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+The Project Gutenberg eBook of How Two Boys Made Their Own Electrical
+Apparatus, by Thomas M. (Thomas Matthew) St. John
+
+
+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: How Two Boys Made Their Own Electrical Apparatus
+       Containing Complete Directions for Making All Kinds of Simple Apparatus for the Study of Elementary Electricity
+
+
+Author: Thomas M. (Thomas Matthew) St. John
+
+
+
+Release Date: March 15, 2009  [eBook #28335]
+
+Language: English
+
+Character set encoding: ISO-646-US (US-ASCII)
+
+
+***START OF THE PROJECT GUTENBERG EBOOK HOW TWO BOYS MADE THEIR OWN
+ELECTRICAL APPARATUS***
+
+
+E-text prepared by Peter Vachuska, Chuck Greif, Greg Bergquist, and the
+Project Gutenberg Online Distributed Proofreading Team
+(https://www.pgdp.net)
+
+
+
+Note: Project Gutenberg also has an HTML version of this
+      file which includes the original illustrations.
+      See 28335-h.htm or 28335-h.zip:
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+      or
+      (https://www.gutenberg.org/dirs/2/8/3/3/28335/28335-h.zip)
+
+
+Transcriber's Note
+
+      The punctuation and spelling from the original text have been
+      preserved faithfully. Only obvious typographical errors have
+      been corrected.
+
+
+
+
+
+HOW TWO BOYS MADE THEIR OWN ELECTRICAL APPARATUS
+
+by
+
+THOMAS M. ST. JOHN, Met. E.
+
+       *       *       *       *       *
+
+HOW TWO BOYS MADE THEIR OWN ELECTRICAL APPARATUS
+
+By THOMAS M. ST. JOHN, Met. E.
+
+EIGHTH EDITION Price, postpaid, $1.00
+
+This book contains 141 pages, 125 illustrations, and directions for
+making 152 pieces of apparatus. Size, 5x7-1/2; red cloth.
+
+CONTENTS: Chapter I. Cells and Batteries.--II. Battery Fluids and
+Solutions.--III. Miscellaneous Apparatus and Methods of
+Construction.--IV. Switches and Cut-Outs.--V. Binding-Posts and
+Connectors.--VI. Permanent Magnets.--VII. Magnetic Needles and
+Compasses.--VIII. Yokes and Armatures.--IX. Electro-Magnets.--X.
+Wire-Winding Apparatus.--XI. Induction Coils and Their
+Attachments.--XII. Contact Breakers and Current Interrupters.--XIII.
+Current Detectors and Galvanometers.--XIV. Telegraph Keys and
+Sounders.--XV. Electric Bells and Buzzers.--XVI. Commutators and Current
+Reversers.--XVII. Resistance Coils.--XVIII. Apparatus for Static
+Electricity.--XIX. Electric Motors.--XX. Odds and Ends.--XXI. Tools and
+Materials.
+
+     "The author of this book is a teacher and writer of great
+     ingenuity, and we imagine that the effect of such a book as this
+     falling into juvenile hands must be highly stimulating and
+     beneficial. It is full of explicit details and instructions in
+     regard to a great variety of apparatus, and the materials required
+     are all within the compass of very modest pocket-money. Moreover,
+     it is systematic and entirely without rhetorical frills, so that
+     the student can go right along without being diverted from good
+     helpful work that will lead him to build useful apparatus and make
+     him understand what he is about. The drawings are plain and
+     excellent. We heartily commend the book."--Electrical Engineer.
+
+     "Those who visited the electrical exhibition last May cannot have
+     failed to notice on the south gallery a very interesting exhibit,
+     consisting, as it did, of electrical apparatus made by boys. The
+     various devices there shown, comprising electro-magnets, telegraph
+     keys and sounders, resistance coils, etc., were turned out by boys
+     following the instructions given in the book with the above title,
+     which is unquestionably one of the most practical little works yet
+     written that treat of similar subjects, for, with but a limited
+     amount of mechanical knowledge, and by closely following the
+     instructions given, almost any electrical device may be made at
+     very small expense. That such a book fills a long-felt want may be
+     inferred from the number of inquiries we are constantly receiving
+     from persons desiring to make their own induction coils and other
+     apparatus."--Electricity.
+
+     "At the electrical show in New York last May one of the most
+     interesting exhibits was that of simple electrical apparatus made
+     by the boys in one of the private schools in the city. This
+     apparatus, made by boys of thirteen to fifteen years of age, was
+     from designs by the author of this clever little book, and it was
+     remarkable to see what an ingenious use had been made of old tin
+     tomato-cans, cracker-boxes, bolts, screws, wire, and wood. With
+     these simple materials telegraph instruments, coils, buzzers,
+     current detectors, motors, switches, armatures, and an almost
+     endless variety of apparatus were made. In his book Mr. St. John
+     has given directions in simple language for making and using these
+     devices, and has illustrated these directions with admirable
+     diagrams and cuts. The little volume is unique, and will prove
+     exceedingly helpful to those of our young readers who are fortunate
+     enough to possess themselves of a copy. For schools where a course
+     of elementary science is taught, no better text-book in the first
+     steps in electricity is obtainable."--The Great Round World.
+
+Exhibit of Experimental Electrical Apparatus
+
+AT THE ELECTRICAL SHOW, MADISON SQUARE GARDEN, NEW YORK.
+
+While only 40 pieces of simple apparatus were shown in this exhibit, it
+gave visitors something of an idea of what young boys can do if given
+proper designs.
+
+[Illustration:
+
+"HOW TWO BOYS MADE THEIR OWN ELECTRICAL APPARATUS"
+Gives Proper Designs--Designs for over 150 Things.]
+
+BY THE SAME AUTHOR--(LIST R)
+
+LIST NO. LIST PRICE
+
+R1--FUN WITH MAGNETISM. A book and complete outfit of apparatus for
+sixty-one experiments. Weight 4 ounces. Price $0.35
+
+R2--FUN WITH ELECTRICITY. A book and complete outfit of apparatus for
+sixty experiments. Weight 1 pound. Price $0.65
+
+R3--FUN WITH PUZZLES. A book and complete outfit for four hundred
+puzzles with key to them. One pound. Price $0.35
+
+R4--FUN WITH SOAP-BUBBLES. A book and complete outfit of apparatus for
+fancy bubbles and films. One pound. Price $0.35
+
+R5--FUN WITH SHADOWS. A book and complete outfit of apparatus for shadow
+pictures, pantomimes, etc. One pound. Price $0.35
+
+R6--FUN WITH PHOTOGRAPHY. A book and complete outfit of apparatus for
+amateur work. One pound. Price $0.65
+
+R7--FUN WITH CHEMISTRY. A book and complete outfit of apparatus for
+forty-one experiments. One pound. Price $0.65
+
+R41--ELECTRIC SHOOTING GAME. Absolutely harmless; fascinating. Paper
+bullets shot by electricity. One pound. Price $0.35
+
+R42--ELECTRIC AIR-SHIPS AND OTHER GAMES. Great fun. Get into the game;
+be an aviator at home; for two players. One pound. Price $0.35
+
+R43--ELECTRIC FORTUNE-TELLER tells a lot. Mysteriously electric. Comic
+and otherwise. In preparation. One pound. Price $0.35
+
+R51--HOW TWO BOYS MADE THEIR OWN ELECTRICAL APPARATUS. A book containing
+complete directions for making many kinds of electrical apparatus.
+Seventh edition; 141 pages; cloth. Price $1.00
+
+R52--THE STUDY OF ELEMENTARY ELECTRICITY AND MAGNETISM BY EXPERIMENT. A
+text-book for students and others. Systematic course for home or school.
+220 pages; 200 experiments; cloth; fourth edition. Price $1.25
+
+This book with 105 pieces of apparatus complete, by express $6.25
+
+R53--THINGS A BOY SHOULD KNOW ABOUT ELECTRICITY explains in simple
+language things a boy wants to know, things he should know. Seventh
+edition. 180 pages; cloth. Price $1.00
+
+R54--REAL ELECTRIC TOY-MAKING FOR BOYS contains complete directions for
+making and using many electrical toys. Over 100 original drawings,
+diagrams and plates. Second edition; 140 pages, cloth. Price $1.00
+
+R55--WIRELESS TELEGRAPHY FOR AMATEURS AND STUDENTS contains theoretical
+and practical information, together with directions for performing
+numerous experiments on wireless with simple home-made apparatus. Third
+and enlarged edition in preparation. Price $1.00
+
+R56--ELECTRICAL HANDICRAFT contains complete directions for making and
+using nearly 150 pieces of electrical apparatus, including various
+devices and outfits for experimental purposes. New ideas and inexpensive
+supplies. Cloth; 252 pages; 250 drawings. Second edition. Price $1.00
+
+R57C--THE STUDY OF ELECTRIC MOTORS BY EXPERIMENT contains sixty
+experiments that bear directly upon the construction, operation and
+explanation of electric motors, together with much helpful information
+upon the apparatus required. Over 100 pages; paper cover. Price $0.35
+
+R58--THINGS A BOY SHOULD KNOW ABOUT WIRELESS contains much practical and
+some theoretical information on the operation and explanation of
+wireless outfits, together with numerous wiring-diagrams. Third edition;
+126 pages; cloth. Price $1.00
+
+Ask your Bookseller, Toy-dealer or Electrical Store for our Books,
+Games, Toys and Electrical Apparatus.
+
+Write for Catalogue.
+
+THOMAS M. ST. JOHN, Cascade Ranch, East Windham, N.Y.
+
+       *       *       *       *       *
+
+
+HOW TWO BOYS MADE THEIR OWN ELECTRICAL APPARATUS
+
+Containing Complete Directions for Making All Kinds of Simple
+Apparatus for the Study of Elementary Electricity
+
+by
+
+THOMAS M. ST. JOHN, Met. E.
+
+Author of "Fun With Magnetism," "Fun With Electricity,"
+"The Study of Elementary Electricity and Magnetism
+by Experiment," "Things A Boy Should Know
+About Electricity," etc.
+
+Eighth Edition
+
+
+
+
+
+
+
+Thomas M. St. John
+Cascade Ranch
+East Windham      New York
+
+Copyright, 1898,
+by Thomas M. St. John
+
+
+
+
+How Two Boys Made Their Own Electrical Apparatus.
+
+
+TABLE OF CONTENTS.
+
+CHAPTER.                                                       PAGE.
+
+    I. Cells and Batteries,                                        5
+
+   II. Battery Fluids and Solutions,                              15
+
+  III. Miscellaneous Apparatus and Methods of Construction,       20
+
+   IV. Switches and Cut-Outs,                                     28
+
+    V. Binding-Posts and Connectors,                              32
+
+   VI. Permanent Magnets,                                         37
+
+  VII. Magnetic Needles and Compasses,                            40
+
+ VIII. Yokes and Armatures,                                       45
+
+   IX. Electro-Magnets,                                           51
+
+    X. Wire-Winding Apparatus,                                    60
+
+   XI. Induction Coils and Their Attachments,                     64
+
+  XII. Contact Breakers and Current Interrupters,                 75
+
+ XIII. Current Detectors and Galvanometers,                       78
+
+  XIV. Telegraph Keys and Sounders,                               92
+
+   XV. Electric Bells and Buzzers,                               104
+
+  XVI. Commutators and Current Reversers,                        110
+
+ XVII. Resistance Coils,                                         114
+
+XVIII. Apparatus for Static Electricity,                         117
+
+  XIX. Electric Motors,                                          122
+
+   XX. Odds and Ends,                                            133
+
+  XXI. Tools and Materials,                                  137-141
+
+
+
+
+A WORD TO BOYS.
+
+
+The author is well aware that the average boy has but few tools, and he
+has kept this fact constantly in mind. It is a very easy matter for a
+skilled mechanic to make, with proper tools, very fine-looking pieces of
+apparatus. It is not easy to make good apparatus with few tools and a
+limited amount of skill, unless you follow simple methods.
+
+By following the methods given, any boy of average ability can make the
+apparatus herein described.
+
+Most of the illustrations have been made directly from apparatus
+constructed by young boys.
+
+It is impossible to describe the different pieces of apparatus in any
+special or logical order. It is taken for granted that you have some
+book of simple experiments and explanations to serve as a guide for the
+order, and to give you an idea of just the apparatus needed for the
+special experiments.
+
+It would be foolish to start in and make all the apparatus described,
+without being able to intelligently use it in your experiments. Take up
+a systematic course of simple experiments, and make your own apparatus,
+as needed.
+
+Before making any particular piece of apparatus, read what is said about
+the other pieces of the same general nature. This will often be a great
+help, and it may suggest improvements that you would like to have.
+
+In case your apparatus does not work as expected, read the directions
+again, and see if you have followed them. Wrong connections, poor
+connections, short circuits, broken wire, etc., will make trouble. With
+a little patience and care you will be able to locate and correct any
+troubles that may come up in such simple apparatus.
+
+THOMAS M. ST. JOHN.
+
+
+
+
+How Two Boys Made Their Own Electrical Apparatus
+
+
+
+
+CHAPTER I.
+
+CELLS AND BATTERIES.
+
+
+APPARATUS 1.
+
+_1. Carbon-Zinc Cell._ Fig. 1. If you have some rubber bands you can
+quickly make a cell out of rods of zinc and carbon. The rods are kept
+apart by putting a band, B, around each end of both rods. The bare wires
+are pinched under the upper bands. The whole is then bound together by
+means of the bands, A, and placed in a tumbler of fluid, as given in
+App. 15. This method does not make first-class connections between the
+wire and rods. (See Sec. 3.)
+
+[Illustration: Fig. 1.]
+
+
+APPARATUS 2.
+
+[Illustration: Fig. 2.]
+
+_2. Carbon-Zinc Cell._ Fig. 2. In case you want to make your cell out of
+carbon and zinc rods, and do not have any means of making holes for them
+in the wood, as in App. 3 and 4, you will find this method useful. Cut
+grooves, G, into one side of the wood, A, which should be about 4-1/2 x
+1 x 1/2 in. The grooves should be quite deep, and so placed that the
+rods will be about 1/4 in. apart. A strip of tin, T, 1/2 in. wide,
+should be bent around each rod. The screw, S, put through the two
+thicknesses of tin will hold the rod in place. Another screw, X, acts as
+a binding-post. The zinc rod only is shown in Fig. 2. The carbon rod is
+arranged in the same way. Use the fluid of App. 15.
+
+3. Note. When the bichromate solution of App. 15 is used for cells, the
+strong current is given, among other reasons, because the zinc is
+rapidly eaten up. This action goes on even when the circuit is broken,
+so always remove and wash the zinc as soon as you have finished.
+
+
+APPARATUS 3.
+
+_4. Carbon-Zinc Cell._ Fig. 3. The wooden cross-piece, A, is 4-1/2 x 1 x
+1/2 in. The carbon and zinc rods, C and Z, are 4 in. long x 1/2 in. in
+diameter. The holes are bored, if you have a brace and bit, so that they
+are 3/4 in. apart, center to center. This makes the rods 1/4 in. apart.
+To make connections between the rods and outside wires, cut a shallow
+slot at the front side of each hole, so that you can put a narrow strip
+of tin or copper, B, in the hole by the side of each rod. Setscrews, S,
+screwed in the side of A, will hold the rods in place, and at the same
+time press the strips, B, against them. Connections can easily be made
+between wire and B by using a spring binding-post, D, or by fastening
+the wire direct to the strips, as shown in App. 4.
+
+[Illustration: Fig. 3.]
+
+Use the battery fluid given in App. 15, and use a tumbler for the
+battery jar. This cell will run small, well-made motors, induction
+coils, etc. (See Sec. 3.)
+
+
+APPARATUS 4.
+
+_5. Carbon-Zinc Cell._ Fig. 4. The general construction of this cell is
+the same as that of App. 3. There are 2 carbons, C, each 4 x 1/2 in. The
+holes for these are bored in A 1-1/4 in. apart, center to center. The
+zinc rod, Z, is a regular battery zinc, 6 x 3/8 in., and has a
+binding-post, Y, of its own. The rods, C, are held in A, and connections
+are made as explained in App. 3.
+
+[Illustration: Fig. 4.]
+
+The wire, X, is fastened direct to the strips, B, as shown. When ready
+to use this cell, be sure that the wire connecting the carbons does not
+touch Z. (Why?) The other wire is connected to Y. The wooden piece is
+4-1/2 x 1 x 1/2 in. Use the battery fluid of App. 15 in a tumbler. This
+cell will run small motors, and is good for induction coils, etc. (See
+Sec. 3.)
+
+
+APPARATUS 5.
+
+[Illustration: Fig. 5.]
+
+_6. Experimental Cell._ Fig. 5. Cut a strip each of copper, C, and zinc,
+Z. (See list of materials.) They should be about 2 in. wide and 4 in.
+long. Punch a hole through each, one side of the center, for screws, E.
+The wooden cross-piece, A, should be 4-1/2 x 1 x 7/8 in. The
+battery-plates, or elements, should be screwed to this, taking care that
+the screws, E, do not touch each other. If the holes are made in the
+position shown in Fig. 5, the screws can be arranged some distance
+apart.
+
+The wires leading from the cell may be fastened under the screws with
+copper burs, or spring binding-posts (App. 42) can be slipped on the top
+of the plates.
+
+The solution to be used will depend upon what the cell is to do. For
+simple experiments use the dilute acid (App. 14). If for small motors,
+use the formula given in App. 15. The zinc should be well amalgamated.
+(App. 20.)
+
+
+APPARATUS 6.
+
+[Illustration: Fig. 6.]
+
+_7. Experimental Cell._ Fig. 6. In some experiments a comparison is made
+between cells with large plates and cells with small ones. This form
+will be convenient to use where narrow plates are desired. Those shown
+are 4 x 1/2 in. They are screwed to the cross-piece, which is 4-1/2 x 1
+x 7/8 in. Do not let the screws touch each other. The wires are fastened
+under the screw-heads.
+
+
+APPARATUS 7.
+
+[Illustration: Fig. 7.]
+
+_8. Experimental Two-fluid Cell._ Fig. 7. This cell has a zinc strip, Z,
+and copper cylinder, C, for the "elements." The porous cup, P C, is
+fully described in App. 11. Z is 5 x 1 in., and should be well
+amalgamated (App. 20). (Study reasons for amalgamation.) A zinc rod,
+like that shown in Fig. 4, may be used instead of the strip. The copper
+cylinder, C, nearly surrounds P C, and is made from a piece of thin
+sheet-copper, 6 x 2 in. The narrow strip, or leader, A, is 5 x 1/2 in.
+To fasten it to C, punch two small holes in C and A, put short lengths
+of stout copper wire through the holes, and hammer them down so that
+they will act as rivets, R. C can be hung centrally in the tumbler by
+bending A as shown. Y and X are spring binding-posts (App. 42). The
+battery wires can be fastened directly to Z and A, as suggested in Fig.
+4.
+
+9. Setting up the Cell. Arrange as in Fig. 7, but remove Z from P C.
+Pour some of the acid solution of App. 14 into P C until it stands about
+2-1/2 in. deep, and at once pour the copper solution of App. 16 in the
+tumbler, on the outside of P C, until it stands at the same height as
+the liquid in P C. As soon as the liquids have soaked into P C, you can
+put Z in place, when the cell will be ready for use. Remove and wash Z,
+when you have finished, and if you wish to use this cell occasionally,
+remove the liquids and wash P C thoroughly in water. When dry it will be
+as good as new. The acid rapidly acts upon Z, so it is better to remove
+Z if you wish to leave the experimenting even for a few minutes only.
+
+Put a few crystals of copper sulphate (blue vitriol) in the tumbler
+under the copper, to keep the copper solution saturated. (See text-book
+for the chemical action in this two-fluid cell.)
+
+
+APPARATUS 8.
+
+_10. Two-fluid Battery._ Fig. 8. When two or more cells are joined
+together the combination is called a battery. Fig. 8 shows two
+experimental cells joined in series. (Study methods of joining cells.)
+For convenience, and to keep them from being easily overturned, a frame
+has been made for them. The base, B, is 8 x 4 x 7/8 in. To the back of
+this is nailed the upright board, A, 8 x 4-1/2 x 1/2 in. On the top of A
+are 3 binding-posts, 1, 2, 3, which consist of metal strips 1-1/4 x 1/2
+in. At the lower ends are screws which are connected with the cells, as
+shown. Spring binders can be easily slipped on and off the upper ends of
+the strips, so that one or two cells can be used at will. Bent strips,
+C, are nailed to B, to hold the tumblers firmly in place. This framework
+is not necessary, of course, to the proper working of the battery, but
+with it you are much less liable to upset the cells.
+
+[Illustration: Fig. 8.]
+
+
+APPARATUS 9.
+
+_11. Gravity Cell._ Fig. 9. In the two-fluid cell of App. 7 the fluids
+were kept apart by the porous cup. The gravity cell is really a
+two-fluid cell in which the two liquids are kept separate by the joint
+action of the current and the force of gravity. This cell is used for
+telegraph lines and for other closed-circuit work.
+
+12. Construction. The zinc and copper, Z and C, Fig. 9, can be purchased
+about as cheaply as you can make them. There are many forms of the
+zincs, the one shown being called the crow-foot shape. The copper may be
+star-shaped, or as shown. If you wish to make C, use thin sheet-copper.
+Brush copper, 1-3/4 in. wide, is excellent for the purpose. Use a piece
+12 or 15 in. long, and fasten to one end of it a copper wire, W, which
+must be covered with paraffined paper, or with rubber or glass tubing,
+where it passes up through the zinc sulphate solution and near Z. The
+glass jar, J, may be made from a large glass bottle. (See index for
+battery jars.)
+
+13. To Set Up the Cell. (A) Place C upon the bottom of J, with W in the
+position shown. (B) Put in enough copper sulphate crystals to cover the
+bottom of J, but do not try to entirely cover C. At the start 1/2 lb.
+will be enough. (C) Pour in clean water until J is half full. (D) In
+another vessel dissolve 1 or 2 oz. of zinc sulphate in enough water to
+complete filling, J. (E) Hang Z in place (Fig. 9). Z must never touch C.
+They should be about 3 in. apart. A wire is attached to Z by the screw,
+S, and the hole, H. (F) Pour the zinc sulphate solution into J until it
+is within an inch of the top. It should cover Z.
+
+[Illustration: Fig. 9.]
+
+(G) Connect the wires leading from Z and C to your sounder and key. (See
+diagram.) The cell will be weak at first, and it may not be able to run
+your sounder. If this is the case, "short-circuit" it by allowing the
+current to run around and around through the sounder and key, the switch
+being closed. You may also "short-circuit" the cell by joining the two
+wires together. This will, in a few hours, make the dividing line
+between the blue and white quite distinct, when the cell will be
+stronger. If you have a short line only, the battery may be
+short-circuited through your sounder or other coils of wire for 5 or 6
+hours a day, without working it too much. It may be necessary to draw
+off some of the clear zinc sulphate, replacing it with clear water, if
+the blue line gets too low. Add water occasionally to make up for
+evaporation.
+
+14. Regulating. The two solutions are kept apart by gravity, as the
+copper sulphate is heavier than the zinc sulphate. The dividing line
+between the blue and white solutions is fairly clear when the battery
+works well, and it should be about half way between C and Z, or about at
+J, Fig. 9. Never allow the blue to get as high as Z, as this indicates
+that the cell is not worked enough. The dividing line can be lowered by
+allowing it to run a buzzer or bell for a few hours, or by simply
+short-circuiting it. If the blue gets much below J it indicates that you
+are working the cell too hard, or that you need more copper sulphate.
+The harder the cell works, the more zinc sulphate is formed, and the
+lower the dividing line becomes.
+
+15. Gravity Batteries of two more cells are needed when used on
+telegraph lines. You will need 1 cell to each sounder; that is, for a
+short line in the house with two sounders, use 2 cells. If you use a few
+hundred feet of wire running to a friend's house, use 3 cells. They must
+be joined in series; that is, the copper of one to the zinc of the
+other. (See diagram of complete telegraph line.) Do not use ground
+connections for short lines and home-made sounders; use a return wire.
+Do not use different kinds of cells upon the same line.
+
+
+APPARATUS 10.
+
+_16. Storage Battery._ To show the principle of storage batteries it is
+only necessary to use two plates of lead dipped in the battery fluid of
+App. 14. The cell may be made as in App. 5, Fig. 5, the only difference
+being that both plates are of sheet-lead. It will be an advantage to
+make the plates rough by hammering against them a coarse file. (See
+explanations and experiments with this form of cell in text-book.)
+
+
+APPARATUS 11.
+
+[Illustration: Fig. 10]
+
+_17. Porous Cups for Two-fluid Cells._ Fig. 10. Very good porous cups
+can be made from ordinary blotting-papers, the average ones measuring
+9-1/2 x 4 in. White ones should be used, so that you will not be
+bothered with the color coming out. Soak the edge along one end of the
+blotter in paraffine (Index) for about 1/4 in. When this is cold, roll
+the blotter into the form of a cylinder that is a little over 1 in.
+inside diameter, and have the paraffined end on the outside. This will
+make 2 thicknesses of paper all around, and a little to spare. Rub a hot
+nail over the paraffine to melt it, and stick the end to the cylinder.
+By putting on a little more paraffine along the edge where the end laps
+over, a good solid cylinder can be made. The cylinder should be
+strengthened still more by dipping each end into melted paraffine for
+about 1/8 in. The dark stripes around the ends and down the front of the
+cylinder (Fig. 10) are to represent the paraffine. Cut out a bottom
+about 1/4 in. larger all around than the cylinder. This may be
+paraffined to make it stiff. It should be fastened to the cylinder with
+paraffine. Paraffine is not acted upon or softened by water or acid, as
+is the case with glue.
+
+
+APPARATUS 12.
+
+_18. Porous Cups for Two-fluid Cells._ Instead of the blotters of App.
+11, you can use short lengths of mailing-tubes, which are used to
+protect pictures, etc., when sent by mail. If you find that the
+particular tube tends to unwind when soaked, you can use a little
+paraffine along the edges of the spiral, as suggested in App. 11.
+Bottoms can be made for the cups as before.
+
+
+APPARATUS 13.
+
+_19. Porous Cups for Two-fluid Cells._ Ordinary unglazed earthen
+flower-pots make good cups. The hole in the bottom should be closed with
+a cork, or by fastening a piece of pasteboard over the hole with
+paraffine. The pasteboard may be fastened to the under side of the
+bottom more easily than to the upper side.
+
+20. Note. It is a good idea to soak the top edge of porous cups for
+about 1/4 in. in paraffine to keep the solutions from crawling up by
+capillary attraction. If the solutions constantly evaporate from the
+soaked tops of the cups, they not only waste but they get the whole
+thing covered with crystals.
+
+
+
+
+CHAPTER II.
+
+BATTERY FLUIDS AND SOLUTIONS.
+
+
+_21. Sulphuric Acid._ THIS ACID MUST BE HANDLED WITH GREAT CARE, as it
+(the concentrated) is very strong, and will burn the hands, eat holes in
+clothing, carpets, etc.; it will even char wood. Do not let any of it
+drop anywhere accidentally. If you wish to pour concentrated acid into a
+bottle, place the bottle to be filled upon a plate, and wipe all drops
+of acid from the outside of it afterward. The concentrated acid should
+be kept in tightly-corked bottles, as it absorbs moisture from the air
+very rapidly. Ordinary corks should be paraffined if they are to be used
+in acid bottles, or they will be soon eaten up.
+
+22. Mixing. When sulphuric acid and water are mixed, considerable heat
+is produced. Never pour water into the acid, as the heat would be
+produced so rapidly that the vessel containing the mixture might break.
+Always pour the acid into the water, and thoroughly stir the mixture at
+the same time. Earthen vessels do not break when heated as easily as
+glass ones. The mixing may be done in ordinary glass fruit-jars, if care
+be taken to pour the acid slowly into the water. The jars should be set
+in some larger dish, or in the sink, before adding the acid. If they get
+too hot, allow them to cool a little before proceeding with the mixing.
+As the acid is much heavier than water, it will immediately sink to the
+bottom of the jar, unless constantly stirred.
+
+23. There are different grades of acid upon the market. For battery
+purposes you do not need the chemically pure (C P) acid. The ordinary
+"commercial acid" is all right, even though it is a little dark in
+color. You can get this at any drug-store. Get 5 or 10 cents' worth at a
+time.
+
+
+APPARATUS 14.
+
+_24. Battery Fluid for Simple Cells._ For the simple cell (App. 5), when
+it is to be used for experiments with detectors or in the study of
+polarization, etc., a very dilute acid is best. Mix 1 fluid ounce of
+commercial acid with 1 pint of water. This will make 17 fluid ounces
+(See App. 19), and your mixture will be one-seventeenth acid. Make up a
+pint or quart bottle of this at a time, and label it with the date:
+
+Dilute sulphuric acid.
+1 part acid, 16 parts water.
+Apparatus 14.
+
+25. Note. Do not fail to paste a label on all bottles as soon as you
+have put anything into them. Give the date, contents, and any other
+information that will help you to reproduce the mixture again. Do not
+write on them any abbreviations or other things that you will soon
+forget.
+
+
+APPARATUS 15.
+
+_26. Battery Fluid; Bichromate Solution._ For running small motors,
+shocking coils, etc., this solution will be found good when used with
+the zinc and carbon elements given in App. 3 and 4. The bichromate
+destroys the hydrogen bubbles which help to polarize cells so rapidly
+when the plain dilute acid (App. 14) is used. (Study polarization.) The
+zinc used in this fluid must be well amalgamated (App. 20).
+
+Directions. With 1 quart of cold water placed in a glass or earthen
+dish, slowly mix 4 fluid ounces of commercial sulphuric acid. Read
+Sec. 22 carefully. When this gets about cold, add 4 ounces of
+bichromate of potash. Powdered bichromate will dissolve more quickly
+than the lump. Keep this fluid in corked bottles, labelled, with date:
+
+Bichromate Battery Fluid.
+Apparatus 15.
+
+27. Always take the zinc from this fluid as soon as you have finished
+experimenting, or even if you have no use for the cell for a few
+minutes. The zinc and fluid are rapidly destroyed in bichromate cells
+even when the circuit is open. Always wash the carbon and zinc as soon
+as you take them from the fluid.
+
+
+APPARATUS 16.
+
+_28. Battery Fluid._ For 2-fluid cells (App. 7), a saturated solution of
+copper sulphate (blue vitriol) is needed. Place some of the crystals in
+a glass jar, with water, stir them around, and add the sulphate as long
+as it is dissolved. A few extra crystals should be left in the stock
+bottle so that the solution will always be saturated.
+
+
+APPARATUS 17.
+
+_29. Vinegar Battery Fluid._ For a few of the experiments with
+detectors, etc., good strong vinegar does well as the exciting fluid.
+This may be used with the copper and zinc or carbon and zinc elements.
+The amount of current given with vinegar and App. 4 or 5 is sufficient
+to show many of the simpler experiments.
+
+
+APPARATUS 18.
+
+_30. Battery Fluid._ Strong brine, made by dissolving ordinary salt in
+water, will produce quite a little current with App. 4 or 5. The
+presence of the current is easily shown with the astatic detectors.
+
+
+APPARATUS 19.
+
+_31. Measures for Water, Acids, etc._ If you do not own a graduated
+glass, such as druggists use for measuring liquids, the following plan
+will be found useful. In the mixing of battery fluids, etc., while it is
+not necessary to be absolutely exact, it is necessary to know
+approximately what you are doing.
+
+An ordinary glass pint fruit jar may be taken as the standard. This
+holds 16 fluid ounces, or 2 ordinary teacupfuls. A teacupful may then be
+taken as 1/2 pint, or 8 fluid ounces. You can probably find a small
+bottle that will hold 1 or 2 oz., and you can easily tell how much it
+holds by filling it and counting the number of times it is contained in
+the pint can.
+
+A slim bottle holding 1/2 pint can be made into a convenient measuring
+glass by scratching lines on it with the sharp edge of a hard file. The
+lines should be placed, of course, so that they will show how much
+liquid you must put into it to make 1 oz., 2 oz., etc. Instead of the
+file marks, a narrow strip of paper may be pasted upon the bottle, and
+the divisions shown by lines drawn upon the paper.
+
+
+APPARATUS 20.
+
+_32. To Amalgamate Battery Plates._ To keep the zinc plates or rods in
+cells from being eaten or dissolved when the circuit is opened, they
+should be amalgamated; that is, they should have a coating of mercury.
+The local currents (see text-book) aid in rapidly destroying the zinc,
+unless it is amalgamated. Do not amalgamate copper plates--merely the
+zinc ones.
+
+33. Place a few drops of mercury in a butter dish. Dip the zinc into the
+solution of App. 14, then lay it upon a flat board. This is necessary
+with thin sheet-zinc, as it becomes very brittle when coated with
+mercury, and will not stand hard rubbing. If you also dip a very narrow
+piece of tin into the dilute sulphuric acid, you can use this as a spoon
+and lift one drop of mercury at a time from the butter dish to the zinc.
+By tapping the tin upon the zinc, the mercury will leave the tin. Put
+the mercury only where the zinc will be under the solutions in the cell,
+then rub the drops around with a small cloth that has been dipped in the
+acid. The zinc will become very bright and silvery, due to the mercury.
+Do not get too much mercury on it, just enough to give it a thin coat,
+as it will make the thin zinc so brittle that it will very easily break.
+Amalgamate both sides of the zinc.
+
+
+
+
+CHAPTER III.
+
+MISCELLANEOUS APPARATUS AND METHODS OF CONSTRUCTION.
+
+
+APPARATUS 21.
+
+_34. For Annealing and Hardening Steel._ (See text-book for reasons why
+some parts of electrical apparatus should be made of hard steel, while
+other parts should be made of soft iron.)
+
+35. To anneal or soften spring steel so that you can bend it without
+breaking it, heat it in a candle, gas, or alcohol flame until it is
+red-hot; allow the steel to cool in the air slowly.
+
+36. To harden steel, heat as before, then suddenly plunge the red-hot
+piece into cold water. This will make the steel very hard and brittle.
+
+Small pieces may be held by pinching them between two pieces of wood.
+Needles and wires may be stuck in a cork, which will serve as a handle.
+(See text-book.)
+
+
+APPARATUS 22.
+
+[Illustration: Fig. 11.]
+
+_37. Alcohol Lamp._ Fig. 11. An alcohol lamp is very useful in many
+experiments, and it is better than a candle for annealing or hardening
+steel needles when making small magnets (App. 21). You can make a good
+lamp by using a small bottle with a wide opening. A vaseline bottle or
+even an ink bottle will do. Make a hole about 1/4 in. in diameter
+through the cork with a small round file, or burn it through with a hot
+nail. Make a cylinder of tin about 1-1/2 in. long and just large enough
+to push through the hole. The tin may be simply rolled up. If you have
+glass tubing, use a short length of that instead of the tin. For the
+wick, roll up some flannel cloth. This should not fit the inside of the
+tin tube too tightly. The alcohol should be put into the lamp when you
+want to use it, and that left should be put back into the supply-bottle
+when you have finished, as alcohol evaporates very rapidly. The flame of
+this lamp is light-blue in color, and very hot.
+
+Caution. Do not have your supply-bottle of alcohol near the lamp when
+you light the latter, or near any other flame. The vapor of alcohol is
+explosive.
+
+
+APPARATUS 23.
+
+_38. Spool Holder for Wire._ Fig. 12. When winding magnets it is
+necessary to have the spool of wire so arranged that it will take care
+of itself and not interfere with the winding. If you have a brace and
+bit, bore a hole in a base 7/8 in. thick for a 1/4 in. dowel. The dowel
+should fit the hole tight. The spools of wire purchased can then be
+placed upon the dowel, where they will unwind evenly. The base may be
+nailed or clamped to a table.
+
+[Illustration: Fig. 12.]
+
+
+APPARATUS 24.
+
+_39. Spool Holder for Wire._ If you have no brace and bit to make App.
+23, nail a spool to a wooden base, place a short length of dowel in the
+spool, and use this combination as a spool holder. Make the dowel fit
+the spool by winding paper around it.
+
+
+APPARATUS 25.
+
+_40. To Make Holes in Wood._ If you have a brace and a set of bits, or
+even a small hand-drill, it will be an easy matter to bore holes in
+wood. An awl should be used to make holes for screws, such as those
+used in making binding-posts, etc., as the wood is very liable to split
+if a screw is forced into it without a previously-made hole.
+
+Red-hot nails, needles, etc., are easily made to burn holes of desired
+diameters. They may be heated in a gas flame or by means of the alcohol
+lamp (App. 22). Flat pieces of hot steel will burn narrow slots, and
+small, square holes may be made with hot nails.
+
+
+APPARATUS 26.
+
+_41. To Make Holes in Sheet-Metal._ Fig. 13. Holes may be punched in
+sheet-tin, copper, zinc, etc., in the following manner: Set a block of
+hard wood, W, on end; that is, place it so that you will pound directly
+against the end of the grain. Lay the metal, T, to be punched, upon
+this, and use a flat-ended punch. A sharp blow upon a good punch with a
+hammer will make a fairly clean hole; that is, it will cut out a piece
+of metal, and push it down into the wood. A sharp-pointed punch will
+merely push the metal aside, and leave a very ragged edge to the hole. A
+punch may be made of a nail by filing its end flat.
+
+[Illustration: Fig. 13.]
+
+
+APPARATUS 27.
+
+_42. To Punch Holes through Thick Yokes, etc._ As soon as 5 or 6 layers
+are to be punched at one operation, the process becomes a little more
+difficult than that given in App. 26. If you have an anvil, you can
+place the yoke over one of the round holes in it, and punch the tin
+right down into the hole, the ragged edges being afterward filed off.
+Hold the yoke as in App. 79 or 80 for filing. As you will probably have
+no anvil, lay an old nut from a bolt upon the end of the block of wood
+(App. 26), place the metal to be punched over the hole, and imagine that
+you have an anvil. Very good results may be obtained by this method. The
+size of nut used will depend upon the size of hole wanted.
+
+
+APPARATUS 28.
+
+_43. To Straighten Wires._ It is often necessary to have short lengths
+of wires straight, where they are to be made into bundles, etc. To
+straighten them, lay one or two at a time upon a perfectly flat surface,
+place a flat piece of board upon them, then roll them back and forth
+between the two. The upper board should be pressed down upon the wires
+while rolling them. If properly done, the wires can be quickly made as
+straight as needles.
+
+_44. Push-Buttons._ Nearly every house has use for one or more
+push-buttons. The simple act of pressing your finger upon a movable
+button, or knob, may ring a bell a mile away, or do some other equally
+wonderful thing.
+
+
+APPARATUS 29.
+
+_45. Push-Button._ Fig. 14. This is made quickly, and may be easily
+fastened to the window or door-casing. One wire is joined to A and the
+other to C. B is a strip of tin or other metal, about 5/8 in. wide and 2
+in. long. It is bent so that it will not touch A unless it is pressed
+down. This may be placed anywhere, in an electric-bell circuit or other
+open circuit, where it is desired to let the current pass for a moment
+only at a time.
+
+[Illustration: Fig. 14.]
+
+
+APPARATUS 30.
+
+_46. Push-Button._ Fig. 15 and Fig. 16. By placing App. 29 in a box, we
+can make something that looks a little more like a real push-button.
+Fig. 15 shows a plan with the box-cover removed, and Fig. 16 shows a
+view of the inside of it, a part of the box being cut away. C, Fig. 15,
+is a wooden pill-box 1 in. high and 1-3/4 in. in diameter. Make a 1/4
+in. hole in the cover of C for the "button," G, which is a short piece
+of 1/4 in. dowel. This rests upon a single thickness of tin, D, which is
+cut into a strip 3/8 in. wide and about 1-1/4 in. long. In the bottom of
+C are two holes just large enough to allow the screws E and F to pass
+through. The wires, A and B, pass from the binding-posts, X and Y,
+through small holes burned through the sides of the box, and are
+fastened under the screw-heads. The whole box is screwed to the wooden
+base, which is 3 x 4 x 7/8 in., by the screws, E and F. D should have
+enough spring in it to raise itself and G when the pressure of the
+finger is removed. The circuit will be closed only when you press the
+button.
+
+[Illustration: Fig. 15.]
+
+[Illustration: Fig. 16.]
+
+
+APPARATUS 31.
+
+_47. Push-Button._ Figs. 17, 18, 19. Fig. 17 shows a top view or plan of
+the apparatus. Fig. 18 is a sectional view; that is, we suppose that the
+button has been cut into two parts along its length and through the
+center line. Fig. 19 is an enlarged detail drawing of the underside of
+the spool, C. The same part is marked by the same letter in all of the
+figures.
+
+[Illustration: Fig. 17.]
+
+[Illustration: Fig. 18.]
+
+[Illustration: Fig. 19.]
+
+Saw an ordinary spool, C, into two parts. One-half of C will serve as
+the outside case for the button. The part to be pressed with the finger
+is a short length of 1/4 in. dowel. To keep this from falling out of the
+hole in C, a short piece of wire nail, N, has been put through a small
+hole in its lower end. A slot, F, has been burned or cut into the
+underside of C, so that N can pass up and down in it when D is raised
+and lowered. The rod, D, rests upon A, one of the contacts. This is a
+straight piece of tin, cut as shown in Fig. 17, the narrow part being
+1/4 in. wide and 1-1/4 in. long. The wide part is 3/4 in. wide and 1 in.
+long. The other contact, B, is the same size as A. A deep groove, a
+little over 1/4 in. wide, is cut into the base so that the narrow part
+of B can be bent down below the end of A. The base shown is 4 x 2-1/2 x
+7/8 in. The spool, C, is fastened to the base by 2 screws or wire nails
+put up through the base, their positions being shown by the dots at E,
+Fig. 17. X and Y, Fig. 18, are 2 screw binding-posts. It is evident that
+the current cannot pass from X to Y, unless the button, D, be pressed
+down so that the end of A will touch B.
+
+
+APPARATUS 32.
+
+_48. Sifter for Iron Filings._ Fig. 20. In making magnetic figures with
+iron filings, it is an advantage to have the particles of iron fairly
+small and uniform in size. A simple sifter may be made by pricking holes
+in the bottom of a pasteboard pill-box with a pin. The sifter may be put
+away with the filings in it, provided you turn it upside down.
+
+[Illustration: Fig. 20.]
+
+
+APPARATUS 33.
+
+_49. Sifter for Iron Filings._ Fig. 21. Punch small holes in the cover
+of a tin box with a small wire nail. If you have occasion to use sifters
+for other purposes, the different sizes can be made by using larger and
+smaller nails to punch the different tin covers. But one size of nail
+should be used for one sifter.
+
+[Illustration: Fig. 21.]
+
+
+APPARATUS 34.
+
+_50. Sifters_ may be made by pricking holes in an envelope. A sifter
+with very small holes can be made of a piece of muslin cloth. This can
+be used in the form of a little bag, or a piece of it can be pasted over
+the open bottom of a pill-box.
+
+
+APPARATUS 35.
+
+_51. To Cut Wires, Nails, etc._ If you have no wire-cutters, or large
+shears, you can cut large or small wires by hammering them against the
+sharp edge of another hammer, an anvil, or a piece of iron. Do not let
+the hammer itself hit upon the edge of the anvil. The above process will
+make a V-shaped dent on one side of even large wires, or nails, when
+they may be broken by bending back and forth.
+
+
+
+
+CHAPTER IV.
+
+SWITCHES AND CUT-OUTS.
+
+
+_52. Switches, Cut-Outs._ Where apparatus is to be used frequently, such
+as for telephone and telegraph lines, it pays to make your switches,
+etc., carefully. The use of these switches, etc., will be shown in the
+proper place. Their construction only will be given here.
+
+
+APPARATUS 36.
+
+_53. Cut-Out._ Fig. 22. Details. X, Y, and Z represent 3 binding-posts
+like App. 42. These are fastened to a wooden base that is about 3 x 5 x
+3/4. The ends of the wires shown come from and go to the other pieces of
+apparatus. Q shows a stout wire or strip of 2 or 3 thicknesses of tin.
+Suppose we have an apparatus, as, for example, an electric bell, which
+we want to have ring when someone at a distance desires to call us. If
+we use a telephone or telegraph instrument we shall want to cut the bell
+out of the circuit as soon as we hear the call and are ready to talk.
+Suppose the current comes to us through the wire, A, Fig. 22. It can
+pass by the wire, C, through the bell and back to X. If we wanted simply
+to have the bell ring, the current could pass directly from X into the
+earth, or over a return wire back to the push-button at our friend's
+house. If, however, we are to use some other instrument, by lifting the
+end of Q out of X and pushing it into Y, the bell will be cut out, and
+the current can pass on wherever we need it.
+
+[Illustration: Fig. 22.]
+
+
+APPARATUS 37.
+
+_54. Cut-Out._ Fig. 23. The main features of this are like those of App.
+36. The three binding-posts are like App. 46. Instead of a band of metal
+to change connections, as Q in App. 36, a stout copper wire is used.
+This can be easily changed from one of the upper binding-posts to the
+other, thereby throwing in or cutting out any piece of apparatus joined
+with the upper connectors.
+
+[Illustration: Fig. 23.]
+
+
+APPARATUS 38.
+
+[Illustration: Fig. 24.]
+
+_55. Switch._ Fig. 24. This simple switch has but one contact point, D,
+which is a screw-head. This switch may be used anywhere in the circuit
+by simply cutting the wire carrying the current, and joining the ends of
+the wire to the binding-posts X and Y. The metal strip, E, is made of 2
+or 3 thicknesses of tin. It is 5/8 in. wide and about 5 in. long, and
+presses down upon D, when swung to the left, thus closing the circuit.
+The short metal strips shown are 5/8 x 1-1/4 in. The upper strip is
+joined to the end of E by a coiled copper wire, C W. (See App. 50.) If
+the current enters by the wire, A, it will pass through C W, E, D and
+out at B. The strip E is pivoted at F by a small screw. The base may be
+3 or 4 x 5 x 7/8 in.
+
+
+APPARATUS 39.
+
+_56. Switch._ Fig. 25. By increasing the number of contact points and
+the wires leading from them, a switch may be made to throw in one or
+more pieces of apparatus. This variety of switch is useful in connection
+with resistance coils (Index). By joining the ends of the coils with the
+points 1, 2, 3, etc., more or less resistance can be easily thrown in by
+simply swinging the lever, E, around to the left or right. The uses of
+this will be again referred to.
+
+[Illustration: Fig. 25.]
+
+Details. The base of the one shown in Fig. 25 is 4 x 5 x 7/8 in. thick.
+The switch, E, is a band of 2 thicknesses of tin 5/8 in. wide. It is
+pivoted at F with a screw. To the end of E is fastened a copper wire,
+which leads to the upper binding-post, X (App. 46). The apparatus has 5
+contact points, marked 1, 2, 3, etc. These consist of brass screws and
+copper washers. With F as a center draw the arc of a circle that has a
+radius of 4 in. Place the screws 1, 2, etc., along this arc, and about
+5/8 in. apart, center to center; that is, the screws are all 4 in. from
+F, and are, therefore, in the form of a curve.
+
+The last screw forms a part of the binding-post, Y. Suppose 4 pieces of
+apparatus, marked A, B, C, and D, be connected with 1, 2, etc., as
+shown. These may be, for example, coils of wire to be used as resistance
+coils. If the current enters at X, it will pass along at E and be ready
+to leave at Y, as soon as E touches one of the contact points. If E be
+placed upon 1, the current will be obliged to pass through all of the
+coils, A, B, etc., before it can get to Y. In this case the resistance
+will be greatest. If E be now moved on to 2, only A will be cut out, and
+the total resistance reduced. By placing E upon 4, but one coil, D, will
+be in the circuit. When E is upon 5 the current will pass through the
+switch with practically no resistance. This is the principle upon which
+current regulators work. (Study resistance in text-book.) When E is in
+the position shown in Fig. 25 no current can pass.
+
+
+
+
+CHAPTER V.
+
+BINDING-POSTS AND CONNECTORS.
+
+
+_57. Binding-Posts_ are used to make connections between two pieces of
+apparatus, between two or more wires, between a wire and any apparatus,
+etc., etc. They are used simply for convenience, so that the wires can
+be quickly fastened or unfastened to the apparatus. There are many ways
+of making them at home. The following forms will be found useful and
+practical. Although some that are given are really connectors instead of
+binding-posts, we shall give them the general name of binding-posts.
+
+
+APPARATUS 40.
+
+_58. Binding-Post._ About the simplest form is a screw, or a nail with a
+flat head. The bare wire may be placed under the head of the screw or
+nail before forcing it entirely into the wood. This will keep the end of
+the wire in place, and another wire may be joined electrically to the
+first by merely touching it to the screw-head, or by placing it under
+the screw-head.
+
+
+APPARATUS 41.
+
+_59. Binding-Post._ Fig. 26. This consists of a screw and a copper
+washer or "bur." The screw is a "round-headed brass" one, 5/8 in. long,
+number 5 or 7. The copper burs are No. 8, and fit nicely around the
+screws. By using 2 burs instead of 1, several wires may be easily joined
+together at one point. Scrape the covering from the ends of the wires,
+and place them between the burs.
+
+[Illustration: Fig. 26.]
+
+
+APPARATUS 42.
+
+_60. Binding-Post._ Fig. 27. A coiled spring serves very well as a
+connector. One end should be fastened to the apparatus, as shown, by
+clamping it under a screw-head. The other end of the coil should be
+pulled out a little, away from the other turns, so that you can stretch
+the spring in order to put the bare ends of wires between the turns. Any
+number of wires placed between these turns will be pinched and
+electrically connected. The coil should be about 1/2 in. long and less
+than 1/2 in. in diameter. You can make a coil by tightly wrapping stiff
+iron wire around a pencil. The steel wire springs taken from old
+window-shades are excellent for this purpose. They may be cut into
+lengths with tinner's shears.
+
+
+APPARATUS 43.
+
+_61. Binding-Post._ Fig. 28. Two copper or tin strips fastened at one
+end by a screw, the upper strip being bent a little at one end, make a
+connector that is useful for some purposes, where you want to make and
+break the connection frequently. The bare end of the wire which belongs
+to the apparatus is fastened under the screw-head. The outside wire, or
+wires, to be connected are pushed between the strips of metal. Another
+way is to fasten the outside wire to a strip of metal about 1/2 in.
+wide, and then push this between the strips shown in the figure. The
+strips shown should be about 3/4 in. wide and 1-1/4 in. long.
+
+[Illustration: Fig. 27.]
+
+[Illustration: Fig. 28.]
+
+[Illustration: Fig. 29.]
+
+
+APPARATUS 44.
+
+_62. Binding-Post._ Fig. 29. A combination made between App. 42 and 43
+does well. Fasten a metal strip, 3/4 in. x 1-1/4 in., to the apparatus
+by means of a screw. The apparatus wire should be fastened under the
+screw-head. A short length of spring may be pushed upon the upright part
+of the strip, as shown. Into this you can quickly fasten the outside
+wires.
+
+
+APPARATUS 45.
+
+_63. Binding-Post._ Fig. 30. This makes a very simple and practical
+binding-post for home-made apparatus. It consists of a screw-eye,
+preferably of brass. The circle or eye should be about 3/8 or 1/2 in. in
+diameter. The thread on such a screw-eye will be about 1/2 in. long. Two
+copper burs are used to pinch the wires.
+
+
+APPARATUS 46.
+
+_64. Binding-Post._ Fig. 31. This consists of a screw, screw-eye, bur
+and a metal strip, 3/4 x 1-1/4 in. The apparatus wire should be fastened
+under the screw-head. Any outside wires which are to be joined to the
+apparatus should be clamped under the bur by turning the screw-eye. A
+small hole should be made in the wood before putting in the screw-eye.
+(See App. 25.) Do not turn the screw-eye too hard, or you will spoil the
+thread made in the wood.
+
+[Illustration: Fig. 30.]
+
+[Illustration: Fig. 31.]
+
+[Illustration: Fig. 32.]
+
+
+APPARATUS 47.
+
+_65. Binding-Post._ Fig. 32. The size of the bolt used in this form of
+binding-post will depend somewhat upon the thickness of the base of the
+apparatus. In general, a 3/4 or 7/8 in. base should be used where screws
+or screw-eyes are necessary. With this kind (Fig. 32) a thin base can
+be used. The head is shown counter-sunk into the bottom of the base.
+This is not necessary, provided at least 3 heads are placed far enough
+apart to form legs for the apparatus to stand on. Strips of wood may be
+nailed upon the underside of the base to make room for the heads in case
+they are not used as legs. The wires should be pinched between the nut
+and the copper bur shown. If the bolt is too large for a bur, an iron
+washer may be used. A washer may be made of tin, or two nuts may be
+used.
+
+
+APPARATUS 48.
+
+_66. Binding-Post._ Fig. 33. This is a suggestion for a combination of
+App. 44 and 47. It is useful in school apparatus. Wires may be
+permanently fastened on the right, under the nut, and a spring, as in
+App. 44, may be slipped on the metal strip at the left, which is held
+under the head of the bolt.
+
+[Illustration: Fig. 33.]
+
+
+APPARATUS 49.
+
+_67. Mercury Connector._ A cup of mercury may be used as a connector.
+Make a small hole about 1/4 in. in diameter and depth, in a piece of
+wood, and place 2 or 3 drops of mercury in this. The ends of wires
+dipped in this will be electrically connected.
+
+
+APPARATUS 50.
+
+[Illustration: Fig. 34.]
+
+_68. Connector._ Fig. 34. This shows how a wire may be fastened to one
+end of a short strip of tin. At the other end of the strip a slot is
+cut. This may straddle the body of a screw, or when left plain may be
+used to slip between the two metal strips shown in App. 43.
+
+
+APPARATUS 51.
+
+_69. Binding-Post._ Fig. 35. The ends of two or more wires may be
+quickly joined electrically by placing them between the nuts of a short
+bolt. By using 3 nuts the bolt will more easily connect a large number
+of wires.
+
+[Illustration: Fig. 35.]
+
+_Make Additional Notes and Sketches Here._
+
+
+
+
+CHAPTER VI.
+
+PERMANENT MAGNETS.
+
+
+_70. Permanent Magnets_ may be made in many ways and from many different
+kinds of steel. The steel used for needles, watch and clock springs,
+files, cutting tools, etc., is generally of good quality, and it is
+already hard enough to retain magnetism. (See Retentivity in text-book.)
+
+
+APPARATUS 52.
+
+_71. Bar Magnet._ A straight magnet is called a bar magnet. Magnetize a
+sewing-needle. For some experiments a needle-magnet, as we may call it,
+is better than a large magnet.
+
+
+APPARATUS 53.
+
+_72. Bar Magnet._ A harness-needle, which is thicker and stronger than a
+sewing-needle, makes an excellent bar magnet.
+
+
+APPARATUS 54.
+
+_73. Bar Magnet._ For long slim magnets use a knitting-needle. Some
+knitting-pins, as they are sometimes called, break off short when bent,
+but most of them will bend considerably before breaking. These slim
+magnets are excellent for the study of Consequent Poles. (See
+text-book.)
+
+
+APPARATUS 55.
+
+_74. Flexible Bar Magnets._ It is often necessary to have flexible
+magnets so that they may be bent into different shapes. These may be
+made from watch or clock springs, as such steel, called spring steel,
+will straighten out again as soon as the pressure is removed from it.
+Corset steels, dress steels, hack-saw blades, etc., make good thin
+flexible bar magnets.
+
+
+APPARATUS 56.
+
+_75. Strong Bar Magnets_ may be made from flat files. The handle end may
+be broken off so that the two ends of the file shall be nearly alike in
+size. These should be magnetized upon an electro-magnet.
+
+
+APPARATUS 57.
+
+_76. Compound Bar Magnets_ are made by first magnetizing several thin
+pieces of steel, and then riveting them together so that their like
+poles shall be together, and pull together. To make a small compound bar
+magnet, magnetize several harness-needles, or even sewing-needles, and
+then bind them into a little bundle with all the N poles at the same
+end. Melted paraffine dropped in between them will hold them together.
+Rubber bands may be used also, or, if but one end is to be experimented
+with, the points may be stuck into a cork, and the heads used to do the
+lifting.
+
+
+APPARATUS 58.
+
+_77. Small Horseshoe Magnets_ may be made from needles or from other
+pieces of steel used for bar magnets. They should be annealed (App. 21)
+at their centers at least, so that you can bend them into the desired
+shape. In the case of bright needles, like harness-needles, the part
+annealed will become blackened. If you heat the center only, and the
+ends remain bright for about 1/2 inch, you will not need to harden the
+needle again. It is an advantage to have the center of the magnet a
+little soft, as it is not then liable to break. The ends alone may be
+hardened by holding the bent portion away from the candle or gas flame,
+while heating the ends. The bent steel should be magnetized by drawing
+its ends across the poles of a horseshoe magnet.
+
+
+APPARATUS 59.
+
+_78. Flexible Horseshoe Magnets_ may be made of thin spring steel. The
+distance between the poles can be regulated at will by bending the steel
+more or less. The poles may be held at any desired distance apart by
+thread or wire, which should be wound around the legs of the magnet a
+little above the poles. This will keep the steel from straightening out.
+
+
+APPARATUS 60.
+
+_79. Horseshoe Magnet._ Fig. 36 and 37. Magnetize two harness-needles,
+and stick them into a cork so that the poles shall be arranged as shown.
+The distance between the poles can be regulated to suit. This forms a
+very simple and efficient magnet, with the advantages of a real
+horseshoe magnet.
+
+[Illustration: Fig. 36.]
+
+[Illustration: Fig. 37.]
+
+
+APPARATUS 61.
+
+_80. Armatures._ All home-made magnets should be provided with
+armatures, or keepers. These are made of soft iron on the regular
+magnets, and tend to keep the magnet strong. (See text-book.) For the
+bar magnets described, a piece of sheet-tin, upon which to lay them, is
+all that is needed for an armature. The lines of force will pass through
+this. For the horseshoe magnets described, strips of tin, soft iron
+wires, or even a wire nail placed across the poles will greatly aid in
+keeping in the strength. The little magnets should not be dropped or
+jarred. (Study the theory of magnetism in text-book.)
+
+
+
+
+CHAPTER VII.
+
+MAGNETIC NEEDLES AND COMPASSES.
+
+
+_81. Magnetic Needles and Compasses_ consist chiefly of a short
+bar-magnet. When used to tell the directions, north, east, etc., the
+apparatus is generally called a compass. When we speak of the "needle,"
+we really mean the compass-needle. The little magnet may be almost any
+piece of magnetized steel, provided it is arranged so that it can easily
+swing around. There are several ways of supporting the compass-needle.
+It may rest upon a pivot, it may be hung from a fine thread, or it may
+be floated upon water with the aid of a cork, etc.
+
+82. Uses. We all know that compasses are used to point to the north and
+south, and we speak of the "points of the compass." This, of course, is
+the most important use of the compass, and it has been known for
+centuries. In the laboratory it is used to show or detect the presence
+of currents of electricity, and, in connection with coils of wire, it
+may show the relative strengths of two currents, etc. When used for such
+purposes it generally has special forms and sizes. (See Galvanometers
+and Detectors.)
+
+
+APPARATUS 62.
+
+_83. Compass._ An oily sewing-needle will float upon the surface of
+water, when it is carefully let down to the water. A little butter may
+be rubbed upon the previously-magnetized needle to make it float better.
+
+[Illustration: Fig. 38.]
+
+
+APPARATUS 63.
+
+_84. Compass._ Fig. 38 shows a magnetized sewing-needle floated upon a
+cork. The needle may be permanently fastened to the cork with a few
+drops of melted paraffine.
+
+
+APPARATUS 64.
+
+_85. Compass._ Fig. 39. With a sharp knife make a cut part way through a
+flat cork. Into the cut push a short length of magnetized watch-spring.
+In the illustration the spring is shown partly removed from the cut.
+Float the cork.
+
+
+APPARATUS 65.
+
+_86. Compass._ Fig. 40. Stick a pin, P, into a pasteboard, cork, or
+wooden base, B. Bend a piece of stiff paper double, as shown, and then
+stick through it, on each side, a magnetized sewing-needle, S N. The
+north poles of the needles should be at the same end of the paper. Why?
+Balance the paper upon the pin-pivot, and see it fly around to the north
+and south.
+
+[Illustration: Fig. 39.]
+
+[Illustration: Fig. 40.]
+
+[Illustration: Fig. 41.]
+
+
+APPARATUS 66.
+
+_87. Compass._ Fig. 41. It is an advantage to have a magnetic needle
+that is always ready for use. The support is made by driving a pin
+through the top of a wooden pill-box, which should be about 1-3/4 in. in
+diameter. This gives plenty of room under and around the needle. If the
+pin be left too long, it will not be possible to put the bottom and top
+of the box together when you want to put the compass away. Cut the pin
+off (App. 35) at the right length, so that the magnetic needle can be
+safely put away in the closed pill-box.
+
+88. The "Needle," that is the short bar magnet, may be made of
+watch-spring. As the spring is already quite hard and brittle, it may be
+easily broken into desired lengths. It is always better to make 3 or 4
+needles at a time, as some will swing more easily than others, and time
+will be saved in making them. Break off 3 or 4 pieces of thin spring,
+each about 1-1/2 in. long. Bend them as in Fig. 42. A good dent, not a
+hole, should be made at the center of each to keep them upon the support
+or pin-point. A "center punch," not too sharp, is the best tool to use,
+but a slight dent may be made with a sharp wire nail, provided the
+watch-spring is first annealed or softened. (See App. 21.) Do not place
+the spring directly upon iron or steel when making the dent, as these
+might injure the point of the punch, and the dent would not be deep
+enough. Fig. 42 shows a good way to make dents in steel springs. Place 2
+or 3 layers of copper or lead between the anvil and the spring. A hammer
+or hatchet will do for the anvil. As the copper will give easily, a good
+dent may be made by striking the punch or nail with a hammer. If the
+spring has been annealed before denting it, it should be hardened again
+(App. 21) before magnetizing it, so that it will retain magnetism well.
+(See Residual Magnetism in text-book.)
+
+[Illustration: Fig. 42.]
+
+89. Balancing. After a dent has been made, place the spring upon its
+support so that the pin-point shall be in the dent. It will, no doubt,
+need balancing. If one end is but slightly heavier than the other, the
+spring may be balanced by magnetizing it so that the lighter end shall
+become a north pole. This will then tend to "dip" and make the needle
+swing horizontally. If one end is much heavier than the other, it should
+first be magnetized and then balanced by cutting little pieces from the
+heavier end with tinners' shears, or by weighting the lighter end with
+thread, which may be wound around it. The finished compass-needle should
+swing very freely, and should finally come to rest in an N and S line
+after vibrating back and forth several times.
+
+
+APPARATUS 67.
+
+_90. Glass-Covered Compass._ A perspective view of this apparatus is
+shown in the tangent galvanometer. (See Index.) The outside band, E, is
+made of thick paper, 1 in. wide, and with such a diameter that it just
+fits around the glass. In this model, the glass from an old alarm-clock
+was used, it being 4 in. in diameter. Four pasteboard strips were sewed
+to the inside of the paper band E. They were made 7/8 in. long, so that
+the glass, when resting upon them, would be near the top of E.
+
+The needle should be not over 1 in. long, if it is to be used in the
+galvanometer. A long slender paper pointer should be stuck to the top of
+the needle. Be careful to have the combined needle and pointer well
+balanced, so that it will swing freely. A circle graduated into 5-degree
+spaces should be fastened under the needle.
+
+_91. Astatic Needles._ In the magnetic needles so far described, the
+pointing-power has been quite strong. By pointing-power we mean the
+tendency to swing around to the N and S. In App. 65 the 2 needle magnets
+had considerable pointing-power, because they helped each other. For
+some experiments in electricity a magnetic needle is required which has
+but little pointing-power; in fact, to detect the presence of very
+feeble currents by means of the needle, the less the pointing-power the
+better. Can you think of any way to arrange App. 65 so that it shall
+have very little pointing-power?
+
+
+APPARATUS 68.
+
+_92. Astatic Needle._ Fig. 43. Turn one of the needle magnets of App. 65
+end for end, so that the N pole of one shall be at the same end of the
+paper as the S pole of the other. You can see that by this arrangement
+one needle pulls against the other. The magnetic field still remains
+about the little magnets, otherwise this combination would be of no
+value in the construction of galvanometers. The more nearly equal the
+magnets are in strength, the less the pointing-power of the combination.
+
+[Illustration: Fig. 43.]
+
+[Illustration: Fig. 44.]
+
+
+APPARATUS 69.
+
+_93. Astatic Needle._ Fig. 44. Magnetize two sewing-needles as equally
+as possible, by rubbing them over the pole of a magnet an equal number
+of times. Remove the covering from a piece of fine copper wire, say No.
+30, and use the bare wire to wind about the needles, as shown. Be sure
+to place the poles of the little magnets as in the Fig. This combination
+may be supported by a fine thread. It is used for Astatic Detectors.
+(See Index.)
+
+
+
+
+CHAPTER VIII.
+
+YOKES AND ARMATURES.
+
+
+_94. Yokes_ are used to fasten two straight electro-magnets together to
+form a horseshoe electro-magnet. The reasons for using them should be
+understood. Soft iron should be used for yokes and armatures, as this is
+the best conductor of lines of magnetic force. Sheet-tin is made of thin
+iron, which is coated with tin. (Try a magnet upon a tin can.) This soft
+iron is very easily handled, bent, and punched, and is very useful for
+many purposes. The tin from old tomato cans, cracker boxes, etc., is
+just as good as any. The method of making your yokes will depend
+entirely upon the tools at your command. Several ways are given. Y, Fig.
+47, shows the position of the yoke.
+
+
+APPARATUS 70.
+
+_95. Yoke._ For the experimental magnets (App. 89) a fairly large yoke
+is required in order to have the magnets far enough apart. If you have
+only a nail punch (App. 26) with which to make holes in tin, you will be
+obliged to punch but one thickness at a time. (See method of punching
+sheet-metal, App. 26.) Cut 5 or 6 pieces of the tin, 3-1/4 x 1 in. With
+a center punch (tools) or sharp-pointed nail make small dents (2 in.
+apart) in each piece to mark the places where the holes are to be
+punched. Punch 5/16 in. holes in each piece. If you do this carefully,
+the holes in the different pieces will match, and the bolts can be
+pushed or screwed into these. When screwing in the bolt magnets turn
+them by their heads; do not pinch the coils, as this loosens the wire.
+
+If you have a good punch, it is better to make the yoke as in App. 27,
+instead of using separate pieces of tin.
+
+
+APPARATUS 71.
+
+_96. Yoke._ Fig. 45 and 46. Cut a strip of tin 6 in. long by 3-1/4 in.
+wide. Bend one end of it so that it will lap over 3/4 in. (Fig. 46);
+hammer it down gently, then bend this over and over until the whole tin
+is used. The final result will be a flat roll, 3-1/4 by about 1 in. This
+should be hammered flat.
+
+[Illustration: Fig. 45.]
+
+[Illustration: Fig. 46.]
+
+If you have the tools it is easy to drill two 5/16 holes in this strip.
+They should be 2 in. apart; that is, 2 in. from the center of one to
+that of the other. Start the holes with a center punch.
+
+_97._ If you have no way of drilling the holes, they must be punched.
+(See App. 27.) This will make the strip bulge out on the underside
+around the holes. This bur, or most of it, should be filed off. (See
+App. 79 for method of filing thin pieces of metal.) The resulting yoke
+may be held firmly to the magnets by the use of 2 extra nuts, as in Fig.
+67. Remember that the magnets must be held firmly in the yoke.
+
+
+APPARATUS 72.
+
+_98. Yoke._ The best way of making this, of course, is to cut a piece of
+bar-iron the right size. For 5/16 bolts the strip of wrought iron should
+be about 3/4 in. wide and 3/16 or 1/4 in. thick. Any blacksmith can make
+this and punch or drill the holes. If taps and dies (tools) are at
+hand, the hole may be drilled and tapped to fit the thread on the bolt.
+It is very easy to make good looking apparatus if you have, and can use,
+a whole machine shop full of tools. The lengths of yokes will depend
+upon the special uses to be made of them.
+
+
+APPARATUS 73.
+
+_99. Yoke._ Fig. 47. The yoke, Y, is a part of a carriage. This can be
+bought at a blacksmith's. The holes are already in, but it may require
+some filing before the nuts of the bolt magnets will fit down firmly.
+
+[Illustration: Fig. 47.]
+
+
+APPARATUS 74.
+
+_100. Tin Armatures_ may be made by bending together 5 or 6 thicknesses
+of tin. Different forms of tin armatures are shown under telegraph
+sounders; these should have a hole punched at the center; through this
+is put a screw. The length of the armature will depend upon the distance
+the magnets are placed apart; they should be about 3/4 in. wide.
+
+
+APPARATUS 75.
+
+_101. Nail Armatures._ Fig. 48. A nail, N, placed through a piece of
+wood, A, will serve as a very simple armature. To make it a little
+heavier, if necessary, a piece of annealed iron wire, W, may be wound
+around N. Care should be taken to have the two parts fairly alike in
+size and weight.
+
+[Illustration: Fig. 48.]
+
+
+APPARATUS 76.
+
+_102. Wire Armatures._ Fig. 49. Annealed iron wires make good armatures.
+The short lengths of wire should be straightened (See App. 28) before
+binding them into a bundle. They may be held together with thread or
+paraffine, until they are in place, as, for example, in a wooden piece,
+A, Fig. 49. The bundle of wires should fit snugly into the hole made
+through A, and the wires should be bound together at each end with wire.
+
+[Illustration: Fig. 49.]
+
+
+APPARATUS 77.
+
+_103. Trembling Armature._ Fig. 50. Armatures to be used upon electric
+bells, automatic current interrupters, buzzers, etc., may be called
+trembling armatures. They may be made entirely of sheet-tin. The part,
+F, which gives it the spring, should be about 5/8 in. wide. Its length
+will depend upon the particular apparatus to be made. It is made of 2
+thicknesses of thin tin. See Fig. 50 for dimensions. The part N projects
+beyond L. This may be used to tap against a regulating screw, or to
+fasten a hammer on for an electric bell. The part, L, should have about
+4 layers of tin on each side of F, and it should pinch F tightly.
+
+[Illustration: Fig. 50.]
+
+
+APPARATUS 78.
+
+_104. Trembling Armature._ Fig. 51. When very rapid motions are desired
+in a trembling armature, App. 77 will be a little heavy. A light and
+quick-acting armature can be made of sheet-tin. The exact dimensions
+will depend upon the use to be made of it, but you will find the
+following a guide. Cut the part, B, E, out of thin tin. The covers and
+bottoms of tin cans are thinner than their bodies. The narrow part, B,
+should be about 1/4 in. wide and 2 in. long for a small apparatus, while
+E may be 3/4 in. square. Through E is a screw, which holds it firmly to
+a wooden piece, D, about 3/4 in. square. The part, E, can be made longer
+than its width, so that two screws can be used; this will keep A from
+jarring up or down.
+
+[Illustration: Fig. 51.]
+
+
+APPARATUS 79.
+
+[Illustration: Fig. 52.]
+
+_105. To File Thin Metal Strips._ Fig. 52. When sheet-metal is punched
+by the methods usually employed by boys, a bulge or bur is made on the
+underside around the hole. If this bur be hammered to flatten it, the
+hole is distorted and made smaller. It is better to file the bur down,
+at least part way. It is not convenient to file a piece of thin metal
+when it is held in a vise. It is better to use either a metal or a
+wooden clamp, as shown in Fig. 52; then the filing can be quickly and
+easily done. Y is the yoke to be filed. It is well to place a piece of
+metal, I, between the table and the end of the screw.
+
+
+APPARATUS 80.
+
+_106. Clamp._ Fig. 53. If you have no clamp to hold metal strips while
+filing them, you can put a screw, S, through one hole to hold the strip
+down fairly tight. Drive a nail, N, behind the strip. This will keep it
+from turning while you file the free end.
+
+[Illustration: Fig. 53.]
+
+       *       *       *       *       *
+
+_Electro-Magnetic Armatures._ A description of this form of armature is
+given in the chapter on electric motors. (See Index.)
+
+
+
+
+CHAPTER IX.
+
+ELECTRO-MAGNETS.
+
+
+_107. Electro-Magnets_ are absolutely necessary in the construction of
+most pieces of electrical apparatus. There are several ways of making
+them at home. To quickly make a good-looking one, a winder (App. 93) is
+required. We shall divide our electro-magnets into four parts: Core,
+washers, insulation, and coil.
+
+Of course, you know that when a current of electricity passes through a
+wire, a magnetic field is produced around the wire. A coil of wire, or
+helix, has a stronger field than a straight wire carrying the same
+current, because each turn or convolution adds its field to that of the
+other turns. By having the center of the helix made of iron, instead of
+air, wood, or other non-magnetic bodies, the strength of the magnet is
+greatly increased. This central core may be fixed permanently in the
+coil, or be removable. For our purposes fixed cores are just as good as
+movable ones, and the coils are easily wound upon them.
+
+When wire is wound by hand from a spool into a coil, or around a core,
+it soon becomes twisted and tangled. Make a winder. This will keep the
+wire straight and save much time.
+
+
+APPARATUS 81.
+
+[Illustration: Fig. 54.]
+
+_108. Electro-Magnet._ Fig. 54. Drive a nail into a board so that it
+will project about 3/4 of an inch. A soft, or wrought-iron, nail is
+best, but a short, thick wire-nail will do. If you do not have a thick
+nail, use an iron screw. Wind 3 or 4 layers of insulated copper wire
+around it, and fasten the bare ends of the wire down with bent pins.
+Number 24 wire will be found a good size for experimental purposes.
+Touch the wires leading from the battery to the ends of the coil, and
+see if the nail will lift pieces of iron.
+
+109. Note. Always leave at least 6 in. of wire at the ends of all coils
+and windings. This is needed for connections and repairs, as the wire is
+liable to get broken at any time around the binding-posts.
+
+110. Note. After you have wound wire upon a core or spool, keep it from
+untwisting by taking a loop or hitch around it with the wire. Fig. 55
+shows how this is done. Pull the end of the wire enough to make the loop
+stay in place.
+
+
+APPARATUS 82.
+
+_111. Electro-Magnet._ Fig. 56. Cut annealed iron wire into pieces, 3
+inches long, straighten them (App. 28), and tie them with thread into a
+bundle about 5/16 in. in diameter. Melted paraffine run in between the
+wires will hold them in together, but stout thread will do. Wind 3 or 5
+layers of No. 24 insulated copper wire upon the soft iron core. This is
+useful for simple experiments, and this idea may be applied to magnets
+to be used in pieces of apparatus. Hold the bundle of wires in a vise,
+and file the ends smooth, before winding on the wire. Paraffine should
+be used to hold the turns of insulated wire together.
+
+[Illustration: Fig. 55.]
+
+[Illustration: Fig. 56.]
+
+[Illustration: Fig. 57.]
+
+
+APPARATUS 83.
+
+_112. Electro-Magnet._ Fig. 57. An electro-magnet with a removable core
+may be made by winding the wire on a spool. The core is made, as in
+App. 82, of soft iron wires, bound together with stout thread. A bolt
+may be used instead of the wire, but the wire loses its magnetism much
+quicker than a soft steel bolt would. (Study residual magnetism.) This
+magnet is strong enough for many purposes, but the wire is too far from
+the core, on account of the thickness of the wood, to make it efficient.
+The wire may be wound on by hand, but a winder (App. 93) will do much
+better and quicker work.
+
+
+APPARATUS 84.
+
+[Illustration: Fig. 58.]
+
+[Illustration: Fig. 59.]
+
+_113. Horseshoe Electro-Magnet._ Fig. 58. Bend soft iron wires, and make
+a bundle of them. If you wish to wind the wire around spools, the bundle
+cannot be very large. It will be found best to make the bundle about 3/8
+in. in diameter, and not to use the spools. Strong paper should be
+wrapped once or twice around the legs of the horseshoe, and the
+insulated wire, say 4 layers, can then be wound directly upon this. (See
+Sec. 115 for method of making connection between the coils.) It is a
+little troublesome to wind wire upon a horseshoe like this, and for
+App. 85. Spools are handier, because each can be wound separately, and
+then be slipped in place. The ends of the horseshoe should be filed
+smooth.
+
+
+APPARATUS 85.
+
+_114. Electro-Magnet._ Fig. 59. An ordinary iron staple is useful as the
+core of a small magnet. One like this is shown also in Fig. 94, used as
+a telegraph sounder. It takes some time to wind 4 layers of wire on to
+each leg of the staple, so be sure to see Sec. 115 about the method of
+winding. In Fig. 59 the half-hitches (Sec. 110) are not shown. Coat the
+finished coils with paraffine.
+
+115. Method of Joining Coils. Fig. 60. If A and B represent the two
+cores of a horseshoe electro-magnet, the coils must be joined in such a
+manner that the current will pass around them in opposite directions, in
+order to make them unlike poles. The current is supposed to pass around
+B, Fig. 60, in the direction taken by clock hands, while it passes
+around A in an anti-clockwise direction. The inside ends, Sec. 123, of
+the coils may be twisted together, or fastened under a screw-head. In
+Fig. 60 one coil is shown to be a continuation of the other.
+
+[Illustration: Fig. 60.]
+
+
+APPARATUS 86.
+
+[Illustration: Fig. 61.]
+
+[Illustration: Fig. 62.]
+
+_116. Electro-Magnet._ Fig. 61. Wind 6 layers of No. 24 or 25 insulated
+copper wire around a 5/16 machine-bolt that is 2-1/2 in. long. Fig. 61
+shows one method of holding the bolt solidly in an upright position, so
+that magnetic figures can be easily made and the magnet studied. Two
+nuts are used, the lower one being counter-sunk, so that the base will
+stand flat upon the table. This bolt is shown without washers (Sec. 119),
+and will do fairly well to show the action of electro-magnets. The ends
+of the wire should always be left 5 or 6 in. long, and be led out to
+binding-posts. The coil may be held in place, and its turns kept from
+untwisting by coating it with paraffine. The base may be of any desired
+size.
+
+
+APPARATUS 87.
+
+_117. Electro-Magnet Core._ Fig. 62. This shows another method of
+fastening a bolt-core in an upright position. This is done without the
+use of two nuts. A strip of tin, T, 1 in. wide, is punched and slipped
+onto the 5/16 bolt before the nut is screwed on and the coil wound. This
+is fastened to the base by screws, S. Washers, W, are here shown. (See
+Sec. 119 for washers.)
+
+
+APPARATUS 88.
+
+_118. Bolt Electro-Magnets_ are easy to make, according to the
+directions given, and they are, when finished, more like the regular
+purchased magnets than any of the other forms described. With proper
+batteries (App. 3, 4, etc.,) they can be used for a great variety of
+purposes, as will be seen. There are many forms of bolts in the market,
+but the ordinary "machine bolt," 5/16 in. in diameter, is best for our
+purposes. The ones 2 and 2-1/2 in. long are used.
+
+119. Washers or coil ends are used on the bolt magnets so that
+considerable wire can be wound on closely and evenly. These are made out
+of thick pasteboard, which cuts smoother if it has been soaked in melted
+paraffine. Unless you know how, you will find it a hard job to make the
+hole in the exact center of the washer. The method of easily making
+washers is illustrated in Fig. 63.
+
+First place a spool (the end of which is 7/8 or 1 in. in diameter) upon
+the table, and lay the pasteboard upon this. Push a large round nail
+through the pasteboard into the hole in the spool. The nail should be
+nearly as large as the hole. Use the large nail as a handle, and with
+the shears cut around the edge of the spool end. Cut the washer as round
+as possible, and be careful not to cut into the spool.
+
+The holes in the washers will be a little smaller than the 5/16 bolt.
+This will make the washers hold tightly to the bolt when you force them
+on. Fig. 64 shows the bolt-core, with the washers in place. If you
+cannot get a large nail, a lead-pencil, or sharpened dowel, will do to
+force through the pasteboard.
+
+[Illustration: Fig. 63.]
+
+120. Insulation of Cores. While the covering on the wire would probably
+be all that is necessary to thoroughly insulate the coil from the core,
+it is better to wind a layer or two of paraffine paper around the bolt
+(Fig. 65) before winding.
+
+[Illustration: Fig. 64.]
+
+[Illustration: Fig. 65.]
+
+[Illustration: Fig. 65-1/2.]
+
+121. The Coils of wire to be used upon the bolt-cores should be put on
+with the winder (App. 93). For all ordinary purposes No. 24 or 25 single
+or double cotton covered copper wire will do. It is better to put on an
+even number of layers. The winding (See Fig. 70) begins at the nut-end
+of the bolt, and by using 6 or 8 layers of wire, instead of 5 or 7,
+both coil ends will be at the same end of the bolt.
+
+122. Method of Winding the Coils. The winders used for bolt magnets are
+described in App. 91, etc. We shall suppose that the washer, W, Fig. 70,
+and the insulation, I, are upon the bolt before screwing it into the
+winder-nut, W N. Make a pinhole, P H, in the right-hand washer, as near
+the bolt-nut, B N, as possible. Stick about 6 in. of the wire through P
+H, and wind this end around W N, as shown, to hold the wire. The supply
+of wire should be upon a spool slipped onto some stationary rod (App.
+23), so that you can give your entire attention to winding. Begin to
+turn the winder slowly at first. Turn the handle towards you when it is
+at the bottom, as in Fig. 70; that is, if you look at it from the side,
+turn the handle clockwise. Let the wire slip through your left hand as
+the turns are made, and guide it so that the turns will be close
+together. If they go on crooked, unwind at once, then rewind properly.
+You can guide the wire best by holding your left hand about 8 or 10
+inches from the bolt. As soon as you reach the left side or head end of
+the bolt, feed the wire towards the right. If at any time the layers
+become rough on account of one turn slipping down between turns of the
+previous layer, fasten a piece of paraffine paper around the coil as
+soon as the imperfect layer is completed. Wind on 8 layers, and count
+the number of turns in one or two of them, so that you can tell about
+how many turns in all you have around the core. Make a "half-hitch" (see
+Sec. 110) with the wire when the last layer is finished, to keep it from
+unwinding, and leave a 6 in. end.
+
+The coil should be protected by fastening around it a piece of
+dark-colored stiff paper. Paraffine paper is good for this purpose. With
+a little practice you will be able to rapidly and neatly wind on the
+wire. The winder-nut, W N, must hold the bolt solidly to keep it from
+wobbling.
+
+123. We shall call the starting end of the wire which passes through P
+H, the inside end, and the end of the last layer the outside end. This
+can pass out between the washer and the paper covering.
+
+
+APPARATUS 89.
+
+_124. Experimental Horseshoe Electro-Magnet._ Fig. 66. Among the most
+useful pieces of apparatus for home use, is a good horseshoe
+electro-magnet. Fig. 66 shows a very convenient and practical form. With
+this, alone, can be shown all the principles of telegraph sounders,
+electric bells, etc. They are excellent for making magnetic figures (See
+text-book). You are supposed to be looking down on the App. in Fig. 66.
+The bolts are 2 in. apart center to center.
+
+[Illustration: Fig. 66.]
+
+The bolt magnets are fully described in App. 88; the binding-posts, as
+App. 46; the yoke, as App. 71; the method of fastening to the base, as
+App. 90; the base is 5 x 4 x 7/8 in.; the magnets are made of 5/16
+bolts, 2-1/2 in. long.
+
+125. To Join the Coils, fasten the two inside ends (Sec.123) of the wire
+to a middle binding-post, and carry the outside ends to the two outside
+binding-posts. In this way you can use either magnet alone, if desired
+(See experiments in text-book), or change the polarity at will by
+changing the connections. (See Sec. 115 and 123.)
+
+
+APPARATUS 90.
+
+_126. Fastenings for Electro-Magnet._ Fig. 67. When both electro-magnets
+are to be permanently fastened to a base, especially if tin yokes are to
+be used, as in App. 89, it is best to use a nut on each side of the
+yoke. It is important to have a perfectly tight connection between bolt
+and yoke. Several ways of fastening the bolts and yokes are shown; but
+it will be found best to cut holes in the base for the lower nuts, and
+to screw the yoke directly to the base. This makes a solid and pleasing
+arrangement. For the experimental magnets (App. 89) make the yoke 3-1/4
+in. long, and place the magnets 2 in. apart center to center.
+
+[Illustration: Fig. 67.]
+
+
+
+
+CHAPTER X.
+
+WIRE WINDING APPARATUS.
+
+
+APPARATUS 91.
+
+_127. Winder._ Fig. 68. In case you do not have any means of making a
+smooth hole for the "bearings" of the winders of App. 93 and 94, you can
+use a spool for the purpose. B is the end of a piece of board about 1
+in. thick, 3 in. wide, and 6 in. long. The spool, A, is laid upon this,
+a band of tin, T, being used to hold it down firmly upon the end of B.
+Screws, S, hold T down. A stove-bolt axle (See App. 93) is shown, and by
+using a nut, as explained, bolt magnets may be wound. By using the
+handle of App. 92, this arrangement can be used to wind almost anything,
+when used together with the attachment of App. 95.
+
+[Illustration: Fig. 68.]
+
+[Illustration: Fig. 69.]
+
+
+APPARATUS 92.
+
+_128. Crank for Winders, etc._ Fig. 69. This form of crank or handle
+will be found easier to make than the one in which a wire is expanded in
+the slot of a stove bolt, and it can be used for many purposes,
+especially where dowels serve as axles. Wrap a little paper around the
+end of the 1/4 in. dowel, D, and push it part way into the spool, A,
+then put in a set-screw, S, to keep A from twisting upon D. The straight
+end of the wire, H, should be put into a hole, B, and another set-screw
+used to fasten it into the spool.
+
+
+APPARATUS 93.
+
+_129. Winder._ Fig. 70. For winding bolt magnets, this form of winder is
+very useful. It consists of a "stove bolt," S B, 2 in. long (total
+length) and 5/16 in. in diameter.
+
+[Illustration: Fig. 70.]
+
+130. Handle or Crank, H, is made of a stout wire, 4 in. long, bent at
+the lower end as shown. H is fastened into the slot of S B. To do this
+the end of H is hammered flat until it will just slip into the slot. It
+may be soldered there, or be made to fit by expanding it so that it will
+press out against the sides of the slot. To do this, place S B into a
+hole in an anvil, or hold it in a vise, being careful not to injure the
+thread. Place the flattened end of H in the slot, and strike it on top
+so that it will expand and be pinched in the slot; but do not pound it
+so hard that you split the bolt head. Three or four good center-punch
+dents upon the wire over the slot will help to expand it.
+
+131. The Framework is made of wood, the dimensions being shown in Fig.
+70. A 5/16 hole should be made for S B, the thread of which will stick
+through about 1/4 in. so that the winder-nut, W N, can be turned onto
+it. W N should be on but 2 or 3 threads of S B. This will leave part of
+it for the thread of the bolt magnet, and when this and S B meet in
+center of W N they will bind against each other and hold the bolt tight.
+The winder can be nailed or screwed at S to the edge of a table or held
+in a vise.
+
+
+APPARATUS 94.
+
+[Illustration: Fig. 71.]
+
+_132. Winder._ Fig. 71. This shows a winder that can be used for several
+purposes by arranging different attachments. It will be first described
+as shown in Fig. 71, where it is being used to wind a bolt magnet. The
+principal dimensions are shown in the figure. It is made of 3/4 in. wood
+about 3 in. wide, the two outer parts X and Z being nailed to the center
+one, Y, which is to be held in a vise, or fastened to the edge of a
+table. A 5/16 in. hole should be made through the upper part X and Z at
+one side of the center, so that a long 5/16 bolt can be put through and
+used as described in App. 93, if desired. A smaller hole, 1/4 in.,
+should be made on the other side of the center for a 1/4 in. dowel. The
+dowel, D, is shown, and this size is a little smaller than the hole in
+ordinary spools, shown at A and B. One-quarter in. dowels can be made to
+fit fairly tight into the holes by wrapping paper around them.
+Five-sixteenth bolts can be screwed into the spool holes, shown by the
+bolt magnet in Fig. 71. To firmly hold a spool from twisting around upon
+the dowel-axle, a set-screw, S S, is needed. These are small screws, say
+5/8 in. long, No. 5. A small hole should be made into the spool before
+forcing in the screw. (App. 25.)
+
+The spools A and B are fastened in this way, by set-screws, to D. The
+handle, H, is made as in App. 93, in this case a short stove bolt, S B,
+being used and screwed into B. Fig. 69 shows a very simple form of
+handle for all such purposes, which may be used instead of the one here
+shown. The details of winding on the wire are given under App. 88.
+
+
+APPARATUS 95.
+
+_133. Attachment for Winder._ Fig. 72. By using this addition to App. 93
+or 94, almost any ordinary kind of windings can be made. The wooden
+block, A, may be about 2 in. square and 7/8 in. thick. A set-screw, S,
+binds it to the dowel-axle, D, which is made to turn by one of the forms
+of cranks given, and which is held in one of the frameworks. Windings
+like that shown in App. 112, Fig. 85, can easily be done with this, the
+upright part, with the two spools, being screwed right to A of Fig. 72.
+
+[Illustration: Fig. 72.]
+
+
+
+
+CHAPTER XI.
+
+INDUCTION COILS AND THEIR ATTACHMENTS.
+
+
+_134. Induction Coils_, or shocking coils, are rather expensive to buy,
+and altogether too complicated for boys to make by the methods usually
+given in books. The method here given is simple, the materials are
+cheap, and if you make them according to directions, you will have an
+apparatus that will, be able to make your friends dance to a rather
+lively tune. The amount of shock can be regulated perfectly (App. 103).
+
+Winding. Full instructions have been given for making bolt magnets (App.
+88). The winding of our induction coils is done in the same way by the
+same winder as the bolt magnets (App. 93), or by hand. You will find it
+a very tiresome and troublesome job, however, to wind on 12 or 15
+hundred turns of fine wire by hand. Make a winder.
+
+Several different forms of induction coils are shown. The coil is the
+most important feature, however, and we shall consider that separately.
+When you understand the construction of one coil, you can readily apply
+this to the different forms. Some form of contact breaker, or current
+interrupter, is needed also. These will be treated by themselves. The
+connections will be discussed under each form of apparatus.
+
+
+APPARATUS 96.
+
+_135. Induction Coil; Construction of Coil Proper._ Figs. 73, 74. An
+induction coil is a peculiar and wonderful apparatus. There are at least
+two coils to each one. These are both wound upon the same core. They
+are made of different sizes of wire, are wound separately, and the
+strangest thing of all is, that these two coils are not connected with
+each other in any way. If they were not thoroughly insulated from each
+other, the coil would be of no value. (Study induction.) The winding of
+the two coils is done as explained in App. 88.
+
+[Illustration: Fig. 73.]
+
+[Illustration: Fig. 74.]
+
+136. The Core is made of a 5/16 machine bolt, 2-1/2 in. long. Leave but
+2 or 3 threads at the end, just enough to fasten it solidly to the
+winder (App. 93). The washers should be about 1-5/8 in. apart inside,
+and they should be made around a spool (Sec. 119) that is fully 1 in.
+in diameter.
+
+137. The Inside or Primary Coil could be wound directly upon the bolt;
+but it is much better to cover the bolt with one or two thicknesses of
+paraffined paper, I (Index), as shown. A pinhole, H, in the washer is
+for the inside end (see Sec. 123) of the primary coil, and the hole,
+J, is for the outside end of it.
+
+The primary coil should be made of 3 layers of wire, which should be
+coarser than that used for the secondary coil. For our purposes it is
+best not to use a wire coarser than No. 20, and not finer than No. 24.
+
+Use No. 24 insulated copper wire if you are going to connect ordinary
+batteries with it. A bichromate cell (App. 4) is best. Put about 6 in.
+(see Sec. 109) of wire through H, and with App. 93 wind on 3 layers of
+say No. 24 wire. There being an odd number of layers, the winding will
+stop at the head end of the bolt, where a half hitch (see Sec. 110)
+should be taken before passing the wire through the hole, J. Cut the
+wire 6 in. from the hole. Write down the number of turns of wire to
+each layer and the total number of turns. You now have a 3-layer coil,
+and a current passed through this will magnetize the bolt; you
+have--so far--merely an electro-magnet. Cover the primary coil with 2
+layers of paraffined paper, K (Fig. 74), and put some paraffine
+between the edges of K and the washers, so that the wire of the
+secondary coil cannot possibly come in contact with that already wound
+on.
+
+138. The Secondary Coil should be made of a large number of turns of
+fine wire. Do not use anything coarser than No. 30. This is a good size,
+as finer wire is very easily broken by unskilled hands. For the size of
+bolt mentioned put on 13 layers. There will be about 100 turns to each
+layer, making a total of about 1,300 turns of No. 30 wire. Write down
+the total number of turns in your coil. To start the secondary coil,
+make a pinhole, L, just outside of the insulation, K, of the primary
+coil. Put 6 in. of wire through this, wind the end around the nut (App.
+93, Fig. 70), and wind on as evenly as possible 13 layers. If the layers
+become rough, it is well to put a band of paper around after each 3 or
+4. When you have finished take a half hitch (Sec. 110), and leave a 6-in.
+length free. Cover the secondary coil with strong paper. This coil may
+be used on any of the forms of shockers given.
+
+
+APPARATUS 97.
+
+139. Induction Coil. Fig. 75. The base is made of a piece of board, 7 x
+5 x 7/8 in. The locations of the different parts are shown in the
+figure. The coil is explained in detail in App. 96. It is fastened to
+the base by a thin copper strip, 4, which is bent over the coil and held
+down by screws, 3. If you haven't any copper you can use a narrow strip
+of tin. Do not use a wide piece of tin or iron. The coil may be held
+down firmly by strong twine placed around each end of it. The twine
+should pass through holes in the base, and be tied on the underside of
+the base. The binding-posts are like App. 46.
+
+140. The Current Interrupter consists of a tin or copper strip, R, 6 in.
+long and 1/2 or 3/4 in. wide. At one end of R is a screw, S, which is
+used as a binding-post for the outside end, B, of the primary coil. (See
+Sec. 137.) Along the center line of the strip, R, are driven 1-in. wire
+nails, Q. These are placed 1/4 in. apart, and they should go into the
+wood enough only to make them solid. (See Fig. 81.) Do not drive them in
+so far that they will split the base. A stout wire, P, fastened at one
+end only completes the interrupter.
+
+[Illustration: Fig. 75.]
+
+141. The Connections. The binding-posts, W and X, should be connected
+with the wires leading from a battery. Use the bichromate batteries of
+App. 3 or 4. A dry battery will do. If the current enters at X, it will
+pass around the primary coil (Sec. 137) and out through B into R. It can
+go no farther until the free end of P is made to touch R, or one of the
+nails, Q, when the circuit will be closed. The current will fly around
+and around through the battery, primary coil, and interrupter as long as
+the end of P touches a nail. The battery current does not get into the
+secondary coil at all. You can see, then, that the primary circuit, that
+is, the one passing through the coarse wire, will be rapidly opened and
+closed by bumping the free end of P along upon the row of nails.
+
+The wires, C and D, coming from the secondary coil (Sec. 138) are in
+connection with Y and Z, to which are connected the wires leading from
+the handles (App. 101) held by the person receiving the shock.
+
+142. To use the coil, arrange as explained. Let your friend hold the
+handles (App. 101) while you scrape the end of P back and forth along
+the row of nails. For those who cannot stand much of a shock, use a
+regulator (App. 103).
+
+
+APPARATUS 98.
+
+_143. Induction Coil._ Fig. 76. In case you wish to make the interrupter
+as a separate piece of apparatus, as App. 104, this arrangement will be
+found good. The base is 5 x 4 x 7/8 in. The coil is explained in App.
+96, and the methods of holding it to the base are given in App. 97. The
+binding-posts are like App. 46.
+
+[Illustration: Fig. 76.]
+
+The Connections. We shall suppose that you have the interrupter of App.
+104, Fig. 81. The ends of the primary coil (Sec. 137) are fastened
+under the screws of X and W, and those of the secondary coil to Y and
+Z. Connect one battery wire with X and the other battery wire to the
+interrupter at S, Fig. 81. Fasten the end of a stout wire to W, and
+leave the other end free to scrape along on the nails, Q, of the
+interrupter. This will then open and close the primary circuit. The
+handles (App. 101) are connected with Y and Z, as explained in App. 97.
+Use the battery of App. 3 or 4.
+
+
+APPARATUS 99.
+
+_144. Induction Coil._ Fig. 77. If you wish to fasten your coil in an
+upright position the apparatus will look like Fig. 77. The base may be 5
+x 4 x 7/8 in. The binding-posts are like App. 46. The coil is made as
+explained in App. 96; but to have all the ends of the coils come out at
+the bottom, as shown, an even number of layers of wire will be
+necessary. It will be just as well to have an odd number of layers as
+before, and to bring the wire ends down the side of the coil. The coil
+is fastened to the base with screws, S, passing through a tin strip, T,
+which has a hole punched for the bolt. T is squeezed between the regular
+nut on the bolt and an extra one on the underside of it. See Fig. 61 for
+suggestion of another method of holding bolts upright. The connections
+should be made with an outside interrupter, battery, and handles, as
+explained in App. 98.
+
+[Illustration: Fig. 77.]
+
+
+APPARATUS 100.
+
+_145. Induction Coil._ Fig. 78, 78-A, 78-B. In case you wish to make a
+larger coil than those already described, the following will be found
+practical. It is made in the same general way as before, an automatic
+interrupter, however, being added.
+
+The Core is a machine-bolt, 4-1/2 in. long and 5/16 in. in diameter. You
+may use a carriage-bolt of the same dimensions, if you file away the
+square shoulder at the head end, so that it will be the same size as the
+body of the bolt. Paste a piece of thick paper upon the head, so that A
+will strike the paper instead of the iron. The Washers should be made
+around a spool that is fully 1 in. in diameter. (See Sec. 119.) The core
+should be insulated with paraffine paper before winding on the primary
+coil. (See App. 88.) The washers are 3-7/8 in. apart, inside. The
+winding of the coils should be done with App. 93, or some other winder.
+The winder-nut, W N, Fig. 70, must hold the long core perfectly tight,
+to avoid wobbling. The base is 8 x 5 x 7/8 in. The different parts are
+placed as shown. The coil is fastened to the base as in App. 97. For
+binding-posts see App. 46.
+
+[Illustration: Fig. 78.]
+
+146. The Primary Coil (Sec. 137) is made by winding 3 layers of No. 24
+insulated copper wire upon the insulated core. One end, 6, is fastened
+to W (See Sec. 109), and the other end, 5, is held under the screw-head,
+R. Wind at least two layers of paraffined paper around this coil before
+winding on the secondary coil.
+
+147. The Secondary Coil (Sec. 138) is made of No. 30 insulated copper
+wire, there being 11 or 13 layers, each having about 200 turns. This
+makes, in all, about 2,500 turns of fine wire. If your winder works
+properly and the long core is strongly held by the winder-nut, you will
+have no trouble, although it takes a little time to wind on so many
+turns. The ends of this coil, 7 and 8, are fastened to Y and Z, which
+are made like App. 46. It will be found best to wrap a piece of thin
+paper around the coil after every 3 or 4 layers are wound on. This
+makes better insulation, and makes the winding easier. Protect the coil
+by covering it with thick paper. The whole coil, when completed, is
+about 1 in. in diameter.
+
+[Illustration: Fig. 78-A.]
+
+[Illustration: Fig. 78-B.]
+
+148. The Automatic Interrupter (Figs. 78, 78-A, 78-B) consists of
+several parts. B, E, C is a piece of thin tin, all in one piece. The
+part, B, is 1/4 in. wide and 1-3/4 in. long. Its exact height above the
+base will depend upon the diameter of your coil. For the coil here
+described, 1 in. in diameter, the top edge of B is 5/8 in. above the
+base. See Fig. 78-B for shape of B, E, C before bending it, and for its
+dimensions. Around the end of B are tightly wound several turns of tin,
+making the armature or hammer, A, which should not be allowed to strike
+against the head of the bolt on account of residual magnetism. (See
+text-book.) A piece of thick paper pasted on the head for A to strike
+upon is best. A will probably not get near enough to the bolt to strike
+it, but this will depend upon how you arrange the parts.
+
+D is a wooden piece, 1 in. high, 1 in. wide, and 3/8 or 1/2 in. thick;
+it is nailed to the base. Through its center is a hole for the
+screw-eye, S I, which is the regulating-screw. F is a piece of copper,
+brass, or tin, 5/8 x 1-3/4 in. It is held to the base by the screw, S,
+and is bent so that it presses tightly against S I. Through F is a
+screw, R, to hold one end of the primary coil.
+
+149. Adjustment and Use. The battery wires should be joined to W and X,
+and the handles to the secondary coil at Y and Z, unless a regulator
+(App. 103) is used. Let us consider the primary circuit. If the current
+enters at W it will pass through the primary coil and out at X, after
+going through 5, R, F, S I, B, E, and C. The instant that the current
+passes, the bolt becomes magnetized; this attracts A, which pulls B away
+from the end of S I, thus automatically opening the circuit. B at once
+springs back to its former position against S I, as A is no longer
+attracted; the circuit is closed and the operation is rapidly repeated.
+B should press gently against S I, which must be screwed back and forth,
+until the best results are obtained. While not in use A should be about
+1/8 or 3/16 in. from the bolt-head. The armature, A, should vibrate back
+and forth very rapidly. If this coil gives too much shock with one cell
+of App. 3 or 4, put a regulator (App. 103) between Y and one of the
+handles (App. 101).
+
+
+APPARATUS 101.
+
+_150. Handles for Shocking Coils._ Fig. 79. Ordinary sheet-tin makes
+good handles. Cut 2 pieces, each 6 x 4-1/2 in., and connect a stout
+copper wire to each. This may be done as suggested in Fig. 79, where the
+tin laps tightly over the bare end of the wire, or by punching 4 or 5
+holes through the tin, and weaving the wire back and forth through the
+holes. Be sure that a tight and permanent connection is made. The wires
+joined to the handles should be about No. 20, and be 4 or 5 feet long.
+Roll the tin into a cylinder, so that the connection will be on the
+inside.
+
+[Illustration: Fig. 79.]
+
+
+APPARATUS 102.
+
+_151. Handles for Shocking Coils._ Very neat handles may be made from
+4-in. lengths of brass tubing that is about 3/4 in. in diameter. The
+wires leading to the coil may be soldered to the handles.
+
+
+APPARATUS 103.
+
+_152. Current Regulator for Induction Coils._ Fig. 80. If your coil
+gives too much of a shock with one cell of App. 3 or 4, you can pull the
+carbon and zinc partly out of the solution to weaken the shock, or you
+can use a water regulator. T is an ordinary tin tomato can nearly filled
+with water, L is a lamp chimney. One wire, A, is fastened to T directly,
+or by a spring binding-post. The other wire, B, is fastened to a piece
+of copper, C, which may be raised or lowered inside of L. D is a piece
+of pasteboard with a small hole in its center.
+
+153. Use. If this apparatus be put anywhere in the primary circuit, the
+amount of shock can be regulated by raising or lowering C. When C is
+raised, the current has to pass through a longer column of water than it
+does when C is near the bottom of L. When C touches T, the current
+passes easily. If it were not for the chimney, the current would pass to
+the sides of T.
+
+[Illustration: Fig. 80.]
+
+
+
+
+CHAPTER XII.
+
+CONTACT BREAKERS AND CURRENT INTERRUPTERS.
+
+
+_154. Contact Breakers; Current Interrupters._ It is often necessary to
+make and break the electric current at frequent intervals. This can be
+done by an ordinary key (App. 118) by rapidly raising and lowering it.
+It is more convenient, however, to use some other form of apparatus. The
+current may be interrupted automatically; that is, it may be made to do
+the work itself (App. 100), or each make and break in it may be governed
+by the student.
+
+
+APPARATUS 104.
+
+[Illustration: Fig. 81.]
+
+_155. Interrupter._ Fig. 81. The body of this consists of a strip of
+wood, 6 or 7 in. long, 1-1/2 in. wide, and 7/8 in. thick. Cut a strip of
+tin 1 in. wide and long enough to bend down over the ends of the wood.
+Fasten the tin to the wood with small wire nails, driving the nails into
+the ends as well as into the top of the strip. Make a "center line"
+along the tin as a guide, and then drive 1-in. wire nails through the
+tin into the wood, so that they will make a row the length of the wood,
+and stand about 1/4 in. apart. On one end make a hole through the tin,
+and put in a screw-eye binding-post (App. 45). It is evident that if a
+wire from one pole of a battery be connected with the binding-post, it
+will also be electrically connected with the tin strip and nails. By
+touching the wire from the other battery-pole to the tin or to any nail,
+the circuit will be closed. If this last-mentioned wire be drawn along
+entirely above the tin, so that its end can bump along from one nail to
+another, you can see that the current will be closed every time a nail
+is touched, and be opened every time it jumps through the air. This
+apparatus can be connected with shocking coils, induction apparatus,
+etc., etc. Its use will be more clearly shown in connection with such
+apparatus.
+
+
+APPARATUS 105.
+
+[Illustration: Fig. 82.]
+
+_156. Interrupter._ Fig. 82. The nails in this apparatus are placed in a
+circle about 4 in. in diameter. They are electrically connected to each
+other by a bare copper wire, which is wound around each nail several
+times, and then led out to one of the binding-posts. In the center of
+the circle is a nail, or screw, which is connected by a wire to the
+other binding-post, care being taken not to allow the two wires to touch
+each other. Around the central screw is wound one end of a stout wire,
+the other end of which reaches out from the screw far enough to touch
+the nails. When this stout wire touches any nail, a current entering one
+binding-post can pass through nails, screw, etc., and out at the other
+binding-post. When the end of the stout wire is between two nails, the
+current cannot flow. By placing the finger against this stout wire and
+turning it around rapidly, the current can be interrupted as desired.
+The base should be about 5 x 6 x 7/8 in.
+
+
+APPARATUS 106.
+
+_157. Interrupter._ Wind the end of the wire from one pole of the
+battery around the handle of the file. Scrape the other wire along the
+rough file. As it jumps from one ridge to another the current will be
+rapidly interrupted.
+
+
+APPARATUS 107.
+
+_158. Interrupter._ Hold the end of the wire from one pole of a battery
+upon a saw-blade. Draw the other wire along over the teeth of the saw.
+As the wire jumps from one tooth to the next the current will be broken.
+
+
+APPARATUS 108.
+
+_159. Automatic Interrupter._ An ordinary electric bell, or buzzer, may
+be used as an interrupter. Every time the vibrating armature swings, the
+circuit is opened. The combination of a battery, induction coil, and
+electric bell makes a very good outfit for medical purposes. The
+automatic interrupter used on App. 100 should be studied.
+
+
+
+
+CHAPTER XIII.
+
+CURRENT DETECTORS AND GALVANOMETERS.
+
+
+_160. Current Detectors; Galvanometers._ When a wire carrying a current
+of sufficient strength is properly brought near a magnetic needle, the
+latter will be deflected from its N and S line. The conducting wire has
+a magnetic field while the current passes through it, and this gives the
+wire the power to act upon a magnetic needle just as another magnet
+would.
+
+The action of detectors, etc., depends upon this fact; and, strange to
+say, the magnetic field about the wire disappears the instant the
+current ceases to pass. The combination, thus, of a coil of wire and a
+magnetic needle, properly arranged, makes an instrument with which the
+presence of electricity can be detected. When the strength of a current
+is to be measured, or the strengths of two currents are to be compared,
+the apparatus is called a galvanometer. The method of making these
+pieces of apparatus will depend upon the strength of current to be
+tested or measured.
+
+
+APPARATUS 109.
+
+_161. Current Detector._ Figs. 38 and 40 show magnetic needles. These
+may be used to detect a current by holding the conducting wire near them
+and parallel to the needle. This form is not sensitive to weak currents.
+The delicacy of the apparatus is increased by allowing the wire to pass
+above and below the needle several times as in the next apparatus.
+
+
+APPARATUS 110.
+
+_162. Current Detector._ Fig. 83 consists, like all detectors, of a coil
+and a magnetic needle. The other parts are merely for convenience. Each
+turn of the coil helps to move the needle when the current passes.
+
+[Illustration: Fig. 83.]
+
+163. The Coil is made by winding 10 feet of No. 30 insulated copper wire
+around the end of a broom-handle or other cylinder that is about 1 inch
+in diameter. This length of wire makes about 32 turns around such a
+cylinder. The exact length of wire for this makes no difference. After
+winding it, the coil should be slipped from the handle, being careful to
+hold it in such a way that it cannot uncoil and spring away from you.
+Tie the coil together with thread, in 3 or 4 places, to keep it in
+shape, and leave 5 or 6 in. of wire free at each end, so that
+connections can be made with other pieces of apparatus. After this is
+done press the coil into the shape shown, Fig. 83. This brings the wire
+near the needle and allows a longer needle to be used. The coil may be
+fastened to a pasteboard base. To do this, prick 4 holes in the base
+near the ends of the oval coil, and pass a strong thread through these
+with the aid of a sewing-needle. Tie the thread on the underside of the
+base at each end. If this is well done, the coil will be held firmly in
+an upright position. Paraffine may be used instead of the thread.
+
+The ends of the wire should be made bare, and these may be sewed to the
+base to keep them in place.
+
+164. The Needle may be supported upon a pin or needle-point. The piece
+of needle should be stuck through a cork which has a slot cut into its
+underside, so that it will straddle the lower part of the coil. The
+height of the needle-point should be fixed so that the horizontal ends
+of the magnetic needle will be near the axis of the coil, that is, along
+its central line.
+
+165. To Use the Detector, turn its base around until the coil is in the
+N and S line--that is, until the magnetic needle is parallel to the
+length of the coil and wholly inside of it. Touch the ends of the coil
+with the two ends of the wire, which is supposed to carry a current. The
+needle will fly around until it is nearly perpendicular to its former
+position, if the current is strong enough.
+
+
+APPARATUS 111.
+
+[Illustration: Fig. 84.]
+
+_166. Current Detector._ Fig. 84. To make a more substantial detector
+than App. 110, the coil should be fastened to a wooden base. The coil
+may be made of 10 ft. No. 30 wire, as explained. (Sec. 163.) A hole
+should be made in the base with a small awl or with a hot wire, and
+into this should be set a pin, head down. The hole need not be larger
+than the pin-head, and when you find out how high the pin-point should
+be above the base, the pin may be fastened in place with a little
+paraffine, which should be pressed into the hole around the pin. The
+coil may be fastened in place with paraffine. The ends of the coil may
+be connected with binding-posts, described in App. 46, as shown, or
+with any other desired form.
+
+The base should be 4 x 5 x 7/8 inches. The coil looks well when placed
+about 1 in. from the edge of the base. The binding-posts may be about 1
+in. from the edges.
+
+
+APPARATUS 112.
+
+_167. Current Detector._ Fig. 85. This is more troublesome to make than
+App. 111, but perhaps it looks more scientific.
+
+168. The Coil is wound around 2 ordinary spools which are glued to a
+vertical piece, which, in turn, is screwed to a base. You should not use
+iron nails or screws in the construction of electrical apparatus, when a
+magnetic needle is to be used in connection with it, as these would
+attract the needle. The spools may be pushed onto dowels which are
+fastened into the vertical piece. Small brass screws are good for the
+purpose also, if you haven't good glue or the dowels. This coil, etc.,
+may be used in connection with an astatic needle. The coil may be wound
+with App. 93 or 94, if you make the attachment of App. 95, and screw the
+upright carrying the spools to the attachment.
+
+[Illustration: Fig. 85.]
+
+The binding-posts, shown in Fig. 85, are not to be advised. It will be
+better to use those of App. 45. The magnetic needle is supported by a
+sewing-needle stuck through a cork. This may be fastened to the base
+with paraffine.
+
+_169._ It is often troublesome to turn the apparatus around until the
+needle becomes parallel to the length of the coil. To avoid this, a
+small bar magnet, shown in the Fig. 85, may be laid on top of the coil.
+A magnetized sewing-needle will do, and this will keep the magnetic
+needle quiet and parallel to it when the current is not passing through
+the coil. Of course, it takes a little more current to move the magnetic
+needle when the bar magnet is in place, than it does without the magnet.
+
+_170._ By allowing the current to enter the right-hand binding-post, as
+you look at it from the front (Fig. 85), it will go around the coil in
+the direction of the hands of a clock, that is, from left to right on
+top. This, of course, is not necessary to merely detect the presence of
+a current. In order, however, to determine the direction of currents by
+means of a magnetic needle, study the effect with a single turn of wire
+at first. (See text-book.)
+
+171. Dimensions. The base is 5 x 4 x 5/8 in. The upright piece is 5 x
+3-1/2 x 5/8 in. The spools are 2-1/2 in. apart center to center.
+
+
+APPARATUS 113.
+
+[Illustration: Fig. 86.]
+
+_172. Astatic Current Detector._ Fig. 86. The ordinary magnetic needle
+points to the north quite strongly. It is evident, then, that this
+pointing-power must be overcome by the magnetic field around the coil of
+wire, before the needle can be forced from the N and S line. Very weak
+currents will not visibly move the magnetic needle in the detectors so
+far described. You should remember that no action will take place unless
+the magnetic field around the magnetic needle is acted upon by that
+around the coil. In order to make an instrument that will be very
+sensitive, we must have strong fields about the needle and coil, and we
+must, at the same time, decrease the pointing-power of the needle. We
+can increase the strength of the field about the needle, and at the same
+time decrease its pointing-power by using an astatic needle. (See App.
+69.) The arrangement shown in Fig. 86 is a very simple one, and it is
+quite sensitive.
+
+173. Details of Construction. The base is 4 x 5 x 7/8 in. The coil is
+made from 10 ft. of No. 30 insulated copper wire. (See Sec. 163 for
+details about coil making.) The binding-posts are like App. 41. The
+Astatic Needle is described for App. 69. The needles may be broken off,
+if too long for the coil. They are supported by a fine thread hung from
+a screw-eye, which may be turned to adjust the position of the needles.
+This is not necessary, as the thread may be hung from a plain wire arm
+that reaches out from the upright rod. This rod is a 6-in. piece of
+dowel, 1/4 or 5/16 in. in diameter. It stands in an ordinary spool which
+should be glued to the base. Do not nail it to the base. The wire arm
+may be of iron, as it is some distance above the needle; but it is
+better to use a stiff brass or copper one. In the figure one end of the
+wire is twisted around the screw-eye, making a nut for the screw-eye to
+turn in.
+
+Hang the astatic needle so that the wire between the two parts will not
+quite touch the coil. The needles should be parallel to the coil before
+testing for currents. They will fly around very decidedly with even
+fairly weak currents.
+
+
+APPARATUS 114.
+
+[Illustration: Fig. 87.]
+
+_174. Astatic Current Detector._ Fig. 87. For a description of the
+wood-work, coil, etc., see App. 112; for the astatic needle see App. 69;
+for the method of supporting the needle see App. 113, Fig. 86. The top
+part of the coil is spread apart a little to allow the lower needle to
+be dropped through the opening thus made, and to allow the wire joining
+the two needles to be free to turn. The needles may be broken off a
+little, if necessary, or an opening may be cut into the vertical part of
+the frame, so that they can swing more freely. This detector will
+indicate quite feeble currents.
+
+
+APPARATUS 115.
+
+_175. Astatic Detector._ Fig. 88. As previously Stated, the
+sensitiveness of a detector can be made greater by increasing the
+strength of the coil-field for a given current. This may be done by
+increasing the number of turns of wire in the coil. The most convenient
+way will be to use two coils, one on each side of the astatic needle.
+
+176. The Support, or framework, is a lamp chimney. By this the astatic
+needle is suspended and protected from air currents. The chimney should
+be at least 3 in. in diameter at the bottom, about 10 in. high, with a
+plain round top. Upon the top of the chimney is placed the cover of a
+wooden pill-box, 2 in. in diameter.
+
+177. The Coils should be made separately, for convenience. Each should
+be of 10 ft. No. 30 wire. (See details Sec. 163.) Cut out a round piece
+of stiff pasteboard, just large enough to go inside of the bottom of
+the chimney. Fasten the coils to this by sewing (Sec. 163), or with
+paraffine, so that they shall be symmetrically located and 3/8 in.
+apart. The pasteboard circle may be fastened to the base with small
+brass screws. Do not use any iron nails or tacks. In this, all four
+ends of wire are brought out under the edge of the chimney (Fig. 88).
+Cut little grooves in the base for the wire to sink into, so that the
+chimney will rest firmly upon the base all around. The ends of the
+wires are fastened to three binding-posts.
+
+[Illustration: Fig. 88.]
+
+178. Joining the Coils. The end of one coil must be joined to the
+beginning of the other properly, or the action of one will destroy that
+of the other. Fig. 89 shows the two coils, A and B. If the current
+enters at the binding-post, X, it will pass through the turns of coil A,
+in the direction of clock-hands, then out to Y, where B begins, around B
+in the same way, and then to Z. Y may be simply a screw-eye
+binding-post (App. 41). By this arrangement one or both coils can be
+used at a time. If the current is very weak, use both coils; that is,
+connect the ends of wires to be tested with the two outside
+binding-posts. If they are joined to the middle and one outside post,
+one coil only will be in the circuit.
+
+179. The Base should be about 7 x 5 x 7/8 in. Fasten three bent brass or
+copper strips to the base with brass screws to hold the chimney steady.
+By bending them in more or less you can make a snug fit around the
+chimney.
+
+180. Adjusting the Needle. In the center of the box-cover is a small
+hole. The thread from the needle passes through this. The upper end of
+the thread is wound around a screw-eye, which is screwed into the cover
+near one edge. By turning the cover around, the needle can be made to
+hang parallel to the coils, and by turning the screw-eye, the needle can
+be raised or lowered. A small hole should be made in the cover before
+putting in the screw-eye, or you will be liable to split the wood.
+
+[Illustration: Fig. 89.]
+
+181. Use. This apparatus will indicate very slight currents; in fact, as
+feeble ones as the student will have occasion to experiment with, such
+as induced currents, currents of thermo-electricity, and currents
+produced by exceedingly weak batteries. (See text-book.)
+
+
+APPARATUS 116.
+
+_182. Tangent Galvanometer._ Fig. 90. For the uses of this form of
+galvanometer see text-book. Do not use any iron in making this
+apparatus. The base is 5 x 4 x 7/8 in. At its front end are three
+binding-posts. The pasteboard band, G, is 1-1/4 in. wide and 6 in. in
+diameter. Cut the pasteboard 21 in. long and 1-1/4 in. wide, then bend
+it into the form of a circle. There will be a lap of about 3 in., and
+you can make it solid by sewing the two ends together at the lap.
+
+[Illustration: Fig. 90.]
+
+183. The Coils maybe made of No. 24 insulated copper wire, which should
+be wound on before fastening G to the base. There are two separate
+coils, one having five turns and the other ten turns. Leaving a 6-in.
+length, A, for connections, wind five turns of wire on to G, putting
+them on clockwise; that is, pass them over the top of G from left to
+right. Tie thread around G and the wire to hold them together after you
+have five turns on, and cut a 6-in. end, B. Now begin with C, and wind
+on ten turns, bringing the end of them out at D. Punch holes, F, through
+G on each side of the coils, run twine, T, through them, and tie T on
+the outside of G. Do this in three or four places, to firmly hold the
+coils.
+
+184. Fastening Coils to Base. The band and coils will not rest squarely
+upon the base, so cut two pieces of wood, E, about 2 x 1/4 x 1/4 in., to
+be put under G, one being on each side of the coil. Make holes through
+the base, pass strong cord, H, through them, and over the inside of G,
+then tie under the base. This should tightly squeeze E, and hold G
+upright and firm.
+
+185. The Connections. A and B are the ends of the five-turn coil; C and
+D are the ends of the ten-turn coil. If the battery-wires are connected
+with X and Y, the current will pass through five turns of wire; if
+connected with Y and Z, it will pass through ten turns; if with X and Z,
+the current will pass through the entire fifteen turns. In this way the
+strength of the magnetic field about the coil can be regulated, and its
+effect upon the magnetic needle, M, changed.
+
+186. To Support the Needle, glue or sew two strips, I, to G. They must
+be in such a position that the poles of M will be as nearly as possible
+in a horizontal line drawn through the center of the circle, G. After
+you have made M (App. 66), and have found where the pieces, I, should
+be, fasten them to G, and then to I glue a pasteboard strip, J, about
+1-1/4 in. wide. Run a pin, P, up through the center of J to support M.
+
+187. The Magnetic Needle, M, should not be over 1 in. long for this kind
+of an instrument. (See App. 66 for full directions for making it.) On
+the top of M should be fastened a light paper pointer or index, L. The
+short end should be made large, so that the long slim end will not
+over-turn M; that is, the pointer should balance itself. It may be
+fastened to M with paraffine or a drop of sealing-wax. If carefully
+balanced, the pointer can be made quite long.
+
+188. The Graduated Circle, K, is described. (Index.) With this you can
+tell through how many degrees the needle is deflected, when the current
+passes. The strength of different currents can be compared, and many
+interesting experiments performed with the tangent galvanometer. For
+clearness, the circle, K, is shown small. In order to have the divisions
+on it far enough apart, K should be about 4 in. in diameter. The zero
+points should be at the front and back of the instrument, when a pointer
+is used on the needle.
+
+189. How to Use It. For full explanations, and for the study of
+experimental cells, etc., by means of the tangent galvanometer, see
+text-book. It will be impossible for you to get M exactly in the center
+of G; you cannot get the pointer exactly at right angles with M; hence,
+if you pass a certain current through the coils, and the pointer reads
+20 degrees, you will find, if you reverse the current, making it go
+through the coil in an opposite direction, that the pointer may read 24
+degrees on the opposite side of the zero. To get the true reading, then,
+take the average of the two, which in the case mentioned would be 22
+degrees. (See current reversers.)
+
+
+APPARATUS 117.
+
+_190. Tangent Galvanometer._ Fig. 91. The base consists of 2 parts, A
+and B. It is not necessary to use two pieces if you have wood that is at
+least 7/8 in. thick. This is given as a suggestion in case you have
+nothing but thin boards. By screwing B to A the base is made thick
+enough to take the screws for binding-posts. The base proper, A, is
+8-1/2 x 5 x 1/2 in. If you make this of 7/8 in. stuff, you will not need
+B.
+
+The Back, C, is 10 x 8-1/2 x 1/2 in. It is screwed to the base. Do not
+use nails, as these affect the magnetic needle. Find the center of C,
+and with this as a center, draw two circles, (that is, the
+circumferences of two circles,) one 5 in. in diameter to show where to
+cut out a hole, H, and the other 7 in. in diameter to serve as a guide
+for fastening on the spools, F.
+
+[Illustration: Fig. 91.]
+
+The Spools, F, are glued to C. If you have brass screws, these may be
+used instead of the spools; they should be left sticking out from C
+about 1 in. Around the spools or screws, fasten a pasteboard band, G, on
+which to wind the wire. G may be about 1 in. wide; it should be kept in
+the circular form by sewing the ends together where they lap. (Read
+directions in App. 116.)
+
+191. The Coils on this model are 4 in number. (See App. 116 for the
+method of winding.) The first coil is made of coarse wire, No. 18, its
+ends being joined to the binding-posts, V and W. The second coil has 5
+turns of No. 24 insulated copper wire, its ends being joined to W and X.
+The third coil has 10 turns of the same size wire, No. 24, and is joined
+to X and Y. The fourth coil has 20 turns of the same joined to Y and Z.
+If you want to use the galvanometer for quite weak currents, it would
+be well to make a fifth coil of 20 turns of No. 30 wire, and join it
+with Z and a new binding-post. The ends of the coils are run through
+small screw-eyes before passing to X, Y, etc. This is not necessary, it
+merely keeps them in place.
+
+The Binding-Posts are like App. 43. Any other desired style may be used,
+those of App. 46 being preferred.
+
+The Hole, H, is 5 in. in diameter. It should be cut out about 1/2 in.
+below the center of the circles to allow for D, and for the pin-point
+which supports the magnetic needle, the poles of which should be in the
+line passing through the center of the coils. The method of cutting the
+hole, H, through C, will depend upon the tools at your service.
+
+D is the front edge of an adjustable table, like that explained.
+(Index.) It is 4-1/4 in. wide. It supports the magnetic needle which is
+inside of E.
+
+E is the outside of a glass-covered compass. (See App. 67 for details.)
+The needle should not be over 1 in. long.
+
+
+
+
+CHAPTER XIV.
+
+TELEGRAPH KEYS AND SOUNDERS.
+
+
+APPARATUS 118.
+
+[Illustration: Fig. 92.]
+
+_192. Telegraph Keys._ Fig. 92. Telegraph keys are merely pieces of
+apparatus by which the circuit can be conveniently and rapidly opened or
+closed at the will of the operator. An ordinary push-button may be used
+to turn off and on the current, but it is not so convenient as a "key."
+Fig. 92 shows a side view of a simple key. C is a metal strip about 3/4
+in. wide and 4 or 5 in. long. At the left end it is fastened to the base
+with a screw, A. Another screw, X, serves as one binding-post. Y is
+another screw binding-post. W is a short wire, used to regulate the
+amount of spring to the key. This is done by moving W to the right or
+left. If the current enters at X, it will pass along C and out at Y,
+when C is pressed down. By moving C up and down according to a
+previously arranged set of signals, messages can be sent by means of the
+electric current. (See telegraph alphabet.) This apparatus is not a good
+one where the line is to be run with a "closed circuit battery," or
+where it is to be used very often. It will do, however, for places where
+a push-button would be too tiresome to use. The right end of C is
+curved. This curve serves as a handle. D and E are wires leading from X
+and Y.
+
+
+APPARATUS 119.
+
+_193. Telegraph Key._ Fig. 93. The base is 5 x 4 x 7/8 in. The key, C,
+is made of two thicknesses of tin. It is made into a strip 5-1/2 x 3/4
+in., then the front end is bent up for a handle, as suggested in Fig.
+92, the front end being above the base so that it will not touch the
+strap, D, unless it is pressed down. C is fastened to the base by a
+screw, H, which also binds one end of the copper wire, C W. About 3/4
+in. from H is placed X, which is a screw-eye binding-post. Under C is
+the wire, W, which is used to regulate the amount of spring in C, by
+moving it forward or backward. S I shows the position of a screw-eye, or
+of an ordinary screw put into the base through C. The hole in C should
+be made so that C can move up and down easily around the screw. This is
+used to make a click when the key is allowed to spring up. The downward
+click is made when C strikes D at each depression.
+
+[Illustration: Fig. 93.]
+
+The Strap, D, is made of tin. It is 4 x 1/2 in. before bending up the
+right end a little. It is fastened to the base by the screw, F, and by
+the other binding-post, Y. Its right end is raised enough to allow the
+arm, E, to pass under it, but it must press down well upon E when E is
+forced toward F.
+
+The Swinging Arm or Switch, E, is also made of tin, and measures,
+finished, 4-1/2 x 1/2 in. Its front end should be bent up a little for
+convenience in handling it. (See Fig. 92.) E is pivoted at G by a screw,
+which also binds the wire, C W. Fig. 24 shows another way to make the
+pivot and connection.
+
+194. Operation. See Fig. 99 for the details of the connections of a
+home-made telegraph line. When you are using the line and telegraphing
+to your friend, the switch, E, of your instrument must be open, as in
+Fig. 93, and the corresponding switch on his instrument must be closed;
+that is, the circuit must be opened and closed at but one place at a
+time. As soon as you have finished, your switch must be closed. He will
+open his and proceed. When you have both finished, both switches must be
+closed. If your friend left his switch open, you could not call him over
+the line, as no current could pass into his sounder.
+
+195. Batteries. As the circuit has to be left closed for hours and
+perhaps days at a time, so that either operator can call the other, a
+closed-circuit battery is necessary. (See App. 9.) A dry cell,
+Leclanche, or other open-circuit cell would not be at all suitable for a
+telegraph line, as it would soon polarize. Large Daniel cells, which are
+2-fluid cells like App. 7, or gravity cells (App. 9) are the best for
+your line.
+
+
+APPARATUS 120.
+
+_196. Telegraph Sounder._ Fig. 94. The wood-work consists of 2 parts;
+the base, B, is 6 x 4 x 3/4 in., and the back, A, is 6 x 5 x 1/2 in. A
+is nailed or screwed to B.
+
+The Magnet, M, is fully described in App. 85. M is held firmly to A by
+cord or wire, which should pass around it near the poles and at the
+curved part. The wire should pass through small holes in A, and be tied
+at the back. Wire nails driven into A at the sides of M will keep it
+from moving about. The wires from the magnet coils are led to two spring
+binding-posts, X and Y.
+
+[Illustration: Fig. 94.]
+
+197. The Armature, C, is made of a narrow piece of thin iron, about
+5-1/2 x 1/4 x 1/8 in. It may be made by bending up 3 or 4 thicknesses of
+tin into that shape. This is the part which will be attracted by M, when
+the current passes, and which will make the clicks by which the message
+can be read. (See telegraph alphabet.) There are many ways by which C
+can be held near M. The figure shows how it can be done entirely with
+1-in. wire nails. At the right end of C two nails are driven into A
+above and below C. They are just far enough apart to allow the left end
+of C to be raised and lowered without binding; in other words, these
+nails make a pivot for C to swing upon, and they help to support it at
+the same time. The left end of C must not quite touch the poles of M
+when the current passes, because the residual magnetism would keep C
+from dropping back into place. To adjust the armature, pass the current
+through M, hold C so that it will not quite touch the poles, then drive
+in the upper nail, 2. Put another nail, 1, below C, so that M will not
+have to lift C more than 1/8 or 3/16 in. Try the nails in different
+positions until C quickly rises and falls when the circuit is closed and
+opened. A nail, 3, driven in front of C, will keep its right end in
+place. No springs are needed, as gravity acts upon C instantly, bringing
+it to the lowest position as soon as the current ceases to flow.
+
+198. The Battery will depend upon how much you want to use the sounder.
+If just to show the principle of it, almost any cell of medium strength
+will do, like that of App. 3, 4 or 5. A dry battery will do, but if you
+use the sounder much, an open-circuit battery will soon use itself up.
+Where much work is needed of the battery use App. 9.
+
+[Illustration: Fig. 95.]
+
+The Key like App. 119 is best. Push-buttons are handy where used only
+for experiments, and not for the actual sending of messages.
+
+
+APPARATUS 121.
+
+_199. Telegraph Sounder._ Fig. 95. This makes a simple and efficient
+sounder for short lines. The base, B, is 7 x 4-1/2 x 7/8 in. The back,
+A, is 7 x 4-1/2 x 1/2 in.; it is nailed to B. The piece D is 4 x 3/4 x
+3/4 in.; it is nailed to A. C is a wooden piece 1-1/2 x 3/4 x 3/4 in.;
+it is nailed to A, and in its top is a screw, E, which is used as a
+regulating-screw to keep the armature, L, from touching the poles.
+
+200. The Armature, L, is explained as App. 77. The two thicknesses of
+tin at F must not be too thick, or it will take too much battery power
+to work the sounder. If you find that it is too stiff to bend down, when
+the current is on, try the arrangement of App. 122, which is easier to
+make and regulate. The whole point depends upon the tin you have. The
+end of L must tap against E. A hole is punched in the part F, and a
+screw, G, holds it to D. L should rest about 1/8 in. above the poles and
+gently press against a screw or nail, V.
+
+201. The Magnets are like App. 89. They are made as in App. 88, and held
+down like App. 90. These should be placed very near the back, A, so that
+the armature will be over them. If your yoke is not too wide the coils
+may rest against A. Y and Z are binding-posts like App. 46.
+
+202. Connections. Join the coils as explained in Sec. 125 and see Sec.
+115. Instead of a third or middle binding-post, as in Fig. 66, hold the
+two inside ends between a screw-head and a copper bur. The method of
+joining the wires for a line with two outfits, is shown in App. 124. If
+you have but one key, sounder, and battery, simply join the line wire
+to the return wire there shown. A gravity cell is best. (See App. 9.)
+
+203. Hints About Adjusting. If you have the right spring to the part F,
+of the armature, you will have no trouble. It must not be so weak that
+it allows L to strike upon the poles, as the residual magnetism
+(Text-book) will hold L down after the current has ceased to pass. No
+springs are necessary, if your tin is right. Do not have L too far away
+from the poles. The distance is regulated by the position of V. If you
+have trouble in getting it to work see App. 122. The poles must be
+opposite in nature.
+
+
+APPARATUS 122.
+
+[Illustration: Fig. 96.]
+
+_204. Telegraph Sounder._ Fig. 96. The magnets, connections, etc., are
+like those of App. 121, no binding-posts, etc., being here shown. The
+armature is straight, however, the part F resting upon D. A hole is made
+in the end of F, and through this is a screw or nail, S. The hole must
+be large enough to allow S to pass through easily. This acts as a
+bearing or pivot. L is kept up against V by the rubber-band, J, one end
+of which passes around the end of L; to the other end of J is a thread,
+which is tied around a screw-eye, K. By turning the screw-eye, the band
+may be made to pull more or less upon L. In this way the apparatus may
+be regulated according to your battery. The general dimensions and
+explanations are given in App. 121. D is made of such a height that it
+will bring L about 1/8 or 3/16 in. above the poles.
+
+
+APPARATUS 123.
+
+[Illustration: Fig. 97.]
+
+_205. Telegraph Sounder._ Figs. 97 and 98. This apparatus looks a little
+more like a regular sounder than App. 121 and 122, but it is much harder
+to make and adjust. In this the lower nuts of the bolts are not sunk
+into the base, and the magnets are made of 2-in. bolts. If you change
+this and fasten them like App. 89 and 90, it will simply change the
+dimensions of the small parts. The sizes given are for this particular
+instrument.
+
+Fig. 97 shows a perspective view, and Fig. 98 is a plan or top-view of
+it, with dimensions.
+
+[Illustration: Fig. 98.]
+
+206. The Base, B, is 6 x 4 x 7/8 in. The magnet, M, is explained in App.
+89. Its wires are attached to the binding-posts like App. 46. The
+armature, A, is 2-1/2 x 3/4 x 1/8 in., and made as described in App. 71.
+The piece, D, is 2-1/2 x 1-3/8 x 1/2 in., and is screwed to B from
+below, after the two uprights, C, are nailed to it. The uprights, C, are
+2-3/4 x 7/8 x 1/2 in. They are nailed to D. The nail, N, runs through
+both uprights, and acts as the bearing for F to rock up and down upon.
+The hole for N is 2 in. above B. It must not be too loose in the holes,
+or F will rock sidewise, and allow A to touch one of the magnets. The
+upright, E, is 2-3/4 x 3/4 x 3/4 in., and is screwed or nailed to B from
+below. A screw, G, is put into the side of E near the top. This screw
+has the underside of the head filed flat, and against this the screw, L,
+taps when the armature is attracted. The arm, F, which carries the
+armature, A, is 4-1/2 x 1/2 x 1/2 in., and is pivoted by means of N,
+which passes through it and the uprights C. F must swing up and down
+freely. The hole for N, in this model, is 1-3/4 in. from the armature
+end.
+
+207. The armature is fastened to F by a screw, S. A copper bur is put
+under the head of S to aid in keeping A from rocking sidewise. Through
+F, and about half way between C and L, is put a screw, I, the lower end
+of which taps against the head of a screw, H, which is put into D. By
+unscrewing H a little, F will be raised, and A will be brought nearer
+the poles of M. The rubber-band, J, is placed over the head of I, and
+has tied to it a thread, O, which in turn is tied to a screw-eye, K. K
+screws into the end of B, and by turning it one way or the other, the
+tension, or pull, on J may be increased or diminished. There must be
+enough spring in J to pull A up after the current ceases; it must not
+pull so much that the magnet cannot draw A down hard enough to make a
+good click between L and G.
+
+The Magnet, M, is explained in App. 89, and the construction of one bolt
+magnet is given in detail in App. 88. In this particular sounder the
+bolts are 2 in. long under the heads, thus bringing the tops of the
+bolt-heads about 2-1/4 in. above B. M is held to the base by a band of
+tin, T. The yoke may be screwed to B, as suggested in App. 90. This is
+the better plan.
+
+208. Adjustment. You will find, although you make all of the parts with
+the dimensions given, that you will have to try, and change, and adjust
+before everything will work perfectly. A must not be allowed to touch
+the poles of M when it is pulled down, on account of the residual
+magnetism, which would keep it pulled down. Adjust this with F. The
+armature must not be pulled too far up from the poles of M by the
+tension in J; adjust this with I and H. If your battery is weak, the
+pull of J must be small, just enough to raise A.
+
+The Battery. It is supposed, if you make an instrument like this, that
+you expect to use it for a line. In that case make a regular gravity
+battery like the cell of App. 9. See Fig. 99 for line connections, and
+Fig. 98 for plan view of this sounder.
+
+
+APPARATUS 124.
+
+_209. Telegraph Line; Connections._ Fig. 99 shows the complete
+connections for our telegraph line, with two complete outfits. The
+capital letters are used on the right side, R, and small letters are on
+the left side, L. The batteries, B, b, are like App. 9. The keys, K, k,
+are like App. 119. The sounders, S, s, are like App. 121 or 122.
+
+[Illustration: Fig. 99.]
+
+210. The two stations, R and L, may be near each other, or in different
+houses. The return wire, R W, passes from the copper of b to the zinc of
+B. This is important. If the cells are not joined properly, they will
+not work. It is better to have the cells together, on a short line,
+joined in series. The line wire, L W, and the return wire, R W, may be
+made of insulated copper wire for short lines in the house. Ordinary
+annunciator wire, No. 20, is good and cheap. The kind that is double
+cotton wrapped, waxed, and paraffined, has about 235 ft. to the pound.
+You should get at least 5 ft. for 1 cent. If your line stretches from
+one house to another you will find it better to use iron wire.
+Galvanized iron or steel wire No. 14 is good. This size weighs about
+100 lbs. to the mile. The return and line wires must not touch each
+other at any point; they must not touch any pipe or other piece of metal
+that will short circuit your batteries. It is best to use porcelain or
+glass insulators to support your wires if the line is long; but for
+short lines, where you use a return wire, you may support the wires upon
+poles or trees by means of loops made of strong cord or wire.
+
+211. Operation. Suppose R (right) and L (left) have a line. By studying
+Fig. 99 you will see that R's switch, E, is open while e is closed. The
+whole system, then, has but one place where the circuit is open. As soon
+as R presses his key, K, the circuit is closed, the current from both
+cells rushes around through K, S, L W, s, k, b, R W, and B. This
+magnetizes the bolts of both S and s, and their armatures come down with
+a click upon the regulating-screws, where they remain as long as the
+current passes. As soon as R raises his key the armatures rise, making
+the up-click. R can, in this way, regulate the time between the two
+clicks. If he presses K down and lets it up quickly, the two clicks that
+his friend L hears from s are close together; this makes what is called
+a dot. If R holds K down longer, it makes a longer time between the
+clicks for L to hear, and this makes a dash. R, of course, hears his own
+sounder, which is making the dots and dashes also.
+
+As soon as R has finished, he closes his switch, E. L then opens his
+switch and proceeds to answer. Both E and e should be left closed when
+you are through talking.
+
+(Read Sec. 194, 195, and study what is said in App. 9 about the gravity
+cell to be used on such a line.)
+
+_212. Telegraph Alphabet._ The letters are represented by combinations
+of dots, dashes and spaces. A dot is made by pressing the key down, and
+raising it at once; that is, the key is raised as soon as it strikes.
+This makes the letter E. The dash is made by pressing down the key, and
+allowing the current to pass about as long as it takes to make 3 dots;
+this makes the letter T. A long dash for L should take about as long as
+for 5 dots. Spaces occur in a letter and between words. To make a dash
+you hesitate while the lever of the key is down, to make a space, you
+hesitate while the key is up. H is made with 4 dots without hesitation
+or space. By putting a space between the dots the letter &, Y or Z is
+made according to the position of the space. Notice that letters
+containing dashes do not contain spaces. A space is really the opposite
+of a dash. The letters C, E, H, I, O, P, R, S, Y, Z, and & are made
+entirely of dots or of dots and spaces.
+
+You should notice that several letters are the reverse of others; A is
+the reverse of N, B of V, D of U, C of R, Q of X, and Z of &. The
+student should study some book upon telegraphy, if he desires to become
+expert. Punctuation marks are left out of the alphabet here given, as
+boys will find very little use for them.
+
+A _ ___
+B ___ _ _ _
+C _ _  _
+D ___ _ _
+E _
+F _ ___ _
+G ___ ___ _
+H _ _ _ _
+I _ _
+J ___ _ ___ _
+K ___ _ ___
+L ______
+M ___ ___
+N ___ _
+O _  _
+P _ _ _ _ _
+Q _ _ ___ _
+R _  _ _
+S _ _ _
+T ___
+U _ _ ___
+V _ _ _ ___
+W _ ___ ___
+X _ ___ _ _
+Y _ _  _ _
+Z _ _ _  _
+& _  _ _ _
+
+1 _ ___ ___ _
+2 _ _ ___ _ _
+3 _ _ _ ___ _
+4 _ _ _ _ ___
+5 ___ ___ ___
+6 _ _ _ _ _ _
+7 ___ ___ _ _
+8 ___ _ _ _ _
+9 ___ _ _ ___
+0 ______
+
+
+
+
+CHAPTER XV.
+
+ELECTRIC BELLS AND BUZZERS.
+
+
+APPARATUS 125.
+
+_213. Electric Buzzer._ Fig. 100. A buzzer is, in construction, very
+similar to an electric bell; in fact, you will have a buzzer by removing
+the bell from any ordinary electric bell. They are used in places where
+the loud sound of a bell would be objectionable. As the buzzer is easier
+to make than a bell, we shall discuss it first.
+
+214. The arrangement of the parts, (Fig. 100), is very much like that of
+the sounder of App. 121, Fig. 95. The armature is, in this case, a
+vibrating one and acts on the same principle as the automatic
+interrupter on App. 100, which you should study. (See Sec. 148.) The
+general dimensions may be taken from App. 121. The base, B, in this case
+is about 1 in. wide. D also is made 1 in. wide. H is 1 x 1 x 1/2 in.,
+and is nailed to A. Through its center is a hole for the regulating
+screw-eye, I. The end of I presses against F. The exact position of H
+will have to be determined after the magnets are in place. The armature,
+L, should be about 1/8 or 3/16 in. above the poles. They are not allowed
+to strike the poles, as a screw, E, regulates that. (See Sec. 203). Y and
+Z are two binding-posts, like App. 46. To these are connected the battery
+wires. The strip of tin or copper, which forms Y, is cut like a letter T
+there being three holes in it, one near the end of each arm. The
+screw-eye, 2, and the screw, 3, are put through the horizontal part of
+the T, and the regulating-screw, I, passes through the hole in the
+vertical part which springs up against I, thus forming an electrical
+connection between Y and I. The magnets are made and fastened as in App.
+89.
+
+215. Connections. The inside ends of the magnet coils, (Sec. 123), are
+fastened between a screw-head and a copper bur, S. One outside end goes
+to Z, and the other under the screw, G, which holds F to D.
+
+[Illustration: Fig. 100.]
+
+216. Adjustment. The part, F, and the screw, E, must be just high enough
+to keep L from striking the poles of M. If F is too weak, it will bend
+down to M. If F is too strong, it will take too much battery power to
+run it. In case there is not strength enough in F to quickly raise L
+when the current ceases to pass, arrange a screw-eye and rubber band as
+shown in Fig. 96. I should be slowly turned one way or the other, until
+it touches F just right to allow L to vibrate back and forth rapidly.
+
+217. Operation. We shall suppose that you have all parts adjusted and
+the battery wires joined to Y and Z. If the current enters at Z, it will
+fly around through the coils, through G, F, up I, through the T-shaped
+tin and out at Y. The current was in L, but it could not get out at any
+other place than at Y. As soon as the bolts were magnetized, L was
+forcibly drawn down, pulling F away from I, thus opening the circuit.
+As the bolts were no longer magnets, F sprang right back to I, the
+current passed long enough to re-magnetize the bolts. This operation was
+rapidly repeated.
+
+218. Use. If you wish to use the buzzer simply to call some one
+occasionally, a dry battery or Leclanche cell is best. This apparatus is
+good to work a gravity cell when it needs regulating.
+
+
+APPARATUS 126.
+
+[Illustration: Fig. 101.]
+
+_219. Electric Bell._ Fig. 101. Before making this bell, carefully read
+the directions and explanations given for the electric buzzer, App. 125.
+The parts are very much alike in the two instruments, and most of the
+lettering of them has been made the same in the illustrations. If you
+look at Fig. 101 from the side, with the letters M and Q at the bottom,
+you will see that this bell is merely a modified form of App. 125.
+
+The Base is 7 x 5 x 1/2 in. To the upper end of this is nailed the
+cross piece, D. To D are fastened the binding-posts.
+
+The Parts, F, G, H, I, J, K, L, M, N, P, Q, are the same as explained in
+App. 121 and 125.
+
+The Magnet is fastened to the base by a tin strip, C, which is screwed
+down at both ends. By nailing a strip, like D, along the left side of
+the base, the magnet may be fastened to this. This strip would take the
+place of the base of App. 125.
+
+The piece, F, of two thicknesses of tin, is made longer than it was in
+App. 125; in fact, it projects through L and forms the part N. To the
+lower end of N is fastened a large bullet. Hold the cutting-edge of a
+strong knife-blade upon the bullet, and with a few taps of a hammer
+drive the blade into it to make a gash.
+
+Put the end of N into the cut, then hammer the bullet so that N will be
+pinched. If you have no bullet, cut a long strip of tin, about 3/8 in.
+wide, and wind this about the end of N to serve as a ball.
+
+The Bell, E, may be taken from an old alarm-clock. This is not screwed
+directly to the base, as it would not ring well. After you have the
+ball, O, properly fixed, hold E, so that O will strike it near its rim;
+then cut a piece of wood about 5/8 x 5/8, and long enough to put under
+E, to raise its rim to the right place. This piece must be screwed to
+the base from the underside, and on to its top is placed the screw which
+passes through the bell. In other words, E is mounted upon a rod which
+is fastened to the base.
+
+The Adjustments are made as in App. 125. By bending N a little, O can be
+made to tap E properly.
+
+The Battery for a bell that is to be used much should be an open circuit
+one, such as the Leclanche, or the ordinary dry batteries. It is cheaper
+to buy a dry battery than it is to make one suitable for bells. A and B
+show wires that lead to the bell from the battery. One of the wires
+should be passed through a push-button.
+
+
+APPARATUS 127.
+
+_220. Electric Bell._ By arranging the buzzer of App. 125 with a bell,
+you can use the same for an electric bell. The part, F, should be made
+long enough to extend entirely through L, and project beyond L for about
+2 in. To the end of this is fastened a large bullet, or a band of tin.
+(See App. 126.)
+
+[Illustration: Fig. 102.]
+
+
+APPARATUS 128.
+
+_221. Combination Buzzer and Telegraph Sounder._ Fig. 102. This
+apparatus is good for experimental purposes, where you do not wish to go
+to the trouble to make two separate pieces. For the dimensions and
+explanations see App. 121 and 125. There is but a slight change in App.
+125 to make this.
+
+222. Connections. The inside ends (Sec. 123) of the magnet wires are
+fastened together at S. The outside ends are joined to the two
+binding-posts, Y and Z, made like App. 46. A wire, P, joins Y with the
+screw in T, which is a piece of stiff tin or copper, which presses down
+upon the top of I. In this way a connection may always be had between I
+and T. A wire, R, joins F electrically with X; it is held under the head
+of the screw, G. (See App. 125 about adjustments.)
+
+223. Operation. When you wish to use the apparatus as a buzzer, join
+your battery wires to X and Z. If the current enters Z, it will pass
+through the magnet coils out to Y, through P, T, I, F, and R to X. If
+you use it as a telegraph sounder, join the battery wires to Y and Z.
+The current will then pass simply through the coils; it will not bother
+to go into P, F, etc., as it has no place it can escape. If used simply
+for experimental purposes almost any cell of sufficient strength will
+do. If for telegraph, use App. 9; if for buzzer, use an open circuit
+cell, as, for example, a dry cell.
+
+
+
+
+CHAPTER XVI.
+
+COMMUTATORS AND CURRENT REVERSERS.
+
+
+_224. Commutators and Current Reversers_ are useful in some experiments,
+as, for example, those with tangent galvanometers (App. 116, 117), in
+which readings are made with the current passing around the coil in one
+direction, and again made at once with the current reversed. The use of
+commutators on motors and dynamos should be understood. The reversers
+herein shown are, of course, not at all like those used on motors.
+Current reversers are used in connection with the needle-telegraph and
+many other instruments.
+
+[Illustration: Fig. 103.]
+
+
+APPARATUS 129.
+
+_225. Current Reverser._ Fig. 103. The base is 5 x 4 x 7/8 in. To this
+are fastened four metal straps, A, B, C, and D. These may be made of
+brass, aluminum, or even of tin. If made of tin, use one thickness of
+metal for C and D, and two thicknesses for A and B. Each strap has two
+1/8 in. holes punched in it, their positions being shown by the
+screw-heads and screw-eye binding-posts.
+
+Construction. C is 3-3/4 x 1/2 in. Fasten this to the base first. At the
+left end is a small screw, while the right end is held down by the
+binding-post, W. The keys, A and B, should have quite a little spring to
+them. These are cut 5 x 3/4 in. The front end of each is bent over a
+little (see the key App. 118, Fig. 92) so that they may be more easily
+grasped. The length after bending will be less than 5 in. The front ends
+should be raised from the base (Fig. 92) so that they will not touch C,
+unless pressed down. The 1/8 in. holes in the end of A are about 3/4 in.
+apart, one being used for a screw to hold it to the base, and the other
+for the binding-post, Y. The strap, D, is 3-3/4 x 1/2 in. It is fastened
+at one end by a screw, and at the other end by X. D is bent about 3/4
+in. from each end, so that its middle part stands above the base about
+1/4 in. The straps, A and B, press up against D, unless they are held
+down with the hand.
+
+226. Connections. W and X are joined to the poles of the battery to be
+used. Y and Z are joined to the apparatus in which the current must be
+passed in one direction, and then in the opposite direction. A tangent
+galvanometer, or a needle-telegraph instrument, for example, may be
+connected with Y and Z.
+
+227. Operation. Suppose that the battery current enters at W. As long as
+both keys are raised, the current can go no farther. Now, imagine that
+we press A down solidly upon C, the current will pass along A, which
+does not now touch D, out through Y into the galvanometer, back to Z,
+into D, and to the battery again; that is, the current will enter the
+galvanometer from Y. Now, suppose that we let A spring up against D
+again, and press B down, the current still coming into W from the
+battery; the current will pass along B, out through Z, into the
+galvanometer, back to Y, through D, and back to the battery. It is
+evident, then, that the current can be made to pass out of Y or Z to the
+galvanometer at will by pressing down A or B.
+
+
+APPARATUS 130.
+
+[Illustration: Fig. 104.]
+
+_228. Current Reverser._ Fig. 104. The wooden base is 7 x 5 x 7/8 in. To
+this are fastened two brass or tin straps, C and D, 5 x 1/2 in. They are
+fastened at the front ends by screws, S, while the binding-posts, Y and
+Z, hold the other ends solid. X and W are two screw-eye binding-posts
+(App. 45). The small square piece of wood, T, is 3 x 3 x 1/2 in. Through
+the corners of T, and in positions so that they will be directly over C
+and D, are put four screw binding-posts, 1, 2, 3, 4 (App. 41). The
+screws, however, pass entirely through T, and stick out about 1/4 in. on
+the underside of it. The wire, A, connects W, 1 and 4, while the wire,
+B, connects X, 2 and 3. A and B must not touch each other where they
+cross on the top of T. N is a wire nail that serves as a handle. If we
+were to place T, holding the four corner screws, upon the straps, C and
+D, it is evident that all the screws would touch the straps, if they
+were properly adjusted. We must fix things so that two only can touch
+the straps at a time. Put a screw, Q, through the center of T, from the
+bottom, so that it will stick out of the bottom more than the screws, 1,
+2, etc. The screws, 2 and 4, will be lifted from C and D when the
+handle, N, is pressed down. By raising N, the top, T, can be made to
+rock up and down upon Q as a pivot. By lifting N far enough, 2 and 4
+will be pressed against C and D, while 1 and 3 will be raised. A spring,
+R, is shown joined to T and to the base. This will hold the screws, 2
+and 4, down upon C and D, unless N is pressed down.
+
+229. Operation. We shall first suppose that the spring, R, is holding 2
+and 4 in contact with C and D; 1 and 3 will, of course, be held up in
+the air. Imagine that we have a galvanometer connected with Y and Z. If
+the battery current enters at W, it will pass along A to 4, before it
+can find a chance to escape. It will pass through 4 into D, and into the
+galvanometer by way of Z, then back by way of Y, up 2, and out to the
+battery from X. If we now press the handle, N, down, the current will
+pass from W to 1, down 1 through C and Y to the galvanometer. It will
+return to the battery by way of Z, D, 3, B, and X. The current can then
+be rapidly reversed by raising and lowering N.
+
+
+
+
+CHAPTER XVII.
+
+RESISTANCE COILS.
+
+
+APPARATUS 131.
+
+_230. Resistance Coils._ Fig. 105. For experiments in resistance (See
+text-book), a set of standard resistances is necessary. There are many
+ways in which the resistances may be made; you can arrange them upon a
+long board, upon a rack, or wind the wires around spools. We generally
+speak of resistance coils. The Ohm is taken as the standard. If you use
+copper wire, you may take 9 ft. 9 in. of No. 30 insulated wire as your
+standard Ohm. You could, of course, take any other length of any size as
+your standard, but it will be best to make your coils with a certain
+number of Ohms resistance. If you have no No. 30 wire, you may use 39
+ft. 1 in. of No. 24 insulated copper wire for 1 Ohm. (See wire tables in
+text-book.)
+
+[Illustration: Fig. 105.]
+
+231. To avoid the magnetic effect (See resistance coils, in text-book),
+the wire should be measured off, then doubled, before winding it upon
+the spools. The wire may be held to the spool with paraffine. Fig. 105
+shows how the doubled wire looks on the spool, a few turns only being
+shown. Do not use any nails or other iron in connection with the coils
+proper.
+
+232. By making 4 coils having, respectively, 1, 2, 2, and 5 Ohms
+resistance, you will be able to use any number of Ohms from 1 to 10.
+These will be very handy in connection with a "Wheatstone's bridge" for
+comparing resistances. (See text-book for experiments). The coils should
+be mounted upon a base with proper binding-posts, so that one or more
+coils can be used at a time. (See App. 132.) For the 2-Ohm coil use, of
+course, twice as much of the same kind of wire as for the 1-Ohm coil.
+
+
+APPARATUS 132.
+
+[Illustration: Fig. 106.]
+
+_233. Resistance Coils._ Fig. 106. The construction of one coil is given
+in App. 131. To have the set of coils so that they can be easily used,
+place the spools upon a base which, in the model, is 8-1/2 x 4 x 7/8 in.
+The spools are 1-3/4 in. apart, center to center, and should be glued to
+the base. Fig. 106 is a plan of the apparatus. U, V, etc., are
+binding-posts like App. 46. The figures between them show how many Ohms
+resistance there are in the coil above. The coils A, B, C, D, and E are
+wound respectively for 1, 2, 2, 5 and 10 Ohms.
+
+234. Connections. If you join a Wheatstone's bridge, for example, with
+U and V (Fig. 106), the resistance added will be but 1 Ohm; if you join
+with U and W, the coils A and B will be in the circuit and make 3 Ohms
+resistance; if V and X, 4 Ohms; if V and Y, 9 Ohms; if U and Z, the
+whole, or 20 Ohms.
+
+
+APPARATUS 133.
+
+_235. Resistance Coils._ For use in some experiments in comparing the
+resistance, diameter, lengths, etc., of wires (See text-book), it is
+very handy to have coils made a certain number of meters long. (The
+meter is a French unit of measure and represents 39.3705 of our inches).
+German-silver wire has a much greater resistance than copper wire of the
+same size and length.
+
+(a) Make a coil (See App. 131 for method) containing 1 meter of No. 30
+German-silver wire.
+
+(b) Make a coil with 2 meters No. 30 German-silver wire.
+
+(c) Make one with 2 meters of No. 28 German-silver wire.
+
+(d) Make one with 20 meters of No. 30 copper wire.
+
+The above wire must be insulated if it is to be wound upon spools. Bare
+wire may be arranged on boards or racks so that the current may not be
+short circuited.
+
+
+
+
+CHAPTER XVIII.
+
+APPARATUS FOR STATIC ELECTRICITY.
+
+
+_236. Static or Frictional Electricity._ There are many interesting and
+instructive experiments in this branch of electricity. All that can be
+done here is to explain a few pieces of simple apparatus to show the
+presence of static electricity, it being taken for granted that you know
+how to produce it, and that you have some book of simple experiments.
+
+_237. Electroscopes_ are instruments for showing the presence of static
+electricity.
+
+
+APPARATUS 134.
+
+_238. Thread Electroscope._ A piece of ordinary thread may be used for
+this purpose. Tie one end of it to the back of a chair or other support.
+
+
+APPARATUS 135.
+
+_239. Pith-Ball Electroscope._ Fig. 107. The pith from elder,
+corn-stalk, milk-weed, etc., is very light and porous. When this is tied
+to the end of a silk thread, we get the pith-ball electroscope, so much
+talked about in nearly every text-book on physics. The upper end of the
+thread may be tied to any suitable support. Fig. 117 shows a book, lead
+pencil, and a small weight to hold the pencil steady. The thread is tied
+to one end of the pencil.
+
+[Illustration: Fig. 107.]
+
+
+APPARATUS 136.
+
+_240. Support for Electroscopes, etc._ Fig. 108. Glue or nail a spool,
+S, to a wooden base, B, measuring about 4 x 5 in. Wrap some paper
+around a 7 in. length of 1/4 in. dowel, D, to make it fit the hole in S.
+Wind one end of a wire, W, around the top end of D. To the outer end of
+W tie a silk thread, S T, on the lower end of which may be tied a piece
+of pith or material to serve as an electroscope.
+
+[Illustration: Fig. 108.]
+
+
+APPARATUS 137.
+
+_241. Carbon Electroscope._ Carbon will be found to make a most
+excellent electroscope, as it is light and a good conductor of
+electricity. Light an ordinary match and let it burn until it is charred
+through and through. The black substance remaining is carbon. Tie a
+small piece of the carbon, about 1/4 in. long, to one end of a silk
+thread, and support the thread as in Fig. 107 or 108.
+
+
+APPARATUS 138.
+
+_242. Pivoted Electroscope._ Fig. 109 and 110. Fold a piece of stiff
+paper double, then cut it into the shape shown. It should be about 3 in.
+long and 1 in. wide when opened out. A hole, B, about 1/2 in. in
+diameter should be cut in it while folded. A piece of paper, C, should
+be pasted to A, so that its top, where it is creased, will be about 1/8
+in. above the top of A. The support consists of a pin, E, stuck through
+a cork, D. Balance the paper on the pin, which passes up through the
+hole, B. An electrified body brought near this apparatus will make it
+whirl around very decidedly.
+
+[Illustration: Fig. 109.]
+
+[Illustration: Fig. 110.]
+
+
+APPARATUS 139.
+
+_243. Fancy Electroscope._ Fig. 111. Fold a piece of stiff paper double,
+then cut out some fancy-shaped figure, as suggested, and draw the face,
+clothes, etc., to suit. This being folded through the center for
+cutting, it can be balanced upon a pin-point as explained in App. 138.
+
+[Illustration: Fig. 111.]
+
+[Illustration: Fig. 112.]
+
+
+APPARATUS 140.
+
+_244. Box-Cover Electroscope._ Fig. 112. A pasteboard box-cover,
+balanced upon a pin, makes a fairly good electroscope, although it is
+not nearly so sensitive as App. 138. The pin may be stuck in the upper
+end of the dowel, D, shown in Fig. 108.
+
+
+APPARATUS 141.
+
+_245. Leaf Electroscope._ Fig. 113. This is a very sensitive instrument,
+and can be used to tell the kind of static electricity on a body, as
+well as the mere presence of it. (See experiments in text-book.) The
+lamp chimney acts as a support for the leaves, L, and it protects them
+from currents of air. A tin box-cover, C, has a small hole punched
+through its center. Through this is pushed one end of a wire, W. This
+may be a hairpin, straightened. The upper end is bent over at right
+angles, after passing it through the hole. The lower end is bent as
+shown. On this horizontal part is fastened the leaf. These should be
+made of aluminum leaf, or of Dutch metal. The former will stand more
+rough handling than the latter. Goldleaf is used for very sensitive
+instruments. It is a little too delicate for unskilled hands.
+
+[Illustration: Fig. 113.]
+
+[Illustration: Fig. 114.]
+
+246. To cut the aluminum leaf, place it between two pieces of paper,
+then cut paper and all into the desired shape. The piece should be about
+3 in. long and 1 in. wide. Fold this across the middle, and stick it to
+the underside of the wire (Fig. 113). Saliva will make it adhere to the
+wire, if you have nothing better.
+
+
+APPARATUS 142.
+
+_247. To Show Where a Charge of Static Electricity Resides._ Fig. 114.
+This shows a tin baking-powder box placed upon a hot tumbler. A moist
+cotton thread is hung over the edge of the box. (See experiments in
+text-book.) The box will become charged by touching it with a charged
+body. The thread will show whether the charge resides upon the inside or
+upon the outside of the box.
+
+
+APPARATUS 143.
+
+[Illustration: Fig. 115.]
+
+_248. Support for Electrified Combs._ Fig. 115. In the study of static
+electricity, ordinary ebonite combs can be used to great advantage. A
+bent hairpin will serve as a cradle to support them. A silk thread may
+be tied to the wire, but a narrow silk ribbon is better than thread, as
+it will hold the comb steady.
+
+
+
+
+CHAPTER XIX.
+
+ELECTRIC MOTORS.
+
+
+_249. An Electric Motor_ is really a machine. If it be supplied with a
+proper current of electricity, its armature will revolve; and, if a
+pulley or wheel be fastened to the revolving shaft, a belt can be
+attached, and the motor made to do work. There are many kinds of motors,
+and many simple experiments which aid in understanding them. All that
+can be done here, however, is to show how to make simple motors. (See
+text-book for experiments.)
+
+
+APPARATUS 144.
+
+_250. Electric Motor._ Fig. 116, 117. Fig. 116 shows a plan or top view,
+and Fig. 117 shows a side view, with a part of the apparatus removed,
+for clearness.
+
+The base, B, is 5 x 4 x 7/8 in. The upright, U, is 3-1/2 x 1-1/2 x 1/2
+in., and is nailed or screwed to B. The binding-posts, X and Y are like
+App. 46. 4 is a screw binding-post.
+
+251. The Field-Magnets, as the large electro-magnets on a motor are
+called, are made of 5/16 machine-bolts, 2-1/2 in. long. The washers are
+1-1/2 in. apart inside. (See App. 88 for full directions.) The bolt
+cores are 2 in. apart, center to center. (See App. 89.) The tin yoke, D,
+is made like App. 71, and it is fastened to the base, like App. 90. The
+hole for the screw, however, is made a little to one side of the center,
+so that a dent can be made at the center for the bottom of the shaft, 8,
+to turn in. Make the dent with a center punch. The yoke is fastened to
+B, so that one edge of it is 1-1/2 in. from the back edge of B. (Fig.
+116).
+
+252. The Armature, A, is made of 6 or 8 thicknesses of tin, 2-1/2 in.
+long and 3/4 wide. (See App. 71.) In its center is punched or drilled a
+1/4 in. hole, so that it can be slipped onto the 1/4 in. "sink-bolt," 8.
+If you have taps you can make the hole a little smaller than 1/4 in.,
+and thread it so that it will screw onto 8. A must be heavy enough to
+revolve a few times when once started. It is pinched between two nuts, 9
+and 11, so that it just clears the poles when it turns. (See App. 145
+for another form of armature.)
+
+[Illustration: Fig. 116.]
+
+253. The shaft or axle, 8, is made of a "sink-bolt" that is 3 in. long
+and 1/4 in. in diameter. These sink-bolts are threaded over their entire
+length, and are furnished with two nuts, 9 and 11, Fig. 117. File or
+grind the end of 8 to a point, so that it will turn easily in a dent
+made for it in the yoke, D, or in a dent made in another piece of tin
+fastened over the yoke. The shaft is held in a vertical position by the
+arm, C.
+
+254. The Arm, C, is made of 2 or 3 thicknesses of tin. It is 3 x 3/4
+in.; it has in one end a hole for the shaft to revolve in easily, and in
+its other end a slot is cut. A screw-eye and bur are used to hold C to
+the upright, U. By this means the shaft can be moved and regulated as to
+position.
+
+[Illustration: Fig. 117.]
+
+255. The Commutator, 9, (Fig. 117), is made of one of the nuts furnished
+with the shaft. Two of its corners are filed or ground off, so that it
+has the shape shown at the right, in Fig. 117. The copper wire, 10, rubs
+against 9, as the pointed part of it comes around. 10 is really a
+"brush," and carries the current into 9 at the right time.
+
+256. Connections. Join the two inside ends (Sec. 123) of the coils to 4.
+The outside end of 2 is joined to X; the outside end, 7, of the other
+coil, 6, is carried up under or around the screw-eye, S I, and then its
+bare end reaches out and gently scrapes against the top of the shaft, 8.
+The wire, 10, leads from Y to the back of the base, where it is carried
+up to a screw, 12, which holds it to U. Its bare end reaches out to
+gently scrape against the commutator, 9, when it swings around. This
+wire, 10, should not press against 9 during the entire revolution.
+
+257. Adjustment. Suppose the current enters at X. When the "brush," 10,
+presses against the commutator, 9, the current passes through X, 1, 2,
+3, 4, 5, 6, 7, down 8 to 9, and out through 10 to Y. (The current, of
+course, goes down into D and into the bolt-cores also; but it can go no
+farther, if the coils are properly insulated, and A is not allowed to
+touch the cores. It is better to have the end of the shaft rest upon a
+piece of glass, having a slight depression made with a file, or in a
+dent made in tin which rests upon wood, the tin having no connection
+with D.) If 10 should continue to press against 9, the current would
+continue to pass, and A would be held firmly in place, directly over 2
+and 6, and, of course, the shaft could not revolve. If, however, the
+brush leaves 9 (See plan of 9 at side of Fig. 117), just as A gets over
+the coils, or an instant before it gets there, the weight of A will
+carry it beyond the coils. No current should pass again, until A is at
+least at right angles to a line drawn through the center of the coils.
+If the current again passes, the ends of A will be attracted by the
+bolt-cores.
+
+In other words, the current should pass a little less than one-half of
+the time, and this is divided into two parts. Suppose you start A with
+your finger; the current should be shut off automatically just before
+the center of A gets over the center of the bolt-cores. A makes 1/4 of a
+revolution without current, and just after it gets beyond this, the
+current passes for nearly 1/4 of a revolution, which brings the ends
+over the poles again. The next 1/4 of a turn it has no current, because
+the flat side of 9 is opposite the brush, 10, as during the first 1/4.
+The last 1/4 the current passes again. The exact position of the
+commutator will depend upon the way you arrange the brush. The positions
+of 9 and 10 can be found by trial, so that the circuit will be promptly
+opened and closed at the proper moment. Start the motor by turning the
+armature.
+
+258. Batteries. The amount of power needed will depend upon how well you
+make the motor. One cell of App. 3 or 4 will run a well made one, but it
+is better to use 2 cells. Join the wires to X and Y.
+
+[Illustration: Fig. 118.]
+
+
+APPARATUS 145.
+
+_259. Armature for Motors._ Fig. 118 shows another form of armature that
+may be used for small motors like App. 144; in fact, you may find that
+this form is easier to make than that of App. 144. M is a 5/16 machine
+screw, 1-1/2 in. long, 9 being the nut furnished with it. 9 is filed as
+explained in Sec. 255, and forms the commutator. C is the arm (Sec.
+254). A is the armature (Sec. 252). A is held firmly in place between
+the spool, E, and 9. S is a set-screw which passes through E, and holds
+the piece of 1/4 in. dowel, F, in place. N is a needle-point fastened
+in the end of F. N revolves in a dent made in a piece of tin, H, which
+rests upon a wooden strip, G. G is cut away on its underside, so that
+it will straddle the yoke, D, Fig. 117; it is nailed to the base. This
+is given as a suggestion. By making F a little longer, N can turn in a
+dent made in the yoke, below G.
+
+260. Adjustments. M, being 5/16 in. in diameter, will screw solidly into
+the hole in E. Place 9 upon it first, then A, and screw it about 1/2 way
+into E. 9 will serve as a lock-nut by turning it so that it will pinch A
+and hold it firmly against the top of E. F should reach half way into E.
+Put N in place after you have H and G arranged. You can then cut the
+upper end of F at such a place that it will bring A about 1/8 in. from
+the top of the magnet-cores. Paper wrapped around F will make a good fit
+in E. The current should enter M and leave 9, as fully explained in App.
+144. (See Sec. 257).
+
+
+APPARATUS 146.
+
+_261. Electric Motor._ Fig. 119, 120, 121, 122. Fig. 119 shows a front
+view, and Fig. 120 a side view of the whole motor. Fig. 121 shows the
+part that revolves, and includes the shaft, armature and commutator.
+Fig. 122 shows a section of the commutator. All the dimensions are taken
+from a model. You can modify the size to suit.
+
+262. Wood-work. The base is 7 x 5 x 7/8 in. The uprights, U, are 3-1/2 x
+1 x 3/4 in. They are screwed or nailed to the base from below, their
+1-in. sides being towards you in Fig. 119. They are 4-1/4 in. apart,
+inside, in this model. The piece, A, is 2-1/2 x 7/8 x 5/8 in., and is
+cut away on the underside to straddle the yoke. Fig. 118 is a
+suggestion as to its shape. A is screwed or nailed to B.
+
+263. Tin-work. The horizontal arm, T, is made of 3 thicknesses, and
+holds the shaft in a vertical position. T is 6-1/4 x 3/4. In its ends
+are slots, and in its center is a hole so that the 1/4 in. shaft can
+revolve easily, but not too loosely. The slots allow an adjustment, the
+screws, S, holding T to U. The shaft rests in a dent made in a piece of
+tin which is tacked to A. The yokes are elsewhere described.
+
+[Illustration: Fig. 119.]
+
+264. Field-Magnets. In this model they were made of 5/16 bolts, 2 in.
+long, placed 2 in. apart center to center. The washers are 1-1/8 in.
+apart inside. (See App. 88 for full directions.) App. 89 and 71 should
+be studied. Except in size, they are made as in App. 144. They have 8
+layers of No. 24 or 25 wire.
+
+265. The Armature, Fig. 121, on this style of motor consists of a
+regular horseshoe electro-magnet, made in the same general way as the
+field-magnets. The electro-magnets, 12 and 16, are smaller, however,
+than the field-magnets. The cores are 1/4 in. stove-bolts, 1-1/4 in.
+long under the head. They are placed 2 in. apart, center to center. They
+are insulated and wound as fully explained in App. 88. These 1/4 in.
+bolts require a change in your winder. (See App. 147 for this.) If you
+wish to use 5/16 bolts, you may use the same axle for your winder as
+before. The washers are 5/8 in. apart, inside. The cores are wound with
+4 or 6 layers of No. 24 or 25 wire. This makes them about 3/4 in. in
+diameter. They are held in a tin yoke, 14, made of 5 or 6 thicknesses of
+tin. 14 is 3 x 3/4 in., and has 3 holes punched in it. The two outside
+holes are 2 in. apart. Through these pass the bolts, which are held
+firmly by the 2 nuts. The shaft, S B, is a sink-bolt, 3 in. long, and
+1/4 in. in diameter. (See Sec. 253.) The inside ends (Sec. 123) of the
+coils should be firmly twisted together or held under the top nuts to
+make a good connection between them.
+
+[Illustration: Fig. 120.]
+
+266. The Commutator is in two parts, which must be insulated from each
+other. The 2 sections are made out of thin tin or copper in the shape of
+an inverted T, as shown at 10, Fig. 121. The arms of the T are about
+3/8 in. wide, the horizontal ones reaching about half around the spool,
+E. The vertical arm reaches over the top of E, and is held down by a
+small screw, J. The sections, 10, must not touch the shaft. The outside
+wires (Sec. 123) of 12 and 16 are fastened under these screws, J, and
+they must not touch the shaft. Bend the tin sections so that they will
+be as nearly round as possible. The spool, E, has been sawed off so that
+it will go between the field-magnets. Wind paper around the shaft to make
+it fit solidly into E. S is a small screw that holds E in place, if the
+paper does not hold it tight enough.
+
+[Illustration: Fig. 121.]
+
+[Illustration: Fig. 122.]
+
+Fig. 122 shows a section of the spool and tin sections with the brushes
+pressing against them. The sections do not touch each other, and the
+brushes touch opposite sections. It is evident, then, that the current
+must pass through the coils 12 and 16 in order to get from one section
+of the commutator to the other, provided you have no short circuits
+through the shaft or elsewhere. The slots in the commutator must be
+directly under the center line of the yoke, 14, as seen in Fig. 121.
+
+267. The brushes, 9 and 19, Fig. 120, are made of very thin tin or
+copper. They are cut to the shape shown, the narrow part being about 1/8
+in. wide, and long enough to reach at least to the center-line of the
+apparatus. The foot, or bottom part of the brushes, should be about
+1-1/4 x 3/4 in. These are used to fasten them to the base and to make
+connections. If you have no thin metal for brushes, use copper wires,
+and arrange them so that they will press gently against the commutator.
+
+268. Connections. The inside ends (Sec. 123) of the field-magnets are
+held at 4. The outside end of coil 2 is joined to X, and that of coil
+6 to 8, the foot of the brush which presses against 10. The section,
+10, of the commutator is joined to 11, the outside end of coil 12, its
+inside end being fastened to the inside end of coil, 16, either by
+twisting them together, or by fastening them under the top nuts of the
+armature yoke, 14. The outside end of coil 16 is joined to the other
+commutator section, 18. The brush, 19, completes the circuit. In the
+foot of 19 is the binding-post, Y.
+
+If the current enters at X, it will pass through 1, 2, 3, 4, 5, 6, 7, 8,
+9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and out at Y, provided 10 and
+18 are in contact with 9 and 19. Be careful not to have any short
+circuits. If, for example, the wire 7 touches 4, or if 3 touches 8, or
+if the wires 11 and 17 touch the shaft, your current will not pass where
+you expect, and you will have trouble.
+
+269. Adjustment. The armature cores should just clear the poles of the
+field-magnets as they turn. This must be regulated by the thickness of A
+and the position of the nuts on the shaft, S B. The slots in the
+commutator must be under the center of the yoke, 14. The brushes, 9 and
+19, must touch 10 and 18, but not so hard that they will stop the motor.
+Wire brushes are more easily adjusted than tin or sheet-copper ones. The
+tin arm, T, must hold the shaft properly. The point of the shaft must
+allow it to turn easily. The motor will turn clockwise if the
+attachments are made as shown. Use 1 or 2 good bichromate cells, like
+App. 3 or 4.
+
+270. Operation. The current will pass through the field-coils in the
+same direction, as long as the battery wires are not changed. The
+current is reversed in the armature-coils every time the brushes change
+from one section to the other of the commutator; that is, it flows in
+one direction during one-half of a revolution, and in the opposite
+direction during the other half. This reverses the poles of the
+armature-magnets every 1/2 revolution. (See text-book for full
+explanations and for simple experiments with electric motors.)
+
+
+APPARATUS 147.
+
+_271. Attachment for Winder._ In winding small electro-magnets for
+armature, etc., in which cores are used that are not 5/16 in. in
+diameter, your winder will have to be slightly changed. Its 5/16
+stove-bolt will have to be removed, and a 1/4 in. one put in instead.
+This may be done by making a handle for the 1/4 in. bolt. To keep this
+from wobbling in the 5/16 hole, wind stiff paper around the bolt until
+it fits quite tightly. The whole winder is explained as App. 93.
+
+
+
+
+CHAPTER XX.
+
+ODDS AND ENDS.
+
+
+APPARATUS 148.
+
+_272. Graduated Circles._ Fig. 123. For compasses (App. 67), and for use
+in connection with tangent galvanometers (App. 116), a graduated circle
+is necessary. Fig. 123 is a reduced drawing from an original that is 4
+in. in diameter. The long lines are 10 degrees apart, the smallest
+divisions shown being 5 degrees apart. Single degrees can be determined
+with considerable accuracy with the eye.
+
+[Illustration: Fig. 123.]
+
+To divide the circle. Divide the circumference into 4 equal parts; these
+will be 90 degrees from each other, there being 360 degrees in every
+circle. Divide each quarter into nine equal parts with a pair of
+dividers; these will be for the long lines, 10 degrees apart. Divide
+each of these into two equal parts. If you are used to drawing, you can
+divide the circle still more, but 5-degree divisions will do.
+
+
+APPARATUS 149.
+
+_273. Adjustable Table._ Fig. 124. A table that can be raised or lowered
+is useful. The one shown at D, Fig. 124, is used for the galvanometer of
+App. 117. The dimensions are given in the figure. The upright piece, U,
+is fastened to D with brass screws, not with nails, as these would
+affect the needle. It is placed at one side of D so that the compass
+needle placed in the center of D will also be in the center of the wire
+coils when used in App. 117. The table is fastened in any position by a
+screw-eye, S I, which presses a copper washer, W, against U. S I works
+through a narrow slot, S, and screws into the back of the galvanometer.
+By making S longer, the table may be used for other laboratory purposes,
+if it is joined with some other form of standard.
+
+[Illustration: Fig. 124.]
+
+
+APPARATUS 150.
+
+_274. Glue Pot._ If you have occasion to use glue, you can make a good
+glue pot out of 2 tin cans, one being placed inside the other. Put 1/4
+teacupful of glue in the inside can. If you have time, cover it with
+cold water, and let it soften. If you are in a hurry, cover it with hot
+water. Set this inside can into the other, in which you have boiling
+water. Do not let the water boil over. The solder will not melt from
+ordinary tomato cans, if you keep water in them. Thin the glue with a
+little hot water until it drips from the brush in drops. Have the glue
+hot and fairly thin, and apply quickly. Hold the pieces of wood together
+by pressure until the glue hardens.
+
+
+APPARATUS 151.
+
+_275. Paraffine Paper and Cardboard_ are extremely useful for insulating
+purposes. The paraffine used in candles will do, if you cannot get it in
+block form. While ordinary paper will do for simple apparatus to wind
+about coils, etc., you will find that paraffine paper can be handled
+very rapidly. To melt the paraffine you should use a double boiler, or
+one made of a shallow basin set in a pan of water. The water should be
+boiled. This will melt the paraffine in the basin. Strips of paper just
+passed through the melted paraffine will become soaked, and the
+paraffine will quickly harden in the air. Allow thick cardboard to soak
+for a minute or two, to drive out all the air. This makes excellent
+washers for electro-magnets. (See Sec. 119.) To make one piece of this
+paper stick to another, merely pass a clean hot nail over the two where
+they lap. To hold coils of wire together, or to wooden bases, use a few
+drops of paraffine applied with a large hot nail.
+
+276. Caution. Do not heat paraffine directly upon the fire or over a
+burner, unless you watch it constantly. It will burn if its temperature
+is raised too much. It is better to heat it with steam, as you do glue.
+
+
+APPARATUS 152.
+
+_277. Battery Jars._ For small cells, use glass tumblers. Ordinary glass
+fruit jars are good. Even earthen bowls may be used, and for large
+cells--if you have nothing better--you can use small earthen crocks or
+jars.
+
+278. Glass Bottles can be cut off so that they will make excellent jars.
+If you have thin bottles, you can cut them with strong cord. Tie one end
+of the cord, which should be 5 or 6 feet long, to a door knob or to a
+solid post. Tie the other end around your body. Make one complete turn
+of the cord around the bottle where you wish to cut it; draw the cord
+tight by stepping back, and with both hands draw the bottle back and
+forth vigorously many times, so that the cord will rub it hard and make
+it very hot. Do not let the cord move lengthwise upon the bottle. This
+will make a circle around the bottle that is very hot. Immediately
+plunge the bottle into cold water, the colder the better. Use ice-water,
+if you have it. If you produce heat enough, the bottle should crack all
+the way around very neatly. File off any sharp corners and edges with a
+wet file.
+
+279. A hot iron can be used with success to cut off a bottle. File a
+deep groove first, hold the red-hot iron first on one side of file mark
+and then on the other to start the crack. You can lead the crack
+wherever you wish by keeping the iron about 1/8 in. ahead of it.
+
+280. A small gas-flame will be much better than a hot iron, and you may
+easily use it, if you have glass tubing, rubber tubing, etc., in your
+shop. Draw out the glass so that the gas will burn in a fine needle-like
+flame about 1 in. long. Keep the point of the flame about 1/4 in. ahead
+of the crack. The glass tube should be held in a rubber tube connected
+with the gas pipe.
+
+
+
+
+CHAPTER XXI.
+
+TOOLS AND MATERIALS.
+
+
+_281. Your Workshop._ If possible, keep all your work, tools and
+apparatus in one room, and lock the door when you leave.
+
+The work-bench may be made of an old kitchen table, or of a strong,
+large box. The tool chest may be made of any clean box about the size of
+a soap box. Shelves can be made by setting soap or starch boxes on their
+sides, one above the other.
+
+_282. The tools_ needed are generally mentioned in the proper places,
+under the directions for construction. It is better to buy your tools as
+required, than to buy too many at once, some of which you may not need.
+If you have absolutely no tools, not even a saw or hammer, you will be
+obliged to buy or borrow, although a great deal can be done with a good
+knife. Do not be satisfied with rough-looking pieces of apparatus.
+
+There are a few important tools needed for this work. While substitutes
+can be found for most of them, the boy who has access to a wood-working
+bench and tools will be able to do better and more rapid work than the
+boy who has no such tools.
+
+283. List of tools. The following tools are needed, if rapid, accurate
+work is desired:
+
+(1.) Lead pencil. (2.) A rule, divided into sixteenths for measuring. A
+straight foot rule will do,--cost one cent. (3.) Steel point for
+scratching lines on tin and copper. A stout needle-point is just the
+thing. (4.) An awl for making holes in wood; one that is a little less
+than 1/8 in. in diameter is best. (See App. 25.) (5.) A try-square with
+a 6 in. blade, so that you can mark out your apparatus with square
+corners. You can use a square-cornered box or piece of pasteboard, if
+you have no try-square. (6.) Chisels are very useful, but you can do
+wonders with a good sharp knife. (7.) Screw-driver. Do not use a good
+knife-blade for a screw-driver. (8.) A saw, one with teeth that are not
+too coarse is to be preferred. (9.) A plane is extremely useful to make
+your wood-work smooth and neat; but a great deal can be done with the
+sharp edges of broken glass, followed by a good rubbing with fine
+sand-paper. (10.) A brace and a set of bits may be needed in 2 or 3
+cases, but nearly all of the holes can be made as in App. 25. (11.)
+Punches for sheet-tin, etc., will save much time. (See App. 26, 27.) For
+small holes in binding-posts, etc., use a flat-ended punch, 1/8 in. in
+diameter. You should have one 1/4 or 5/16 in. in diameter, if you make
+your yokes, armatures, etc., as in Chapter VIII. A blacksmith will help
+you out with this. (12.) A center-punch or sharp-pointed punch for
+making dents in metal. A sharp-pointed wire nail will do for tin and
+copper. (13.) Files for metal. (14.) Some sort of a vice or clamp. (See
+App. 79, 80.) (15.) Shears for cutting sheet-tin, etc. A pair of old
+shears will do. (16.) An anvil or piece of old iron that may be used to
+hammer on to flatten tin, etc. An old flat-iron makes a good anvil.
+(17.) Hammer.
+
+The small hollow handle tool sets are very handy, and they contain small
+chisels, awls, screw-driver, etc. These sets cost from 50 cents up.
+
+_284. Materials._ For wood you will find the sides and ends of clean
+soap or starch boxes about the right thickness; they are fairly smooth
+to begin with. For thin wood use cigar boxes. The pieces from old boxes
+should be removed with care, and saved in one place, which may be called
+your lumber yard. All nails should be removed with a claw-hammer. Look
+out for nails when using a saw, plane or other edged tool. (See Sec.
+297.) The edges of bases, etc., may be bevelled as shown in Fig. 95.
+This is not necessary, but it adds greatly to the appearance.
+
+285. Screw-Eyes. Brass screw-eyes, with copper burs, make excellent
+binding-posts. (App. 45, 46.) Those that are 3/8 in. in diameter inside
+the circle are about right. These are about 1-1/4 in. long in all, with
+a 1/2 in. thread.
+
+286. Copper Burs, such as are used with rivets, are very handy. The size
+that is 1/2 in. in diameter, with a 1/8 in. hole, is good.
+
+[Illustration: Fig. 125.]
+
+287. Copper Wire. This can be bought at an electrician's. The only
+trouble, however, in buying small quantities is that you may have to pay
+a large price in proportion. If you get it on 1/2 lb. spools you can
+handle it much better (see App. 23) than you can if you have it in a
+tangle. It is well to have 1/2 lb. of No. 24 or 25 for electro-magnets,
+current-detectors, etc., etc. 1/2 lb. of No. 30 will not be too much, if
+you make induction coils. If you handle your wire carefully, single
+cotton-covered will do. Double cotton-covered is better than single, but
+it costs more. Be careful not to injure the covering. (See below for
+splicing wire.) Look out for broken wire.
+
+288. Splicing Wire. Fig. 125. Do not simply touch two wires together
+and imagine that you have a good connection; a mere twist is not
+sufficient. Clean the ends of old wire thoroughly with a file or
+knife-blade, and join them as shown in Fig. 125.
+
+289. Copper. Sheet-copper can be purchased at a tinsmith's or at a
+hardware store. Electricians usually have a thin variety of copper
+called brush copper, which makes good battery-plates, binding-posts,
+etc. You can cut this thin copper with an ordinary pair of shears.
+
+290. Iron. For thin sheet-iron, nothing is better than sheet-tin. (See
+tin.) Hoop iron is thicker than tin, and makes good yokes, etc. In many
+cases, ordinary nails may be used where a magnetic substance is needed.
+Annealed iron wire is extremely soft. (See text-book for experiments
+with steel and iron.)
+
+291. Steel. Old files, watch-springs, clock-springs, corset-steels,
+knitting-needles, harness-needles, hack-saw blades, sewing-needles,
+etc., are generally made of a good quality of steel.
+
+292. Zinc, in the sheet form, can be bought at a hardware store. For a
+few cents you can get quite a large piece. Get the thick pieces for
+heavy battery-plates of an electrician. You do not need anything that is
+thicker than 1/8 in. The zinc rods are usually amalgamated.
+
+293. Lead can be bought at a plumber's, tinsmith's, or hardware store.
+You may want some for a storage cell.
+
+294. Nails. Wire nails are best for light work. Get an assortment from
+1/2 in. long up to 1-1/2 in.
+
+295. Screws. It is better to use brass screws around electrical
+apparatus. For the small work, for binding-posts, etc., use 5/8 No. 5.
+Another handy size is No. 7, from 3/4 to 1-1/4 in. long. The
+round-headed screws are best, unless you want to countersink them.
+
+296. Tin. This is really thin sheet-iron, covered with tin. Save up
+tomato-cans, cracker-boxes, condensed-milk cans, etc. The cracker-boxes
+are just as good as sheet-tin, as the pieces are large and clean. You
+can remove the solder from cans by heating them in the kitchen fire.
+Knock out the bottoms with a poker when the solder gets soft. Clean the
+tin with sand-paper.
+
+297. Carbons. You can get carbon rods or plates at an electrician's. If
+you have arc electric lights in your city, you will be able to pick up
+carbons; these, however, generally have a coating of copper, which must
+be eaten off with dilute nitric acid. This is a bother. You will find it
+cheaper to buy the 1/2 in. rods that are 12 in. long, and uncoated.
+
+298. Shellac. Your wood-work will be much improved by using shellac upon
+it after you have thoroughly sand-papered it. You can get it, all
+prepared, at a paint store. Wood-alcohol is used to thin it if it gets
+too thick. Keep it in a wide-mouth bottle. Paint it on quickly and
+evenly with a brush, and do not go over it again when it is partly dry.
+Wait until it is thoroughly hard before putting on a second coat. It
+should be fairly thin to spread well. Clean your brush in wood-alcohol
+before putting it away, and keep the shellac bottle tightly corked. A
+small tin can or a teacup is best to hold the shellac when using it.
+
+
+
+       *       *       *       *       *
+
+
+
+THINGS A BOY SHOULD KNOW ABOUT ELECTRICITY.
+
+By THOMAS M. ST. JOHN, Met. E.
+
+The book contains 180 pages, and 260 illustrations; it measures
+5 x 7-1/2 in., and is bound in cloth.
+
+Seventh Edition      Price, postpaid, $1.00
+
+     CONTENTS: Chapter I. About Frictional Electricity.--II. About
+     Magnets and Magnetism.--III. How Electricity is Generated by the
+     Voltaic Cell.--IV. Various Voltaic Cells.--V. About Push-Buttons,
+     Switches and Binding-Posts.--VI. Units and Apparatus for Electrical
+     Measurements.--VII. Chemical Effects of the Electric
+     Current.--VIII. How Electroplating and Electrotyping are Done.--IX.
+     The Storage Battery and How it Works.--X. How Electricity is
+     Generated by Heat.--XI. Magnetic Effects of the Electric
+     Current.--XII. How Electricity is Generated by Induction.--XIII.
+     How the Induction Coil Works.--XIV. The Electric Telegraph, and How
+     it Sends Messages.--XV. The Electric Bell and Some of its
+     Uses.--XVI. The Telephone, and How it Transmits Speech.--XVII. How
+     Electricity is Generated by Dynamos.--XVIII. How the Electric
+     Current is Transformed.--XIX. How Electric Currents are Distributed
+     for Use.--XX. How Heat is Produced by the Electric Current.--XXI.
+     How Light is Produced by the Incandescent Lamp.--XXII. How Light is
+     Produced by the Arc Lamp.--XXIII. X-Rays, and How the Bones of the
+     Human Body are Photographed.--XXIV. The Electric Motor and How it
+     Does Work.--XXV. Electric Cars, Boats and Automobiles.--XXVI. A
+     Word About Central Stations.--XXVII. Miscellaneous Uses of
+     Electricity.
+
+This book explains, in simple, straightforward language, many things
+about electricity; things in which the American boy is intensely
+interested; things he wants to know; things he should know.
+
+It is free from technical language and rhetorical frills, but it tells
+how things work, and why they work.
+
+It is brimful of illustrations--the best that can be had--illustrations
+that are taken directly from apparatus and machinery, and that show what
+they are intended to show.
+
+This book does not contain experiments, or tell how to make apparatus;
+our other books do that. After explaining the simple principles of
+electricity, it shows how these principles are used and combined to make
+electricity do every-day work.
+
+       *       *       *       *       *
+
+_Everyone Should Know About Electricity._
+
+       *       *       *       *       *
+
+A VERY APPROPRIATE PRESENT
+
+
+Things a Boy Should Know About Wireless
+
+By
+THOMAS M. ST. JOHN, Met. E.
+
+Author of "Things a Boy Should Know about Electricity," "Fun with
+Electricity," "The Study of Elementary Electricity and Magnetism by
+Experiment," "The Study of Electric Motors by Experiment," "Electrical
+Handicraft," Etc., Etc.
+
+126 Pages--109 Illustrations and Diagrams
+Bound in Cloth--Net $1.00
+
+This book contains much practical and some theoretical information
+regarding the operation and explanation of wireless outfits. It
+discusses enough of the theoretical side to make the student sure of
+himself and to give a well-rounded knowledge of this most practical
+subject.
+
+The author has explained the various pieces of apparatus needed in a
+wireless station in such a clear manner that the student can not fail to
+understand how they work and why they work. The numerous drawings and
+diagrams simplify the discussions to such an extent that the reader will
+not want to skip a single paragraph.
+
+"Things a Boy Should Know About Wireless" will be welcomed by thousands
+of enthusiasts and it should find its way into every library.
+
+From
+
+THOMAS M. ST. JOHN
+
+Cascade Ranch.
+East Windham,--N.Y.
+
+
+The Study of Elementary Electricity and Magnetism by Experiment
+
+By THOMAS M. ST. JOHN, Met. E.
+
+FOURTH EDITION        Price, postpaid, $1.25.
+
+The book contains 220 pages and 168 illustrations. It measures
+5 x 7-1/2 in., and it is bound in green cloth.
+
+     CONTENTS: Part I. Magnetism.--Chapter I. Iron and Steel.--II.
+     Magnets.--III. Induced Magnetism.--IV. The Magnetic Field.--V.
+     Terrestrial Magnetism. Part II. Static Electricity.--VI.
+     Electrification.--VII. Insulators and Conductors--VIII. Charging
+     and Discharging Conductors.--IX. Induced Electrification.--X.
+     Condensation of Electrification.--XI. Electroscopes.--XII.
+     Miscellaneous Experiments.--XIII. Atmospheric Electricity. Part
+     III. Current Electricity.--XIV. Construction and Use of
+     Apparatus.--XV. Galvanic Cells and Batteries.--XVI. The Electric
+     Circuit.--XVII. Electromotive Force.--XVIII. Electrical
+     Resistance.--XIX. Measurement of Resistance.--XX. Current
+     Strength.--XXI. Chemical Effects of the Electric Current.--XXII.
+     Electromagnetism.--XXIII. Electromagnets.--XXIV. Thermo
+     electricity.--XXV. Induced Currents.--XXVI. The Production of
+     Motion by Currents.--XXVII. Applications of Electricity.--XXVIII.
+     Wire Tables.--Apparatus List.--Index.
+
+This is a text-book for amateurs, students, and others who want to take
+up a systematic course of electrical experiments at home or in school.
+It will give a practical and experimental knowledge of elementary
+electricity, and thoroughly prepare students for advanced work. Full
+directions are given for
+
+TWO HUNDRED EXPERIMENTS.
+
+The experiments and discussions are so planned that the student is
+always prepared for what follows. Although the experiments may be
+performed with the apparatus that is usually found in school
+laboratories, the author has designed a complete set of apparatus for
+those who want to have their own outfit.
+
+       *       *       *       *       *
+
+_If you want to take up a systematic course of experiments--experiments
+that will build a lasting foundation for your electrical knowledge--this
+book will serve as a valuable guide._
+
+
+Jan. 1, 1918 STUDENT'S DISCOUNT DISCONTINUED
+
+PRICE TO ALL, $6.25
+
+Owing to greatly increased costs of labor and materials the discount of
+65c formerly allowed on this set has been discontinued. Complete sets
+only now sold. Shipping weight on improved sets 10 lbs. securely packed
+in wooden box. Sent by parcel post if proper postage is included in your
+remittance; otherwise by express charges collect.
+
+
+Fun With Magnetism and Fun With Electricity have started more young men
+upon electrical careers than any other scientific outfits ever placed
+before the public. The thousands upon thousands that have been sold in
+all parts of the world have furnished fun and science for people of all
+ages, and the mere fact that they are listed by the New York Board of
+Education, and recommend to the pupils and teachers of the New York
+public and private schools is a guarantee of their value. Were it not
+for the fact that these are made in such large quantities and sold by
+stores, agents and mail-order houses, the price would be much higher.
+Don't fail to get these. They have a national reputation.
+
+FUN WITH MAGNETISM
+
+This outfit contains a 32-page book of instructions, with 45
+illustrations, together with a complete set of apparatus for performing
+61 fascinating experiments. It will give you some new ideas about
+magnetism and start you at the right place in your study of electricity.
+Think what that means--to start right!
+
+The book contains experiments with the horseshoe magnet, with bar
+magnets, with floating magnets, etc., etc., thus giving a practical
+knowledge of the subject; and it is all done in such an interesting way
+that one can't help remembering it. Every experiment clinches some fact
+and every fact is important.
+
+Amusing Experiments.--Something for Nervous People to Try.--The Jersey
+Mosquito.--The Stampede.--The Runaway.--The Dog-fight.--The
+Whirligig.--The Naval Battle.--A String of Fish.--A Magnetic Gun.--A Top
+Upside down.--A Magnetic Windmill.--A Compass Upside down.--The Magnetic
+Acrobat.--The Busy Ant-hill.--The Magnetic Bridge.--The
+Merry-go-Round.--The Tight-rope Walker.--A Magnetic Motor Using
+Attractions and Repulsions.--And 43 Others.
+
+No. R1--"Fun with Magnetism," Complete Outfit, postpaid $0.35
+
+[Illustration]
+
+FUN WITH ELECTRICITY
+
+The author of this Fun with Science series has spent a great deal of
+time and money in experimenting to devise apparatus that will do the
+proper work and be, at the same time, simple and cheap, and in no outfit
+has he succeeded better than in Fun with Electricity. When you think of
+an outfit retailing for 50c. and covering the whole subject of "Static
+Electricity," giving 60 scientific experiments upon its production,
+conduction and induction, with a 55-page book of instructions with 38
+drawings, and a complete set of apparatus of 20 articles for performing
+these 60 experiments, you will understand why the sales of this outfit
+have been enormous. As the subject is presented in a fascinating
+way--and not as mere dry science--every one likes to do the experiments.
+No wonder these sets are highly praised by parents and educators in
+every part of the country!
+
+There is Fun in these Experiments: Chain Lightning.--An Electric
+Whirligig.--The Baby Thunderstorm.--A Race with Electricity.--An
+Electric Frog Pond.--An Electric Ding-Dong.--The Magic Finger.--Daddy
+Long-Legs.--Jumping Sally.--An Electric Kite.--Very Shocking.--Condensed
+Lightning.--An Electric Fly-Trap.--The Merry Pendulum.--An Electric
+Ferry-Boat.--A Funny Piece of Paper.--A Joke on the Family
+Cat.--Electricity Plays Leap-Frog.--Lightning Goes Over a
+Bridge.--Electricity Carries a Lantern.--And 40 Others.
+
+There isn't an outfit anywhere at any price that gives better value for
+the money. An ideal present for a boy.
+
+No. R2--"Fun with Electricity," Complete Outfit, postpaid $0.65
+
+
+FUN WITH PUZZLES
+
+Here is an outfit that every boy and girl should have, for it is
+amusing, instructive and educational. It is real fun to do puzzles and
+to puzzle your friends, and this book contains some real brain-teasers
+that will make you think. The book contains 15 chapters, 80 pages, and
+128 illustrations, and measures 5x7-1/2 inches. If you can't do any
+particular puzzle you will find its solution in the "key," which is
+bound with the book. If you want to win prizes by doing the puzzles in
+the magazines, you will find this book of four hundred puzzles a regular
+school of puzzles that will give you a thorough training for this kind
+of work. The book alone is well worth the price, to say nothing of the
+outfit of numbers, counters, pictures, etc.
+
+Contents of Book: Chapter (1) Secret Writing. (2) Magic Triangles,
+Squares, Rectangles, Hexagons, Crosses, Circles, etc. (3) Dropped Letter
+and Dropped Word Puzzles. (4) Mixed Proverbs, Prose and Rhyme. (5) Word
+Diamonds, Squares, Triangles, and Rhomboids. (6) Numerical Enigmas. (7)
+Jumbled Writing and Magic Proverbs. (8) Dissected Puzzles. (9) Hidden
+and Concealed Words. (10) Divided Cakes, Pies, Gardens, Farms, etc. (11)
+Bicycle and Boat Puzzles. (12) Various Word and Letter Puzzles. (13)
+Puzzles with Counters. (14) Combination Puzzles. (15) Mazes and
+Labyrinths.
+
+Secret Writing is explained in this book, and it shows how you can write
+letters to your friends and be sure that no one can read them unless
+they are also in the secret. This one thing alone will give you a great
+deal of enjoyment. Get this outfit and have some fun.
+
+No. R3--"Fun with Puzzles," Complete Outfit, postpaid $0.35
+
+       *       *       *       *       *
+
+FUN WITH SOAP-BUBBLES
+
+Fancy Bubbles and Films are not easily blown without special apparatus,
+and even with the proper outfit one must "know how." That's why we
+furnish a 16-page book with every set to show just how to do it. With
+the aid of the 21 illustrations and the directions you can produce
+remarkable results that will surprise and entertain your friends. A
+child can do it as well as a grown person.
+
+[Illustration]
+
+Soap-Bubble Parties using these outfits create real sensations. Why not
+be the first in your town to give a "Fun with Soap-Bubbles Party?" Just
+write and ask about the price for any special number of them--say six or
+a dozen.
+
+Contents of Book: Twenty-one Illustrations.--Introduction.--The Colors
+of Soap-Bubbles.--The Outfit.--Soap Mixture.--Useful Hints.--Bubbles
+Blown with Pipes.--Bubbles Blown with Straws.--Bubbles Blown with the
+Horn.--Floating Bubbles.--Baby Bubbles.--Smoke Bubbles.--Bombshell
+Bubbles.--Dancing Bubbles.--Bubble Games.--Supported Bubbles.--Bubble
+Cluster.--Suspended Bubbles.--Bubble Lamp Chimney.--Bubble
+Lenses.--Bubble Basket.--Bubble Bellows.--To Draw a Bubble Through a
+Ring.--Bubble Acorn.--Bubble Bottle.--A Bubble Within a Bubble.--Another
+Way.--Bubble Shade.--Bubble Hammock.--Wrestling Bubbles.--A Smoking
+Bubble.--Soap Films.--The Tennis Racket Film.--Fish-net
+Film.--Pan-shaped Film.--Bow and Arrow Film.--Bubble Dome.--Double
+Bubble Dome.--Pyramid Bubbles.--Turtle-back Bubbles.--Soap-Bubbles and
+Frictional Electricity.
+
+"There is nothing more beautiful than the airy-fairy soap-bubble with
+its everchanging colors." This outfit gives the best possible amusement
+for old and young.
+
+No. R4--"Fun with Soap-Bubbles," Complete Outfit, postpaid $0.35
+
+Three extra packages of prepared soap, postpaid .10
+
+
+FUN WITH SHADOWS
+
+No wonder shadow-making has been popular for several centuries! What
+could give keener delight than comical shadow-pictures, pantomimes,
+entertainments, etc.? Professional shadowists use wires, forms, and
+various devices to aid them, and that is why they get such wonderful
+results on the stage. Do you want to do the same thing right in your own
+home and entertain your friends with all kinds of fancy shadows? You can
+do it with this outfit, for the book contains 100 illustrations and
+diagrams with directions for using the numerous articles included in the
+box. You will be surprised to see how easily you can make these funny
+shadows with the aid of the outfit. Better get one now and make shadows
+like a professional.
+
+[Illustration]
+
+The Outfit contains everything necessary for all ordinary shadow
+pictures, shadow entertainments, shadow plays, etc. The following
+articles are included: One book of Instructions called "Fun with
+Shadows"; 1 Shadow Screen; 2 Sheets of Tracing Paper; 1 Coil of Wire for
+Movable Figures; 1 Cardboard Frame for Circular Screen; 1 Cardboard
+House for Stage Scenery; 1 Jointed Wire Fish-pole and Line; 2 Bent Wire
+Scenery Holders; 4 Clamps for Screen; 1 Wire Figure Support; 1 Wire for
+Oar; 2 Spring Wire Table Clamps; 1 Wire Candlestick Holder; 5 Cardboard
+Plates containing the following printed figures that should be cut out
+with shears; 12 Character Hats; 1 Boat; 1 Oar-blade; 1 Fish; 1
+Candlestick; 1 Cardboard Plate containing printed parts for making
+movable figures.
+
+No. R5--"Fun with Shadows," Complete Outfit, postpaid $0.35
+
+       *       *       *       *       *
+
+FUN WITH PHOTOGRAPHY
+
+Popular Pastimes are numerous, but to many there is nothing more
+fascinating than photography. The magic of sunshine, the wonders of
+nature, and the beauties of art are tools in the hands of the amateur
+photographer. If you want to get a start in this up-to-date hobby, this
+outfit will help you. You will enjoy the work and be delighted with the
+beautiful pictures you can make.
+
+The Outfit contains everything necessary for making prints--together
+with other articles to be used in various ways. The following things are
+included: One Illustrated Book of Instructions, called "Fun With
+Photography"; 1 Package of Sensitized Paper; 1 Printing Frame, including
+Glass, Back, and Spring; 1 Set of Masks for Printing Frame; 1 Set of
+Patterns for Fancy Shapes; 1 Book of Negatives (Patented) Ready for Use;
+6 Sheets of Blank Negative Paper; 1 Alphabet Sheet; 1 Package of Card
+Mounts; 1 Package of Folding Mounts; 1 Package of "Fixo."
+
+[Illustration]
+
+Contents of Book: Chapter I. Introduction.--Photography.--Magic
+Sunshine.--The Outfit.--II. General Instructions.--The Sensitized
+Paper.--How the Effects are Produced.--Negatives.--Prints.--Printing
+Frames.--Our Printing Frame.--Putting Negatives in Printing
+Frame.--Printing.--Developing.--Fixing.--Drying--- Trimming.--Fancy
+Shapes.--Mounting.--III. Negatives and How to Make Them.--The
+Paper.--Making Transparent Paper.--Making the Negatives.--Printed
+Negatives.--Perforated Negatives.--Negatives Made from Magazine
+Pictures.--Ground Glass Negatives.--IV. Nature Photography.--Aids to
+Nature Study.--Ferns and Leaves.--Photographing Leaves.--Perforating
+Leaves.--Drying Leaves, Ferns, etc., for Negatives.--Flowers.--V.
+Miscellaneous Photographs.--Magnetic Photographs.--Combination
+Pictures.--Initial Pictures.--Name Plates.--Christmas, Easter and
+Birthday Cards.
+
+No. R6--"Fun with Photography," Complete Outfit, Postpaid $0.65
+
+
+FUN WITH CHEMISTRY
+
+[Illustration: Fun With Chemistry]
+
+Chemistry is universally considered to be an interesting subject, even
+in school, and it is certainly an important one in these days of
+scientific progress. This outfit starts you at the right place and
+presents the elements of the subject in a most interesting fashion. The
+experiments are so enjoyable that you will take pleasure in doing them
+over and over again, and you will want to do them for your friends. You
+can have a lot of fun with this set, and even if you have taken advanced
+courses in the subject you will find something new in these experiments.
+The more you know about chemistry the more you will enjoy it, for then
+you can more easily appreciate what a splendid outfit this is for the
+money.
+
+The Outfit contains over 20 different articles, including chemicals,
+test-tubes, adjustable ring-stand, litmus paper, filter paper, glass
+tubing, etc.; in fact, everything needed for the forty-one experiments.
+The Book of Instructions is fully illustrated, and measures 5x7-1/2
+inches.
+
+Fun Found Here: From White to Black, or the Phantom Ship.--Yellow
+Tears.--Smoke Pearls.--An Ocean of Smoke.--A Tiny Whirlwind.--A Smoke
+Cascade.--An Explosion in a Teacup.--A Gas Factory in a
+Test-Tube.--Making Charcoal.--Flame Goes Over a Bridge.--A Smoke
+Toboggan-Slide.--Fountains of Flame.--Making an Acid.--Making an
+Alkali.--A Chemical Fight.--Through Walls of Flame.--An Artificial Gas
+Well.--A Lampblack Factory.--Steam from a Flame.--The Flame that
+Committed Suicide.--Chemical Soup.--A Baby Skating-Rink.--A Magic
+Milk-Shake.--The Wizard's Breath.--A Chemical Curtain.--Scrambled
+Chemicals.--And Many Other Experiments.
+
+No. R7--"Fun with Chemistry," Complete Outfit, postpaid $0.65
+
+       *       *       *       *       *
+
+ELECTRIC SHOOTING GAME
+
+Shooting Animals by electricity is certainly a most original game, and
+it will furnish a vast amount of amusement to all. The game is patented
+and copyrighted--because it is really a brand-new idea in games--and it
+brings into use that most mysterious something called electricity. While
+the electricity is perfectly harmless, there being no batteries, acids
+or liquids, it is very active and you will have plenty to laugh at. It
+is so simple that the smallest child can play it and so fascinating that
+grandpa will want to try it.
+
+The "game-preserve" is neatly printed in colors, and the birds and wild
+animals are well worth hunting. Each has a fixed value--and some of them
+must not be shot at all--so there is ample chance for skill.
+Tissue-paper bullets are actually shot from the "electric gun" by
+electricity, and it is truly a weird sight to see them shoot through the
+air impelled by this unseen force.
+
+The Outfit contains the "Game-Preserve," the "Electric Gun," the
+"Shooting-Box," and the "Electric Bullets," together with complete
+illustrated directions, all placed in a neat box.
+
+No. R41--"Electric Shooting Game," complete, postpaid $0.35
+
+       *       *       *       *       *
+
+NEW IDEA TIT-TAT-TOE
+
+Splendid game for two, three, or four players; great improvement upon
+the good old game; fascinating game instantly learned; nothing better
+for children's parties and progressive birthday parties; box with
+game-board, 12 men, directions; discount for party orders.
+
+No. R21--New Idea Tit-Tat-Toe, sample, postpaid $0.15
+
+
+Electric Air-Ships and Other Games
+
+(patented)
+
+[Illustration]
+
+This is the age of air-ships and electricity, so what could be more
+up-to-date than electric "air-ships" that will float and dive and race
+around at the will of the operator? In this game Mr. St. John has again
+made use of a scientific principle, the "air-ships" being actually
+controlled by electricity. They are made to act in a most peculiar
+manner, with no wires, no fuss, no danger. They are under perfect
+control and can be made to ascend to the ceiling, drop to the floor or
+race across the room, as desired. You simply can't imagine how
+entertaining it is to see a lot of excited people managing these aerial
+racers, each eager to win.
+
+The outfit contains illustrated directions and materials for two
+players, including the apparatus for producing the electricity and the
+"repeller" for managing the "air-ships" in mid-air. The little
+"air-ships" are actually made of metal and they can be instantly formed.
+Here's the latest sport for all ages, because the little ones can play
+too. Get into the game and be an aviator.
+
+No. R42--"Electric Air-Ships and Other Games," postpaid $0.35
+
+AVIATION TOURNAMENTS AT HOME
+
+
+REAL ELECTRIC TOY-MAKING FOR BOYS
+
+_By THOMAS M. ST. JOHN. Met. E._
+
+This book contains 140 pages and over one hundred
+original drawings, diagrams, and full-page plates.
+
+It measures 5x7-1/2 in., and is bound in cloth.
+
+SECOND EDITION Price, postpaid, $1.00
+
+CONTENTS: Chapter I. Toys Operated by Permanent Magnets.--II. Toys
+Operated by Static Electricity.--III. Making Electromagnets for
+Toys.--IV. Electric Batteries.--V. Circuits and Connections.--VI. Toys
+Operated by Electromagnets. VII. Making Solenoids for Toys.--VIII. Toys
+Operated by Solenoids.--IX. Electric Motors.--X. Power, Speed, and
+Gearing.--XI. Shafting and Bearings.--XII. Pulleys and
+Winding-Drums.--XIII. Belts and Cables.--XIV. Toys Operated by Electric
+Motors.--XV. Miscellaneous Electric Toys.--XVI. Tools.--XVII.
+Materials.--XVIII. Various Aids to Construction.
+
+While planning this book, Mr. St. John definitely decided that he would
+not fill it with descriptions of complicated, machine-made instruments
+and apparatus, under the name of "Toy-Making," for it is just as
+impossible for most boys to get the parts for such things as it is for
+them to do the required machine work even after they have the raw
+materials.
+
+Great care has been taken in designing the toys which are described in
+this book, in order to make them so simple that any boy of average
+ability can construct them out of ordinary materials. The author can
+personally guarantee the designs, for there is no guesswork about them.
+Every toy was made, changed, and experimented with until it was as
+simple as possible; the drawings were then made from the perfected
+models.
+
+As the result of the enormous amount of work and experimenting which
+were required to originate and perfect so many new models, the author
+feels that this book may be truly called "Real Electric Toy-Making for
+Boys."
+
+       *       *       *       *       *
+
+Every Boy Should Make Electrical Toys.
+
+
+A MOTOR THAT CAN DO THINGS
+
+The "St J. Motor No. 1" (List No. 2201) is designed for students and
+others who want a small motor for experimental purposes as well as
+for all of the work that any small motor can do. We believe this to
+be the best small motor made, and we know that it can be used in
+more ways than any other motor of equal cost ever built. It has four
+binding-posts,--making it possible to energize the field or armature
+separately,--and so it can be used in circuits with reversers and
+rheostats for experiments. The speed and direction of rotation can be
+changed at will, thus adapting it for running toys, etc. As the
+binding-posts are mounted upon the frame, this motor can be taken from
+the base for remounting and using in many ways, and as it has a
+three-pole armature it will start promptly in any position. The shaft
+carries a pulley, and a fan can be added at any time. One cell will give
+a high speed, and more cells may be added, according to the work it has
+to do.
+
+Motor No. 1 stands 3-1/2 inches high. It is finished in black enamel
+with nickel-plated trimmings,--strong and well made. With it are
+furnished three nickel-plated connecting-straps, which are to be used
+for connecting the field and armature in "series" or "shunt." So much
+can be done with this motor that it is simply impossible to tell it
+here; in fact, it is used as the basis for a whole book of 60
+experiments called "The Study of Electric Motors by Experiment," and,
+when used in connection with the other parts of the Motor Outfits, it
+will give a practical knowledge of motors that no other plan can give.
+
+[Illustration: No. 2201]
+
+These motors and motor outfits have been highly praised by electrical
+experts and educators as being invaluable to students. They can do
+everything the big motors can do, and if used with the rheostats,
+reversers and other apparatus in the outfits, the student will have a
+whole motor laboratory.
+
+Why not get a motor that has brains and that can do tricks and
+experiments? Any good motor will go when you turn on the power; but that
+doesn't mean much when it comes to understanding things.
+
+No. 2201--"St. J. Motor No. 1," with Wiring-Diagrams $1.35
+
+If sent by mail, postage extra, shipping weight one pound.
+
+
+"ST. J." ELECTRIC MOTOR OUTFIT
+
+These outfits have been designed for students and others who want to do
+real experimental work with motors, so as to get right down to the
+bottom of the matter and thoroughly master the foundation principles of
+the subject. It is simply astonishing to see how much can be learned
+with one of these outfits, especially if the work be done as fully
+detailed in "The Study of Electric Motors by Experiment." Every
+electrical laboratory should have one of these sets, and the more you
+know about motors the more you will appreciate an outfit of this kind.
+
+Don't simply read about motors--get right down to the practical part of
+it and experiment for yourself. Every experiment will settle an
+important point in your mind.
+
+ELECTRIC MOTOR OUTFIT No. 2226X contains everything needed for sixty
+interesting and profitable experiments. With the improved apparatus that
+we now give we feel that this is the most complete set ever sold for the
+money. The following articles are included, packed in a wooden box:
+
+THE "ST. J." MOTOR, fully described on another page, is well called "A
+motor that can do things."
+
+THE FIVE-POINT RHEOSTAT is used as a "starting-box" in the
+armature-circuit and in various other ways to regulate speed. (See cut.)
+
+THE ELEVEN-POINT RHEOSTAT is used to regulate the "field-magnetism," as
+one method of speed-regulation, and for other purposes. (See cut.)
+
+THE DOUBLE-KEY CURRENT REVERSER is, really, a key, a two-point switch,
+and a current-reverser combined. On this account it can be used in many
+ways, shown in numerous wiring-diagrams. (See cut.)
+
+THE HANDY CURRENT-DETECTOR is used as a current-detector and as a device
+for studying the counter-electromotive force of motor while running.
+
+THE TWO-POINT SWITCH is useful in quickly switching the current wherever
+it is needed, and for many other experiments.
+
+THE STRAP KEY protects the batteries and closes the circuit.
+
+THE MINIATURE ELECTRIC LAMP AND SOCKET are used in the motor-circuit to
+prove certain things and form an attractive addition to the outfit.
+
+THE MAGNETIC NEEDLE in the new outfits is nickel-plated and serves as a
+compass for studying the magnetism of the poles, etc.
+
+IN ADDITION to the articles mentioned above, the outfit contains a Set
+of Wires for Connections, a Box of Iron-Filings for studying lines of
+force, an Experimental Package containing Iron, Steel, etc., three
+Connecting-Wires, and
+
+THE BOOK OF INSTRUCTIONS, called "The Study of Electric Motors by
+Experiment." This contains 10 chapters, 110 pages, and over 70
+illustrations and diagrams. Bound in stiff paper.
+
+BATTERIES are not included, unless ordered extra. Three of our No. 1101
+batteries cost 36c., and extra postage for 2 lbs.
+
+No. 2226X--Complete Motor Outfit, as above (P. weight, 3 lbs.) $3.75
+
+       *       *       *       *       *
+
+THE STUDY OF ELECTRIC MOTORS BY EXPERIMENT
+
+contains Sixty Experiments that Bear Directly upon the Construction,
+Operation, and Explanation of Electric Motors, together with Much
+Helpful Information upon the Experimental Apparatus Required. This book
+will be a great help to those who want to do real experimental work with
+motors. It contains 10 chapters, 110 pages, over 70 illustrations and
+diagrams, and you can not afford to be without it.
+
+No. R57P--"Study of Motors," bound in paper, postpaid $0.35
+
+No. R57C--"Study of Motors," bound in cloth, postpaid $0.60
+
+
+Fun With Telegraphy (PATENTED)
+
+TWO GREAT OUTFITS FOR STUDENTS
+
+[Illustration]
+
+These two outfits are similar in construction, although they differ in
+details, each being designed for its special work. The "keys,"
+"sounders" and "binding-posts" are neatly mounted upon ebonized bases
+measuring 6-1/2x3-3/4 in., these also serving as sounding-boards.
+
+"Fun with Telegraphy" is the original low-price telegraph outfit for
+students that has sold by the thousands and given universal
+satisfaction. It is considered the best 50-cent outfit ever produced,
+and, although we have made several improvements lately, the price is the
+same as before. In connection with a peculiar oscillating electro-magnet
+and a queer anvil, the sounding-board aids in giving out a loud, clear
+click that is found elsewhere only in noisy railroad sounders. This
+outfit is best adapted for a learner's set of one instrument and a
+battery to be used on the table for practising, either with or without
+the "codegraph," and not for telegraphing over wires to other stations.
+
+Outfit: Illustrated Book of Instructions, called "Fun with Telegraphy";
+Telegraph "Key"; Telegraph "Sounder"; Nickel-Plated "Binding-Posts";
+Insulated Wires for Connections.
+
+No. R8--"Fun with Telegraphy," without battery, postpaid $0.50
+
+No. R8, R8B--"Fun with Telegraphy," with one dry battery, postpaid, .65
+
+"Improved Telegraphy No. 2."--In answer to a number of requests for an
+improved outfit for regular line work between two stations a few hundred
+feet apart, we now offer this set, which is, in general, similar in plan
+to our first "Telegraphy No. 2." We have replaced the single
+electro-magnet of the old set, as shown in the cut, with two larger ones
+of superior construction, thus making the instrument much more
+sensitive. The key has also been greatly improved, and we now have a
+fine set at low cost.
+
+No expensive gravity batteries are needed with this ingenious
+arrangement, as it is designed to work with dry batteries which are
+clean and cheap. By means of a peculiar switch, either station may
+"call" the other at any time, even though the line is kept on "open
+circuit." There is absolutely no waste of current when the line is not
+in use--and, even then, only at the instant the dots and dashes are
+made. This is certainly a great advantage over the old-fashioned methods
+with gravity batteries which amateurs have heretofore been obliged to
+use. With this instrument you have a learner's set as well as one that
+can be used to send messages to another station. If you do not care for
+the superior advantages of "Semi-Wireless," this outfit will give entire
+satisfaction for ordinary work.
+
+Outfit: Illustrated Book of Instructions called "Telegraphy Number Two";
+Improved Telegraph "Key"; Telegraph "Sounder" with Double
+Electromagnets: Special "Switch" for controlling the batteries;
+Nickel-plated Screw "Binding-posts"; Insulated Wires for connections.
+
+No. 2307--"Improved Telegraphy Number Two" (no batteries), postpaid,
+$1.00
+
+No. 2307B--Same as No. 2307, but with two dry batteries, postpaid, 1.35
+
+
+The Codegraph (PATENTED)
+
+NOTE--Continental
+Code sent unless
+otherwise ordered.
+
+[Illustration]
+
+The Codegraph is a brand-new scheme for thoroughly and rapidly learning
+the telegraphic code, and it has been worked out with the beginner in
+mind. This code-learning system really adapts itself to the beginner,
+and it gives a personal touch to each individual student according to
+his needs. No other system can do so much, for the student sees, hears
+and feels every letter and signal.
+
+The greatest trouble that every one has in learning by listening to
+regular messages is in separating the letters and words as they come in
+so fast. There is no time to think, and letters pile up in the mind. The
+codegraph avoids all confusion because every letter is under perfect
+control and may be repeated as many times as desired; hard things can be
+made easy; words and sentences can be built at will. We guarantee that
+any one of average ability can make rapid improvement with the
+codegraph.
+
+What It Is. A complete codegraph outfit, as shown in the cut, has three
+main parts: (1) The "plate and pen," (2) some form of "key and sounder"
+and (3) two batteries. While any key and sounder can be used with the
+plate, we wish to call especial attention to the duplex sounder shown,
+as this has been designed to do double work. If you already have "Fun
+with Telegraphy," for example, and want to order the "Codegraph Plate
+and Pen," we will include, free of charge, an extra attachment for
+connecting up your instrument.
+
+The Plate and Pen. When the pen is lightly drawn over the plate, the
+sounder responds and shows exactly how every letter and signal should
+sound. The student can then practise each letter until perfect. The
+surface of the plate is covered with a special insulating enamel, bare
+spots corresponding to correct dots and dashes. The polished brass plate
+measures about 6x8 inches and has a most elegant appearance. The book
+tells all about practising, etc.
+
+Duplex Codegraph Key and Sounder, as shown, has a double action and is
+the latest thing in code-learning devices. By the mere turning of a
+switch you can have the ordinary telegraph clicks or the wireless
+buzzes, making two sounders in one and at the cost of one. The
+combination sounder and a substantial key are mounted upon a finely
+finished base with nickel-plated trimmings, binding-posts, switch, etc.
+If you want to become an operator in the shortest possible time, no
+matter whether you have ever tried before or not, get one of these
+outfits and begin at once. You will be pleased right from the start,
+because you will make rapid progress right from the start.
+
+No. 2350--"Codegraph Plate and Pen," with Book of Instructions      $1.00
+      If sent by mail, postage extra                                  .12
+No. 2351--"Duplex Codegraph Key and Sounder" (no batteries)          1.00
+      If sent by mail, postage extra                                  .10
+No. 1102--Two Dry Batteries, as shown                                 .25
+      If sent by mail, postage extra                                  .10
+Special--Complete Codegraph Outfit, as in cut, postpaid              2.50
+
+
+TELEGRAPH AND TELEPHONE SETS (LIST T)
+
+ORIGINAL OUTFITS that are worthy of your attention and that give fine
+results; products of hundreds of experiments and models that give best
+value for least money. A complete line of outfits beginning with "Fun
+with Telegraphy" and ending with combined "Semi-Wireless Telegraph,
+Telephone and Electric Light Signal Sets," with endless possibilities.
+
+Don't forget to add postage according to weight and zone.
+
+List No. List Price
+
+2302--"NEW FUN WITH TELEGRAPHY." A Book, Key, Sounder, Wires. Nicely
+mounted, sensitive, adjustable, improved, practical. (P. Wt. 1 lb.)
+$0.35
+
+2302B1--Same as No. 2302, but with 1 dry battery. (P. Wt. 1 lb.) $0.50
+
+2308--"NEW TELEGRAPHY NUMBER TWO." For regular line-work: has ingenious
+switch; uses dry batteries. Key, Sounder, Book, Wires. (P. Wt. 1 lb.)
+$0.75
+
+2308B2--Same as No. 2308 but with two dry batteries. (P. Wt. 2 lbs.)
+$1.00
+
+2304--"CLICKERBUZZ" TWO-STATION TELEGRAPH OUTFIT. Special value; loud,
+resonant, substantial, very neat and does several things. Complete with
+two separate No. 2580 "WONDERBUZZ" Instruments, Morse Code, Continental
+Code, Wire for short Line, Pkg. small Telegraph blanks, Instructions and
+Wiring Diagrams. (P. Wt. 2 lbs.) $2.00
+
+2304B4--Same as No. 2304 but with four dry batteries. (P. Wt. 3 lbs.)
+$2.50
+
+2350--CODEGRAPH PLATE, PEN AND BOOK. Teaches Continental Wireless Code,
+giving correct sounds on your buzzer or on ours. Original, practical,
+solves home study. (Weight 1 pound.) Price $1.00
+
+2355--CODEGRAPH OUTFIT MOUNTED on ebonized base with High-pitch
+Nickel-plated Buzzer, Binding-posts and Key, Books and Wires. Fine set
+for practice and study. Continental Code. (Weight, 2 lbs.) Price $2.75
+
+2355B2--Same as 2355, but with 2 batteries. (Wt. 3 lbs.) Price $3.00
+
+2580--"SEMI-WIRELESS WONDERBUZZ," a real wonder that can actually be
+used in 40 hookups. A basic instrument around which to build
+Code-teaching Devices, Blinker Signal Systems, numerous Click
+Telegraphs, Buzz Telegraphs, Semi-wireless Telegraphs, several Telephone
+Plans, combined Telegraph and Telephone schemes over the same wire,
+actual Room-to-room Wireless, etc., etc. Can't begin to tell it all
+here. An all-useful instrument with directions. (Weight, 1 lb.) Price
+$1.00
+
+2576--THE "WONDERPHONE" is a practical, inexpensive telephone set;
+sensitive, strong and well made. Outfit for one station: Receiver,
+Carbon Grain Transmitter, both with flexible wires, Combination
+Binding-post and Instrument Support, Battery Box, Wire for Connections,
+50 ft. of Line Wire, Directions. (Weight, 1 lb.) Price $1.50
+
+2576B2--Same as No. 2576, but with 2 batteries, (Wt. 2 lbs.) Price
+$1.75
+
+2582--"SEMI-WIRELESS TELEGRAPH, TELEPHONE, AND ELECTRIC LIGHT SIGNAL
+SET." A Combination of the "Wonderbuzz," the "Wonderphone," Night Signal
+Attachment, and a Lot of Extras, Line Wire, Etc. A set that beats them
+all and does most. No other system does so much for the money and no
+other can do so much for ten times the money. A wonder combination of
+usefulness. Please read about the "Wonderbuzz" and the "Wonderphone."
+The latest word in telegraphy from Cascade Ranch. (Weight, 2 lbs.) Price
+$2.75
+
+2582B2--Same as No. 2582 but with 2 batteries. (Wt. 3 lbs.) $3.00
+
+No. STJC--SAVE-TIME-JIFFY-CODE. Learn to send and receive slowly in an
+hour or less. In a day you can telegraph in a jiffy, any message,
+punctuation, numbers, sentence-signals and the whole business. Every boy
+a telegrapher. Fun to make your own Cipher Codes on this as a basis.
+Complete, postpaid 6c., two for $0.10
+
+2425--"DANDY HANDIPHONE." An inexpensive house-to-house telephone.
+Sensitive, attractive, practical, efficient. Rings bell or buzzer to
+call, using dry batteries. Will work as far as any battery-phone, and
+farther than many of them. A dandy Handiphone. In preparation.
+
+Be sure to add postage according to weight and zone.
+
+THOMAS M. ST. JOHN, Cascade Ranch, East Windham, N.Y.
+
+
+
+***END OF THE PROJECT GUTENBERG EBOOK HOW TWO BOYS MADE THEIR OWN
+ELECTRICAL APPARATUS***
+
+
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