$ increases and that of~$X$ diminishes, so that
+now less than twelve units of~$U$ are needed to make an
+equivalent to one unit of~$X$; or in other words, the
+interval between the worths at the margin of a unit of~$U$
+and a unit of~$X$ is diminishing. To begin with, then,
+%% -----File: 096.png---Folio 73-------
+$u$~and~$x$ differ less in worth, at the margin, to~\Person{B} than
+they do to~\Person{A}, but the difference in worth to~\Person{B} is constantly
+increasing and that to~\Person{A} constantly diminishing
+as the exchange goes on. There must, therefore,
+come a point at which the expanding smaller difference
+and the contracting greater difference will coincide.\footnote
+ {Unless, indeed, the whole stock of \Person{A}'s~$X$ or of \Person{B}'s~$U$ is exhausted
+ before equilibrium is reached. See \Pageref{82}.}
+The conditions for a profitable exchange will then cease
+\Pagelabel{73}%
+to exist; but at the same moment the marginal worths
+of $u$~and~$x$ will come to stand in precisely the same ratio
+for~\Person{A} and for~\Person{B}. Wherever, then, articles possessed in
+common by \Person{A} and~\Person{B} differ in the ratio of their unitary
+marginal utilities as estimated by \Person{A} and~\Person{B}, the conditions
+of a profitable exchange exist, and this exchange itself
+tends to remove the difference which gives rise to it.
+We may take it, then, that in a state of equilibrium the
+ratios of the unitary marginal utilities of any articles, $X$,~$Y$,
+$Z$,~etc., possessed in common by \Person{A},~\Person{B}, \Person{C},~etc., taken
+two by two, viz.\ $x : y$, $x : z$, $y : z$,~etc., \emph{are severally identical
+for all the possessors}. Any departure from this state of
+equilibrium tends to correct itself by giving rise to
+exchanges that restore the equilibrium on the same or
+another basis.
+
+To give precision and firmness to this conception, we
+may work it out a little farther. Let us call such a
+table as the one given on pp.~\Pageref[]{69},~\Pageref[]{70} a ``scale of the relative
+unitary marginal utilities to~\Person{A} of the commodities he
+possesses,'' or briefly, ``\Person{A}'s~relative scale.'' How shall
+we bring the relative scales of~\Person{B}, \Person{C},~etc.\ into the form
+most convenient for comparison with~\Person{A}'s? In \Person{A}'s~relative
+scale the unitary marginal utilities of all the articles,
+that is to say, $u$,~$v$, $w$,~$x$, $y$,~$z$, were expressed in terms of
+the unitary marginal utility of~$Z$, that is to say,~$z$. And
+in like manner \Person{B}'s~relative scale expressed $u$~and~$x$ in terms
+of~$z$. But now suppose \Person{C}~possesses $S$,~$T$, $V$,~$X$, and~$Y$,
+but no $U$,~$W$, or~$Z$. It is obvious that, in so far as he
+possesses the same commodities as \Person{A}~and~\Person{B}, his relative
+%% -----File: 097.png---Folio 74-------
+scale, when there is equilibrium, must coincide with
+theirs. But when we attempt to draw out that scale by
+direct reference to \Person{B}'s~wants, we find ourselves unable
+to express the unitary marginal utilities of his commodities
+in terms of the unitary marginal utility of~$Z$, for
+since he has no~$Z$ (and perhaps does not want any) we
+cannot ask him to estimate its marginal usefulness to
+him.\footnote
+ {We shall see presently (\Pageref{82}) that the estimate must positively
+ be made in terms of a commodity possessed, and that even if \Person{B} wants~$Z$,
+ and knows exactly how much he wants a first unit of it, that want
+ will not serve as the standard unit of desire unless he actually possesses
+ some quantity of~$Z$.}
+But it is obvious that \Person{A}'s~scale fixes the relative
+marginal utilities of the units $v$,~$x$, and~$y$ in terms
+of each other as well as in terms of~$z$, and unless they
+are the same to~\Person{C} that they are to~\Person{A} the conditions
+of an advantageous exchange between \Person{A}~and~\Person{C} will
+arise and will continue till $v$,~$x$,~$y$ coincide on the
+two relative scales. In like manner \Person{B}'s~scale expresses
+the marginal utilities of the units $s$~and~$t$ in terms
+of each other, and \Person{C}'s~scale must, when there is
+equilibrium, coincide with~\Person{B}'s in respect of these two
+units. Now, even though \Person{C} not only possesses no~$Z$,
+but does not even desire any, there is nothing to prevent
+him, for convenience of transactions with \Person{A}~and~\Person{B},
+from estimating $s$,~$t$, $v$,~$x$, and~$y$ not in terms of each
+other, but in terms of~$z$, placing it hypothetically in his
+own scale in the same place relatively to the other units
+which it occupies for \Person{A}~and~\Person{B}. Thus he may express
+his desire for the commodities he has or wants to have,
+in terms of a desire to which he is himself a stranger,
+but the relative strength of which in other men's minds
+he has been able to ascertain.
+
+Lastly, if \Person{C} knows that he can at any time get $S$~and~$T$
+from~\Person{B}, and $V$,~$X$ and~$Y$ from~\Person{A}, in exchange for~$Z$,
+on definite terms of exchange, then, although he may
+not want~$Z$ for himself, and may have no possible use
+for it, yet he will be glad to get it, though only as representing
+the things he does want, and for which he
+%% -----File: 098.png---Folio 75-------
+will immediately exchange it, unless indeed he finds it
+more convenient to keep a stock of~$Z$ on hand ready to
+exchange for~$S$, $T$,~etc.\ as he wants them for actual
+consumption than to keep those commodities themselves
+in any large quantities.
+
+All this is exactly what really takes place. Gold
+(in England) is the~$Z$ adopted for purposes of reference
+(and also, though less exclusively, as a vehicle of
+exchange). Gold is valuable for many purposes in
+the arts and sciences, and, therefore, there are always
+a number of persons who want gold to use, and
+will give other things in exchange for it. Most of
+us possess, and use in a very direct manner, a small
+quantity of gold which we could not dispense with
+without great immediate suffering and the risk of serious
+ultimate detriment to our health, viz., the gold stoppings
+\index{Gold stoppings in teeth}%
+of some of our teeth. There is a constant demand for
+gold for this use. Lettering and ornamenting the backs
+of books is another use of gold in which vast numbers
+of persons have an immediate interest as consumers.
+Plate and ornaments are a more obvious if not more
+important means of employing gold for the direct
+gratification of human desires or supply of human wants.
+In short, there are a great number of well-known and
+easily accessible persons who, for one purpose or another
+of direct use or enjoyment, desire gold, and since these
+persons desire many other things also, their wants
+furnish a scale on which the unitary marginal utilities
+of a great variety of articles are registered in terms of
+the unitary marginal utility of gold, and if the relative
+scales of any two of these gold-and-other-commodities-desiring
+individuals differ, then exchanges will be made
+until they coincide. Other persons who have no direct
+desire or use for gold desire a number of the other commodities
+which find a place in the scale of the gold-desiring
+persons, and can, therefore, compare the
+relative positions they occupy in their own scale of
+desires with that which is assigned them in the scale of
+%% -----File: 099.png---Folio 76-------
+the gold-desiring people, and if these relative positions
+vary exchanges may advantageously be made until they
+coincide. Thus the non-gold-desiring people may find
+it convenient to express their desires in terms of the
+gold-desire to which they are themselves strangers, and
+seeing that the gold-desiring people are accessible and
+numerous, even those who have no real personal gold-desire
+will always value gold, because they can always
+get what they want in exchange for it from the gold-desiring
+people. Indeed, as soon as this fact is generally
+known and realised, people will generally find it convenient
+to keep a certain portion of their possessions not
+in the form of anything they really want, but in the
+form of gold.
+
+We may, therefore, measure all concrete utilities in
+terms of gold, and so compare them one with another.
+Only we must remember that by this means we reach
+a purely objective and material scale of equivalence, and
+that the fact that I can get a sovereign for either of
+two articles does not prove, or in any way tend to prove,
+that the two articles really confer equivalent benefits,
+\emph{unless it is the same man who is willing to give a sovereign
+for either}.
+
+\Person{A}'s and \Person{B}'s desires for $U$~and~$W$, when measured in
+their respective desires for~$Z$, are indeed equivalent;
+but the \emph{measure itself} may mean to the two men things
+severed by a hell-wide chasm; for \Person{A}'s desire for~$U$, $W$,
+and~$Z$ alike may be satisfied almost to the point of
+satiety, so that an extra unit of~$Z$ would hardly confer
+any perceptible gratification upon him; whereas \Person{B} may
+be in extreme need alike of~$U$, $W$, and~$Z$, so that an
+extra unit of~$Z$ would minister to an almost unendurable
+craving.
+
+Or again, \Person{A} may possess certain commodities, $V$, $X$,
+$Y$, which \Person{B} does not possess, and is not conscious of
+wanting at all (say billiard tables, pictures by old
+\index{Billiard-tables}%
+\index{Pictures}%
+masters, and fancy ball costumes), and in like manner
+\index{Fancy ball costumes}%
+\Person{B} may possess $W$~and~$T$ (say corduroy breeches and
+\index{Corduroys}%
+%% -----File: 100.png---Folio 77-------
+tripe), which \Person{A} neither possesses nor desires. Now in
+\index{Tripe}%
+\Person{B}'s scale of marginal utilities we may find that $t=\dfrac{z}{80}$
+(taking $t$ = one cut of tripe, and $z$ = the gold in a
+sovereign),\footnote
+ {These cannot be regarded as ``small'' units in the technical
+ sense, in this case. We are speaking in this example strictly of the
+ values of units at the margin, and they will not coincide even roughly
+ with the ideal ``usefulness'' of the commodity at the margin.}
+whereas in \Person{B}'s scale one $v=50z$. Then
+taking one~$z$ as a purely objective standard, and neglecting
+the difference of its meaning to the two men, and
+regarding \Person{A}~and~\Person{B} as forming a ``community,'' we
+might say that in that community $z=80t$ and $v=50z$,
+or $v=4000t$, \ie~one~$v$ is worth $4000$~times as much as
+one~$t$. By this we should mean that the man in the
+community who wants~$Z$ will give $4000$~times as much
+for a unit of it as you can get out of the man who
+wants~$T$ in exchange for a unit of that. But this does
+not even tend to show that a unit of~$V$ will give the
+man who wants it $4000$~times the pleasure which the
+other man would derive from a unit of~$T$. Nay, it is
+quite possible that the latter satisfaction might be positively
+the greater of the two.\Pagelabel{77}%
+
+\begin{Remark}
+Note, then, that the function of gold, or money, as a
+standard, is to reduce all kinds of services and commodities
+to an objective scale of equivalence; and this constitutes its
+value in commercial affairs, and at the same time explains
+the instinctive dislike of money dealings with friends which
+many men experience. Money is the symbol of the exact
+balancing and setting off one against the other of services
+rendered or goods exchanged; and this balancing can only
+be affected by absolutely renouncing all attempts to arrive at
+a \emph{real} equivalence of effort or sacrifice, and adopting in its
+place an external and mechanical equivalence which has no
+tendency to conform to the real equivalence. It is the
+systematising of the individualistic point of view which says,
+``One unit of~$Z$ may be a very different thing for \Person{A}~or~\Person{B} to
+\Pagelabel{78}%
+\emph{give}, but it is exactly the same thing for me to \emph{get}, wherever
+%% -----File: 101.png---Folio 78-------
+it comes from; and, therefore, I regard it as the same thing
+all the world over, and measure all that I get or give in
+terms of it.'' Where the relations to be regulated are themselves
+prevailingly external and objective, this plan works excellently.
+But amongst friends, and wherever friendship or
+any high degree of conscious and active goodwill enters into
+the relations to be regulated, two things are felt. In the first
+place we do not wish to keep an evenly balanced account, and
+to set services, etc., against each other, but we wish to act on the
+principle of the mutual gratuitousness of services; and in the
+second place, so far as any idea of a rough equivalence enters
+our minds at all, we are not satisfied with anything but a
+real equivalence, an equivalence, that is, of sacrifice or effort;
+and this may depart indefinitely from the objective equivalence
+in gold. This also explains the dislike of money and money
+dealings which characterises such saints as St.~Francis of
+\index{Francis of Assisi}%
+Assisi. Money is the incarnate negation of their principle of
+mutual gratuitousness of service.
+
+Under what circumstances the objective scale might be
+supposed roughly, and taken over a wide area, to coincide
+with the real scale, we shall ask presently. If such circumstances
+were realised, and in as far as they actually are
+realised, it is obvious that the objective scale has a social
+and moral, as well as a commercial, value. (Compare \Pageref{86}.)
+\end{Remark}
+
+In future we may speak of a man's desire or want of
+``gold'' without implying that he has any literal gold-desire
+at all, but using the ``unitary marginal utility of
+gold'' as the standard unit of desire, and expressing
+the (objective) intensity of any man's want of anything
+in terms of that unit. It is abundantly obvious from
+what has gone before in what way we shall reduce to
+this unit the wants of a man who has no real desire for
+gold at all. When we use gold in this extended and representative
+sense we shall indicate the fact by putting it in
+quotation marks: ``gold.'' Thus any one who possesses
+anything at all must to that extent possess ``gold,''
+though he may be entirely without gold.
+
+The result we have now reached is of the utmost
+importance. We have shown that in any catallactic community,\footnote
+ {I mean by a catallactic community one in which the individuals
+ freely exchange commodities one with another, each with a view to
+ making the enjoyment he derives from his possessions a maximum.}
+%% -----File: 102.png---Folio 79-------
+when in the state of equilibrium, the marginal
+utilities of units of all the commodities that enter into the
+circle of exchange will arrange themselves on a certain
+relative scale or table in which any one of them can
+be expressed in terms of any other, and that that scale
+will be general; that is to say, it will accurately translate
+or express, \emph{for each individual in the community}, the
+worth at the margin of a unit of any of the commodities
+he possesses, in terms of any other.
+
+The scope and significance of this result will become
+more and more apparent as we proceed; but we
+can already see that the desiredness at the margin of a
+unit of any commodity, expressed in terms of the desiredness
+at the margin of a unit of any other commodity,
+is the same thing as the \emph{value-in-exchange} (or exchange-value)
+of the first commodity expressed in terms of the
+second.
+
+We have therefore established a precise relation between
+value-in-use and value-in-exchange; for we have
+discovered that the value-in-exchange of an article conforms
+to the place it occupies on the (necessarily coincident)
+relative scales of all the persons in the community
+who possess it. Now to every man the
+marginal utility of an article, that is to say of a unit of
+any commodity, is determined by the average between
+the marginal usefulness of the commodity at the beginning
+and its marginal usefulness at the end of the
+acquisition of that unit; and this marginal usefulness
+itself is the first derived function, or the differential
+coefficient, of the total utility of the stock of the commodity,
+which the man possesses. Or briefly, \emph{the value-in-exchange
+\Pagelabel{79}%
+of a commodity is the differential coefficient of
+the total \DPtypo{utilily}{utility}, to each member of the community, of the stock
+of the commodity he possesses}.
+
+``The things which have the greatest value-in-use
+%% -----File: 103.png---Folio 80-------
+have frequently little or no value-in-exchange; and, on
+the contrary, those which have the greatest value-in-exchange
+have frequently little or no value-in-use. Nothing
+is more useful than water; but it will purchase scarce
+\index{Water}%
+anything; scarce anything can be had in exchange for
+it'' (Adam Smith). Now that we know exchange-value
+to be measured by marginal usefulness, we can well
+understand this fact. For as the total value in use of a
+thing approaches its maximum its exchange-value tends
+to disappear. Were water less abundant its value-in-use
+would be reduced, but its exchange-value would be
+so much increased that there would be ``scarce anything
+that could not be had in exchange for it.'' As it
+is the total effect of water is so near its maximum that
+its effectiveness at the margin is comparatively small.
+
+\Pagelabel{80}%
+Before proceeding farther we will look somewhat
+more closely into this matter of the identity of the
+exchange-value of a unit of any commodity and its
+desiredness at the margin of the stocks of the persons
+who possess it.
+
+%[** TN: Kept pound signs upright on this page; italicized in original.]
+In practical life, if I say that the exchange-value of a
+horse is £31, I am either speaking from the point of view
+\index{Horse}%
+of a buyer, and mean that a horse of a certain quality could
+be got in exchange for $8$~oz.~of gold;\footnote
+ {About $7.97$~oz.~of gold is contained in £31.}
+or I am speaking from
+the point of view of a seller, and mean that a man could
+get $8$~oz.~of gold for the horse; but I cannot mean both,
+for notoriously (if all the conditions remain the same)
+the buying and selling prices are never identical. What
+then do I mean when, speaking as an economist, I suppose,
+without further specification, that the exchange-value
+of a horse in ounces of gold is~$8$? I mean that
+the offer of anything \emph{more} than the $8$~oz.~of gold for
+a horse of the quality specified will \emph{tend to induce} some
+possessor of such a horse to part with him, and the offer
+of such a horse for anything \emph{less} than $8$~oz.~of gold will
+\emph{tend to induce} some possessor of gold to take the horse
+in exchange for some of it; and if I reduce the friction
+%% -----File: 104.png---Folio 81-------
+of exchange (both physical and mental) towards the
+vanishing point, I may say that every man who is
+willing to give \emph{any} more than 8~oz.\ of gold for a horse
+can get him, and every man who is willing to take \emph{any}
+less than 8~oz.\ of gold for a horse can sell him.
+
+The exchange-value of a horse, then, in ounces of gold,
+represents a quantity of gold such that a man can get
+anything short of it for a horse, and can get a horse for
+anything above it. And obviously, if the conditions remain
+the same, every exchange will tend to destroy the
+conditions under which exchanges will take place, for
+after each exchange the number of people who desire to
+exchange on terms which will ``induce business'' tends to
+be reduced by two.
+
+Thus if the exchange value of a horse is 8~oz.\ of
+gold, that means that the ratio ``1 horse to 8~oz.\ gold''
+is a point \emph{on either side of which} exchanges will take
+place, each exchange, however, tending to produce an
+equilibrium on the attainment of which exchange will
+cease.
+
+Now we have shown in detail that the relative scale
+of marginal utilities is a table of precisely such ratios,
+between units of all commodities that enter into the
+circle of exchange. Any departure in the relative scale
+of any individual from these ratios will at once induce
+exchanges that will tend to restore equilibrium. We
+find, then, that the relative scale is, in point of fact, \emph{a
+table of exchange values}, and that the exchange value of
+an article is simply its marginal utility measured in the
+marginal utility of the commodity selected as the standard
+of value. And, after all, this is no more than the
+simplest dictate of common sense and experience; for we
+have seen that the conditions of exchange are that some
+one should be willing, as a matter of business, to give more
+(or take less) than 8~oz.\ of gold for a horse; but what could
+induce that willingness except the fact that the marginal
+utility of a horse is greater, to the man in question, than
+the marginal utility of 8~oz.\ gold? And what should
+%% -----File: 105.png---Folio 82-------
+induce any other man to do business with him except
+the fact that to that other man the marginal utility of a
+horse is \emph{not} greater than that of 8~oz.\ of gold? In other
+words, the conditions of exchange only exist when there
+is a discrepancy in the relative scales of two individuals
+who belong to the same community; and, as we have seen,
+the exchange itself tends to remove this discrepancy.
+
+\Pagelabel{82}%
+Thus, \emph{the function of exchange is to bring the relative
+scales of all the individuals of a catallactic community into
+correspondence}, and the equilibrium-ratio of exchange
+between any two commodities is the ratio which exists
+between their unitary marginal utilities when this correspondence
+has been established. Thus if the machinery
+of exchange were absolutely perfect, then, \emph{given the
+initial possessions of each individual in the community}, there
+would be such a redistribution of them that no two men
+who could derive mutual satisfaction from exchanges
+would fail to find each other out; and so in a certain
+sense the satisfactions of the community would be
+maximised by the flow of all commodities from the
+place in which they were relatively less to the place in
+which they were relatively more valued. But the conformity
+of the net result to any principle of justice or
+of public good \emph{would depend entirely on initial conditions}
+prior to all exchange.
+
+It must never be forgotten that the coincident relative
+scales of the individuals who make up a community
+severally contain the things actually possessed (or commanded)
+only, not all the things \emph{wanted} by the respective
+individuals. If a man's \emph{initial} want of~$X$ relatively to
+his (marginal) want of ``gold'' is not so great as the
+\emph{marginal} want of~$X$ relatively to the (marginal) want of
+gold experienced by the possessors of~$X$, then he will not
+come into the possession of~$X$ at all, and all that we
+shall learn from the fact of his having no~$X$, together
+with an inspection of the position of~$X$ in the relative
+scale of marginal utilities, is that he desires~$X$ with less
+\emph{relative} intensity than its possessors do. But this does
+%% -----File: 106.png---Folio 83-------
+not by any means prove that his actual want of~$X$ is less
+pressing than theirs. It may very well be that he wants
+X far more than they do, but seeing that he has very
+little of anything at all, his want of ``gold'' exceeds
+theirs in a still higher degree. And, again, if one man
+wants~$X$ but does not want~$Y$, and another wants~$Y$ but
+does not want~$X$, and if the man who wants~$X$ wants it
+more, relatively to ``gold,'' than the man who wants~$Y$,
+it does not in the least follow that the one wants~$X$
+absolutely more than the other wants~$Y$, for we have no
+means of comparing the want of ``gold'' in the two
+cases, so that we measure the want of~$X$ and the want
+of~$Y$ in two units that have not been brought into
+any relation with each other. All this is only to
+say that because I cannot ``afford to buy'' a thing it
+does not follow that I have less need of it or less desire
+to have it than another man who can and does afford it.
+
+Obvious as this is, it is constantly overlooked in
+amateur attempts ``to apply the principles of political
+economy to the practical problems of life.'' We are
+told, for instance, that where there is no ``demand'' for
+a thing it shows that no one really wants it. But before
+we can assent to this proposition we must know what is
+meant by ``demand.''
+
+Now if I want a thing that I have not got, there are
+many ways of ``demanding'' it. I may beg for it. I
+may try to make people uncomfortable by forcing the
+extremity of my want upon them. I may try to terrify
+them into giving me what I want. I may attempt to
+seize it. I may offer something for it which stands
+lower than it on the relative scale of marginal utilities
+in my community. I may offer to work for it. All
+these forms of ``demand,'' and many more, the economists
+have with fine, if unconscious, irony classed
+together under one negative description. Not one of
+them constitutes an ``effective'' demand. An ``effective''
+demand (generally described, with the omission of the
+adjective, as ``demand'' simply) is that demand, and
+%% -----File: 107.png---Folio 84-------
+that demand only, which expresses itself in the offer in
+exchange for the thing demanded of something else that
+stands at least as high as it does on the relative scale of
+marginal utilities. No demand which expresses itself in
+any language other than such an offer is recognised as a
+demand at all---it is not ``effective.'' Now this phraseology
+is convenient enough in economic treatises, but
+unhappily the lay disciples of the economists have a
+tendency to adopt their conclusions and then discard
+their definitions. Thus they learn that it is waste of
+effort to produce a commodity or render a service which
+is less wanted than some other commodity or service
+that would demand no greater expenditure (whether of
+money, time, toil, or what not); they learn that what
+men want most they will give most for; and the conclusion
+which seems obvious is announced in such terms
+as these: ``Political economy shows that it is a mistake
+and a waste to produce or provide anything for people
+which they are not willing to pay for at a fair remunerative
+rate;'' or, ``It is false political economy to subsidise
+anything, for if people won't pay for a thing it
+shows they don't want it.'' Of course political economy
+does not really teach any such thing, for if it did it
+would teach that a poor man never ``wants'' food as
+much as a rich one, that a poor man never ``wants'' a
+holiday as much as a rich one; in a word, that a man who
+\index{Holiday}%
+has not much of anything at all has nearly as much of
+everything as he wants---which is shown by his being
+willing to give so very little for some more.
+
+The fallacy, of course, lies in the use made of the
+assertion that ``what men want most they will give most
+for.'' This is true only if we are always speaking of the
+\emph{same men}, or if we have found a measure which can
+determine which of two different men is really giving
+``most.'' Neither of these conditions is fulfilled in the
+case we are dealing with. ``When two men give the
+same thing, it is not the same thing they give,'' and if
+$A$ spends £100 on a continental tour and $B$ half a crown
+%% -----File: 108.png---Folio 85-------
+on a day at the sea-side no one can say, or without
+further examination can even guess, which of them has
+given ``most'' for his holiday.
+\index{Holiday}%
+
+\begin{Remark}
+Again, some confusion may be introduced into our
+thoughts by the fact that desires not immediately backed by
+any ``effective'' demand for gratification sometimes succeed in
+getting themselves indirectly registered by means of secondary
+desires which they beget in the minds of well-disposed
+persons who are in a position to give ``effect'' to them.
+Thus we may suppose that Sarah Bernhardt is charging three
+\index{Sarah@{\textsc{Sarah Bernhardt}}}%
+hundred guineas as her fee for reciting at an evening party,
+and that the three hundred guineas would provide a weeks'
+holiday in the country for six hundred London children. A
+benevolent and fashionable gentleman is in doubt which of
+these two methods of spending the sum in question he shall
+adopt, and after much debate internal makes his selection.
+What do we learn from his decision? We learn whether \emph{his}
+desire to give his friends the treat of hearing the recitation or
+to give the children the benefit of country air is the greater.
+It tells us nothing whatever of the relative intensity of the
+desire of the guests to hear the recitation and of the children
+to breathe the purer air. The primary desires concerned have
+not registered their relative intensities at all, it is only the
+secondary desires which they beget in the benevolent host
+that register themselves; and if the result proclaims the fact
+that the marginal utility of a recitation from the tragic
+actress is just six hundred times as great as the marginal
+utility of a week in the country to a sick child, this does not
+mean that the pleasure or advantage conferred on the company
+by the recitation is (or is expected to be) six hundred
+times as great as that conferred upon each child by the holiday;
+nor does it mean that the company would have estimated
+their pleasure in their own ``gold'' at the same sum
+as that at which the six hundred children would have estimated
+their pleasure in their ``gold,'' but that the host's
+desire to give the pleasure to the company is as great as
+his desire to give the pleasure to the six hundred children.
+And since we have supposed the host's desires to be the
+only ``effective'' ones, they alone are commercially significant.
+No kind of equation---not even an objective one---is established
+%% -----File: 109.png---Folio 86-------
+between the primary desires in question, viz.\ those of
+the guests and of the children respectively.\footnote
+ {It is interesting to note that there are considerable manufactures
+ of things the direct desire for which seldom or never asserts itself at
+ all. There are immense masses of tracts and Bibles produced, for
+\index{Bibles}%
+\index{Tracts}%
+\Pagelabel{86}%
+ instance, which are paid for by persons who do not desire to use them
+ but to give them away to other persons whose desire for them is not
+ in any way an effective factor in the proceeding. And there are
+ numbers of expensive things made expressly to be bought for ``presents,''
+ \index{Presents}%
+ and which no sane person is ever expected to buy for himself.}
+\end{Remark}
+
+The exchange value, then, of any commodity or service
+indicates its position on \emph{its possessors'} relative scale
+of unitary marginal utilities; and if expressed in ``gold''
+it indicates the ratio between the unitary marginal
+desiredness of the commodity and that of ``gold'' upon
+all the (necessarily coincident) relative scales of \emph{all the
+members of the community who possess it}.
+
+\begin{Remark}
+\index{Poor men's wares|(}%
+\index{Rich men's wares|(}%
+I have repeatedly insisted on the fact that we have no
+common measure by which we can compare the necessities,
+wants, or desires of one man with those of another. We
+cannot even say that ``a shilling is worth more to a poor
+man than to a rich one,'' if we mean to enunciate a rule that
+can be safely applied to individual cases. The most we can
+say is, that a shilling is worth more to a man \emph{when he is poor}
+than (\textit{c{\oe}teris paribus}) to \emph{the same man} when he is rich.
+
+But if we take into account the principle of averages, by
+which any purely personal variations may be assumed to
+neutralise each other over any considerable area, then we
+may assert that shillings either are or ought to be worth
+more to poor men than to rich. I say ``either are or ought
+to be;'' for it is obvious that the rich man already has his
+desires gratified to a greater extent than the poor man, and
+if in spite of that they still remain as clamorous for one
+shilling's worth more of satisfaction, it must be because his
+tastes are so much more developed and his sensitiveness to
+gratification has become so much finer that his organism even
+when its most imperative claims are satisfied still remains
+more sensitive to satisfactions of various kinds than the
+other's. But if the poor man owes his comparative freedom
+%% -----File: 110.png---Folio 87-------
+from desires to a low development and blunted powers, then
+the very fact that though he has so few shillings yet one in
+addition would be worth no more to him than to his richer
+neighbour is itself the indication of social pressure and
+inequality. On the assumption, then, that the humanity of
+\Pagelabel{87}%
+all classes of society ought ideally to receive equal development,
+we may say that shillings either are or ought to be
+worth more to poor men than to rich. Thus, if \Person{A}~manufactures
+articles which fetch 1s.~each in the open market and
+are used principally by rich men, and if \Person{B}~produces articles
+which fetch the same price but are principally consumed by
+poor men, then the commercial equivalence of the two wares
+does not indicate a social equivalence, \ie\ it does not indicate
+that the two articles confer an equal benefit or pleasure on
+the community. On the contrary, if the full humanity of
+\Person{B}'s~customers has not been stunted, then his wares are of
+higher social significance than~\Person{A}'s.
+
+It is obvious, too, that if \Person{C}'s wares are such as rich and
+poor consume alike, the different lots which he sells to his
+different customers, though each commercially equivalent to
+the others, perform different services to the opulent and the
+needy respectively.
+
+Now, anything which tends to the more equal distribution
+of wealth tends to remove these discrepancies. Obviously if
+all were equally rich the neutralising, over a wide area, of
+individual variations would take full effect; and if a thousand
+men were willing to give a shilling for \Person{A}'s~article and five
+hundred to give a shilling for~\Person{B}'s, it would be a fair assumption
+that though fewer men wanted \Person{B}'s~wares than~\Person{A}'s, yet
+those who did want them wanted them (at the margin) as
+much; nor would there be any reason to suppose that different
+lots of the same ware ministered, as a rule, to widely
+different intensities of marginal desire; the irreducible variations
+of personal constitution and habit being the only
+source of inequality left.
+
+It is true that the desire for \Person{A}'s~and~\Person{B}'s wares might not
+be equally legitimate, from a moral point of view. I may
+``want'' a shameful and hurtful thing as much as I ``want''
+a beautiful and useful one. The State usually steps in to
+say that certain wants must not be provided for at all---in
+England the ``want'' of gaming tables, for instance---and a
+%% -----File: 111.png---Folio 88-------
+man's own conscience may preclude him from supplying many
+other wants. But on the supposition we are now making
+equal intensity of commercial demand would at least represent
+(what no one can be sure that it represents now) equal
+intensity of desire on the part of the persons respectively
+supplied. If wealth were more equally distributed, therefore,
+it would be nearer the truth than it now is to say that
+when we supply what will sell best we are supplying what is
+wanted most.
+\index{Rich men's wares|)}%
+\index{Poor men's wares|)}%
+
+These considerations are the more important because, in
+general, this index of price is almost the only one we can
+have to guide us as to what really is most wanted. When
+we enter into any extensive relations with men of whom we
+have little personal knowledge it is impossible that we should
+form a satisfactory opinion as to the real ``equivalence'' of
+services between ourselves and them, and it would be an
+immense social and moral amelioration of our civilised life if
+we could have some assurance that a moderate conformity
+existed, over every considerable area, between the price a
+thing would fetch and the intensity of the marginal want of
+it. This would be an ``economic harmony'' of inestimable
+importance. Within the narrower area of close and intimate
+personal relations attempts would still be made, as now, to
+get behind the mere ``averaging'' process and consider the
+personal wants and capacities of the individuals, the ideal
+being for each to ``contribute according to his powers and
+receive according to his needs.'' Thus the different principles
+of conducting the affairs of business and of home would
+remain in force, but instead of their being, as they are now,
+in many respects opposed to each other the principles of
+business would be a first approximation---the closest admitted
+by the nature of the case---to the principles on which
+we deal with family and friends.
+
+Now certain social reformers have imagined an economic
+Utopia in which an equal distribution of wealth, such as we
+have been contemplating, would be brought about as follows:---Certain
+industrial, social and political forces are supposed to
+be at work which will ultimately throw the opportunities of
+acquiring manual and mental skill completely open; and
+skill will then cease to be a monopoly. Seeing, then, that
+there will only be a small number of persons incapable of
+%% -----File: 112.png---Folio 89-------
+doing anything but heaving, it will follow that the greater
+part of the heaving work of the world will be done by persons
+capable of doing skilled work. And hence again it will
+follow that every skilled task may be estimated in the foot-tons,
+which would be regarded by a heaver as its equivalent
+in irksomeness. And if we ask ``What heaver?''\ the answer
+will be ``The man at present engaged in heaving who estimates
+the relative irksomeness of the skilled task most lightly,
+and would therefore be most ready to take it up.'' Then the
+reward, or wages, for doing the task in question will be the
+same as for doing its equivalent (so defined) in foot-tons.
+If more were offered some of the present heavers would
+apply. If less were offered some of those now engaged in
+the skilled work would do heaving instead. To me personally
+heaving may be impossible or highly distasteful, but
+as long as some of my colleagues in my task are capable of
+heaving and some of the heavers capable of doing my task, a
+scale of equivalence will be established at the margin between
+them, and this will fix the scale of remuneration. Thus earnings
+will tend to equality with efforts, estimated in foot-tons.
+
+From this it would follow that inequalities of earnings
+could not well be greater than the natural inequalities of
+mere brute strength; for since foot-tons of labour-power are
+the ultimate measure of all remunerated efforts, he who has
+most foot-tons of labour-power at his disposal is potentially
+the largest earner.
+
+Again, the reformers who look forward to this state of
+things hold that forces are already at work which will ultimately
+dry up all sources of income except earnings, so that
+we shall not only have earnings proportional to efforts, estimated
+in foot-tons, but also incomes proportional to earnings.
+Thus inequalities in the distribution of wealth will be restrained
+within the limits of inequalities of original endowment
+in strength.
+
+The speculative weakness of this Utopia obviously lies in
+its taking no sufficient account of differences of personal
+ability. Throwing open opportunities might level the rank
+and fill up all trades, including skilled craftsmen, artists, and
+heavers; but it would hardly tend to diminish the distance,
+for example, between the mere ``man who can paint'' and
+the great artist.
+%% -----File: 113.png---Folio 90-------
+
+Nevertheless it is interesting to inquire how things would
+go in such a Utopia. In the first place we are obviously as
+far as ever from having established any common measure
+between man and man or any abstract reign of justice; for a
+foot-ton is not the same thing to~\Person{A} and to~\Person{B}, neither is there any
+justice in a strong man having more comforts than a weak one.
+
+Nevertheless there would be greater equality. For the
+number of individual families whose ``means'' in foot-tons of
+labour-power lie near about the average means, is much
+greater than the number of families whose present means in
+``gold'' lie near the average means. As this statement deals
+with a subject on which there is a good deal of loose and inaccurate
+thought, it may be well to expand the conception.
+
+If $\dfrac{a+b+c+d+e}{5}$ remains the same, then the arithmetical
+average of the five quantities remains the same. Suppose
+that average is~$200$. Then we may have $a=b=c=d=e=200$,
+or we may have $a=996$, $b=c=d=e=1$, or $a=394$,
+$b=202$, $c=198$, $d=200$,~$e=6$. In all these cases the
+average is~$200$, but in the second case not one of the several
+quantities lies anywhere near the average. So again, if we
+pass from the case $a=b=c=d=e=200$ to the case $a=997$,
+$b=c=d=e=1$, we shall actually have raised the average,
+but we shall have removed each quantity, severally, immensely
+farther away from that average.
+
+Now if we reflect that the average income of a family of
+five in the United Kingdom is estimated at £175~per annum,
+it is obvious that an enormous number of families have incomes
+a long way below the average. It is held to be self-evident
+that a smaller number of families fall conspicuously
+short of the average means in labour-power.
+
+Further, the extremes evidently lie within less distance of
+the average in the case of labour-power than in the case of
+``gold.'' There are, it is true, some families of extraordinary
+\index{Athletes}%
+athletic power, races of cricketers, oarsmen, runners, and so
+forth, but if we imagine such a family, while still remaining
+an industrial unit, to contain six or seven members each able
+to do the work of a whole average family, we shall probably
+have already exceeded the limit of legitimate speculation,
+and this would give six or seven times the average as the
+upper limit. Whereas the average ``gold'' income (as given
+%% -----File: 114.p n g----------
+%[Blank Page]
+%% -----File: 115.p n g----------
+\begin{figure}[p]
+ \begin{center}
+ \Fig{18}
+ \Input[4.5in]{115a}
+ \end{center}
+\end{figure}
+%[To face page 91.]
+%% -----File: 116.png---Folio 91-------
+above) being £175, we have only to think of the incomes of
+our millionaires to see how much further above the average
+the upper limit of ``gold'' incomes rises than it could possibly
+do in the case of labour-power.
+
+The lower limit being zero in both cases does not lend
+itself to this comparison.
+
+It may be urged, further, that there is no such broad
+distinction between the goods required by the strong (?~skates,
+\index{Skates}%
+bicycles, etc.) and those required by the ``weak'' (?~respirators,
+\index{Bicycles}%
+\index{Respirators}%
+reading-chairs, etc.) as there is between those demanded
+\index{Reading-chairs}%
+by the ``rich'' and those demanded by the ``poor.'' So
+that the analogue of the cases mentioned on \Pageref{87} would
+hardly occur; especially when we take into account the
+balancing effect of the association of strong and weak in the
+same family.
+
+The whole of this inquiry may be epitomised and elucidated
+by a diagramatic illustration.
+
+The unitary marginal utilities of $U$~and~$V$ stand in the
+ratio of~$3:4$ on the relative scale of the community in which
+\Person{A}~and~\Person{B} live. \Person{A}~possesses a considerable supply both of $U$~and~$V$.
+Parts of the curves are given in \Figref{18}~\Person{A}~(i), where
+the ``gold'' standard is supposed to be adopted in measuring
+marginal usefulness and utility. \Person{B}~possesses a little~$V$, but
+no~$U$, and would be willing (as shown on the curves \Figref{18}~\Person{B}~(i\DPtypo{.}{}))
+to give $\dfrac{v}{2}$ for~$u$ ($v$~and~$u$ being small units of $V$~and~$U$),
+but since $u$ is only worth half as much as $v$ to him, he will
+not buy it on higher terms than this. Now we have supposed
+the ratio of utilities of $u$~and~$v$ on the relative scale to
+be~$3:4$. That is to say, if $u$ contains three small units of
+utility then $v$ contains four. Therefore $\dfrac{u}{3}$ has the same value-in-exchange
+or marginal utility as $\dfrac{v}{4}$, and $\dfrac{3u}{3}$, or $u$ has the
+same value-in-exchange as $\dfrac{3v}{4}$; therefore an offer of $\dfrac{3v}{4}$, but
+nothing lower than this, constitutes an ``effective'' demand
+for~$u$; whereas \Person{B} only offers $\dfrac{v}{2}$ or $\dfrac{2v}{4}$ for it. Measuring the
+intensity of a want by the offer of ``gold'' it prompts, we
+should say, that \Person{B} wants $v$ as much as \Person{A} does, but wants $u$
+%% -----File: 117.png---Folio 92-------
+less than \Person{A} does. This, however, is delusive, for we do not
+know how much each of them wants the units of ``gold'' in
+which all his other wants are estimated. Suppose we say,
+``What a man wants he will work for,'' and ascertain that \Person{A}
+would be willing to do half a foot-ton of work for a unit of
+``gold,'' whereas \Person{B} would do one and a half foot-tons for it.
+This would show that, measured in work, the standard unit
+was worth three times as much to \Person{B} as to~\Person{A}. Reducing the
+units on the axis of~$y$ to $\frac{1}{2}$ for~\Person{A}, and raising them to $\frac{3}{2}$ for~\Person{B},
+we shall have the curves of \Figref{18}~\Person{A}~(ii) and \Person{B}~(ii) showing
+the respective ``wants'' of \Person{A}~and~\Person{B} estimated in willingness
+to do work. It will then appear that \Person{B} wants $v$ three
+times as much and $u$ twice as much as \Person{A} does; but his
+demand for~$u$ is still not effective, for he only offers $\dfrac{v}{2}$ or $\dfrac{2v}{4}$
+for it, and its exchange-value is $\dfrac{3v}{4}$. There is only enough
+$U$ to supply those who want a unit of it at least as much as
+they want $\frac{3}{4}$ of a unit of $V$, and \Person{B} is not one of these.
+
+Now if \Person{A} and \Person{B} had both been obliged to earn their
+``gold'' by work, with equal opportunities, then obviously
+the unitary marginal utility of ``gold,'' estimated in foot-tons,
+must have been equally high for both of them, since each
+would go on getting ``gold'' till at the margin it was just
+worth the work it cost to get and no more. And therefore
+the marginal utilities of $u$~and~$v$ (whether measured in foot-tons
+or in ``gold'') must also have stood at the same height
+for \Person{A}~and~\Person{B}. Hence \Person{B} could not have been wholly without
+$U$ while \Person{A} possessed it, unless, measured in foot-tons, its
+marginal usefulness was less to him than to~\Person{A}.
+
+It would remain possible that a foot-ton might represent
+widely different things to the two men; but the contention is
+that this is less probable, and possible only within narrower
+limits, than in the corresponding case of ``gold'' under our
+present system. I need hardly remind the reader that the
+assumptions of \Figref{18} are arbitrary, and might have been
+so made as to yield any result desired. The figure illustrates
+a perhaps rational supposition, and throws light on the
+nature and effects of a change of the standard unit of utility.
+It does not prove anything as to the actual result which
+would follow upon any specified change of the standard.
+%% -----File: 118.png---Folio 93-------
+
+The whole of this note must be regarded as a purely speculative
+examination of the conditions (whether possible of
+approximate realisation or not) under which it might be
+roughly true that ``what men want most they will pay most
+for.''
+\end{Remark}
+
+\Pagelabel{93}%
+We have now gained a distinct conception of what
+is meant by the exchange-value of a commodity. It is
+identical with the marginal utility which a unit of the
+commodity has to every member of the community
+who possesses it, expressed in terms of the marginal
+utility of some concrete unit conventionally agreed
+upon. There is no assignable limit to the divergence
+that may exist in the \emph{absolute} utility of the standard
+unit at the margin to different members of the community,
+but the \emph{relative} marginal utilities of the standard
+unit and a unit of any other article must be identical to
+every member of the community who possesses them, on
+the supposition of perfectly developed frictionless exchange,
+and ``small'' units.
+
+We may now proceed to show the principle on which
+to construct collective or social curves of quantity-possessed-and-marginal-usefulness
+without danger of
+being misled by the equivocal nature of the standard,
+or measure, of usefulness which we shall be obliged to
+employ.
+
+In approaching this problem let us take an artificially
+simple case, deliberately setting aside all the secondary
+considerations and complications that would rise in
+practice.
+
+We will suppose, then, that a man has absolute control
+\index{Mineral spring}%
+of a medicinal spring of unique properties, and that
+its existence and virtues are generally known to the
+medical faculty. We will further suppose that the
+owner is actuated by no consideration except the desire
+to make as much as he can out of his property, without
+exerting himself to conduct the business of bottling and
+disposing of the waters. He determines, therefore, to
+allow people to take the water on whatever terms
+%% -----File: 119.png---Folio 94-------
+prove most profitable to himself, and to concern himself
+no further in the matter.
+
+Now there are from time to time men of enormous
+wealth who would like to try the water, and would give
+many pounds for permission to draw a quart of it, but
+these extreme cases fall under no law. One year the
+owner might have the offer of £50 for a quart, and for
+the next ten years he might never have an offer of more
+than £5, and in neither case would there be any regular
+flow of demand at these fancy prices. He finds that in
+order to strike a broad enough stratum of consumers to
+give him a basis for averaging his sales even over a series
+of years he must let people draw the water at not more
+than ten shillings a quart, at which price he has a small
+but appreciable and tolerably steady demand, which he
+can average with fair certainty at so much a year. This
+means that there is no steady flow of patients to whom
+the marginal utility of a quart of the water is greater
+than that of ten shillings. In other words, the initial
+utility of the water to the community is ten shillings a
+quart. Clearly, then, the curve of quantity-and-marginal-usefulness
+of the water cuts the axis of~$y$ (that is to say,
+begins to exist for our purposes) at a value representing
+ten shillings a quart. If we were to take our unit on $x$ to
+represent a quart and our unit on~$y$ to represent a shilling,
+then we should have the corresponding values $x=0$, $y=10$.
+But since we shall have to deal with large quantities of
+the water, it will be convenient to have a larger unit for
+diagramatic purposes; and since the rate of 10s.~per
+quart is also the rate of £5000 per $10,000$ quarts, we
+may keep our corresponding values $x=0$, $y=10$, while
+interpreting our unit on~$x$ as $10,000$ quarts and our unit
+on~$y$ as £500 ($= 10,000$ shillings). The curve, then,
+cuts the axis of~$y$ at the height~$10$; which is to say that
+the initial \emph{usefulness} of the water to the community is
+£500 per $10,000$ quarts, or ten shillings a quart, which
+latter estimate being made in ``small'' units may be
+converted into the statement that the initial \emph{utility} of a
+%% -----File: 120.png---Folio 95-------
+quart of the water is equal to that of ten shillings, of
+two quarts twenty shillings, etc.\footnote
+ {Whereas it cannot be said that the initial utility of $10,000$ quarts
+ is £500, for the initial usefulness is not sustained throughout
+ the consumption of $10,000$ quarts.}
+
+But at this price customers are few, and the owner
+makes only a few pounds a year. He finds that if he
+lowers the price the increased consumption more than
+compensates him, and as he gradually and experimentally
+lowers the price he finds his revenue steadily rising.
+Even a reduction to nine shillings enables him to sell
+\begin{figure}[hbt]
+\Pagelabel{96}%
+ \begin{center}
+ \Fig{19}
+ \Input{120a}
+ \end{center}
+\end{figure}
+about $1000$ quarts a year, and so to derive a not inconsiderable
+income (£450) from his property. A further
+reduction of a shilling about doubles his sale, and he
+sells $2000$ quarts a year at eight shillings, making £800
+income. When he lowers the price still further to six
+shillings, he sells between $5000$ and $6000$ quarts a year,
+and his income rises to £1500.
+
+Before following him farther we will look at the problem
+%% -----File: 121.png---Folio 96-------
+from the other side. At first no one could get a
+quart of the water unless its marginal utility to him
+was as great as that of ten shillings. Now the issue
+just suffices to supply every one whose marginal want of
+a quart is as high as six shillings. These and these only
+possess the water, and on their relative scales it stands
+as having a marginal utility of six shillings a quart.
+This, then, may be called the marginal utility of the
+water \emph{to the community}; only we must bear in mind that
+we have no reason to suppose that the marginal wants
+of the possessors are \emph{in themselves} either all equal to
+each other or all more urgent than those of the yet unsupplied;
+but relatively to ``gold'' they will be so.
+
+We will now suppose that the owner tries the effect
+of lowering the price further still, and finds that when
+he has come down to four shillings a quart he sells
+$11,000$ quarts a year, so that his revenue is still increasing,
+being now more than £2200 per annum. This means
+that over $11,000$ quarts are needed to supply all those
+members of the community to whom the marginal utility
+of a quart is as great as the marginal utility of four
+shillings. Still the owner lowers the price, and discovers
+at every stage \emph{what quantity of the water it is that has the
+unitary marginal utility to the community corresponding to
+the price he has fixed}. By this means he is tracing the
+curve of price-and-quantity-demanded, and he is doing so
+by giving successive values to~$y$ and ascertaining the
+values of~$x$ that severally correspond to them. \Figref{19}
+shows the supposed result of his experiments, which,
+however, he will not himself carry on much beyond
+$y=1$, which gives $x=10$,\footnote
+ {In the diagram $y=\dfrac{120-x}{10x+10} - \dfrac{x^2-20x+100}{50}$.}
+and represents an income of
+ten units of area, each unit representing £500, or £5000
+in all. The price is now at the rate of £500 per $10,000$
+quarts, or one shilling per quart, and the annual sales
+amount to $100,000$ quarts. Up to this point we have
+supposed that every reduction of the price has increased
+%% -----File: 122.png---Folio 97-------
+the total pecuniary yield to the owner. But this cannot
+go on for ever, inasmuch as the owner is seeking to
+increase the value of $x × y$ by diminishing $y$ and increasing
+$x$, and since in the nature of the case $x$ cannot be
+indefinitely extended (there being a limit to the quantity
+of the water wanted by the public at all) it follows that
+as $y$ diminishes a point must come at which the increase
+of~$x$ will fail to compensate for the decrease of~$y$, and $xy$
+will become smaller as $y$ decreases. This is obvious from
+the figure. We suppose, then, that when the owner has
+already reduced his price to one shilling a quart he finds
+that further reductions fail to bring in a sufficient increase
+of custom to make up for the decline in price. To make
+the public take $160,000$ quarts a year he would not only
+have to give it away, but would have to pay something
+for having it removed.
+
+We have supposed the owner to fix the price and to
+let the quantity sold fix itself to correspond. That is,
+we have supposed him to say: Any one on whose relative
+scale of marginal utilities a quart of this water
+stands as high as $y$~shillings may have it, and I will see
+how many quarts per annum it will take to meet
+the ``demand'' of all such. Hence he is constructing
+a curve in which the price is the variable and the
+quantity demanded at that price is the function. This
+is a curve of price-and-quantity-demanded. It is usual
+to call it a ``curve of demand'' simply, but this is
+an elliptical, ambiguous, and misleading phrase, which
+should be strictly excluded from elementary treatises.
+We have seen (\Pageref{12}) that a curve is never a curve
+of height, time, quantity, utility, or any other \emph{one} thing,
+but always a curve of connection between some \emph{two}
+things. The amounts of the things themselves are always
+represented by straight lines, and it is the connection of
+the corresponding pairs of these lines that is depicted on
+the curve. If we not only always bear this in mind,
+but always express it, it will be an inestimable safeguard
+against confusion and ambiguity, and we may
+%% -----File: 123.png---Folio 98-------
+make it a convention always to put the magnitude
+which we regard as the variable first. Thus the curve
+we have just traced is a curve of price-and-quantity-demanded.
+
+But it would have been just as easy to suppose our
+owner to fix the quantity issued, and then let the price
+fix itself. The curve itself would, of course, be the
+same (compare pp.~\Pageref[]{3},~\Pageref[]{13}), but we should now regard it as
+a curve of quantity-issued-and-intensity-of-demand. The
+price obtainable always indicating the intensity of the
+demand for more when just so much is issued. From
+this point of view also it might be called a ``curve of
+demand,'' but ``demand'' would then mean intensity of
+demand (the quantity issued being given), and would
+be measured by the price or~$y$. In the other case ``demand''
+would mean quantity demanded (at a given
+price), and would be measured by~$x$.
+
+Now this curve of quantity-issued-and-intensity-of-demand
+is the same thing as the curve of quantity-possessed-(by
+the community)-and-marginal-usefulness,
+or briefly quantity-and-price. Thus if we call the curve
+a curve of price-and-quantity we indicate that we are
+supposing the owner to fix the price and let the
+quantity sold fix itself, whereas if we call it the curve
+of quantity-and-price we are supposing the owner to fix
+the amount he will issue and let the price fix itself. In
+either case we put the variable first, and call it the
+curve of the variable-and-function.
+
+Regarding the curve as one of quantity-and-price
+then, we suppose the owner to say: I will draw $x$~times
+$10,000$ quarts (of course $x$ may be a fraction) from my
+spring every year, and will see how urgent in comparison
+with the want of ``gold'' the want that the last quart
+meets turns out to be. In this case it is obvious that
+as the owner increases the issue the new wants satisfied
+by the larger supply will be less urgent, relatively to
+``gold,'' than the wants supplied before, but still the
+marginal utility of a quart relatively to ``gold'' will be
+%% -----File: 124.png---Folio 99-------
+the same to all the purchasers, and will be greater to
+them than to any of those who do not yet take any.
+Thus as the issue increases the marginal utility to the
+community of a quart steadily sinks on the relative scale
+of the community, and shows itself, as in the case of the
+individual, to be a decreasing function of the quantity
+possessed, each fresh increment meeting a less urgent
+want than the last. But meanwhile the \emph{total} service
+done to the community by the water is increased by
+every additional quart. The man who bought one
+quart a year for ten shillings, and who buys two quarts
+a year when it comes down to eight shillings, and ten
+quarts a year when it is only a shilling, would still be
+willing to give ten shillings for a single quart if he could
+not get it cheaper, and the second and following quarts,
+though not ministering to so urgent a want as the first,
+yet in no way interfere with or lessen the advantage it has
+already conferred, while they add a further advantage of
+their own. Thus from his first quart the man now gets
+for a shilling the full advantage which he estimated at ten
+shillings, and from the second quart the advantage he
+estimated at eight shillings, and so on. It is only the last
+quart from which he derives an advantage no more than
+equivalent to what he gives for it. We may, therefore,
+still preserving the ``gold'' standard, say that the total
+utility of the $q$~quarts which \Person{A} consumes in the year is
+made up of the whole sum he would have given for
+one quart rather than have none, \emph{plus} the whole quantity
+he would have given for a second quart sooner than
+have only one $+ \ldots +$ the whole sum he gives for the
+$q$th~quart sooner than be satisfied with $(q-1)$. In like
+manner the successive quarts, up to~$p$, which \Person{B} adds to
+his yearly consumption as the price comes down, each
+confers a fresh benefit, while leaving the benefits already
+conferred by the others as great as ever. Thus we
+should construct for \Person{A},~\Person{B}, \Person{C}, etc., severally, curves of
+quantity-and-total-utility of the water, on which we
+could read the total benefit derived from any given
+%% -----File: 125.png---Folio 100-------
+quantity of the water by each individual measured in
+terms of the marginal utility to him of the unit of gold.
+And regarding the total utility as a function of the
+quantity possessed, we shall, of course, find that each
+consumer goes on possessing himself of more till the
+first derived function (rate at which more is adding to
+his satisfaction) coincides with the price at which he can
+purchase the water.
+
+In like manner we may, if we choose, add up all the
+utilities of the successive quarts to \Person{A},~\Person{B}, \Person{C}, etc.,
+measured in ``gold,'' as they accrue (neglecting the fact
+that they are not subjectively but only objectively
+commensurate with each other), and may make a curve
+showing the grand total of the utility to the community
+of the whole quantity of water consumed. And this
+curve would of course continue to rise (though at a
+decreasing rate) as long as any one who had anything to
+give in exchange wanted a quart more of the water than
+he had.
+
+Thus we have seen that as the issue increases the
+utility of a quart at the margin to each individual and
+to the whole community continuously falls on the relative
+scale, the exchange value of course (recorded in the
+price) steadily accompanying it; while at the same time
+each extra quart confers a fresh advantage on the
+community without in any way interfering with or
+lessening the advantages already conferred; that is to
+say, the total advantage to the community increases as
+the issue increases, whereas the marginal usefulness constantly
+decreases. The maximum total utility would
+be realised when the issue became free, and every one
+was allowed as much of the water as he wanted, and
+then the marginal utility would sink to nothing, that is
+to say, no one would attach any value to more than he
+already had. This is in precise accordance with the
+results already obtained with reference to a single individual.
+The total effect is at its maximum when the
+marginal effectiveness is zero.
+%% -----File: 126.png---Folio 101-------
+
+But now returning to the owner of the spring, we
+note that his attention is fixed neither upon the total
+nor the marginal utility of the water, but on the total
+price he receives, and we note that that price is represented
+in the diagram by a rectangle, the base of
+which is~$x$, or the quantity sold measured in the unit
+agreed upon, and the height~$y$, the price or rate per unit
+(determined by its marginal usefulness) at which when
+issued in that quantity the commodity sells. The area,
+therefore, is~$xy$. And this brings us to the important
+principle involved in what is known as the ``law of indifference.''
+By this law the owner finds himself obliged to
+sell \emph{all} his wares at the price which \emph{the least urgently needed}
+will fetch, for he cannot as a rule make a separate bargain
+with each customer for each unit, making each pay as
+much for each successive unit as that unit is worth to him;
+since, unless he sold the same quantity at the same price
+to all his customers, those whom he charged high would
+deal with those whom he charged low, instead of directly
+with him. ``There cannot be two prices for the same
+article in the same market.'' Thus we see again, and
+see with ever increasing distinctness, that the exchange
+value of a commodity is regulated by its marginal
+utility, and is independent of the service which that
+particular specimen happens to render to the particular
+individual who purchases it.
+
+Thus (if we bear in mind the purely relative and
+therefore socially equivocal nature of our standard of
+utility) we may now generalise the conclusions we
+reached in the first instance with exclusive reference to
+the individual. From the collective as from the individual
+point of view the marginal utility of a commodity
+is a function of the quantity of it possessed or commanded.
+If the quantity changes, the communal marginal
+utility and therefore the exchange-value changes
+with it; and this altogether irrespective of the nature
+of the causes which produce the change in quantity.
+Whether it is that nature provides so much and no
+%% -----File: 127.png---Folio 102-------
+more, or that some one who has power to control the
+supply chooses, for whatever reason, to issue just so
+much and no more, or that producers think it worth
+while to produce so much and no more---all this, though
+of the utmost consequence in determining whether and
+how the supply can be further changed, is absolutely immaterial
+in the primary determination of the marginal
+utility, and therefore of the exchange-value, so long as
+just so much and no more \emph{is} issued. This amount is
+the variable, and, given a relation between the variable
+and the function (\ie~given the curve), then, when the
+variable is determined, no matter how, why, or by
+whom, the function is thereby determined also (compare
+\Pageref{62}).
+
+\emph{Exchange value, then, is relative marginal value-in-use,
+and is a function of quantity possessed.}\Pagelabel{102}%
+
+\begin{Remark}
+The ``Law of Indifference'' is of fundamental importance
+in economics. Its full significance and bearing cannot be
+grasped till the whole field of economics has been traversed;
+but we may derive both amusement and instruction, at the
+stage we have now reached, from the consideration of the
+various attempts which are made to evade it, and from the light
+which a reference to it throws upon the real nature of many
+familiar transactions.
+
+In the first place, then, sale by auction is often an attempt
+\index{Auction}%
+to escape the law of indifference. The auctioneer has, say,
+ten pictures by a certain master whose work does not often
+come into the market, and his skill consists in getting the
+man who is most keen for a specimen to give his full price
+for the first sold. Then he has to let the second go cheaper,
+because the keenest bidder is no longer competing; but he
+tries to make the next man give \emph{his} outside price; and so on.
+The bidders, on the other hand, if cool enough, try to form a
+rough estimate of the \emph{marginal} utility of the pictures, that is
+to say, of the price which the tenth man will give for a
+picture when the nine keenest bidders are disposed of, and
+they know that if they steadily refuse to go above this point
+there will be one for each of them at the price. When the
+%% -----File: 128.p n g----------
+%[Blank Page]
+%% -----File: 129.p n g----------
+\begin{figure}[p]
+ \begin{center}
+ \Fig{20}
+ \Input[4.5in]{129a}
+ \end{center}
+\end{figure}
+%[To face page 103.]
+%% -----File: 130.png---Folio 103-------
+things on sale are such as can be readily got elsewhere, the
+auctioneer is powerless to evade the law of indifference.
+
+Another instance constantly occurs in the stock markets.
+\index{Stock-broking}%
+A broker wishes to dispose of a large amount of a certain
+stock, which is being taken, say, at~$95$. But he knows that
+only a little can be sold at that price, because a few thousands
+would be enough to meet all demands of the urgency represented
+by that figure. In fact, the stock he has to part with
+would suffice to meet all the wants represented by $93$~and
+upwards, and accordingly the law of indifference would compel
+him to part with the first thousand at that rate just as
+much as the last if he were to offer all he means to sell
+at once. This, in fact, will be the selling price of the
+whole when he has completed his operations. But meanwhile
+he endeavours to hold the law of indifference at bay by
+producing only a small part of his stock and doing business
+at~$95$ till there are no more demands urgent enough to prompt
+an offer of more than~$94\frac{7}{8}$. He then proceeds cautiously to
+meet these wants likewise, obtaining in each case the maximum
+that the other party is willing to give; and so on, till,
+if completely successful, he has let the stock down~$\frac{1}{8}$ at a
+time from $95$ to~$93$. By this time, of course, not only his own
+last batch, but all the others that he has sold, are down at~$93$.
+The law of indifference has been defeated only so far as he is
+concerned, and not in its general operation on the market.
+
+The general principle involved is illustrated, without
+special reference to the cases cited, in \Figref{20}. The law of
+indifference dictates that if the quantity~$Oq_4$ is to be sold,
+then $Oq$, $qq_1$, $q_1q_2$, $q_2q_3$, $q_3q_4$ must all be treated indifferently,
+and therefore sold at the price measured by $Op_4$~($=q_4m_4$).
+This would realise an amount represented by the area~$p_4q_4$.
+But the seller endeavours to mask the fact that $Oq_4$ is to be
+sold, and by issuing separate instalments tries to secure the
+successive areas $pq+s_1q_1+s_2q_2+s_3q_3+s_4q_4$. Obviously the
+``limit'' of this process, under the most favourable possible
+circumstances, is the securing of the whole area bounded by
+the curve, the axes, and the line~$q_nm_n$ (where $q_n$~stands for the
+last of the series $q$,~$q_1$,~etc.)\footnote
+ {If $Op$ or~$q^m$ is~$f(Oq)$, \ie~if $y$ is~$f(x)$, then the area in question
+ will be $\int_0^xf(x)\,dx$ (see pp.~\Pageref[]{23},~\Pageref[]{31}). The meaning of this symbol may
+ now be explained. The sum of all the rectangular areas is $pq+s_1 q_1
+ +s_2 q_2+ \text{etc.}$, or $qm\centerdot Oq+q_1 m_1\centerdot qq_1+q_2 m_2\centerdot q_1q_2+ \text{etc.}$, but $qm$ is
+ $f(Oq)$, $q_1m_1$ is $f(Oq_1)$, $q_2 m_2$ is $f(Oq_2)$, etc. Therefore the sum of the
+ areas is
+ \[
+ f(Oq)\centerdot Oq+f(Oq_1)\centerdot qq_1+f(Oq_2)\centerdot q_1q_2+ \text{etc.}
+ \]
+ But $Oq=qq_1=q_1q_2= \text{etc.}$ We may call this quantity ``the increment
+ of $x$,'' and may write it $\Delta x$. The sum of the rectangular areas will then
+ be
+ \begin{gather*}
+ \{f(Oq)+f(Oq_1)+f(Oq_2) + \text{etc.}\} \Delta x,\\
+ \text{or}\ \operatorname{sum} \{f(Oq)\} \Delta x,\ \text{or}\ \textstyle\sum \{f(Oq)\} \Delta x.
+ \end{gather*}
+ When we wish to indicate the limit of any expression into which
+ $\Delta x$, \ie~an increment of~$x$, enters, as the increment becomes smaller
+ and smaller, it is usual to say that $\Delta x$becomes~$dx$. In the
+ limit then $\sum \{f(Oq)\}\Delta x$ becomes $\int f(Oq)dx$, where $\int$ is simply the
+ letter~\emph{s}, the abbreviation of ``sum.'' The symbol then means, the
+ limit of the sum of the areas of the rectangles as the bases become
+ smaller and the number of the rectangles greater. But we have further
+ to indicate the limits within which we are to perform this summing of
+ the rectangles. If we wished to express the area $q_1m_1m_3q_3$ the limits
+ would be $Oq_1$~and~$Oq_3$. We should wish to sum all the rectangles
+ bounded by~$f(Oq_1)$, \ie~$q_1m_1$, and~$f(Oq_3)$, \ie~$q_3m_3$.
+ This we should
+ indicate thus---
+ \[
+ \int^{O_{q_3}}_{O_{q_1}}f(O_q)\centerdot dx
+ \]
+ And the area~$OPm_nq_n$ will be
+ \[
+ \int_0^{Oq_n}f(Oq)\centerdot dx
+ \]
+ This means that the values successively assumed by~$Oq$ in the expression,
+ $\operatorname{sum} (Oq\centerdot dx)$ are, respectively, all the values between $Oq_1$~and~$Oq_3$,
+ or all the values between $O$~and~$Oq_n$. Finally, since the successive
+ values of~$Oq$ are the successive values of~$x$, and since $Oq_n$ is the
+ last value of~$x$ we are to consider, we may write the expression for
+ $OPm_nq_n$
+ \[
+ \int_0^xf(x)\centerdot dx
+ \]
+ or the expression for $q_1m_1m_nq_n$
+ \[
+ \int_{q_1m_1}^x f(x)\centerdot dx
+ \]
+ remembering the $x$ in~$f(x)$ stands for all the successive values of the
+ variable,~$x$, whereas in, $\int_0^x$ or $\int_{q_1m_1}^x$ or generally $\int_{\text{constant}}^x$ $x$ stands
+ only for the \emph{last} of the values of the variable considered.}
+If the law of indifference takes
+%% -----File: 131.png---Folio 104-------
+full effect the seller is apt to regard the area~$Pp_n m_n$ as a
+territory to be reclaimed. The public, he thinks, has got it
+without paying for it. If the law of indifference is completely
+evaded, the public, in its turn, is apt to think that it
+has been cheated to the extent of this area.
+
+We may now consider some more special cases of attempts
+to escape the action of the law of indifference. The system
+of ``two prices'' in retail dealing is a good instance. It is an
+attempt to isolate two classes of customers and to confine the
+action of the law of indifference to equalising the prices within
+these classes, taken severally. In fact, the principle of ``fixed
+prices in retail trade'' is strictly involved in the frank acceptance
+of the law of indifference; and all evasions or modifications
+of that principle are attempts to escape the action of
+the law. The extent to which ``double prices'' prevail in
+London is perhaps not generally realised. A differential
+charge of a halfpenny or penny a quart on milk, for instance,
+\index{Milkman@{Milkman's prices}}%
+according to the average status (estimated by house rent) of
+%% -----File: 132.png---Folio 105-------
+the inhabitants of each street or neighbourhood, seems to be
+common.
+
+It is clear, too, that when he has established a system of
+differential charges, the tradesman can, if he likes, sell to the
+low-priced customer at a price which would not pay him\footnote
+ {This phrase is used in anticipation, but is perhaps sufficiently
+ clear (see below).}
+if
+charged all round; for the small profit he would make on each
+transaction would not enable him to meet his standing expenses.
+Having met them, however, from the profits of his high-priced
+business, he may now put down any balance of receipts over
+expenses out of pocket on the other business as pure gain. If in
+\Figref{20} the rectangles represent not the actual receipts for the
+respective sales, but the balance of receipts over expenses out of
+pocket on each several transaction, we may suppose that the
+dealer requires to realise an area of~$20$ in order to meet his
+standing expenses and make a living. He can do business
+to the extent of~$Oq_4$ at the (gross)\footnote
+ {\textit{I.e.}~surplus of receipts over expenses out of pocket \emph{on that transaction},
+ all standing expenses being already incurred.}
+rate of profit~$Op_4$, which gives
+him his area of~$20$, \ie~$p_4q_4$. If he did business to the extent
+of~$Oq_n$ at a uniform (gross) profit of~$Op_n$, he would only
+secure an area of~$18$, \ie~$p_nq_n$, and so could not carry on business
+at all. But if he can keep $Oq_4$ at the profit~$Op_4$, and
+%% -----File: 133.png---Folio 106-------
+then without detriment to the other add $q_4q_n$ at a profit
+$Op_n$, he secures $20+8$, \ie~$p_4q_4+s_nq_n$. Nay, it is conceivable
+enough that he could not carry on business at all except on
+the principle of double prices. Suppose, in the case illustrated
+by the figure, that he must realise an area of~$25$ in
+order to go on. It will be found that no rectangle containing
+so large an area can be drawn in the curve. The maximum
+rectangle will be found to correspond to the value of
+nearly $4.5$ for~$x$, which will give an area of only a little more
+than $20$. If the law of indifference, then, takes full effect,
+our tradesman cannot do business at all; but if he can deal
+with $Oq_4$ and $q_4q_n$ separately, he may do very well.
+
+In this case the ``double price'' system is the only possible
+one; and the high-priced customers are not really paying an
+unnaturally high price. For unless \emph{some one} pays as high as
+that the ware cannot be brought into the market at all. But
+it would be easy so to modify our supposition as to make the
+tradesman a kind of commercial Robin Hood, forcing up the
+price for one class of customers above the level at which they
+would naturally be able to obtain their goods, and then
+lowering it for others below the paying line.
+
+The differential charges of railway companies illustrate
+\index{Railway@{\textsc{Railway} charges, differential}}%
+this. A company finds that certain goods~$Oq$ must necessarily
+be sent on their line, whereas $qq_4$ may be equally well
+sent by another line. An average surplus of receipts
+over expenses out of pocket represented by an area of four
+units per unit of~$x$ will pay the company; \ie~$Op_4$ per
+unit, giving $p_4q_4$ or $20$ on the carriage of $Oq_4$ would pay.
+On $Oq$ the company puts a charge which will yield gross
+profits at the rate of~$Op$, and thus secure $pq=14$. They
+then underbid the other company for the carriage of~$qq_4$. $Op_4$
+being the minimum average gross profit that will pay (in
+view of standing expenses), they offer to carry at a gross
+profit of~$Op_n$, for their standing expenses are already incurred,
+and they thus secure an extra gross profit of $qs_n$ ($=8$) which,
+together with the $pq$ ($=14$) they have already secured, gives
+them a total of~$22$, or $2$~more than if they had run at
+uniform prices. Of the ten extra units of area which they
+extracted from the consigners of~$Oq$, they have given eight to
+the consigners of~$qq_4$ in the shape of a deduction from the
+legitimate charge.
+%% -----File: 134.p n g----------
+%[Blank Page]
+%% -----File: 135.p n g----------
+%[** TN: Labels have been transcribed faithfully from the original.]
+\begin{figure}[p]
+ \begin{center}
+ \Fig{21}
+ \Input{135a}
+ \end{center}
+\end{figure}
+% [To face page 107.]
+%% -----File: 136.png---Folio 107-------
+
+Another interesting case is that of a theatre. Here the
+\index{Theatre, pit and stalls}%
+``two (or more) price'' system is disguised by withholding
+from the low-price customers certain conveniences which practically
+cost nothing, but which serve as a badge of distinction
+and enable the high-price customers to pay for the privilege
+of being separated from the rest without offensively parading
+before them that this separation is in fact the privilege for
+which they are paying 8s.~each. The accommodation is
+limited, and the nature of the demand varies according to the
+popularity of the piece. Except under quite exceptional circumstances
+custom fixes the charges for stalls and pit, to which we
+will confine ourselves; and though the manager would rather
+fill his floor with stalls than with benches, yet he is glad of all
+the half-crowns which do not displace half-guineas, since his
+expenses out of pocket for each additional pittite are trivial or
+non-existent. Neglecting the difference of space assigned to
+a sitter in a stall and on a bench, let us suppose the whole
+floor to hold $800$~seats, $400$~of which are made into stalls.
+Representing a hundred theatre-goers by a unit on~$x$, and the
+rate of 1s.~a head, or £5 a 100 by the unit on~$y$, and so
+making each unit of area represent £5 receipts, we may
+read the two curves $a$~and~$a'$ in \Figref{21} thus. There is a
+nightly supply of four hundred theatre-goers who value the
+entertainment, accompanied by the dignity and comfort of a
+stall at not less than 10s.~6d.\ a seat (rate of £52:10s.\ per
+hundred seats.) There are also five hundred more who value
+it, with the discomforts of the pit, at 2s.~6d.\ a seat (rate of
+£12:10s.\ per hundred). There is not accommodation for all
+the latter, since there are but four hundred pit seats, and
+custom prevents the manager from filling his pit at a little
+over 3s.~a place as he might do. So he lets his customers fight
+it out at the door and takes in four hundred at 2s.~6d.\ each
+(area~$p'a'$). His takings are $(10.5× 4+2.5× 4) \text{ times £5}=\text{£260}$,
+since each unit of area represents~£5. The areas
+are $pa$~and~$p'a'$. The former $pa$ is as great as the marginal
+utility of the article offered admits of, but the latter
+$p'a'$ is limited horizontally by the space available and vertically
+by custom.
+
+As the public gets tired of the play the curves $a$~and~$a'$ are
+replaced by $b$~and~$b'$. The manager might fill his stalls by
+going down to 8s., and might almost fill his pit at~2s. But
+%% -----File: 137.png---Folio 108-------
+custom forbids this. His prices are fixed and his issue of tickets
+fixes itself. He has 200~stalls and 300~places in the pit
+taken every night. Area $=pb+p'b'$. Receipts $(10.5× 2+2.5× 3)$
+times £5 = £142:10s.
+
+When the manager puts on a new piece the curves $c$~and~$c'$
+\index{Theatre, waiting}%
+\index{Waiting@{Waiting (at theatre)}}%
+replace $b$~and~$b'$; and finding that he can issue six
+hundred stall tickets per night at 10s.~6d., the manager
+pushes his stalls back and cuts down the pit to two
+hundred places, for which six or seven hundred theatre-goers
+fight; several hundred more, who would gladly have
+paid 2s.~6d.\ each for places, retreating when they find
+that they must wait a few hours and fight with wild
+beasts for ten minutes in addition to paying their half-crowns.
+When the two hundred successful competitors find
+that the manager has not sacrificed £80 a night for the
+sake of keeping the four hundred seats they consider due to
+them and their order, they try to convince him that a pittite
+and peace therewith is better than a stalled ox and contention
+with it. It would be interesting to know in what terms they
+would state their case; but evidently the merely commercial
+principles of ``business'' do not command their loyal assent.
+The areas $pc+p'c'$ are $(10.5× 6+2.5× 2) \text{ times £5}=\text{£340}$.
+
+The case of ``reduced terms'' at boarding schools is very
+\index{Reduced terms at school}%
+like the cases of the railway and the theatre. The reader
+may work it out in detail. As long as the school is not full,
+the ``reduced'' pupils do something towards helping things
+along, if they pay anything more than they actually eat and
+break. At the same time it would be impossible to meet the
+standing expenses and carry on the school if the terms were
+reduced all round. If pupils are taken at reduced terms
+when their places could be filled by paying ones, then the
+master is sacrificing the full amount of the reduction.
+
+These instances, which might be increased almost
+indefinitely, will serve to illustrate the importance of the law
+of indifference and the attempts to escape its action.\Pagelabel{108}%
+\end{Remark}
+
+Having now a sufficiently clear and precise conception
+of the marginal utilities of various commodities \emph{to the
+community}, we may take up again from the general
+point of view the investigation which we have already
+%% -----File: 138.png---Folio 109-------
+entered upon (on \Pageref{58}) with reference to the individual,
+and may inquire what principles will regulate the direction
+taken in an industrial community by the labour
+(and other efforts or sacrifices, if there are any others)
+needful to production.
+
+Strictly speaking, this does not come within the
+scope of our present inquiry. We have already seen
+that the exchange value of an article is a function of the
+quantity possessed, completely independent of the way
+in which that quantity comes to be possessed; and
+any inquiries as to the circumstances that determine, in
+particular cases, the actual quantity produced and therefore
+possessed, fall into the domain of the ``theory of
+production'' or ``making'' rather than into that of the
+``theory of value'' or ``worth.'' But the two subjects
+have been so much confounded, and the connection
+between them is in reality so intimate and so important,
+that even an elementary treatment of the subject of
+``value'' would be incomplete unless it included an
+examination of the simplest case of connection between
+value and what is called cost of production. The consideration
+of any case except the simplest would be out
+of place here.
+
+Suppose \Person{A} can command the efforts and sacrifices
+needed to produce either $U$~or~$V$, and suppose the production
+of either will require the same application of
+these productive agents per unit produced. Obviously~\Person{A},
+if he approaches his problem from the purely mercantile
+side, has simply to ask, ``Which of the two, when
+produced, will be worth most in `gold' to the community?''\
+\ie, he must inquire which of the two has the
+highest relative marginal utility, or stands highest on the
+relative scale. Suppose a unit~$u$ has, at the margin,
+twice the relative utility of the unit~$v$; \Person{A}~will then
+devote himself to the production of~$U$, for by so doing
+he will create a thing having twice the exchange value,
+and will therefore obtain twice as much in exchange, as
+if he took the other course. He will therefore produce
+%% -----File: 139.png---Folio 110-------
+$u$ simply because, when produced, it will exchange for
+more ``gold'' than~$v$. \Person{A}~will not be alone in this preference.
+Other producers, whose productive forces are
+freely disposable, will likewise produce~$U$ in preference
+to~$V$, and the result will be a continual increase in the
+quantity of~$U$. Now we have seen that an increased
+quantity of~$U$ means a decreased marginal usefulness of~$U$
+measured in ``gold,'' so that the production of~$U$ in
+greater and greater quantities means the gradual declension
+on the relative scale of its unitary marginal utility,
+and its gradual approximation to that of~$V$, which will
+cause the exchange values of $u$~and~$v$ to become more
+and more nearly equal. But as long as the marginal
+utility of~$u$ stands at all above that of~$v$ on the relative
+scale, the producers will still devote themselves by preference
+to the production of~$U$, and consequently its
+marginal usefulness will continue to fall on the
+scale until at last it comes down to that of~$V$\@. Then
+the marginal utilities and exchange values of $u$~and~$v$
+will be equal, and as the expenditure of productive
+forces necessary to make them is by hypothesis equal
+also, there will be no reason why producers should
+prefer the one to the other. There will now be equilibrium,
+and if more of \emph{either} is produced, then more of
+\emph{both} will be produced in such proportions as to preserve
+the equilibrium now established. In fact the diagram
+(\Figref{14}, \Pageref{60}) by which we illustrated the principle upon
+which a wise man would distribute his own personal
+labour between two methods of directly supplying his
+own wants, will apply without modification to the
+principles upon which purely mercantile considerations
+tend to distribute the productive forces in a mercantile
+society. But though the diagram is the same there is a
+momentous difference in its signification, for in the one
+case it represents a genuine balancing of desire against
+desire in one and the same mind or ``subject,'' where
+the several desires have a real common measure; in the
+other case it represents a mere mechanical and external
+%% -----File: 140.png---Folio 111-------
+equivalence in the desires gratified arrived at by
+measuring each of them in the corresponding desires for
+``gold'' existing respectively in \emph{different} ``\emph{subjects}.''
+
+It only remains to generalise our conclusions. No
+new principle is introduced by supposing an indefinite
+number of alternatives, instead of only two, to lie before
+the wielders of productive forces. There will always be
+a tendency to turn all freely disposable productive forces
+towards those branches of production in which the
+smallest sum of labour and other necessaries will produce
+a given utility; that is to say, to the production of
+those commodities which have the highest marginal
+utility in proportion to the labour, etc., required to produce
+them; and this rush of productive forces into these
+particular channels will increase the amount of the
+respective commodities, and so reduce their marginal
+usefulness till units of them are no longer of more value
+at the margin than units of other things that can be
+made by the same expenditure of productive forces.
+There will then no longer be any special reason for
+further increasing the supply of them.
+
+The productive forces of the community then, like
+the labour of a self-sufficing industrial unit, will tend to
+distribute themselves in such a way that a given sum of
+productive force will produce equal utilities at the
+margin (measured externally by equivalents in ``gold'')
+wherever applied.
+
+To make this still clearer, we may take a single case
+in detail, and supposing general equilibrium to exist
+amongst the industries, may ask what will regulate the
+extent to which a newly developed industry will be
+taken up? But as a preliminary to this inquiry we
+must define more closely our idea of a general equilibrium
+amongst the industries. On \Pageref{73}~\textit{sqq} we established
+the principle that if commodities $A$~and~$B$ are
+freely exchanged, and commodities $B$~and~$C$ are freely
+exchanged also, then the unitary marginal utilities, and
+thus the exchange values of $a$~and~$c$, may be expressed
+%% -----File: 141.png---Folio 112-------
+each in terms of the other, even though it should happen
+that no owners of~$A$ want~$C$, and no owners of~$C$ want~$A$,
+and in consequence there is no direct exchange between
+them. In like manner the principle of the distribution
+of efforts and sacrifices just established enables us to
+select a single industry as a standard and bring all the
+others into comparison with it. It will be convenient,
+as we took gold for our standard commodity, so to take
+gold-digging as our standard industry; and as we have
+\index{Gold-digging}%
+written ``gold'' as a short expression for ``gold and all the
+commodities in the circle of exchange, expressed in terms
+of gold,'' so we may write ``gold-digging'' as a short expression
+for ``gold-digging and all the industries open to
+producers, in equilibrium with gold-digging,'' and we
+shall mean by one industry being in equilibrium with
+another that the conditions are such that a unit of
+effort-and-sacrifice applied at the margin of either
+industry will produce an equivalent utility.\footnote
+ {To speak of the ``margin'' of an industry again involves an
+ anticipation of matters not dealt with in this volume, but I trust it
+ will create no confusion. It must be taken here simply to mean ``a
+ unit of productive force added to those already employed in a certain
+ industry,'' and the assumption is that all units are employed at the
+ same advantage, the difference in the utility of their yields being due
+ simply to the decreasing marginal utility of the same unit of the commodity
+ as the quantity of the commodity progressively increases.}
+If, then,
+a sufficient number of persons have a practical option
+between gold-digging~($\alpha$) and cattle-breeding~($\beta$), this
+\index{Cattle-breeding}%
+will establish equilibrium between these two occupations
+$\alpha$~and~$\beta$ in accordance with the principle just laid
+down; and if a sufficient number of other persons to
+whom gold-digging is impossible have a practical option
+between cattle-breeding~($\beta$) and corn-growing~($\gamma$), then
+\index{Corn-growing}%
+that will establish equilibrium between $\beta$ and~$\gamma$. But
+since there will always be equilibrium between $\alpha$ and~$\beta$
+as long as sufficient persons have the option between
+them, and since that equilibrium will be restored, whenever
+disturbed, by the forces that first established it, it
+follows that if there is equilibrium between $\beta$ and~$\gamma$
+%% -----File: 142.p n g----------
+%[Blank Page]
+%% -----File: 143.p n g----------
+\begin{figure}[p]
+ \begin{center}
+ \Fig{22}
+ \Input{143a}
+ \end{center}
+\end{figure}
+% [To face page 113.]
+%% -----File: 144.png---Folio 113-------
+there will be equilibrium between $\alpha$ and~$\gamma$ also. We
+may therefore conveniently select $\alpha$~or gold-digging as
+the industry of general reference, and may say that a
+man will prefer $\gamma$~or corn-growing to ``gold-digging'' as
+long as the yield is higher in the former industry,
+although as a matter of fact it is not the yield in gold-digging
+but the yield in cattle-breeding (itself equilibrated
+with gold-digging) with which he directly compares
+his results in corn growing. Industries in equilibrium
+with the same are in equilibrium with each
+other.
+
+We assume, then, that there is a point of equilibrium
+about which all the industries, librated with each other
+directly and indirectly, oscillate; and, neglecting the
+oscillations, we use the yield to a given application of
+productive forces in gold-digging as the representative
+of the equivalent yield in all the other industries in
+equilibrium with it.
+
+Now we imagine a new industry to be proposed, and
+producers who command freely disposable efforts and
+sacrifices to turn their attention to it. Their option is
+between the new industry and ``gold-digging,'' in the
+extended sense just explained. We are justified in
+assuming, for the sake of simplicity, that the whole sum
+of the productive forces under consideration would not
+sensibly affect the marginal usefulness of ``gold'' (in the
+extended sense, observe) if applied to ``gold-digging;''
+that is to say, we assume that in no case will the new
+industry draw to itself so great a volume of effort-and-sacrifice
+as to starve the other industries of the world,
+taken collectively, and make the general want of the things
+they yield perceptibly more keen. Therefore, in examining
+the alternative of ``gold-digging,'' we assume that the
+whole volume of labour and other requisites of production,
+or effort-and-sacrifice, which is in question might
+be applied to ``gold-digging'' without reducing the marginal
+usefulness of ``gold,'' or might be withdrawn from
+it without increasing that usefulness. The yield in
+%% -----File: 145.png---Folio 114-------
+``gold'' of any quantity of labour and other requisites,
+then, would be exactly proportional to that quantity.
+
+Fixing on any arbitrary unit of effort-and-sacrifice
+(say $100,000$ foot-tons), and taking as our standard unit
+of utility the gold that it would produce (say $30$~ounces),
+we may represent the ``gold'' yield of any given amount
+of labour and other requisites by the aid of a straight
+line, drawn parallel to the abscissa at a distance of unity
+from it (\Figref{22}). Thus if $Oq$~effort and sacrifice were
+devoted to ``gold-digging,'' the area~$Gq$ would represent
+the exchange value of the result. Now let the upper
+curve on the figure be the curve of quantity-and-marginal-usefulness
+of the new product, the unit of quantity
+being that amount which the unit of labour and other
+requisites ($100,000$ foot-tons) will produce. And here
+we must make a simplification which would be violent
+if we were studying the theory of production, but which
+is perfectly legitimate for our present purpose. We
+must suppose, namely, that however much or little of
+the new product is secured it is always got under the
+same conditions, so that the yield per unit effort-and-sacrifice
+is the same at every stage of the process. But
+though the \emph{quantity} produced by a unit of productive
+force is always the same its marginal usefulness and
+exchange value will of course descend, according to the
+universal law, as the total quantity of the ware increases.
+In the first instance, then, the commercial mind has
+simply to ask, ``Are there persons to whom such an
+amount of this article as I can produce by applying the
+unit of productive force will be worth more than the
+`gold' I could produce by the same application of force?''
+In other words, ``Will the unit of productive force applied
+to this industry produce more than the unit of utility?''
+Under the conditions represented in the figure the
+answer will be a decisive affirmative, and the producer
+will turn his disposable forces of production into the new
+channel. But as soon as he does so the most importunate
+demands for the new article will be satisfied, and if any
+%% -----File: 146.png---Folio 115-------
+further production is carried on it must be to meet a
+demand of decreasing importunacy, \ie~the marginal
+utility of the article is decreasing, and the exchange
+value of the yield of the unit of productive force in
+the new industry is falling. Production will continue,
+however, as long as there is any advantage in the new
+industry over gold-production, \ie~till the yield of unit
+productive force in the new industry has sunk to unit
+utility.
+
+Thus, if $Oq_1$~effort and sacrifice is devoted to the
+new industry, the marginal usefulness of the product will
+be measured by~$q_1f_1$, and the exchange value of the
+whole output by the rectangle bounded by the dotted
+line and $q_1f_1$,~etc. This is much more than $Gq_1$ the
+alternative ``gold'' yield to the same productive force.
+But there is still an advantage in devoting productive
+forces to the new industry, since $q_1f_1$ is greater than~$q_1g_1$,
+and even if the present producers are unable to
+devote more work to it, or unwilling to do so, because
+it would diminish the area of the rectangle (\Pageref{96}), yet
+there will be others anxious to get a return to their
+work at the rate of~$q_1f_1$ instead of~$q_1g_1$. Obviously,
+then, the new commodity will be produced to the extent
+of~$Oq$ where $qf=qg$, \ie,~the point at which the curve
+cuts the straight line~$Gg$, which is the alternative ``gold''
+curve. If production be carried farther it will be carried
+on at a disadvantage. At~$q_2$, for instance, $q_2f_2$~is less
+than~$q_2g_2$, that is to say, if the supply is already~$Oq_2$,
+then a further supply will meet a demand the importunity
+of which is less than that of the demand for the
+``gold'' which the same productive force would yield.
+This will beget a tendency to desert the industry, and
+will reduce the quantity towards~$Oq$.
+
+We have supposed our units of ``gold'' and the new
+commodity so selected that it requires equal applications
+of productive agencies to secure either, but in practice
+we usually estimate commodities in customary units that
+have no reference to any such equivalence. This of
+%% -----File: 147.png---Folio 116-------
+course does not affect our reasoning. If the unit of~$F$ is
+such that our unit of labour and other necessaries yields
+a hundred units of~$F$ and only one unit of~$G$, then,
+obviously, we shall go on producing~$F$ until, but only
+until, the exchange value of a hundred units of~$F$ (the
+product of unit of labour, etc., in~$F$) becomes equal to the
+exchange value of one unit of~$G$ (the product of unit of
+labour, etc., in~$G$). Or, generally, if it needs $x$~times as
+much effort and sacrifice to produce one unit~$A$ as it
+takes to produce one unit~$B$, then it takes as much to
+produce $x$~units $B$ as to produce one unit~$A$, and there
+will always be an advantage either in producing~$xb$ or
+in producing one~$a$, by preference, unless the exchange
+value of both is the same; that is to say, unless the
+marginal value of~$a$ equals $x$~times that of~$b$. Thus, \emph{if $a$~contains
+$x$~times as much work as~$b$, then there will not be
+equilibrium until $A$ and~$B$ are produced in such amounts as
+to make the exchange value of~$a$ just $x$~times the exchange
+value of~$b$}.
+
+This, then, is the connection between the exchange
+value of an article (that can be produced freely and in
+indefinite quantities) and the amount of work it contains.
+Here as everywhere the quantity possessed
+determines the marginal utility, and with it the exchange
+value; and if the curve is given us we have only
+to look at the quantity-index in order to read the exchange
+value of the commodity (see pp.~\Pageref[]{62},~\Pageref[]{67}). But in
+the practically and theoretically very important case of
+commodities freely producible in indefinite quantities
+we may now note this further fact as to the principle
+by which the position of the quantity-index is in its turn
+fixed---that fluid labour-and-sacrifice tends so to distribute
+itself and so to shift the quantity-indexes as to
+make \emph{the unitary marginal utility of every commodity
+directly proportional to the amount of work it contains}.
+
+\begin{Remark}
+This fact, that the effort-and-sacrifice needed to produce
+two articles is, in a large class of cases (those, namely, in
+%% -----File: 148.png---Folio 117-------
+which production is free and capable of indefinite extension),
+proportional to the exchange values of the articles themselves,
+has led to a strange and persistent delusion not only amongst
+the thoughtless and ignorant but amongst many patient and
+earnest thinkers, who have not realised that the exchange
+value of a commodity is a function of the quantity possessed,
+and may be made to vary indefinitely by regulating
+that quantity. The delusion to which I refer is that it is the
+amount of effort-and-sacrifice or ``labour'' needed to produce
+a commodity which \emph{gives that commodity its value in exchange}.
+A glance at \Figref{22} will remind the reader of the magnitude
+and scope of the error involved in this idea. The commodity,
+on our hypothesis, always contains the same amount
+of effort-and-sacrifice per unit, whether much or little is produced,
+but the fact that only the unit of ``labour'' has been
+put into it does not prevent its exchange value being more
+than unity all the time till it exists in the quantity~$Oq$, nor
+does the fact of its containing a full unit of labour keep its
+exchange value up to unity as soon as it exists in excess of
+the quantity~$Oq$. What gives the commodity its value in
+exchange is the quantity in which it exists and the nature of
+the curve connecting quantity and marginal usefulness; and
+it is no more true and no more sensible to say that the
+quantity of ``labour'' contained in an article determines its
+value than it would be to say that it is the amount of money
+which I give for a thing that makes it useful or beautiful.
+The fact is, of course, precisely the other way. I give so
+much money for the thing because I expect to find it useful
+or think it beautiful; and the producer puts so much
+``labour'' into the making of a thing because when made he
+expects it to have such and such an exchange value. Thus
+one thing is not worth twice as much as another because it
+has twice as much ``labour'' in it, but producers have been
+willing to put twice as much ``labour'' into it because they
+know that when produced it will be worth twice as much,
+because it will be twice as ``useful'' or twice as much
+desired.
+
+This is so obvious that serious thinkers could not have
+fallen into and persisted in the error, and would not be
+perpetually liable to relapse into it, were it not for certain
+considerations which must now be noticed.
+%% -----File: 149.png---Folio 118-------
+
+In the first place, if we have not fully realised and completely
+assimilated the fact that exchange value is a function
+of the quantity possessed, and changes as the quantity-index
+shifts, it seems reasonable to say, ``It is all very well to
+say that because people want~$a$ twice as much as~$b$ they
+will be \emph{willing to do} twice as much to get~$a$ as they will to
+get~$b$, but how does it follow that they will be \emph{able to get} the
+article~$a$ by devoting just twice as much labour to it as to~$b$?
+Surely you cannot maintain that it \emph{always happens} that
+the thing people want twice as much needs exactly twice as
+much ``labour'' to produce as the other? And yet you
+admit yourself that the thing which has twice the exchange
+value always does contain twice the ``labour.'' If it is not
+a chance, then, what is it?'' The answer is obvious, and the
+reader is recommended to write it out for himself as clearly
+and concisely as possible, and then to compare it with the
+following statement: If people want~$a$ just twice as much
+as~$b$, and no more, it does not follow that a producer will
+find $a$ just twice as hard to get, but it does follow that if he
+finds~$a$ is \emph{more} than twice as hard to get (say $x$~times as hard)
+he will not get it at all, but will devote his productive
+energies to making~$b$. Confining ourselves, for the sake
+of simplicity, to these two commodities, we note that other
+producers will, for the like reason, also produce~$B$ in preference
+to~$A$. The result will be an increased supply of~$B$,
+and, therefore, a decreased intensity of the want of it;
+whereas the want of~$A$ remaining the same as it was, the
+utility of~$a$ is now more than twice as great as the (diminished)
+utility of~$b$; and as soon as the want of~$b$ relatively to the
+want of~$a$ has sunk to~$\dfrac{1}{x}$, then one~$a$ is worth $x$~$b$'s, and as it
+needs just $x$~times the effort-and-sacrifice to produce~$a$, there
+is now equilibrium, and $A$ and~$B$ will \emph{both} be made in such
+quantities as to preserve the equilibrium henceforth; but the
+proportion of one utility to the other, and the proportion
+of the ``labour'' contained in one commodity to that
+contained in the other, do not ``happen'' to coincide; they
+have been \emph{made} to coincide by a suitable adjustment of efforts
+so as to secure the maximum satisfaction.
+
+Another source of confusion lurks in the ambiguous use
+of the word ``because''; and behind that in a loose conception
+%% -----File: 150.png---Folio 119-------
+of what is implied and what is involved in one thing being
+the ``cause'' of another.
+
+Thus we sometimes say ``$x$~is true because $y$ is true,''
+when we mean not that $y$ being true is the \emph{cause}, but that it
+is the \emph{evidence} of $x$ being true. For instance, we might say
+``prime beef is less esteemed by the public than prime
+mutton, because the latter sells at~$1$d.\ or~$\frac{1}{2}$d.\ more per pound
+than the former.'' By this we should mean to indicate the
+higher price given for mutton not as the cause of its being
+more esteemed, but as the evidence that it is so.\footnote
+ {Such psychological reactions as the desire to put one dish on the
+ table in preference to another, simply because it is known to be more
+ expensive, do not fall within the scope of this inquiry.}
+So again,
+``Is the House sitting?''---``Yes! because the light on the clock-tower
+\index{House of Commons sitting}%
+is shining.'' This does not mean that the light shining
+causes the House to sit, but that it shows us it is sitting.
+
+In like manner a man may say, ``If I want to know how
+much the exchange value of~$a$ exceeds that of~$b$, I shall look
+into the cost of producing them, and if I find four times as
+much `labour' put into~$a$, I shall say $a$~is worth four times~$b$,
+because I find that producers have put four times the
+`labour' into it;'' and if he means by this that he knows
+the respective values in exchange of $a$~and~$b$ on the evidence
+of the amount of effort-and-sacrifice which he finds producers
+willing to put into them respectively, then we have no fault
+to find with his economics, though he is using language
+dangerously liable to misconception. But if he means that
+it is the effort-and-sacrifice, or ``labour,'' contained in them
+which \emph{gives} them their value in exchange, he is entirely
+wrong. As a matter of fact, the defenders of the erroneous
+theory sometimes make the assertion in the erroneous sense,
+victoriously defend it, when pressed, in the true sense, and
+then retain and apply it in the erroneous sense.
+
+Again, though it is never true that the quantity of
+``labour'' contained in an article \emph{gives} it its value-in-exchange,
+yet it may be and often is true, in a certain sense, that the
+quantity of ``labour'' it contains is the \emph{cause} of its having
+such and such a value in exchange. But if ever we allow
+ourselves to use such language we must exercise ceaseless
+vigilance to prevent its misleading ourselves and others.
+%% -----File: 151.png---Folio 120-------
+For what does it mean? The quantity-index and the curve
+fix the value-in-exchange. But the quantity-index may run
+the whole gamut of the curve, and we have seen that what
+determines the direction of its movement and the point at
+which it rests is, in the case of freely producible articles,
+precisely the quantity of ``labour'' contained in the article.
+This quantity of ``labour'' contained, then, determines the
+amount of the commodity produced, and this again determines
+the value-in-exchange. In this sense the amount of
+``labour'' contained in an article is the cause of its exchange
+value. But this is only in the same sense in which the
+approach of a storm may be called the cause of the storm-signal
+\index{Storm-signal}%
+rising. The approach of the storm causes an intelligent
+agent to pull a string, and the tension on the string causes
+the signal to rise. In this sense the storm is the cause of
+the signal rising. But it would be a woful\DPnote{** [sic] legitimate variant} mistake, which
+might have disastrous consequences, to suppose that there is
+any immediate causal nexus between the brewing of the
+storm and the rising of the ball. And if our mechanics
+were based on the principle that a certain state of the atmosphere
+``gives an upward movement to a storm-signal,'' the
+science would stand in urgent need of revision. So in our
+case: Relative ease of production makes intelligent agents
+produce largely if they can; increasing production results in
+falling marginal utilities and exchange-values; therefore, in a
+certain sense, ease of production causes low marginal utilities
+and exchange-values. But there is no immediate causal
+nexus between ease of production and low exchange-values.
+Exchange values, high and low, are found in things which
+cannot be produced at all; and if (owing to monopolies,
+artificial or natural) the intelligent agents who observe how
+easily a thing is produced are not in a position to produce it
+abundantly, or have reasons for not doing so, the ease of
+production may coexist with a very high marginal utility,
+and consequently with a very high exchange value. In such
+a case the amount of ``labour'' contained in the article will
+be small out of all proportion to its exchange-value; and the
+quantity produced may be regulated by natural causes that
+have no connection with effort and sacrifice, or by the desire
+on the part of a monopolist to secure the maximum gains.
+
+Finally, there are certain phenomena, of not rare occurrence
+%% -----File: 152.png---Folio 121-------
+in the industrial world, which really seem at first
+sight to give countenance to the idea that the exchange-value
+of a commodity is determined, not by its marginal
+desiredness, but by the quantity of ``labour'' it contains.
+These phenomena are for the most part explained by the
+principle of ``discounting,'' or treating as present, a state of
+things which is foreseen as certain to be realised in a near
+future. For instance, suppose a new application of science to
+industry, or the rise into favour of a new sport or game, suddenly
+\index{Games@{\textsc{Games}}}%
+creates a demand for special apparatus, and suppose one
+or two manufacturers are at once prepared to meet it. They
+may, and often do, take advantage of the urgency of the want
+of those who are keenest for the new apparatus, and sell it at its
+full initial exchange-value, only reducing their price as it becomes
+necessary to strike a lower level of desire, and thus
+travelling step by step all down the curve of quantity-and-value-in-exchange
+till the point of equilibrium is at last reached, and
+every one can buy the new apparatus who desires it as much
+as the ``gold'' that the same effort-and-sacrifice would produce.
+But it may also happen that the manufacturers who are
+already on the field foresee that others will very soon be
+ready to compete with them, and that it will require a comparatively
+small quantity of the new apparatus to bring it
+down to its point of equilibrium, inasmuch as it cannot,
+in the nature of the case, be very extensively used. They
+feel, therefore, that they have not much to gain by securing
+high prices for the first specimens, and on the other hand, if
+they ``discount'' or anticipate the fall to the point of equilibrium,
+and at once offer the apparatus on such terms as will
+secure all the orders, they will prevent its being worth while
+for any other manufacturers to enter upon the new industry,
+and will secure the whole of the permanent trade to themselves.
+
+Any intermediate course between these two may likewise
+be adopted; but the discounting or anticipation of the foreseen
+event only disguises and does not change the nature of
+the forces in action.
+
+A more complicated case occurs when a man wants a
+single article made for his special use which will be useless
+to any one else. Let us say he wants a machine to do certain
+work and to fit into a certain place in his shop. The importance
+%% -----File: 153.png---Folio 122-------
+to him of having such a machine is great enough
+to make him willing to give £100 for it sooner than go
+without it. But the ``labour'' (including the skill of the
+designer) needed to produce it would, if applied to making
+other machines, or generally to ``gold-digging,'' only produce
+an article of the exchange-value of £50. ``In this case,'' it
+will be said, ``the marginal utility of the machine is measured
+by £100, yet the manufacturer (if his skill is not a monopoly)
+can only get £50 for making it, because it only contains
+labour and other requisites to production represented by that
+sum. Does not this show conclusively that it is the ``labour''
+contained in an article, not its final utility, which determines
+its exchange-value?'' To judge of the validity of this objection,
+let us begin by asking exactly what our theory would
+lead us to anticipate, and then let us compare it with the
+alleged facts. We have seen that in equilibrium the marginal
+utility of the unit of a commodity must occupy the same
+place on the relative scales of all those who possess it;
+and further, that if ever that marginal utility should be
+higher on \Person{A}'s relative scale than on \Person{B}'s, then (if \Person{B} possesses
+any of the commodity) the conditions for a mutually profitable
+exchange exist, though on what terms that exchange
+will be made remains, as far as our investigations have taken
+us, indeterminate, within certain assignable limits. Now if
+we suppose the machine to be actually made we shall have
+this situation: \Person{A}, on whose relative scale the marginal
+utility of the machine stands at £100 has not got it. \Person{B},
+on whose relative scale it stands at zero, possesses it. The
+conditions of a mutually advantageous exchange therefore
+exist. But the terms on which that exchange will take place
+are indeterminate between 0~and~£100. When a single
+exchange has been made, on whatever terms, then the
+article will stand at zero on every relative scale except
+that of its possessor, and no further exchange will be
+made. \emph{If the machine exists}, therefore, its exchange-value
+will be indeterminate between zero and £100. Now if
+we consistently carry out our system of graphic representation
+this position will be reproduced with faultless accuracy.
+The curve of quantity-possessed-and-marginal usefulness with
+reference to the community being drawn out, the vertical
+intercept on the quantity-index indicates the exchange-value
+%% -----File: 154.png---Folio 123-------
+of the commodity. Now in this instance the curve in question
+consists of the rectangle in \Figref{23}~(\textit{a}), where the unit on
+the axis of~$y$ is £100~per machine, and the unit on the axis
+of~$x$ is one machine. For the usefulness of the first machine
+to the community is at the rate of £100~per machine, and
+the usefulness of all other machines at the rate of $0$~per
+machine. Therefore the curve falls abruptly from $1$ to $0$ \emph{at}
+the value $x=1$. But the quantity possessed by the community
+is one machine. Therefore the quantity index is at
+\begin{figure}[hbtp]
+ \begin{center}
+ \Fig{23}
+ \Input[3.5in]{154a}
+ \end{center}
+\end{figure}
+the distance unity from the origin, \Figref{23}~(\textit{b}). What is the
+length of the intercept? Obviously it is indeterminate between
+$0$ and $1$. This is exactly in accordance with the facts.
+Supposing the machine actually to exist, then, our theory
+vindicates itself entirely. But if the machine does not yet
+exist, what does our theory tell us of the prospect of its being
+made? We have seen that a thing will be made if there is a
+prospect of its exchange-value, when made, being at least as
+great as that of anything else that could be made by the same
+effort-and-sacrifice. Now the exchange-value is determined
+by the intercept on the quantity-index. Before the machine
+is made that intercept is $1$ ($=\text{£100}$), but that does not concern
+the maker, for he wants to know what it \emph{will be} when
+the machine is made, not what it is before. But it will be
+indeterminate, as we have seen, and therefore there is no
+security in making the machine. In order to get the
+machine made, therefore, the man who wants it must remove
+the indeterminateness of the problem by stipulating in
+advance that he will give not less than £50 for it. But
+what he is now doing is not getting the machine (which does
+not exist) in exchange for ``gold.'' It is getting control or
+%% -----File: 155.png---Folio 124-------
+direction of a given application of labour, etc. in exchange
+for ``gold,'' and this being so, it is not to be wondered at
+that the price he pays for this ``labour'' should be proportionate
+to the quantity of it he gets.
+
+This is the general principle of ``tenders'' for specific
+work.
+\end{Remark}
+
+\Pagelabel{124}%
+We may appropriately close our study of exchange
+value by a few reflections and applications suggested
+by the ordinary expenditure of private income, and
+especially shopping and housekeeping.
+
+On \Pageref{58} we considered what would be the most
+sensible way of distributing labour amongst the various
+occupations which might claim it on a desert island.
+There labour was the purchasing power, and the question
+was in what proportions it would be best to exchange it
+for the various things it could secure. We were not
+then able to extend the principle to the more familiar
+case of money as a purchasing power, because we had
+not investigated the phenomena of exchange value and
+price. We may now return to the problem under this
+aspect. The principle obviously remains the same.
+Robinson Crusoe, when industrial equilibrium is established
+\index{Robinson Crusoe}%
+in his island, so distributes his labour that the
+last hour's work devoted to each several task results in
+an equivalent mass or body of satisfaction in every case.
+If the last hour devoted to securing \Person{A} produced less
+satisfaction than the last hour devoted to securing \Person{B},
+Robinson would reduce the former application of labour
+till, his stock of \Person{A} falling and its marginal usefulness
+rising, the last hour devoted to securing it produced a
+satisfaction as great as it could secure if applied otherwise.
+He would then keep his supply at this level, or
+advance the supply of \Person{A} and \Person{B} together in such proportions
+as to maintain this relation. If he lets his stock
+of \Person{A} sink lower he incurs a privation which could be
+removed at the expense of another privation not so
+great; if he makes it greater he gets a smaller gratification
+at a cost which would have secured a greater
+%% -----File: 156.png---Folio 125-------
+one if applied elsewhere. In equilibrium, then, the last
+hour's work applied to each task produces an equal
+gratification, removes an equal discomfort, or gratifies
+an equal volume of desire; which is to say, that Robinson's
+supply of all desired things is kept at such a
+level that the unitary marginal utilities of them all
+are directly proportional to the labour it takes to secure
+them.
+
+In like manner the householder or housewife must
+\index{Housekeeper}%
+\Pagelabel{125}%
+aim at making the last penny (shilling, pound, or whatever,
+in the particular case, is the \textit{minimum sensibile}\footnotemark)
+\footnotetext{\Ie, the smallest thing he can ``feel.'' The importance of this
+ qualification will become apparent presently (see \Pageref{129}).}
+expended on every commodity produce the same gratification.
+If this result is not attained then the money
+is not spent to the best advantage. But how is it to be
+attained? Obviously by so regulating the supplies of
+the several commodities that the marginal utilities of a
+pennyworth of each shall be equal. We take it that the
+demand of the purchaser in question is so small a part
+of the total demand for each commodity as not sensibly
+to affect the position of its quantity-index on the national
+register, and we therefore take the price of each commodity
+as being determined, independently of his
+demand, on the principles already laid down. There is
+enough lump sugar available of a given quality to supply
+\index{Sugar}%
+all people to whom it is worth 3d.\ a pound. Our housewife
+therefore gets lump sugar until the marginal utility
+of one pound is reduced to the level represented by 3d.
+Perhaps this point will be reached when she buys six
+pounds a week. The difference between six pounds and
+seven pounds a week is not worth threepence to her.
+The difference between five pounds and six is. Sooner
+than go without any loaf sugar at all she would perhaps
+pay a shilling a week for one pound. That pound
+secured, a second pound a week would be only worth,
+say, eightpence. Possibly the whole six pounds may
+represent a total utility that would be measured by
+%% -----File: 157.png---Folio 126-------
+$(12\text{d.} + 8\text{d.} + 5\tfrac{1}{2}\text{d.} + 4\text{d.} + 3\tfrac{1}{2}\text{d.}+ 3\text{d.})$ three shillings, or
+an average of sixpence a pound, but the unitary marginal
+utility of a pound is represented by threepence.
+Another housekeeper might be willing to give one and
+sixpence a week for a pound of sugar sooner than go
+without altogether, and to give a shilling a week for
+a second pound, but her demand, though more keen, may
+be also more limited than her neighbour's. She gets a
+third pound a week, worth, say, sevenpence to her, and
+a fourth worth threepence, and there she stops, because
+a fifth pound would be worth less than threepence to
+her, and there is only enough for those who think it
+worth 3d.\ a pound or more. She has purchased for a
+shilling sugar the total utility of which is represented
+by $(18\text{d.} + 12\text{d.} + 7\text{d.}+ 3\text{d.} =)$ 3s.~4d., but the unitary
+marginal utility of a pound is 3d., as in the other case.
+
+So with all other commodities. Each should be purchased
+in such quantities that the marginal utility of one
+pennyworth of it exactly balances the marginal utility of
+one pennyworth of any of the rest; the absolute marginal
+utility of the penny itself changing, of course, with
+circumstances of income, family, and so forth, but the
+relative utilities of pennyworths at the margin always
+being kept equal to each other. The clever housekeeper
+has a delicate sense for marginal utilities, and can
+balance them with great nicety. She is always on the
+alert and free from the slavery of tradition. She follows
+changes of condition closely and quickly, and keeps
+her system of expenditure fluid, so to speak, always
+ready to rise or fall in any one of the innumerable and ever
+shifting, expanding and contracting channels through
+which it is distributed, and so always keeping or
+recovering the same level everywhere. She keeps her
+marginal utilities balanced, and never spends a penny on
+A when it would be more effective if spent on B; and
+combines the maximum of comfort and economy with
+the minimum of ``pinching.''
+
+The clumsy housekeeper spends a great deal too much
+%% -----File: 158.png---Folio 127-------
+on one commodity and a great deal too little on another.
+She does not realise or follow the constant changes of
+condition fast enough to overtake them, and buys
+according to custom and tradition. Her system of
+expenditure is viscous, and cannot change its levels
+so fast as the channels change their bore. She can
+never get her marginal utilities balanced, and therefore,
+though she drives as hard bargains as any one,
+and always seems to ``get her money's worth'' in
+the abstract, yet in comfort and pleasure she does
+not make it go as far as her neighbour does, and
+never has ``a penny in her pocket to give to a boy,''\footnote
+ {The absence of which was lamented by an old Yorkshire woman
+ as the greatest trial incident to poverty and dependence.}
+\index{Penny@{\textsc{Penny} ``to give to a boy''}}%
+a
+fact that she can never clearly understand because she
+has not learned the meaning of the formula, ``My coefficient
+of viscosity is abnormally high.''
+
+\begin{Remark}
+It is rather unfortunate for the advance of economic
+science that the class of persons who study it do not as a rule
+belong to the class in whose daily experience its elementary
+principles receive the sharpest and most emphatic illustrations.
+For example, few students of economics are obliged to
+realise from day to day that a night's lodging, and a supper,
+possess utilities that fluctuate with extraordinary rapidity;
+and the tramps who, towards nightfall, in the possession of
+twopence each, make a rush on suppers, and sleep out, if the
+thermometer is at~$45°$, and make a rush on the beds and go
+\index{Thermometer}%
+supperless if it is at~$30°$, have paid little attention to the
+economic theories which their experience illustrates. As a
+rule it seems easier to train the intellect than to cultivate the
+imagination, and while it is incredibly difficult to make the
+well-to-do householder realise that there are people to whom
+the problem of the marginal utilities of a bed and a bowl of
+\index{Bed@{Bed \textit{versus} supper}}%
+stew is a reality, on the contrary, it is quite easy to demonstrate
+the general theory of value to any housekeeper who
+has been accustomed to keep an eye on the crusts, even
+though she may never have had any economic training. For
+the great practical difficulty in the way of gaining acceptance
+for the true theory is the impression on the part of all but
+%% -----File: 159.png---Folio 128-------
+the very poor or the very careful that it is contradicted by
+experience. In truth our theory demands that no want
+should be completely satisfied as long as the commodity that
+satisfies it costs anything at all; for in equilibrium the
+unitary marginal utilities are all to be proportional to the
+prices, and if any want is completely satisfied then the
+unitary marginal utility of the corresponding commodity
+must be zero, and this cannot be proportional to the price
+unless that is zero too. Again, since all the unitary marginal
+utilities are kept proportional to the prices, it follows
+that though none of them can \emph{reach} zero while the corresponding
+commodity has any price, they must all \emph{approach} zero
+together. Now all this, it is said, is contrary to experience.
+In the first place, we all of us have as much bread and meat
+and potatoes as we want, though they all cost something;
+and in the next place, whereas the marginal utility of these
+things has actually reached zero, the marginal utility of pictures,
+horses, and turtle soup has not even approached it, for
+\index{Turtle soup}%
+we should like much more than we get of them all.
+
+We have only to run this objection down in order to see
+how completely our theory can justify itself; but we must
+begin by reminding ourselves---first, that real commodities
+are not infinitely divisible, and that we are obliged to choose
+between buying a \emph{definite quantity} more or no more at all;
+and second, that our mental and bodily organs are only capable
+of discerning certain definite intervals. There may be
+two tones, not in absolute unison, which no human ear could
+distinguish; two degrees of heat, not absolutely identical, which
+the most highly trained expert could not arrange in their
+order of intensity. With this proviso as to the \emph{minimum
+venale}\footnote
+ {The reply, ``We don't make up ha'poths,'' which damps the
+ purchasing ardour of the youth of Northern England, is constantly
+ made by nature and by man to the economist who tries to apply the
+ doctrine of continuity to the case of individuals.}
+and the \textit{minimum sensibile}, let us examine the supposed
+case in detail. A gentleman has as much bread but not as
+much turtle soup as he would like. This is bad husbandry, for
+he ought to stop short of the complete gratification of his desire
+for bread at the point represented by a usefulness of sixteen-pence
+a quartern (for we assume that he takes the best quality),
+and the surplus which he now wastefully expends on reducing
+%% -----File: 160.png---Folio 129-------
+that usefulness to absolute zero might have been spent on
+turtle soup. But let us see how this would work. We must
+not allow him to adopt the royal precept of eating cake when
+he has no bread, but must suppose him \textit{bona fide} to save on
+his consumption of bread in order to increase his expenditure
+on turtle and on nothing else. Probably he already
+resembles Falstaff in incurring relatively small charges on
+\index{Falstaff}%
+account of bread---say his bill is 3d.~a~day. He has as much
+\Pagelabel{129}%
+as he wants, and therefore the marginal utility is zero, but the
+curve descends rapidly, and if we reduce his allowance by
+one-sixth, and his toast at breakfast, his roll at dinner and
+lunch, and his thin bread-and-butter at tea, or with his white-bait,
+are all of them a little less than he wants, he will find
+that the marginal utility of bread has risen far above 1s.~4d.\
+a quartern, and is more like a shilling an ounce. Taking
+the unit of~$x$ as $1$~ounce, and the unit of~$y$ as 1d., it is a
+delicate operation to arrest the curve for some value between
+$x=2\tfrac{1}{2}$, $y=12$, and $x=3$, $y=0$. But let us suppose
+our householder equal to it. He finds that $x=2\tfrac{3}{4}$ gives
+$y=1$, and accordingly determines to dock himself of $\tfrac{1}{12}$
+of his supply and save $\tfrac{1}{4}$d.~a~day on bread. But now
+arises another difficulty. He wants always to have his bread
+fresh, and the $\tfrac{1}{4}$d.~worth he saves to-day is not suitable
+for his consumption to-morrow. The whole machinery
+of the baking trade and of his establishment is too
+rough to follow his nice discrimination. Its utmost delicacy
+cannot get beyond discerning between $2\tfrac{1}{2}$d.~and~3d., and he
+finds that to be sure of not letting the marginal utility of
+bread down to zero he must generally keep it up immensely
+above 1d.~per ounce. Suppose this difficulty also overcome.
+Then our economist saves $\tfrac{1}{4}$d.~a~day on bread or 6d.\ in twenty-four
+days. In one year and 139~days he has saved enough to
+get an extra pint of turtle soup, which (if it does not reduce its
+marginal utility below 10s.~6d.)\ fully compensates him for
+his loss of bread---but not for the mental wear and tear and the
+unpleasantness in the servants' hall which have accompanied
+his fine distribution of his means amongst the objects of
+his appetite. This is in fact only an elaboration of the principle
+laid down on \Pageref{125}.
+
+As a rule, however, it is by no means true that we all
+have as much bread, meat, and potatoes as we want. Omitting
+%% -----File: 161.png---Folio 130-------
+all consideration of the great numbers who are habitually
+hungry, and confining our attention to the comfortable classes
+who always have enough to eat in a general way, we shall
+nevertheless find that the bread-bill is very carefully watched,
+and that a sensible fall in the price of bread would immediately
+cause a sensible increase in the amount taken.
+For instance, if bread were much cheaper, or if the housekeeping
+\index{Resurrection pudding}%
+allowance were much raised, many a crust would be
+allowed to rest in peace which now reappears in the ``resurrection
+pudding,'' familiar rather than dear to the schoolboy,
+who has given it its name; but also known in villadom,
+where his sister uncomplainingly swallows it without vilifying
+it by theological epithets.
+
+The assertion which for a moment seems to be true of
+bread, though it is not, is obviously false when made concerning
+milk, meat, potatoes, etc. The people who have ``as
+much as they want'' of these things are few; and if in most
+cases a more or less inflexible tradition in our expenditure
+prevents us from quite realising that we save out of potatoes
+to spend on literature or fashion, it is none the less true that
+we do so. Indeed, there are probably many houses in which
+sixpence a week is consciously saved out of bread, milk,
+cheese, etc., for the daily paper during the session, when its
+\index{Daily@{\textsc{Daily Paper}}}%
+marginal utility is relatively high, to be restored to material
+purposes when Parliament adjourns.
+
+Before leaving the subject of domestic expenditure, I
+would again emphasise the important part which tradition
+and viscosity play in it. This is so great that sometimes a
+loss of fortune, which makes it absolutely necessary to break
+\index{Fortune, loss of}%
+up the established system and begin again with the results of
+past experience, but free from enslaving tradition, has been
+found to result in a positive increase of material comfort and
+enjoyment.
+
+One of the benefits of accurate account-keeping consists in
+\index{Account-keeping}%
+the help it is found to give in keeping the distribution of
+funds fluid, and preventing an undue sum being spent on any
+one thing without the administrator realising what he is
+doing.\Pagelabel{130}%
+\end{Remark}
+
+A few miscellaneous notes may be added, in conclusion,
+on points for which no suitable place has been
+%% -----File: 162.png---Folio 131-------
+found in the course of our investigation, but which cannot
+be passed over altogether.
+
+\begin{Remark}
+The reader may have observed a frequent oscillation
+between the conceptions of ``so much a year, a month, a day,
+etc.,'' and ``so much'' absolutely. If a man has one watch,
+he will want a second watch less. But we cannot say that
+if he has one loaf of bread he will want a second loaf less.
+We can only say if he has one loaf of bread \emph{a week} (or a day,
+or some other period) he will want a second less. Our
+curves then do not always mean the same thing. Generally
+the length on the abscissa indicates the breadth of a
+stream of supply which must be regarded as continuously
+flowing, for most of our wants are of such a nature as to
+destroy the things that supply them and to need a perpetual
+renewal of the stores provided to meet them. And in the
+same way the area of the curve of quantity-and-marginal-usefulness
+or the height of the curve of quantity-and-total-utility
+does not indicate an absolute sum of gratification or
+relief from pain, but a rate of enjoyment or relief per week,
+month, year, etc. Thus, strictly speaking, the value of~$y$ in
+one of our quantity-and-marginal-usefulness curves measures
+the rate at which increments in the \emph{rate of supply} are increasing
+the \emph{rate of enjoyment}; but we may, when there is no
+danger of misconception, cancel the two last ``rates'' against
+each other, and speak of the rate at which increments in the
+\emph{supply} increase the \emph{gratification}; for the gratification (area)
+and the supply (base), though rates absolutely, are not rates
+with reference to each other, but the ratio of the increase of
+the one to the increase of the other is a rate with reference
+to the quantities themselves.
+
+We must remember, then, that, as a matter of fact, it is
+generally rates of supply and consumption, not absolute
+quantities possessed, of which we are speaking; and especially
+when we are considering the conditions of the maintenance
+of equilibrium. It will repay us to look into this conception
+more closely than we have hitherto done; and as the problem
+becomes extremely complex, unless we confine ourselves
+to the simplest cases, we will suppose only two persons, \Person{A}~and~\Person{B},
+to constitute the community, and only two articles,
+$V$~and~$W$, to be made and exchanged by them, $V$~being made
+%% -----File: 163.png---Folio 132-------
+exclusively by~\Person{A}, and $W$~exclusively by~\Person{B}. Let the curves on
+\Figref{24} represent \Person{A}'s and \Person{B}'s curves of quantity-and-marginal-utility
+of $V$~and~$W$; and let \Person{A} consume~$V$ at the rate of $q_{av}$~per
+day (or month or other unit of time) and $W$~at the rate of~$q_{aw}$,
+while \Person{B} consumes~$V$ at the rate of~$q_{bv}$, and $W$~at the rate of~$q_{bw}$.
+And let the position of the amount indices in the figure
+represent a position of equilibrium. Let us first inquire how
+many of the data in the figures are arbitrary, and then ask
+what inferences we can draw as to the conditions for maintaining
+equilibrium and the effects of failure to comply with
+those conditions.
+
+Since the quantities $q_{av}$, $q_{aw}$, etc. represent rates of consumption,
+it is evident that if equilibrium is to be preserved
+the rate of production must exactly balance them. Now the
+total rate of consumption, and therefore of production, of~$V$
+is $q_{av}+q_{bv}$, and that of~$W$ is $q_{aw}+q_{bw}$, calling these respectively
+$q_v$ and $q_w$, we have
+\begin{align*}
+\text{(i)\ \ } q_{av} &+ q_{bv} = q_v, \\
+\text{(ii) } q_{aw} &+ q_{bw} = q_w.
+\end{align*}
+
+If we call the ratio of the marginal utility of~$w$ to that of~$v$
+on \Person{A}'s relative scale~$r$, then we shall know, by the general
+law, that in equilibrium the respective marginal utilities
+must bear the same ratio on the relative scale of~\Person{B}; and if \Person{A}'s
+curve of quantity-and-marginal-usefulness in~$V$ be $y=\phi_a(x)$,
+and if $y=\psi_a(x)$, $y=\phi_b(x)$, $y=\psi_b(x)$ be the other three curves
+then we shall have
+\[
+\text{(iii)\ (iv) } \frac{\psi_a(q_{aw})}{\phi_a(q_{av})}=\frac{\psi_b(q_{bw})}{\phi_b(q_{bv})}=r,
+\]
+where $\phi_a(q_{av})$ etc.\ are the vertical intercepts on the figures,
+and where each of the ratios indicated is the ratio of the
+marginal utility of~$w$ to that of~$v$ on the relative scale. And,
+finally, since \Person{B} gets all his~$V$ by giving $W$ in exchange for
+it, getting $r$~units $v$ in exchange for one unit~$w$, and since the
+rate at which he gets it is, on the hypothesis of equilibrium,
+the rate at which he consumes it ($q_{bv}$), and the rate at which
+he gives $W$ is the rate at which \Person{A}~consumes it~($q_{aw}$), we have
+\[
+\text{(v) } q_{bv}=rq_{aw},
+\]
+and we suppose, throughout, that the consumption and production
+%% -----File: 164.p n g----------
+%[Blank Page]
+%% -----File: 165.p n g----------
+\begin{figure}[p]
+ \begin{center}
+ \Fig{24}
+% \Input{165a}
+ \end{center}
+\end{figure}
+%[To face page 133.]
+%% -----File: 166.png---Folio 133-------
+go on continuously, that is to say, not by jerks, so
+that the conditions established are never disturbed.
+
+Here, then, we have eleven quantities,
+\[
+q_v, q_w, q_{av}, q_{aw}, q_{bv}, q_{bw},
+\phi_a(q_{av}), \psi_a(q_{aw}), \phi_b(q_{bv}), \psi_b(q_{bw}), r,
+\]
+and we have five relations between them. It follows that
+we may arbitrarily fix any six of the eleven quantities. Our
+five relations will then determine the other five.
+
+Thus, if in the figures we assume that the four curves are
+known, that is equivalent to assuming that $\phi(q_{av})$, etc. are
+given in terms of $q_{av}$, etc., which reduces the number of our
+unknown quantities to seven, between which we have five
+relations. We may therefore arbitrarily fix two of them.
+Say $q_v=13$, $q_w=7$. We shall then have
+\begin{gather*}
+\text{(i)\ \ }q_{av}+q_{bv}=13, \\
+\text{(ii) }q_{bw}+q_{aw}=7, \\
+\text{(iii)\ (iv) }\frac{\psi_a(q_{aw})}{\phi_a(q_{av})}=\frac{\psi_b(q_{bw})}{\phi_b(q_{bv})}=r, \\
+\text{(v) }q_{bv}=rq_{aw},
+\end{gather*}
+which, if the meaning of $\phi_a(x)$ etc.\ be known, as we have
+supposed, gives us five equations by which to determine five
+unknown quantities. If $\phi_a(x)$ etc.\ were interpreted in accordance
+with the formulæ of the curves in the figure, these
+equations would yield the answers
+\begin{align*}
+q_{av} & = 5, \\
+q_{aw} & = 4, \\
+q_{bv} & = 8, \\
+q_{bw} & = 3, \\
+ r & = 2.
+\end{align*}
+
+I do not give the formulæ, and work out the calculation,
+since such artificial precision tends to withdraw the attention
+from the real importance of the diagrammatic method, which
+consists in the light it throws on the nature of processes, not
+in any power it can have of theoretically anticipating concrete
+industrial phenomena.
+
+Now suppose \Person{A} ceases, for any reason, to produce at the
+rate of~$13$, and henceforth only produces at the rate of~$10$.
+The equilibrium will then be disturbed and must be re-established
+under the changed conditions. We shall have the
+same five equations from which to determine the distribution
+%% -----File: 167.png---Folio 134-------
+of $V$ and~$W$, and the equilibrium exchange value between
+them except that (i)~will be replaced by
+\[
+q_{av}+q_{bv}=10.
+\]
+
+If we wrote out $\phi_a(q_{av})$, etc., in terms of $(q_{av}$,~etc., according
+to the formulæ of the curves, we might obtain definite
+answers giving the values of $(q_{av}$,~etc., and $r$~for equilibrium
+under the new conditions; but without doing so we can
+determine by inspection the general character of the change
+which will take place.
+
+If \Person{A} continues, as before, to consume~$W$ at the rate of~$4$,
+giving $V$ for it at the rate of~$8$, he will only be able to consume~$V$
+at the rate of~$2$ himself, and the marginal utility of~$v$
+will rise to more than half that of~$w$. He will therefore
+find that he is buying his last increments of~$W$ at too high
+a price, and will contract his expenditure on it, \ie,~the quantity
+index of~$(q_{aw}$, will move in the direction indicated by the
+arrow-head. But again, if \Person{A}~continues to consume~$V$ at the full
+present rate of~$5$, he will only be able to use it for purchasing~$W$
+at the rate of (the remaining)~$5$, instead of~$8$ as now, and he
+will therefore get less than~$(q_{aw}$. The marginal utility of~$w$
+will therefore be more than twice that of~$v$, and \Person{A}~will find
+that he is enjoying his last increments of~$V$ at too great a
+sacrifice of~$W$. He will therefore consume less~$V$, and the
+quantity index will move in the direction indicated by the
+arrow-head, \ie, \Person{A}~will consume less~$V$ and less~$W$, and the
+unitary marginal values of both of them will rise.
+
+But since we have seen that \Person{A}~gives less~$V$ to~\Person{B} (and
+receives less~$W$ from him), it follows that~\Person{B}, who cannot
+produce~$V$ himself, must consume it at a slower rate than
+before. This is again indicated by the direction of the
+arrow-head on the quantity-index of~$q_{bv}$. Lastly, since \Person{A}~now
+receives less~$W$ than before there is more left for~\Person{B}, who
+now consumes it at an increased rate; as is again indicated
+by the arrow-head of the quantity-index of~$q_{bw}$.
+
+Now since \Person{B}'s~quantity-indexes are moving in opposite
+directions, and the one is registering a higher and the other
+a lower marginal usefulness, it follows that the new value of~$r$
+will be lower than the old one. \Person{A}'s~quantity-indexes, then,
+must move in such a way that the length intercepted on that
+of~$q_{av}$ shall increase more than the length intercepted on that
+%% -----File: 168.png---Folio 135-------
+of~$q_{aw}$. Whether this will involve the former index actually
+moving farther than the latter depends on the character of
+the curves.
+
+The net result is that though the rate of exchange has
+altered in favour of~\Person{A}, yet he loses part of his enjoyment of
+$V$~and of~$W$ alike, while \Person{B}~loses some of his enjoyment of~$V$,
+but is partly (not wholly) compensated by an increased enjoyment
+of~$W$.
+
+If we begin by representing the marginal usefulness of $V$
+and~$W$ as being not only relatively but absolutely equal for
+\Person{A}~and~\Person{B}, then the deterioration in \Person{A}'s~position relatively to
+\Person{B}'s after the change will be indicated by the final usefulness
+of both articles coming to rest at a higher value for him than
+for~\Person{B}.
+
+The only assumption made in the foregoing argument is
+that all the curves decline as they recede from the origin.
+
+It should be noted---first, that we have investigated the
+conditions with which the new equilibrium must comply
+when reached, and the general character of the forces that
+will lead towards it, but not the precise quantitative relations
+of the actual steps by which it will be reached; and second,
+that since the equations (iii)~and~(iv) involve quadratics (if
+not equations of yet higher order), it must be left undetermined
+in this treatise whether or not there can theoretically
+be two or more points of equilibrium.
+
+The investigation of the same problem with any number
+of producers and articles is similar in character. But if we
+discuss the conditions and motives that determine the amounts
+of each commodity produced by \Person{A},~\Person{B},~etc.\ respectively, we shall
+be trespassing on the theory of production or ``making.''
+
+Now, if we turn from the problem of rates of consumption
+and attempt to deal with \emph{quantities possessed}, in the strict
+sense, without reference to the wearing down or renewal of
+the stocks, we shall find the problem takes the following
+form. Given \Person{A}'s~stock of~$V$, an imperishable article which
+both he and~\Person{B} desire; given \Person{B}'s~stock of~$W$, a similar
+article; and given \Person{A}'s and~\Person{B}'s curves of quantity-and-marginal-desiredness
+for $V$ and~$W$ alike; on what principles and
+in what ratio will \Person{A}~and~\Person{B} exchange parts of their stocks?
+The problem appears to be the same as before, but on closer
+inspection it is found that equation~(v) does not hold; for we
+%% -----File: 169.png---Folio 136-------
+cannot be sure that $V$ and~$W$ will be exchanged at a uniform
+rate up to a certain point, and then not exchanged any more.
+Therefore we cannot say
+\[
+q_{bv}= rq_{aw},
+\]
+for in the case of \emph{rates} of production, of exchange, and of consumption,
+every tentative step is reversible at the next moment.
+By the flow of the commodities the conditions assumed as
+data are being perpetually renewed; and if either of the
+exchangers finds that he can do better than he has done as
+yet, he can try again with his next batch with exactly the same
+advantages as originally, since at every moment he starts fresh
+with his new product; and if the stream of this new product
+flows into channels regulated in any other way than that
+demanded by the conditions of equilibrium we have investigated,
+then ever renewed forces will ceaselessly tend with
+unimpaired vigour to bring it into conformity with those
+conditions, so long as the curves and the quantities produced
+remain constant. But when the stocks are absolute, and
+cannot be replaced, then every partial or tentative exchange
+\emph{alters the conditions}, and is so far irreversible; nor is there
+any recuperative principle at work to restore the former conditions.
+The problem, therefore, is indeterminate, since we
+have not enough equations to find our unknown quantities
+by. The limits within which it is indeterminate cannot be
+examined in an elementary treatise. The student will find
+them discussed in F.~Y. Edgeworth's \textit{Mathematical Psychics}
+(London,~1881).
+
+This problem of absolute quantities possessed is not only
+of much greater difficulty but also of much less importance
+than the problem of \emph{rates} of consumption. For when we
+are considering the economic aspect of such a manufacture
+as that of watches, for instance, though the wares are, relatively
+\index{Watches}%
+speaking, permanent, and we do not talk of the ``rate
+of a man's consumption'' of watches, as we do in the case of
+bread---or umbrellas,---yet the \emph{manufacturer} has to consider the
+rate of consumption of watches per~annum, etc., regarded as a
+stream, not the absolute demand for them considered as a volume.
+Hence the cases are very few in which we have to deal
+with absolute quantities possessed, from the point of view of
+the community and of exchange values. But this does not
+%% -----File: 170.png---Folio 137-------
+absolve us from the necessity of investigating the problem
+with reference to the individual, for he possesses some things
+and consumes others, and has to make equations not only
+between possession and possession, and again between consumption
+and consumption, but also between possession and
+consumption. That is to say, he must ask not only, ``Do I
+prefer to possess a book of Darwin's or a Waterbury watch?''
+\index{Darwin's Works}%
+\index{Watches}%
+and, ``Do I prefer having fish for dinner or having a cigar
+\index{Cigar}%
+\index{Fish for dinner}%
+with my coffee?'' but he must also ask, ``Do I prefer to
+\emph{possess} a valuable picture or to \emph{consume} so much a year in
+\index{Pictures}%
+places at the opera?'' or, in earlier life, ``Is it worth while
+\index{Opera@{\textsc{Opera}}}%
+to give up \emph{consuming} ices till I have saved enough to \emph{possess}
+\index{Ices@{\textsc{Ices}}}%
+a knife?'' But these problems generally resolve themselves
+\index{Knife}%
+into the others. The picture is regarded as yielding a
+revenue of enjoyment, so to speak, and so its possession
+becomes a rate of consumption comparable with another rate
+of consumption; and the abstinence from ices is of definite
+duration and the total enjoyment sacrificed is estimated and
+balanced against the total enjoyment anticipated from the
+possession of the knife. If, however, the enjoyment of the
+knife is regarded as a permanent revenue (subject to risks of
+loss) it becomes difficult to analyse the process of balancing
+which goes on in the boy's mind, for he seems to be comparing
+a \emph{volume} of sacrifice and a \emph{stream} of enjoyment, and
+the stream is to flow for an indefinite period. Mathematically
+the problem must be regarded as the summing of a
+convergent series; but if we are to keep within the
+limits of an elementary treatise, we can only fall back
+upon the fact that, however he arrives at it, the boy
+``wants'' the knife enough to make him incur the privations
+of ``saving up'' for the necessary period. He is balancing
+``desires,'' and whether or not we can get behind them and
+justify their volumes or weights it is clear that, as a matter
+of fact, he can and does equate them.
+
+This will serve as a wholesome reminder that we have
+throughout been dealing with the balancing of \emph{desires} of
+equal weight or volume. I have spoken indifferently of
+``gratification,'' ``relief,'' ``enjoyment,'' ``privation,'' and so
+forth, but since it is only with the \emph{estimated} volumes of all these
+that we have to do the only things really compared are the
+\emph{desires} founded on those estimates. And so too the ``sense
+%% -----File: 171.png---Folio 138-------
+of duty,'' ``love,'' ``integrity,'' and other spiritual motives all
+\index{Duty, sense of}%
+inspire desires which may be greater or less than others, but
+are certainly commensurate with them. This thought, when
+pursued to its consequences, so far from degrading life, will
+help us to clear our minds of a great deal of cant, and to
+substitute true sentiment for empty sentimentality. When
+inclined to say, ``I have a great affection for him, and would
+do anything I could for him, but I cannot give money for I
+have not got it,'' we shall do well to translate the idea into
+the terms, ``My marginal desire to help him is great, but
+relatively to my marginal desire for potatoes, hansom cabs,
+\index{Hansom@{\textsc{Hansom Cabs}}}%
+books, and everything on which I spend my money, it is not
+high enough to establish an `effective' demand for gratification.''
+It may be perfectly right that it should be so; but
+then it is not because ``affection cannot be estimated in
+potatoes;'' it is because the gratification of this particular
+affection, beyond the point to which it is now satisfied, is
+(perhaps rightly) esteemed by us as not worth the potatoes
+it would cost. Rightly looked upon, this sense of the
+unity and continuity of life, by heightening our feelings of
+responsibility in dealing with material things, and showing
+that they are subjectively commensurable with immaterial
+things, will not lower our estimate of affection, but will
+increase our respect for potatoes and for the now no longer
+``dismal'' science that teaches us to understand them in their
+social, and therefore human and spiritual, significance.
+\end{Remark}
+%% -----File: 172.png---Folio 139-------
+
+
+\Chapter[Summary---Definitions and Propositions]{%
+Summary of Important Definitions and Propositions Contained in this Book.}
+\Pagelabel{139}
+
+\hspace*{\parindent}I\@. One quantity is a function of another when any change in the
+latter produces a definite corresponding change in the former (\Pagerange{1}{6}).
+
+II\@. The total utility resulting from the consumption or possession
+of any commodity is a function of the quantity of the commodity
+consumed or possessed (\Pagerange{6}{8}).
+
+III\@. The connection between the quantity of any commodity
+possessed and the resulting total utility to the possessor is theoretically
+capable of being represented by a curve (\Pagerange{8}{15}).
+
+IV\@. Such a curve would, as a rule, attain a maximum height,
+after which it would decline; and in any case it would \emph{tend} to reach
+a maximum height (\Pagerange{15}{19}).
+
+V\@. If such a curve were drawn, it would be possible to derive from
+it a second curve, showing the connection between the quantity of
+the commodity already possessed and the rate at which further increments
+of it add to the total utility derived from its consumption or
+possession; and the height of this derived curve at any point would
+be the differential coefficient of the height of the original curve at
+the same point (\Pagerange{19}{39}).
+
+VI\@. The differential coefficient of the total effect or value-in-use
+of a commodity is its marginal effectiveness or degree of final
+utility; as a rule marginal effectiveness is at its maximum when
+total effect is zero, and marginal effectiveness is zero when total
+effect is at its maximum (\Pagerange{39}{41}).
+
+VII\@. For small increments of commodity marginal \emph{effect} varies,
+in the limit, as marginal effectiveness (\Pagerange{41}{46}).
+
+VIII\@. In practical life we oftener consider marginal effects than
+total effects (\Pagerange{46}{48}).
+
+IX\@. In considering marginal effects we compare, and reduce to a
+common measure, heterogeneous desires and satisfactions (\Pagerange{48}{52}).
+
+X\@. A unit of utility, to which economic curves may be drawn, is
+conceivable (\Pagerange{52}{55}).
+
+XI\@. On such curves we might read the parity or disparity of
+worth of stated increments of different commodities, the proper distribution
+of labour between two or more objects, and all other
+phenomena depending on ratios of equivalence between different
+commodities (\Pagerange{55}{61}).
+
+XII\@. In practice the curves themselves will be in a constant
+state of change and flux, and these changes, together with the
+changes in the quantity of the respective commodities possessed,
+%% -----File: 173.png---Folio 140-------
+exhaust the possible causes of change in marginal effectiveness (\Pagerange{61}{67}).
+
+XIII\@. The absolute intensities of two desires existing in two
+different ``subjects'' cannot be compared with each other; but the
+ratio of \Person{A}'s~desire for~$u$ to \Person{A}'s~desire for~$w$ may be compared with
+the ratio of \Person{B}'s~desire for~$u$ or for~$v$ to \Person{B}'s~desire for~$w$ (\Pagerange{68}{71}).
+
+XIV\@. Thus, though there can be no real subjective common
+measure between the desires of different subjects, yet we may have
+a conventional, objective, standard unit of desire by reference to
+which the desires of different subjects may be reduced to an objective
+common measure (\Pagerange{73}{77}).
+
+XV\@. In a catallactic community there cannot be equilibrium as
+long as any two individuals, \Person{A}~and~\Person{B}, possessing stocks of the same
+two commodities $U$~and~$W$ respectively, desire or esteem $u$~and~$w$
+(at the margin) with unlike relative intensity (\Pagerange{71}{73}).
+
+XVI\@. The function of exchange is to bring about a state of
+equilibrium in which no such divergencies exist in the relative intensity
+with which diverse possessors of commodities severally
+desire or esteem (small) units of them at the margin (\Pagerange{80}{82}).
+
+XVII\@. The relative intensity of desire for a unit of any given
+commodity on the part of one who does \emph{not} possess a stock of it,
+may fall indefinitely below that with which one or more of its possessors
+desire it at the margin without disturbing equilibrium (\Pagerange{82}{86}).
+
+XVIII\@. Hence in every catallactic community there is a general
+relative scale of marginal utilities on which all the commodities in
+the circle of exchange are registered; and if any member of the
+community constructs for himself a relative scale of the marginal
+utilities, to him, of all the articles he possesses, this scale will (on
+the hypothesis of frictionless equilibrium) coincide absolutely, as
+far as it goes, with the corresponding selection of entries on the
+general scale; whereas, if he inserts on his relative scale any article
+he does \emph{not} possess, the entry will rank somewhere below (and may
+rank \emph{anywhere} below) the position that would be assigned to it in
+conformity with the general scale.
+
+And this general relative scale is a table of \emph{exchange values}.
+
+Thus the exchange value of a small unit of commodity is, in the
+limit, measured by the differential coefficient of the total utility, to
+any one member of the community, of the quantity of the commodity
+he possesses; and this measure necessarily yields the same result
+whatever member of the community be selected (\Pagerange{71}{86}).
+
+XIX\@. As a rule exchange value is at its maximum when value-in-use
+is zero, and exchange value is zero when value-in-use is at its
+maximum (pp.~\Pageref[]{79},~\Pageref[]{80}, \Pagerange{93}{102}).
+
+XX\@. If we can indefinitely increase or decrease our supplies of two
+commodities, then we may indefinitely change the ratio between
+the marginal effects to us, of their respective units (\Pagerange{108}{124}).
+
+XXI\@. Labour, money, or other purchasing power, secures the
+maximum of satisfaction to the purchaser when so distributed that
+equal outlays secure equal satisfactions to whichever of the alternative
+margins they are applied (\Pagerange{124}{130}).
+\Pagelabel{140}
+%% -----File: 174.png---Folio 141-------
+
+% INDEX OF ILLUSTRATIONS
+\cleardoublepage%
+\phantomsection\pdfbookmark[0]{Index of Illustrations}{Index}%
+\label{indexpage}%
+\printindex
+
+\iffalse
+Account-book@{\textsc{Account-book}}#Account-book 68
+
+Account-keeping 130
+
+Air, fresh#Air 52
+
+Athletes 90
+
+Auction 102
+
+Bath-room@{\textsc{Bath-room}}#Bath-room 47
+
+Bed@{Bed \textit{versus} supper}#Bed 127
+
+Beer 8
+
+Bibles 86
+
+Bicycles 91
+
+Billiard-tables 76
+
+Blankets 6
+
+Body, falling 2
+
+Books 52, 69
+
+Bradgate Park 68
+
+Carbon@{\textsc{Carbon Furnace}}#Carbon 37
+
+Cattle-breeding 112
+
+China 50, 56
+
+Cigar 137
+
+Cloth, price of#Cloth 1
+
+Coal 39, 47, 53, 63
+
+Coats 69
+
+Cooling iron 2
+
+Corduroys 76
+
+Corn-growing 112
+
+Daily@{\textsc{Daily Paper}}#Daily 130
+
+Darwin's Works 137
+
+Duty, sense of#Duty 138
+
+Eggs@{\textsc{Eggs}, fresh}#Eggs 52
+
+Examination papers 53
+
+Falling@{\textsc{Falling body}}#Falling 2
+
+Falstaff 129
+
+Fancy ball costumes 76
+
+Fire@{Fire in ``practising'' room}#Fire 47
+
+Fish for dinner 137
+
+Foot-tons 53, 54
+
+Fortune, loss of#Fortune 130
+
+Francis of Assisi 78
+
+Friendship 52
+
+Games@{\textsc{Games}}#Games 121
+
+Garden-hose 47
+
+Gimlet 8
+
+Gold-digging 112
+
+Gold stoppings in teeth 75
+
+Hansom@{\textsc{Hansom Cabs}}#Hansom 138
+
+Holiday 84, 85
+
+Horse 80
+
+House of Commons sitting 119
+
+Housekeeper 49, 125
+
+Ices@{\textsc{Ices}}#Ices 137
+
+Iron, cooling#Iron 2
+
+Kitchen@{\textsc{Kitchen Fire}}#Kitchen 47
+
+Knife 137
+
+Lady@{\textsc{Lady Jane Grey}}#Lady 68
+
+Linen 48, 54, 56
+
+Meat@{\textsc{Meat}, butcher's}#Meat 16
+
+Milkman@{Milkman's prices}#Milkman 104
+
+Mineral spring 93
+
+Museum, British 52
+
+Opera@{\textsc{Opera}}#Opera 137
+
+Penny@{\textsc{Penny} ``to give to a boy''}#Penny 127
+%% -----File: 175.png---Folio 142-------
+
+Pictures 76, 137
+
+Plato 68
+
+Poor men's wares 86, 87
+
+Presents 86
+
+Projectile 5, 8, 19, 32
+
+Railway@{\textsc{Railway} charges, differential}#Railway 106
+
+Rainfall 18
+
+Reading-chairs 91
+
+Reduced terms at school 108
+
+Respirators 91
+
+Resurrection pudding 130
+
+Rich men's wares 86, 87
+
+Robinson Crusoe 58, 124
+
+Root-digging 58
+
+Rossetti's Works 47
+
+Rush-gathering 58
+
+Sarah@{\textsc{Sarah Bernhardt}}#Bernhardt 85
+
+Skates 91
+
+Stock-broking 103
+
+Storm-signal 120
+
+Sugar 125
+
+Testing@{\textsc{Testing Machine}}#Testing 13
+
+Theatre, pit and stalls#Theatre 107
+
+Theatre, waiting 69, 108
+
+Thermometer 15, 127
+
+Time, distribution of#Time 60
+
+Tracts 86
+
+Tripe 77
+
+Turkish bath 14
+
+Turtle soup 128
+
+Waistcoat@{\textsc{Waistcoat}}#Waistcoat 47
+
+Waiting@{Waiting (at theatre)}#Waiting 69, 108
+
+Watches 7, 137, 136
+
+Water 47, 80
+
+Wheat 44
+
+Wine 8
+
+THE END
+\fi
+%% -----File: 176.png---Folio 143-------
+
+%[Blank Page]
+
+\backmatter
+\phantomsection
+\pdfbookmark[-1]{Back Matter}{Back Matter}
+
+%%%% LICENSE %%%%
+\pagenumbering{Alph}
+\pagestyle{fancy}
+\phantomsection
+\pdfbookmark[0]{Project Gutenberg License}{License}
+\fancyhf{}
+\fancyhead[C]{\CtrHeading{Project Gutenberg License}}
+\SetPageNumbers
+
+\begin{PGtext}
+End of the Project Gutenberg EBook of The Alphabet of Economic Science, by
+Philip H. Wicksteed
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