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diff --git a/36457-h/36457-h.htm b/36457-h/36457-h.htm new file mode 100644 index 0000000..bae7f90 --- /dev/null +++ b/36457-h/36457-h.htm @@ -0,0 +1,10914 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> + +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1" /> + <title> + The Project Gutenberg eBook of A Treatise on Meteorological Instruments, by Negretti and Zambra. + </title> + + <style type="text/css"> + + p {margin-top: .75em; text-align: justify; margin-bottom: .75em;} + + body {margin-left: 12%; margin-right: 12%;} + + .pagenum {position: absolute; left: 92%; font-size: smaller; text-align: right; font-style: normal;} + + h1,h2,h3,h4,h5,h6 {text-align: center; clear: both;} + + hr {width: 33%; margin-top: 2em; margin-bottom: 2em; margin-left: auto; margin-right: auto; clear: both;} + + table {margin-left: auto; margin-right: auto;} + .botbor {border-bottom: solid black 1px;} + .botbor2 {border-bottom: solid black 3px;} + .bt {border-top: solid black 1px; padding-left: 0.5em; padding-right: 0.5em;} + .btr {border-top: solid black 1px; border-right: solid black 1px; padding-left: 0.5em; padding-right: 0.5em;} + .br {border-right: solid black 1px; padding-left: 0.5em; padding-right: 0.5em;} + .btlr {border-top: solid black 1px; border-left: solid black 1px; border-right: solid black 1px; padding-left: 0.5em; padding-right: 0.5em;} + .bblr {border-bottom: solid black 1px; border-left: solid black 1px; border-right: solid black 1px; padding-left: 0.5em; padding-right: 0.5em;} + .blr {border-left: solid black 1px; border-right: solid black 1px; padding-left: 0.5em; padding-right: 0.5em;} + .bbr {border-bottom: solid black 1px; border-right: solid black 1px; padding-left: 0.5em; padding-right: 0.5em;} + .bb {border-bottom: solid black 1px; padding-left: 0.5em; padding-right: 0.5em;} + .bbtl {border-bottom: solid black 1px; border-top: solid black 1px; border-left: solid black 1px; padding-left: 0.5em; padding-right: 0.5em;} + .bbtr {border-bottom: solid black 1px; border-top: solid black 1px; border-right: solid black 1px; padding-left: 0.5em; padding-right: 0.5em;} + .bbt {border-bottom: solid black 1px; border-top: solid black 1px; padding-left: 0.5em; padding-right: 0.5em;} + .dent {padding-left: 0.5em; padding-right: 0.5em;} + .btrdoub {border-top: solid black 1px; border-right: double; padding-left: 0.5em; padding-right: 0.5em;} + .brdoub {border-right: double; padding-left: 0.5em; padding-right: 0.5em;} + .bbrdoub {border-bottom: solid black 1px; border-right: double; padding-left: 0.5em; padding-right: 0.5em;} + .btrdoub2 {border-top: solid black 1px; border-right: solid black 3px; padding-left: 0.5em; padding-right: 0.5em;} + .brdoub2 {border-right: solid black 3px; padding-left: 0.5em; padding-right: 0.5em;} + .bbrdoub2 {border-bottom: solid black 1px; border-right: solid black 3px; padding-left: 0.5em; padding-right: 0.5em;} + + .giant {font-size: 200%} + .huge {font-size: 150%} + .large {font-size: 125%} + + .blockquot {margin-left: 5%; margin-right: 10%;} + + .right {text-align: right;} + .center {text-align: center;} + + .smcap {font-variant: small-caps;} + .smcaplc {text-transform: lowercase; font-variant: small-caps;} + + .figcenter {margin: auto; text-align: center;} + + .figleft {float: left; clear: left; margin-left: 0; margin-bottom: 1em; margin-top: + 1em; margin-right: 1em; padding: 0; text-align: center;} + + .figright {float: right; clear: right; margin-left: 1em; margin-bottom: 1em; + margin-top: 1em; margin-right: 0; padding: 0; text-align: center;} + + a:link {color:#0000ff; text-decoration:none} + a:visited {color:#6633cc; text-decoration:none} + + .spacer {padding-left: 1em; padding-right: 1em;} + .spacer2 {padding-left: .5em; padding-right: .5em;} + + </style> + </head> +<body> + + +<pre> + +The Project Gutenberg EBook of A Treatise on Meteorological Instruments, by +Henry Negretti and Joseph Zambra + +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: A Treatise on Meteorological Instruments + Explanatory of Their Scientific Principles, Method of + Construction, and Practical Utility + +Author: Henry Negretti + Joseph Zambra + +Release Date: June 18, 2011 [EBook #36457] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK TREATISE ON METEOROLOGICAL INSTRUMENTS *** + + + + +Produced by The Online Distributed Proofreading Team at +https://www.pgdp.net (This file was produced from images +generously made available by The Internet Archive.) + + + + + + +</pre> + + + + +<p class="center"><span class="huge">A TREATISE</span></p> +<p class="center">ON</p> +<p class="center"><span class="huge">METEOROLOGICAL INSTRUMENTS.</span></p> +<p> </p><p> </p> +<p class="center"><small>LONDON:<br /> +PRINTED BY WILLIAMS AND STRAHAN,<br /> +7 LAWRENCE LANE, CHEAPSIDE, E.C.</small></p> + +<p> </p><p> </p><p> </p> +<p class="center"><span class="huge">A TREATISE</span></p> +<p class="center">ON</p> +<p class="center"><span class="giant">METEOROLOGICAL<br />INSTRUMENTS:</span></p> +<p> </p> +<p class="center"><small>EXPLANATORY OF</small></p> +<p class="center"><span class="large">THEIR SCIENTIFIC PRINCIPLES,</span></p> +<p class="center"><span class="large">METHOD OF CONSTRUCTION, AND PRACTICAL UTILITY.</span></p> +<p> </p> +<p class="center">BY</p> +<p class="center"><span class="large">NEGRETTI & ZAMBRA,</span></p> +<p class="center"><small>METEOROLOGICAL INSTRUMENT MAKERS TO THE QUEEN, THE ROYAL OBSERVATORY, GREENWICH,<br /> +THE BRITISH METEOROLOGICAL SOCIETY, THE BRITISH AND FOREIGN GOVERNMENTS,<br /> +ETC. ETC. ETC.</small></p> +<p> </p> +<p class="center">LONDON:<br /> +<small>PUBLISHED AND SOLD AT NEGRETTI & ZAMBRA’S ESTABLISHMENTS:<br /> +1 HATTON GARDEN, E.C., 59 CORNHILL, E.C., 122 REGENT STREET W.,<br /> +AND 153 FLEET STREET, E.C.</small></p> +<p class="center">1864.</p> +<p class="center"><i>Price Five Shillings.</i></p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_v" id="Page_v">[Pg v]</a></span></p> +<h2>PREFACE.</h2> + +<p>The national utilisation of Meteorology in forewarning of storms, and the +increasing employment of instruments as weather indicators, render a +knowledge of their construction, principles, and practical uses necessary +to every well-informed person. Impressed with the idea that we shall be +supplying an existing want, and aiding materially the cause of +Meteorological Science, in giving a plain description of the various +instruments now in use, we have endeavoured, in the present volume, to +condense such information as is generally required regarding the +instruments used in Meteorology; the description of many of which could +only be found in elaborate scientific works, and then only briefly touched +upon. Every Meteorological Instrument now in use being fully described, +with adequate directions for using, the uninitiated will be enabled to +select those which seem to them best adapted to their requirements. With +accounts of old or obsolete instruments we have avoided troubling the +reader; on the other hand, we were unwilling to neglect those which, +though of no great practical importance, are still deserving of notice +from their being either novel or ingenious, or which, without being +strictly scientific, are in great demand as simple weather-glasses and +articles of trade.</p> + +<p>We trust, therefore, that the work (however imperfect), bearing in mind +the importance of the subject, will be acceptable to general readers, as +well as to those for whose requirements it has been prepared.</p> + +<p>The rapid progress made in the introduction of new apparatus of +acknowledged superiority has rendered the publication of some description +absolutely necessary. The Report of the Jurors for Class XIII. of the +International Exhibition, 1862, on Meteorological Instruments, fully bears +out our assertion, as shown by the following extract:—</p> + +<p><span class="pagenum"><a name="Page_vi" id="Page_vi">[Pg vi]</a></span>“The progress in the English department has been very great;—in +barometers, thermometers, anemometers, and in every class of instruments. +At the close of the Exhibition of 1851, there seemed to have arisen a +general anxiety among the majority of makers to pay every attention to all +the essentials necessary for philosophical instruments, not only in their +old forms, but also with the view of obtaining other and better forms. +This desire has never ceased; and no better idea can be given of the +continued activity in these respects, than the number of patents taken out +for improvements in meteorological instruments in the interval between the +recent and preceding exhibitions, which amount to no less than forty-two.” +* * * “In addition to numerous improvements patented by Messrs. Negretti +and Zambra, there is another of great importance, which they did not +patent, viz. enamelling the tubes of thermometers, enabling the makers to +use finer threads of mercury in the construction of all thermometers; for +the contrast between the opaque mercury and the enamel back of the tubes +is so great, that the finest bore or thread of mercury, which at one time +could not be seen without the greatest difficulty, is now seen with +facility; and throughout the British and Foreign departments, the makers +have availed themselves of this invention, the tubes of all being made +with enamelled backs. It is to be hoped that the recent exhibition will +give a fresh stimulus to the desire of improvement, and that the same rate +of progress will be continued.”</p> + +<p>To fulfil the desire of the International Jury in the latter portion of +the above extract will be the constant study of</p> + +<p><span style="margin-left: 8em;">NEGRETTI & ZAMBRA.</span></p> + +<p><i>1st January, 1864.</i></p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_vii" id="Page_vii">[Pg vii]</a></span></p> +<h2>TABLE OF CONTENTS.</h2> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td colspan="2" align="center"><a href="#CHAPTER_I">CHAPTER I.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Instruments for Ascertaining the Atmospheric Pressure.</span></td></tr> +<tr><td><small>SECTION</small></td></tr> +<tr><td align="right">1.</td><td>Principle of the Barometer.</td></tr> +<tr><td align="right">2.</td><td>Construction of Barometers.</td></tr> +<tr><td align="right">3.</td><td>Fortin’s Barometer Cistern.</td></tr> +<tr><td align="right">4.</td><td><span class="smcap">Standard Barometer.</span></td></tr> +<tr><td align="right">5.</td><td>Correction due to Capillarity.</td></tr> +<tr><td align="right">6.</td><td><span class="spacer"> </span>"<span class="spacer"> </span>" Temperature.</td></tr> +<tr><td align="right">7.</td><td><span class="spacer"> </span>"<span class="spacer"> </span>" Height.</td></tr> +<tr><td align="right">8.</td><td>The Barometer Vernier.</td></tr> +<tr><td align="right">9.</td><td><span class="smcap">Self-compensating Standard Barometer.</span></td></tr> +<tr><td align="right">10.</td><td><span class="smcap">Barometer with Electrical Adjustment.</span></td></tr> +<tr><td align="right">11.</td><td><span class="smcap">Pediment Barometers.</span></td></tr> +<tr><td align="right">12.</td><td>The Words on the Scale.</td></tr> +<tr><td align="right">13.</td><td>Correction due to Capacity of Cistern.</td></tr> +<tr><td align="right">14.</td><td><span class="smcap">Public Barometers.</span></td></tr> +<tr><td align="right">15.</td><td><span class="smcap">Fishery or Sea-Coast Barometers.</span></td></tr> +<tr><td align="right">16.</td><td>Admiral FitzRoy’s Words for the Scale.</td></tr> +<tr><td align="right">17.</td><td>Instructions for Sea-coast Barometer.</td></tr> +<tr><td align="right">18.</td><td>French Sea-coast Barometer.</td></tr> +<tr><td align="right">19.</td><td><span class="smcap">Common Marine Barometer.</span></td></tr> +<tr><td align="right">20.</td><td><span class="smcap">The Kew Marine Barometer.</span></td></tr> +<tr><td align="right">21.</td><td>Method of verifying Barometers.</td></tr> +<tr><td align="right">22.</td><td><span class="smcap">FitzRoy’s Marine Barometer.</span></td></tr> +<tr><td align="right">23.</td><td>Words for its Scale.</td></tr> +<tr><td align="right">24.</td><td>Trials of this Barometer under Gun-fire.</td></tr> +<tr><td align="right">25.</td><td><span class="smcap">Negretti and Zambra’s Farmer’s Barometer andDomestic Weather-Glass.</span></td></tr> +<tr><td align="right">26.</td><td>Rules for Foretelling the Weather.</td></tr> +<tr><td align="right">27.</td><td>Causes which may bring about a Fall or a Rise in the Barometer.</td></tr> +<tr><td align="right">28.</td><td>Use of the Barometer in the Management of Mines.</td></tr> +<tr><td align="right">29.</td><td>Use of the Barometer in estimating the Height of Tides.</td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_II">CHAPTER II.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Syphon Tube Barometers.</span></td></tr> +<tr><td align="right">30.</td><td>Principle of.</td></tr> +<tr><td align="right">31.</td><td><span class="smcap">Dial, or Wheel, Barometers.</span></td></tr> +<tr><td align="right">32.</td><td><span class="smcap">Standard Syphon Barometer.</span></td></tr> +<tr><td> <span class="pagenum"><a name="Page_viii" id="Page_viii">[Pg viii]</a></span></td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_III">CHAPTER III.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Barographs, or Self-Registering Barometers.</span></td></tr> +<tr><td align="right">33.</td><td><span class="smcap">Milne’s Self-Registering Barometer.</span></td></tr> +<tr><td align="right">34.</td><td><span class="smcap">Modification of Milne’s Barometer.</span></td></tr> +<tr><td align="right">35.</td><td><span class="smcap">King’s Self-Registering Barometer.</span></td></tr> +<tr><td align="right">36.</td><td><span class="smcap">Syphon, with Photographic Registration.</span></td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_IV">CHAPTER IV.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Mountain Barometers.</span></td></tr> +<tr><td align="right">37.</td><td><span class="smcap">Gay Lussac’s Mountain Barometer.</span></td></tr> +<tr><td align="right">38.</td><td><span class="smcap">Fortin’s Mountain Barometer.</span></td></tr> +<tr><td align="right">39.</td><td><span class="smcap">Newman’s Mountain Barometer.</span></td></tr> +<tr><td align="right">40.</td><td><span class="smcap">Negretti and Zambra’s Patent Mountain and other Barometers.</span></td></tr> +<tr><td align="right">41.</td><td>Short Tube Barometer.</td></tr> +<tr><td align="right">42.</td><td>Method of Calculating Heights by the Barometer; Tables and Examples.</td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_V">CHAPTER V.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Secondary Barometers.</span></td></tr> +<tr><td align="right">43.</td><td>Desirability of Magnifying the Barometer Range.</td></tr> +<tr><td align="right">44.</td><td><span class="smcap">Howson’s Long-Range Barometer.</span></td></tr> +<tr><td align="right">45.</td><td><span class="smcap">McNeil’s Long-Range Barometer.</span></td></tr> +<tr><td align="right">46.</td><td>The Water-glass Barometer.</td></tr> +<tr><td align="right">47.</td><td><span class="smcap">Sympiesometers.</span></td></tr> +<tr><td align="right">48.</td><td><span class="smcap">Aneroids.</span></td></tr> +<tr><td align="right">49.</td><td><span class="smcap">Small Size Aneroids.</span></td></tr> +<tr><td align="right">50.</td><td><span class="smcap">Watch Aneroid.</span></td></tr> +<tr><td align="right">51.</td><td>Measurement of Heights by the Aneroid; Example.</td></tr> +<tr><td align="right">52.</td><td><span class="smcap">Metallic Barometer.</span></td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_VI">CHAPTER VI.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Instruments for Ascertaining Temperature.</span></td></tr> +<tr><td align="right">53.</td><td>Temperature.</td></tr> +<tr><td align="right">54.</td><td>Thermometric Substances.</td></tr> +<tr><td align="right">55.</td><td>Description of the Thermometer.</td></tr> +<tr><td align="right">56.</td><td><span class="smcap">Standard Thermometer.</span></td></tr> +<tr><td align="right">57.</td><td>Method of ascertaining the exact Boiling Temperature; Tables, &c.</td></tr> +<tr><td align="right">58.</td><td>Displacement of the Freezing Point.</td></tr> +<tr><td align="right">59.</td><td>The Scale.</td></tr> +<tr><td align="right">60.</td><td>The method of testing Thermometers.</td></tr> +<tr><td align="right">61.</td><td>Porcelain Scale-Plates.</td></tr> +<tr><td align="right">62.</td><td>Enamelled Tubes.</td></tr> +<tr><td align="right"><span class="pagenum">[Pg ix]</span>63.</td><td><span class="smcap">Thermometers of Extreme Sensitiveness.</span></td></tr> +<tr><td align="right">64.</td><td><span class="smcap">Varieties of Thermometers.</span></td></tr> +<tr><td align="right">65.</td><td><span class="smcap">Superheated Steam Thermometer.</span></td></tr> +<tr><td align="right">66.</td><td><span class="smcap">Thermometer for Sugar Boiling.</span></td></tr> +<tr><td align="right">67.</td><td><span class="smcap">Earth Thermometer.</span></td></tr> +<tr><td align="right">68.</td><td><span class="smcap">Marine Thermometer.</span></td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_VII">CHAPTER VII.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Self-registering Thermometers.</span></td></tr> +<tr><td align="right">69.</td><td>Importance of.</td></tr> +<tr><td align="right">70.</td><td><span class="smcap">Rutherford’s Maximum Thermometer.</span></td></tr> +<tr><td align="right">71.</td><td><span class="smcap">Phillips’s<span class="spacer"> </span>ditto<span class="spacer"> </span>ditto.</span></td></tr> +<tr><td align="right">72.</td><td><span class="smcap">Negretti and Zambra’s Patent Maximum Thermometer.</span></td></tr> +<tr><td align="right">73.</td><td><span class="smcap">Rutherford’s Alcohol Minimum Thermometer.</span></td></tr> +<tr><td align="right">74.</td><td><span class="smcap">Horticultural Minimum Thermometer.</span></td></tr> +<tr><td align="right">75.</td><td><span class="smcap">Baudin’s Alcohol Minimum Thermometer.</span></td></tr> +<tr><td align="right">76.</td><td>Mercurial Minima Thermometers desirable.</td></tr> +<tr><td align="right">77.</td><td><span class="smcap">Negretti and Zambra’s Patent Mercurial Minimum Thermometer.</span></td></tr> +<tr><td align="right">78.</td><td><span class="smcap">Negretti and Zambra’s Second Patent Mercurial Minimum Thermometer.</span></td></tr> +<tr><td align="right">79.</td><td><span class="smcap">Casella’s Patent Mercurial Minimum Thermometer.</span></td></tr> +<tr><td align="right">80.</td><td>Day and Night Thermometer.</td></tr> +<tr><td align="right">81.</td><td><span class="smcap">Sixe’s Self-registering Thermometer.</span></td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_VIII">CHAPTER VIII.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Radiation Thermometers.</span></td></tr> +<tr><td align="right">82.</td><td>Solar and Terrestrial Radiation considered.</td></tr> +<tr><td align="right">83.</td><td><span class="smcap">Solar Radiation Thermometer.</span></td></tr> +<tr><td align="right">84.</td><td><span class="smcap">Vacuum Solar Radiation Thermometer.</span></td></tr> +<tr><td align="right">85.</td><td><span class="smcap">Terrestrial Radiation Thermometer.</span></td></tr> +<tr><td align="right">86.</td><td><span class="smcap">Æthrioscope.</span></td></tr> +<tr><td align="right">87.</td><td><span class="smcap">Pyrheliometer.</span></td></tr> +<tr><td align="right">88.</td><td><span class="smcap">Actinometer.</span></td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_IX">CHAPTER IX.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Deep-Sea Thermometers.</span></td></tr> +<tr><td align="right">89.</td><td><span class="smcap">On Sixe’s Principle.</span></td></tr> +<tr><td align="right">90.</td><td><span class="smcap">Johnson’s Metallic Thermometer.</span></td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_X">CHAPTER X.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Boiling-Point Thermometers.</span></td></tr> +<tr><td align="right">91.</td><td>Ebullition.</td></tr> +<tr><td align="right">92.</td><td>Relation between Boiling-Point and Elevation.</td></tr> +<tr><td align="right"><span class="pagenum"><a name="Page_x" id="Page_x">[Pg x]</a></span>93.</td><td><span class="smcap">Hypsometric Apparatus.</span></td></tr> +<tr><td align="right">94.</td><td>Precautions to ensure Correct Graduation.</td></tr> +<tr><td align="right">95.</td><td>Method of Calculating Heights from Observations with the Mountain Thermometer; Example.</td></tr> +<tr><td align="right">96.</td><td><span class="smcap">Thermometers for Engineers.</span></td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_XI">CHAPTER XI.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Instruments for Ascertaining the Humidity of the Air.</span></td></tr> +<tr><td align="right">97.</td><td>Hygrometric Substances.</td></tr> +<tr><td align="right">98.</td><td><span class="smcap">Saussure’s Hygrometer.</span></td></tr> +<tr><td align="right">99.</td><td>Dew-Point.</td></tr> +<tr><td align="right">100.</td><td><span class="smcap">Drosometer.</span></td></tr> +<tr><td align="right">101.</td><td>Humidity.</td></tr> +<tr><td align="right">102.</td><td><span class="smcap">Leslie’s Hygrometer.</span></td></tr> +<tr><td align="right">103.</td><td><span class="smcap">Daniel’s Hygrometer.</span></td></tr> +<tr><td align="right">104.</td><td><span class="smcap">Regnault’s Condenser Hygrometer.</span></td></tr> +<tr><td align="right">105.</td><td>Temperature of Evaporation.</td></tr> +<tr><td align="right">106.</td><td><span class="smcap">Mason’s Hygrometer.</span></td></tr> +<tr><td align="right">107.</td><td><span class="smcap">Self-registering Hygrometer.</span></td></tr> +<tr><td align="right">108.</td><td>Causes of Dew.</td></tr> +<tr><td align="right">109.</td><td>Plan of Exposing Thermometers.</td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_XII">CHAPTER XII.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Instruments used for Measuring the Rainfall.</span></td></tr> +<tr><td align="right">110.</td><td><span class="smcap">Howard’s Rain-Gauge.</span></td></tr> +<tr><td align="right">111.</td><td><span class="smcap">Glaisher’s Rain-Gauge.</span></td></tr> +<tr><td align="right">112.</td><td><span class="smcap">Rain-Gauge with Float.</span></td></tr> +<tr><td align="right">113.</td><td><span class="smcap">Rain-Gauge with Side Tube.</span></td></tr> +<tr><td align="right">114.</td><td><span class="smcap">FitzRoy’s Rain-Gauge.</span></td></tr> +<tr><td align="right">115.</td><td><span class="smcap">Self-Registering Rain-Gauge.</span></td></tr> +<tr><td align="right">116.</td><td>The principle of Measurement.</td></tr> +<tr><td align="right">117.</td><td>Position for Rain-gauge, &c.</td></tr> +<tr><td align="right">118.</td><td>Cause of Rain.</td></tr> +<tr><td align="right">119.</td><td>Laws of Rainfall.</td></tr> +<tr><td align="right">120.</td><td>Utility of Statistics of Rainfall.</td></tr> +<tr><td align="right">121.</td><td><span class="smcap">New Form of Rain-gauge.</span></td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_XIII">CHAPTER XIII.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Apparatus employed for Registering the Direction, Pressure, and Velocity of the Wind.</span></td></tr> +<tr><td align="right">122.</td><td><span class="smcap">The Vane.</span></td></tr> +<tr><td align="right">123.</td><td><span class="smcap">Lind’s Wind-Gauge.</span></td></tr> +<tr><td align="right">124.</td><td><span class="smcap">Harris’s Wind-Gauge.</span></td></tr> +<tr><td align="right"><span class="pagenum"><a name="Page_xi" id="Page_xi">[Pg xi]</a></span>125.</td><td><span class="smcap">Robinson’s Anemometer.</span></td></tr> +<tr><td align="right">126.</td><td><span class="smcap">Whewell’s Anemometer.</span></td></tr> +<tr><td align="right">127.</td><td><span class="smcap">Osler’s Anemometer and Pluviometer.</span></td></tr> +<tr><td align="right">128.</td><td><span class="smcap">Beckley’s Anemometer.</span></td></tr> +<tr><td align="right">129.</td><td><span class="smcap">Self-Registering Wind-Gauge.</span></td></tr> +<tr><td align="right">130.</td><td>Anemometric Observations.</td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_XIV">CHAPTER XIV.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Instruments for Investigating Atmospheric Electricity.</span></td></tr> +<tr><td align="right">131.</td><td><span class="smcap">Atmospheric Electroscope.</span></td></tr> +<tr><td align="right">132.</td><td><span class="smcap">Volta’s Electrometer.</span></td></tr> +<tr><td align="right">133.</td><td><span class="smcap">Peltier’s Electrometer.</span></td></tr> +<tr><td align="right">134.</td><td><span class="smcap">Bohnenberger’s Electroscope.</span></td></tr> +<tr><td align="right">135.</td><td><span class="smcap">Thomson’s Electrometer.</span></td></tr> +<tr><td align="right">136.</td><td>Fundamental Facts.</td></tr> +<tr><td align="right">137.</td><td>Lightning Conductors.</td></tr> +<tr><td align="right">138.</td><td>Precautions against Lightning.</td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_XV">CHAPTER XV.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Ozone and its Indicators.</span></td></tr> +<tr><td align="right">139.</td><td>Nature of Ozone.</td></tr> +<tr><td align="right">140.</td><td><span class="smcap">Schonbein’s Ozonometer.</span></td></tr> +<tr><td align="right">141.</td><td><span class="smcap">Moffat’s Ozonometer.</span></td></tr> +<tr><td align="right">142.</td><td><span class="smcap">Clark’s Ozone Cage.</span></td></tr> +<tr><td align="right">143.</td><td>Distribution and Effects of Ozone.</td></tr> +<tr><td align="right">144.</td><td><span class="smcap">Lancaster’s Registering Ozonometer.</span></td></tr> +<tr><td> </td></tr> +<tr><td colspan="2" align="center"><a href="#CHAPTER_XVI">CHAPTER XVI.</a></td></tr> +<tr><td colspan="2" align="center"><span class="smcap">Miscellaneous Instruments.</span></td></tr> +<tr><td align="right">145.</td><td><span class="smcap">Chemical Weather Glass.</span></td></tr> +<tr><td align="right">146.</td><td><span class="smcap">Leslie’s Differential Thermometer.</span></td></tr> +<tr><td align="right">147.</td><td><span class="smcap">Romford’s Differential Thermometer.</span></td></tr> +<tr><td align="right">148.</td><td><span class="smcap">Glaisher’s Thermometer Stand.</span></td></tr> +<tr><td align="right">149.</td><td><span class="smcap">Thermometer Screen, for use at Sea.</span></td></tr> +<tr><td align="right">150.</td><td><span class="smcap">Anemoscope.</span></td></tr> +<tr><td align="right">151.</td><td><span class="smcap">Evaporating Dish, or Gauge.</span></td></tr> +<tr><td align="right">152.</td><td><span class="smcap">Admidometer.</span></td></tr> +<tr><td align="right">153.</td><td><span class="smcap">Cloud Reflector.</span></td></tr> +<tr><td align="right">154.</td><td><span class="smcap">Sunshine Recorder.</span></td></tr> +<tr><td align="right">155.</td><td><span class="smcap">Set of Portable Instruments.</span></td></tr> +<tr><td align="right">156.</td><td><span class="smcap">Implements.</span></td></tr> +<tr><td align="right">157.</td><td><span class="smcap">Hydrometer.</span></td></tr> +<tr><td align="right">158.</td><td><span class="smcap">Newman’s Self-Registering Tide-Gauge.</span></td></tr></table> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_xii" id="Page_xii">[Pg xii]</a></span></p> +<h2>TABLES.</h2> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td> </td><td align="right"><small>PAGE</small></td></tr> +<tr><td>Table of Corrections, for Capillary Depression of the Mercury in Boiled and in Unboiled Barometer-Tubes</td><td align="right"><a href="#Page_6">6</a></td></tr> +<tr><td>Tables for Deducing Heights by means of the Barometer:—</td></tr> +<tr><td><span style="margin-left: 2em;">No. 1. Approximate Height due to Barometric Pressure</span></td><td align="right"><a href="#Page_42">42</a></td></tr> +<tr><td><span style="margin-left: 2em;">No. 2. Correction for Mean Temperature of Air</span></td><td align="right"><a href="#Page_44">44</a></td></tr> +<tr><td><span style="margin-left: 2em;">No. 3. Correction due to Latitude</span></td><td align="right"><a href="#Page_44">44</a></td></tr> +<tr><td><span style="margin-left: 2em;">No. 4. Correction due to Approximate Elevation</span></td><td align="right"><a href="#Page_45">45</a></td></tr> +<tr><td>Tables for Determining the Temperature of the Vapour of Boiling Water at any Place:—</td></tr> +<tr><td><span style="margin-left: 2em;">No. 5. Factor due to Latitude</span></td><td align="right"><a href="#Page_62">62</a></td></tr> +<tr><td><span style="margin-left: 2em;">No. 6. Temperature and Tension</span></td><td align="right"><a href="#Page_62">62</a></td></tr> +<tr><td>Table of Temperature of the Soil</td><td align="right"><a href="#Page_69">69</a></td></tr> +<tr><td>Table of Difference of Elevation corresponding to a fall of 1° in the Boiling-point of Water</td><td align="right"><a href="#Page_98">98</a></td></tr> +<tr><td>Table showing Proportion of Salt for various Boiling Temperatures of Sea-Water</td><td align="right"><a href="#Page_100">100</a></td></tr> +<tr><td>Table for finding the Degree of Humidity from Observations with Mason’s Hygrometer</td><td align="right"><a href="#Page_108">108</a></td></tr> +<tr><td>Table showing Amount and Duration of Rain at London, in 1862</td><td align="right"><a href="#Page_112">112</a></td></tr> +<tr><td>Table of Average British Rainfall in Westerly, Central, and Easterly districts</td><td align="right"><a href="#Page_114">114</a></td></tr> +<tr><td>Table showing Force of Wind, for use with Lind’s Wind-Gauge</td><td align="right"><a href="#Page_118">118</a></td></tr> +<tr><td>Tables for Correcting Observations made with—</td></tr> +<tr><td><span style="margin-left: 1em;">Brass Hydrometers</span></td><td align="right"><a href="#Page_142">142</a></td></tr> +<tr><td><span style="margin-left: 1em;">Glass Hydrometers</span></td><td align="right"><a href="#Page_143">143</a></td></tr></table> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<h2>ADDENDA.</h2> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td colspan="2"> </td><td align="right"><small>PAGE</small></td></tr> +<tr><td align="right">1.</td><td>Rule for converting Millimetres into Inches, et vice versa</td><td align="right"><a href="#Page_146">146</a></td></tr> +<tr><td align="right">2.</td><td>Old French Lineal Measure, with English Equivalents</td><td align="right"><a href="#Page_146">146</a></td></tr> +<tr><td align="right">3.</td><td>Rule for finding Diameter of Bore of Barometer Tube</td><td align="right"><a href="#Page_146">146</a></td></tr> +<tr><td align="right">4.</td><td>Wind Scales</td><td align="right"><a href="#Page_147">147</a></td></tr> +<tr><td align="right">5.</td><td>Letters to denote the State of the Weather</td><td align="right"><a href="#Page_147">147</a></td></tr> +<tr><td align="right">6.</td><td>Table of Expansion of Bodies</td><td align="right"><a href="#Page_148">148</a></td></tr> +<tr><td align="right">7.</td><td>Table of Specific Gravity of Bodies</td><td align="right"><a href="#Page_148">148</a></td></tr> +<tr><td align="right">8.</td><td>Important Temperatures</td><td align="right"><a href="#Page_148">148</a></td></tr> +<tr><td align="right">9.</td><td>Table of Meteorological Elements, forming Exponents of the Climate of London</td><td align="right"><a href="#Page_149">149</a></td></tr> +<tr><td align="right">10.</td><td>List of Works on Meteorology</td><td align="right"><a href="#Page_151">151</a></td></tr></table> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_1" id="Page_1">[Pg 1]</a></span></p> +<h2>METEOROLOGICAL INSTRUMENTS.</h2> + +<p>In the pursuits and investigations of the science of Meteorology, which is +essentially a science of observation and experiment, instruments are +required for ascertaining, 1. the pressure of the atmosphere at any time +or place; 2. the temperature of the air; 3. the absorption and radiation +of the sun’s heat by the earth’s surface; 4. the humidity of the air; 5. +the amount and duration of rainfall; 6. the direction, the horizontal +pressure, and the velocity of winds; 7. the electric condition of the +atmosphere, and the prevalence and activity of ozone.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<h2><a name="CHAPTER_I" id="CHAPTER_I"></a>CHAPTER I.</h2> +<p class="center"><span class="large">INSTRUMENTS FOR ASCERTAINING THE ATMOSPHERIC PRESSURE.</span></p> + + +<div class="figright">Fig. 1.<br /><img src="images/fig_1.jpg" alt="" /></div> + +<p><br /><b>1. Principle of the Barometer.</b>—The first instrument which gave the exact +measure of the pressure of the atmosphere was invented by Torricelli, in +1643. It is constructed as follows:—A glass tube, CD (fig. 1), about 34 +inches long, and from two to four-tenths of an inch in diameter of bore, +having one end closed, is filled with mercury. In a cup, B, a quantity of +mercury is also poured. Then, placing a finger securely over the open end, +C, invert the tube vertically over the cup, and remove the finger when the +end of the tube dips into the mercury. The mercury in the tube then partly +falls out, but a column, AB, about 30 inches in height, remains supported. +This column is a weight of mercury, the pressure of which upon the surface +of that in the cup is precisely equivalent to the corresponding pressure +of the atmosphere which would be exerted in its place if the tube were +removed. As the atmospheric pressure varies, the length of this mercurial +column also changes. It is by no means constant in its height; in fact, it +is very seldom stationary, but is constantly rising or falling through a +certain extent of the tube, at the level of the sea, near which the above +experiment is supposed to be performed. It is, therefore, an instrument by +which the fluctuations taking place in the<span class="pagenum"><a name="Page_2" id="Page_2">[Pg 2]</a></span> pressure of the atmosphere, +arising from changes in its weight and elasticity, can be shown and +measured. It has obtained the name <i>Barometer</i>, or measurer of +heaviness,—a word certainly not happily expressive of the utility of the +invention. If the bore of the barometer tube be uniform throughout its +length, and have its sectional area equal to a square inch, it is evident +that the length of the column, which is supported by the pressure of the +air, expresses the number of cubic inches of mercury which compose it. The +weight of this mercury, therefore, represents the statical pressure of the +atmosphere upon a square inch of surface. In England the annual mean +height of the barometric column, reduced to the sea-level and to the +temperature of 32° Fahrenheit, is about 29·95 inches. A cubic inch of +mercury at this temperature has been ascertained to weigh 0·48967 lbs. +avoirdupois. Hence, 29·95 × 0·48967= 14·67 lbs., is the mean value of the +pressure of the atmosphere on each square inch of surface, near the +sea-level, about the latitude of 50 degrees. Nearer the equator this mean +pressure is somewhat greater; nearer the poles, somewhat less. For common +practical calculations it is assumed to be 15 lbs. on the square inch. +When it became apparent that the movements of the barometric column +furnished indications of the probable coming changes in the weather, an +attempt was made to deduce from recorded observations the barometric +height corresponding to the most notable characteristics of weather. It +was found that for fine dry weather the mercury in the barometer at the +sea-level generally stood above 30 inches; changeable weather happened +when it ranged from 30 to 29 inches, and when rainy or stormy weather +occurred it was even lower. Hence, it became the practice to place upon +barometer scales words indicatory of the weather likely to accompany, or +follow, the movements of the mercury; whence the instruments bearing them +obtained the name “Weather Glasses.”</p> + + +<p><br /><b>2. Construction of Barometers.</b>—In order that the instrument may be +portable, it must be made a fixture and mounted on a support; and, +further, to render it scientifically or even practically useful, many +precautions are required in its construction. The following remarks apply +to the construction of all barometers:—Mercury is universally employed, +because it is the heaviest of fluids, and therefore measures the +atmospheric pressure by the shortest column. Water barometers have been +constructed, and they require to be at least 34 feet long. Oil, or other +fluids, might be used. Mercury, however, has other advantages: it has +feeble volatility, and does not adhere to glass, if pure. Oxidised, or +otherwise impure mercury, may adhere to glass; moreover, such mercury +would not have the density of the pure metal, and therefore the barometric +column would be either greater or less than it should be. The mercury of +commerce generally contains lead; sometimes traces of iron and sulphur. It +is necessary, therefore, for the manufacturer to purify the mercury; and +this is done by washing it with diluted acetic, or sulphuric acid, which +dissolves the impurities. No better test can be found for ascertaining if +the mercury be pure than that of filling a delicate thermometer tube; if, +on exhausting<span class="pagenum"><a name="Page_3" id="Page_3">[Pg 3]</a></span> the air from this thermometer, the mercury will freely run +up and down the bore, which is probably one thousandth of an inch in +diameter, the mercury from which this thermometer was made will be found +fit for any purpose, and with it a tube may be filled and boiled, not only +of one inch, but even of two inches diameter. In all barometers it is +requisite that the space above the mercurial column should be completely +void of air and aqueous vapour, because these gases, by virtue of their +elasticity, would depress the column. To exclude these the mercury is +introduced, and boiled in the tube, over a charcoal fire, kept up for the +purpose. In this manner the air and vapour which adhere to the glass are +expanded, and escape away. One can tell whether a barometer has been +properly “boiled,” as it is termed, by simply holding the tube in a +slanting direction and allowing the mercury to strike the top. If the +boiling has been well performed, the mercury will give a clear, metallic +sound; if not, a dull, flat sound, showing some air to be present.</p> + +<p>When the mercury in a barometer tube rises or falls, the level of the +mercury in the cup, or <i>cistern</i>, as it is generally termed, falls or +rises by a proportionate quantity, which depends upon the relative areas +of the interior of the tube and of the cistern. It is necessary that this +should be taken into consideration in ascertaining the exact height of the +column. If a fixed scale is applied to the tube, the correct height may be +obtained by applying a correction for capacity. A certain height of the +mercury is ascertained to be accurately measured by the scale, and should +be marked on the instrument as the <i>neutral point</i>. Above this point the +heights measured are all less, and below, all more, than they should be. +The ratio between the internal diameters of the tube and cistern (which +should also be stated on the instrument, as, for instance, capac. <span style="font-size: 0.8em;"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">50</span>) +supplies the data for finding the correction to be applied. This +correction is obviated by constructing the cistern so as to allow of the +surface of the mercury in it being adjustable to the commencement of the +fixed scale, as by Fortin’s or Negretti’s plan. It is also unnecessary in +barometers constructed on what is now called the “Kew method.” These will +all be detailed in their proper place. The tube, being fixed to the +cistern, may have a moveable scale applied to it. But such an arrangement +requires the utmost care and skill in observing, and is seldom seen except +in first-class Observatories.</p> + + +<div class="figright"><img src="images/fig_2tmb.jpg" alt="" /><br /><a href="images/fig_2.jpg"><small>Larger Image</small></a><br />Fig. 2.</div> + +<p><br /><b>3. Fortin’s Barometer.</b>—Fortin’s plan of constructing a barometer cistern +is shown in fig. 2. The cistern is formed of a glass cylinder, which +allows of the level of the mercury within being seen. The bottom of the +cylinder is made of sheep-skin or leather, like a bag, so as to allow of +being pushed up or lowered by means of a screw, D B, worked from beneath. +This screw moves through the bottom of a brass cylinder, C C, which is +fixed outside, and protects the glass cylinder containing the mercury. At +the top of the interior of the cistern is fixed a small piece of ivory, A, +the point of which<span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span> exactly coincides with the zero of the scale. This +screw and moveable cistern-bottom serve also to render the barometer +portable, by confining the mercury in the tube, and preventing its coming +into the cistern, which is thus made too small to receive it.</p> + +<div class="figleft"><img src="images/fig_3.jpg" alt="" /><br />Fig. 3.</div> + +<p class="center"><br />4. STANDARD BAROMETER.</p> + +<p>Fig. 3 represents a Standard Barometer on Fortin’s principle. The +barometer tube is enclosed and protected by a tube of brass extending +throughout its whole length; the upper portion of the brass tube has two +longitudinal openings opposite each other; on one side of the front +opening is the barometrical scale of English inches, divided to show, by +means of a vernier, <span style="font-size: 0.8em;"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">500</span>th of an inch; on the opposite side is sometimes +divided a scale of French millimetres, reading also by a vernier to <span style="font-size: 0.8em;"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">10</span>th +of a millimetre (see directions for reading the vernier, <a href="#Page_7">page 7</a>). A +thermometer, C, is attached to the frame, and divided to degrees, which +can be read to tenths; it is necessary for ascertaining the temperature of +the instrument, in order to correct the observed height of the barometer.</p> + +<p>As received by the observer, the barometer will consist of two parts, +packed separately for safety in carriage,—1st, the barometer tube and +cistern, filled with mercury, the brass tube, with its divided scale and +thermometer; and 2nd, a mahogany board, with bracket at top, and brass +ring with three adjusting screws at bottom.</p> + +<p><i>Directions for fixing the Barometer.</i>—In selecting a position for a +barometer, care should be taken to place it so that the sun cannot shine +upon it, and that it is not affected by direct heat from a fire. The +cistern should be from two to three feet above the ground, which will give +a height for observing convenient to most persons. A standard barometer +should be compared with an observatory standard of acknowledged accuracy, +to determine its index error; which, as such instruments are graduated by +micrometrical apparatus of great exactitude, will be constant for all +parts of the scale. It should be capable of turning on its axis by a +movement of the hand, so that little difficulty can ever be experienced in +obtaining a good light for observation. Having determined upon the +position in which to place the instrument, fix the mahogany board as +nearly vertical as possible, and ascertain if the barometer is perfect and +free<span class="pagenum"><a name="Page_5" id="Page_5">[Pg 5]</a></span> from air, in the following manner:—lower the screw at the bottom of +the cistern several turns, so that the mercury in the tube, when held +upright, may fall two or three inches from the top; then slightly incline +the instrument from the vertical position, and if the mercury in striking +the top elicit a sharp tap, the instrument is perfect. Supposing the +barometer to be in perfect condition, as it is almost sure to be, it is +next suspended on the brass bracket, its cistern passing through the ring +at bottom, and allowed to find its vertical position, after which it is +firmly clamped by means of the three thumb-screws.</p> + +<p><i>To Remove the Instrument when fixed to another Position.</i>—If it should +be necessary to remove the barometer,—first, by means of the adjusting +screw, drive the mercury to the top of the tube, turning it gently when it +is approaching the top, and cease directly any resistance is experienced; +next, remove from the upper bracket or socket; lift the instrument and +invert it, carrying it with its lower end upwards.</p> + +<p><i>Directions for taking an Observation.</i>—Before making an observation, the +mercury in the cistern must be raised or lowered by means of the +thumb-screw, F, until the ivory point, E, and its reflected image in the +mercury, D, are just in contact; the vernier is then moved by means of the +milled head, until its lower termination just excludes the light from the +top of the mercurial column; the reading is then taken by means of the +scale on the limb and the vernier. The vernier should be made to read +upward in all barometers, unless for a special object, as this arrangement +admits of the most exact setting. In observing, the eye should be placed +in a right line with the fore and back edges of the lower termination of +the vernier; and this line should be made to form a tangent to the apex of +the mercurial column. A small reflector placed behind the vernier and +moving with it, so as to assist in throwing the light through the back +slit of the brass frame on to the glass tube, is advantageous; and the +observer’s vision may be further assisted by the aid of a reading lens. +The object is, in these Standard Barometers, to obtain an exact reading, +which can only be done by having the eye, the fore part of the zero edge +of the vernier, the top of the mercurial column, and the back of the +vernier, in the same horizontal plane.</p> + +<p><i>Uniformity of Calibre.</i>—The diameter of that part of the tube through +which the oscillations of the mercury will take place is very carefully +examined to insure uniformity of calibre, and only those tubes are used +which are as nearly as possible of the same diameter throughout. The size +of the bore should be marked on the frame of the barometer in tenths and +hundredths of an inch. A correction due to capillary action, and depending +on the size of the tube, must be applied to the readings.</p> + + +<p><br /><b>5. Correction due to Capillarity.</b>—When an open tube of small bore is +plunged into mercury, the fluid will not rise to the same level inside as +it has outside.<span class="pagenum"><a name="Page_6" id="Page_6">[Pg 6]</a></span> Hence, the effect of capillary action is to depress the +mercurial column; and the more so the smaller the tube. The following +table gives the correction for tubes in ordinary use:—</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center"><i>Diameter of<br />tube.</i></td><td><span class="spacer"> </span></td> + <td align="center"><i>Depression, in<br />boiled tubes.</i></td><td><span class="spacer"> </span></td> + <td align="center"><i>Depression, in<br />unboiled tubes.</i></td></tr> +<tr><td align="center"><span class="smcaplc">INCH.</span></td><td> </td> + <td align="center"><span class="smcaplc">INCH.</span></td><td> </td> + <td align="center"><span class="smcaplc">INCH.</span></td></tr> +<tr><td align="center">0·60</td><td> </td> + <td align="center">0·002</td><td> </td> + <td align="center">0·004</td></tr> +<tr><td align="center">0·55</td><td> </td> + <td align="center">0·003</td><td> </td> + <td align="center">0·005</td></tr> +<tr><td align="center">0·50</td><td> </td> + <td align="center">0·003</td><td> </td> + <td align="center">0·007</td></tr> +<tr><td align="center">0·45</td><td> </td> + <td align="center">0·005</td><td> </td> + <td align="center">0·010</td></tr> +<tr><td align="center">0·40</td><td> </td> + <td align="center">0·007</td><td> </td> + <td align="center">0·015</td></tr> +<tr><td align="center">0·35</td><td> </td> + <td align="center">0·010</td><td> </td> + <td align="center">0·021</td></tr> +<tr><td align="center">0·15</td><td> </td> + <td align="center">0·044</td><td> </td> + <td align="center">0·029</td></tr> +<tr><td align="center">0·10</td><td> </td> + <td align="center">0·070</td><td> </td> + <td align="center">0·041</td></tr> +<tr><td align="center">0·30</td><td> </td> + <td align="center">0·014</td><td> </td> + <td align="center">0·058</td></tr> +<tr><td align="center">0·25</td><td> </td> + <td align="center">0·020</td><td> </td> + <td align="center">0·086</td></tr> +<tr><td align="center">0·20</td><td> </td> + <td align="center">0·029</td><td> </td> + <td align="center">0·140</td></tr></table> + +<p>This correction is always additive to the observed reading of the +barometer.</p> + + +<p><br /><b>6. Correction due to Temperature.</b>—In all kinds of mercurial barometers +attention must be given to the temperature of the mercury. As this metal +expands and contracts very much for variations of temperature, its density +alters correspondingly, and in consequence the height of the barometric +column also varies. To ascertain the temperature of the mercury, a +thermometer is placed near the tube, and is sometimes made to dip into the +mercury in the cistern. The freezing point of water, 32°F., is the +temperature to which all readings of barometers must be reduced, in order +to make them fairly comparable. The reduction may be effected by +calculation, but the practical method is by tables for the purpose; and +for these tables we refer the reader to the works mentioned at the end of +this book.</p> + + +<p><br /><b>7. Correction due to Height above the Half-tide Level.</b>—Further, in order +that barometrical observations generally may be made under similar +circumstances, the readings, corrected for capacity, capillarity, and +temperature, should be reduced to what they would be at the sea-level, by +adding a correction corresponding to the height above the mean level of +the sea, or of half-tide. For practical purposes of comparison with +barometric pressure at other localities, add one-tenth of an inch to the +reading for each hundred feet of elevation above the sea. For scientific +accuracy this will not suffice, but a correction must be obtained by means +of Schuckburg’s formula, or tables computed therefrom.</p> + +<div class="figleft">Fig. 4.<br /><img src="images/fig_4.jpg" alt="" /></div> + +<div class="figright">Fig. 5.<br /><img src="images/fig_5.jpg" alt="" /></div> + +<p><br /><b>8. The Barometer Vernier.</b>—The <i>vernier</i>, an invaluable contrivance for +measuring small spaces, was invented by Peter Vernier, about the year +1630. The barometer scale is divided into inches and tenths. The vernier +enables us to accurately subdivide the tenths into hundredths, and, in +first-class instruments, even<span class="pagenum"><a name="Page_7" id="Page_7">[Pg 7]</a></span> to thousandths of an inch. It consists of a +short scale made to pass along the graduated fixed scale by a sliding +motion, or preferably by a rack-and-pinion motion, the vernier being fixed +on the rack, which is moved by turning the milled head of the pinion. The +principle of the vernier, to whatever instrumental scale applied, is that +the divisions of the moveable scale are to those in an equal length of the +fixed scale in the proportion of two numbers which differ from each other +by unity.</p> + +<p>The scales of standard barometers are usually divided into half-tenths, or +·05, of an inch, as represented, in fig. 5, by AB. The vernier, CD, is +made equal in length to twenty-four of these divisions, and divided into +twenty-five equal parts; consequently one space on the scale is larger +than one on the vernier by the twenty-fifth part of ·05, which is ·002 +inch, so that such a vernier shows differences of ·002 inch. The vernier +of the figure reading upwards, the lower edge, D, will denote the top of +the barometer column; and is the zero of the vernier scale. In fig. 4, the +zero being in line exactly with 29 inches and five-tenths of the fixed +scale, the barometer reading would be 29·500 inches. It will be seen that +the vernier line, <i>a</i>, falls short of a division of the scale by, as we +have explained, ·002 inch; <i>b</i>, by ·004; <i>c</i>, by ·006; <i>d</i>, by ·008; and +the next line by one hundredth. If, then, the vernier be moved so as to +make <i>a</i> coincide with <i>z</i>, on the scale, it will have moved through ·002 +inch; and if 1 on the vernier be moved into line with <i>y</i> on the scale, +the space measured will be ·010. Hence, the figures 1, 2, 3, 4, 5 on the +vernier measure hundredths, and the intermediate lines even thousandths of +an inch. In fig. 5, the zero of the vernier is intermediate 29·65 and +29·70 on the scale. Passing the eye up the vernier and scale, the second +line above 3 is perceived to lie evenly with a line of the scale. This +gives ·03 and ·004 to add to 29·65, so that the actual reading is 29·684 +inches. It may happen that no line on the vernier <i>accurately</i> lies in the +same straight line with one on the scale; in such a case a doubt will +arise as to the selection of one from two equally coincident, and the +intermediate thousandth of an inch should be taken.</p> + +<p>For the ordinary purposes of the barometer as a “weather-glass,” such +minute measurement is not required. Hence, in household and marine +barometers the scale need only be divided to tenths, and the vernier +constructed to measure <span class="pagenum"><a name="Page_8" id="Page_8">[Pg 8]</a></span>hundredths of an inch. This is done by making the +vernier either 9 or 11-10ths of an inch long, and dividing it into ten +equal parts. The lines above the zero line are then numbered from 1 to 10; +sometimes the alternate divisions only are numbered, the intermediate +numbers being very readily inferred. Hence, if the first line of the +vernier agrees with one on the scale, the next must be out one-tenth of a +tenth, or ·01 of an inch from agreement with the next <i>scale</i> line; the +following vernier line must be ·02 out, and so on. Consequently, when the +vernier is set to the mercurial column, the difference shown by the +vernier from the tenth on the scale is the hundredths to be added to the +inches and tenths of the scale.</p> + +<p>A little practice will accustom a person to set and read any barometer +quickly; an important matter where accuracy is required, as the heat of +the body, or the hand, is very rapidly communicated to the instrument, and +may vitiate, to some extent, the observation.</p> + +<div class="figleft">Fig. 6.<br /><img src="images/fig_6.jpg" alt="" /></div> + +<p class="center"><br />9. SELF-COMPENSATING STANDARD BAROMETER.</p> + +<p>This barometer has been suggested to Messrs. Negretti and Zambra by +Wentworth Erk, Esq. It consists of a regular barometer; but attached to +the vernier is a double rack worked with one pinion, so that in setting or +adjusting the vernier in one position, the second rack moves in directly +the opposite direction, carrying along with it a plug or plunger the exact +size of the internal diameter of the tube dipping in the cistern, so that +whatever the displacement that has taken place in the cistern, owing to +the rise or fall of the mercury, it is exactly compensated by the plug +being more or less immersed in the mercury, so that no capacity correction +is required.</p> + +<p>A barometer on this principle is, however, no novelty, for at the Royal +Society’s room a very old instrument may be seen reading somewhat after +the same manner.</p> + +<p>Fig. 6 is an illustration of the appearance of this instrument. The +cistern is so constructed that the greatest amount of light is admitted to +the surface of the mercury.</p> + + +<p class="center"><br />10. BAROMETER WITH ELECTRICAL ADJUSTMENT.</p> + +<p>This barometer is useful to persons whose eyesight may be defective; and +is capable of being read off to greater accuracy than ordinary barometers, +as will be seen by the following description:—The barometer consists of +an upright tube dipping into a cistern, so contrived, that an up-and-down +movement, by means of a screw, can be imparted to it. In the top of the +tube a piece of platina wire is hermetically sealed. The cistern also has +a metallic connection, so that by means of<span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span> covered copper wires (in the +back of the frame) a circuit is established; another connection also +exists by means of a metallic point dipping into the cistern. The circuit, +however, can be cut off from this by means of a switch placed about midway +up the frame; on one side of the tube is placed a scale of inches; a small +circular vernier, divided into 100 parts, is connected with the dipping +point, and works at right angles with this scale.</p> + +<p>To set the instrument in action for taking an observation, a small battery +is connected by means of two small binding screws at the bottom of the +frame. The switch is turned upwards, thereby disconnecting the dipping +point; the cistern is then screwed up, so that the mercury in the tube is +brought into contact with the platina wire at the top; the instant this is +effected the magnetic needle seen on the barometer will be deflected. The +switch is now turned down; by so doing the connection with the upper wire +or platina is cut off, and established instead only between the dipping +point carrying the circular vernier and the bottom of the cistern; the +point is now screwed by means of the milled head until the needle is again +deflected. We may now be sure that the line on the circular vernier that +cuts the division on the scale is the exact height of the barometer. +Although the description here given may seem somewhat lengthy, the +operation itself is performed in less time than would be taken in reading +off an ordinary instrument.</p> + + +<p class="center"><br />11. PEDIMENT BAROMETERS.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center">Fig. 7.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 8.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 9.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 10.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 11.</td></tr> +<tr><td align="center"><img src="images/fig_7.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_8.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_9.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_10.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_11.jpg" alt="" /></td></tr></table> + +<p>These Barometers, generally for household purposes, are illustrated by +figs. 7 to 11.<span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span> They are intended chiefly for “weather glasses,” and are +manufactured to serve not only a useful, but an ornamental purpose as +well. They are usually framed in wood, such as mahogany, rosewood, ebony, +oak or walnut, and can be obtained either plain or handsomely and +elaborately carved and embellished, in a variety of designs, so as to be +suitable for private rooms, large halls, or public buildings. The scales +to the barometer and its attached thermometer may be ivory, porcelain, or +silvered metal. It is not desirable that the vernier should read nearer +than one-hundredth of an inch. Two verniers and scales may be fitted one +on either side of the mercurial column, so that one can denote the last +reading, and thus show at a glance the extent of rise or fall in the +interval. The scale and thermometer should be covered with plate glass. A +cheap instrument has an open face and plain frame, with sliding vernier +instead of rack-and-pinion motion. The barometer may or may not have a +moveable bottom to the cistern, with screw for the purpose of securing the +mercury for portability. The cistern should not, however, require +adjustment to a zero or fiducial point. It should be large enough to +contain the mercury, which falls from 31 to 27 inches, without any +appreciable error on the height read off on the scale.</p> + + +<p><br /><b>12. The Words on the Scale.</b>—The following words are usually engraved on +the scales of these barometers, although they are not now considered of so +much importance as formerly:—</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>At</td><td>31</td><td>inches</td><td><span class="spacer"> </span></td><td>Very dry.</td></tr> +<tr><td align="center">"</td><td>30·5</td><td align="center">"</td><td> </td><td>Settled fair.</td></tr> +<tr><td align="center">"</td><td>30</td><td align="center">"</td><td> </td><td>Fair.</td></tr> +<tr><td align="center">"</td><td>29·5</td><td align="center">"</td><td> </td><td>Changeable.</td></tr> +<tr><td align="center">"</td><td>29</td><td align="center">"</td><td> </td><td>Rain.</td></tr> +<tr><td align="center">"</td><td>28·5</td><td align="center">"</td><td> </td><td>Much rain.</td></tr> +<tr><td align="center">"</td><td>28</td><td align="center">"</td><td> </td><td>Stormy.</td></tr></table> + +<p>The French place upon their barometers a similar formula:—</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>At</td><td>785</td><td>millimètres</td><td><span class="spacer"> </span></td><td>Très-sec.</td></tr> +<tr><td align="center">"</td><td>776</td><td align="center">"</td><td> </td><td>Beau-fixe.</td></tr> +<tr><td align="center">"</td><td>767</td><td align="center">"</td><td> </td><td>Beau temps.</td></tr> +<tr><td align="center">"</td><td>758</td><td align="center">"</td><td> </td><td>Variable.</td></tr> +<tr><td align="center">"</td><td>749</td><td align="center">"</td><td> </td><td>Pluie ou vent.</td></tr> +<tr><td align="center">"</td><td>740</td><td align="center">"</td><td> </td><td>Grande pluie.</td></tr> +<tr><td align="center">"</td><td>731</td><td align="center">"</td><td> </td><td>Tempête.</td></tr></table> + +<p>Manufacturers of barometers have uniformly adopted these indications for +all countries, without regard to the elevation above the sea, or the +different geographical conditions; and as it can readily be shown that the +height and variations of the barometer are dependent on these, it follows +that barometers have furnished indications which, under many +circumstances, have been completely false. Even in this country, and near +the sea-level, storms are frequent with the barometer not below<span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span> 29; rain +is not uncommon with the glass at 30; even fine weather sometimes occurs +with a low pressure; while it is evident that at an elevation of a few +thousand feet the mercury would never rise to 30 inches; hence, according +to the scale, there should never be fair weather there. If tempests +happened as seldom in our latitude as the barometer gets down to 28 +inches, the maritime portion of the community at least would be happy +indeed. These words have long been ridiculed by persons acquainted with +the causes of the barometric fluctuations; nevertheless opticians continue +to place them on the scales, evidently only because they appear to add to +the importance of the instrument in the eyes of those who have not learned +their general inutility. In different regions of the world, the +indications of the barometer are modified by the conditions peculiar to +the geographical position and elevation above the sea, and it is necessary +to take account of these in any attempt to found rules of general utility +in connection with the barometer as a weather guide. All that can be said +in favour of these words is, that within a few hundred feet of the +sea-level, when the column rises or falls gradually during two or three +days towards “Fair” or “Rain,” the indications they afford of the coming +weather are generally extremely probable; but when the variations are +quick, upward or downward, they presage unsettled or stormy weather.</p> + +<p>Admiral FitzRoy writes:—“The words on the scales of barometers should not +be so much regarded, for weather indications, as the rising or falling of +the mercury; for if it stands at <i>Changeable</i>, and then rises a little +towards <i>Fair</i>, it presages a change of wind or weather, though not so +great as if the mercury had risen higher; and, on the contrary, if the +mercury stands above <i>Fair</i> and falls, it presages a change, though not to +so great a degree as if it had stood lower; besides which, the direction +and force of wind are not in any way noticed. It is not from the point at +which the mercury stands that we are alone to form a judgment of the state +of the weather, but from its <i>rising</i> or <i>falling</i>; and from the movements +of immediately preceding days as well as hours, keeping in mind effects of +change of <i>direction</i> and dryness, or moisture, as well as alteration of +force or strength of wind.”<small><a name="f1.1" id="f1.1" href="#f1">[1]</a></small></p> + + +<p><br /><b>13. Correction due to Capacity of Cistern.</b>—These barometers, having no +adjustment for the zero of the scale, require a correction for the varying +level of the mercury in the cistern, when the observations are required +for strict comparison with other barometric observations, or when they are +registered for scientific purposes; but for the common purpose of +predicting the weather, this correction is unnecessary. The neutral point, +and the ratio of the bore of the tube to the diameter of the cistern, must +be known (see <a href="#Page_3">p. 3</a>). Then the capacity correction, as it is termed, is +found as follows:—Take the fractional part, expressed by the capacity +ratio, of the difference between the observed reading and the height of +the neutral point; then, if the mercury stand <i>below</i> the neutral point, +<i>subtract</i> this result from the reading; if it stand <i>above</i>, <i>add</i> it to +the reading.</p> + +<p><span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span>For example, suppose the neutral point to be 29·95 inches, and the +capacity ratio <span style="font-size: 0.8em;"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">50</span>, required the correction when the barometer reads +30·78.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>Here</td> + <td><span class="spacer"> </span></td> + <td colspan="2">30·78 - 29·95</td> + <td>=</td><td>0·83</td></tr> +<tr><td rowspan="2">Correction</td> + <td> </td> + <td rowspan="2" valign="middle">=</td> + <td align="center" class="botbor">0·83</td> + <td rowspan="2">=</td><td rowspan="2">+0·02</td><td rowspan="2">nearly.</td></tr> +<tr><td> </td><td align="center">50</td></tr> +<tr><td>Scale reading</td><td colspan="4"> </td><td class="botbor">30·78</td></tr> +<tr><td>Correct reading</td><td colspan="4"> </td><td class="botbor2">30·80</td></tr></table> + +<p>Of course the correction could as easily be found to three decimal places, +if desirable. It is evident that the correction is more important the +greater the distance of the top of the mercury from the neutral point.</p> + + +<p class="center"><br />14. PUBLIC BAROMETERS.</p> + +<p>Since the increased attention paid to the signs of forthcoming weather of +late years, and the good which has resulted therefrom to farmers, +gardeners, civil engineers, miners, fishermen, and mariners generally, by +forewarning of impending wet or stormy weather, the desirability of having +good barometers exposed in public localities has become evident.</p> + +<p>Barometers may now be seen attached to drinking fountains, properly +protected, and are frequently consulted by the passers-by. But it is among +those whose lives are endangered by sudden changes in the weather, +fishermen especially, that the warning monitor is most urgently required. +Many poor fishing villages and towns have therefore been provided by the +Board of Trade, at the public expense, and through the humane effort of +Admiral FitzRoy, with first-class barometers, each fixed in a conspicuous +position, so as to be easily accessible to all who desire to consult it. +Following this example, the Royal National Life Boat Institution has +supplied each of its stations with a similar storm warner; the Duke of +Northumberland and the British Meteorological Society have erected several +on the coast of Northumberland; and many other individuals have presented +barometers to maritime places with which they are connected.</p> + +<p>These barometers have all been manufactured by Messrs. Negretti and +Zambra. The form given to the instrument seems well adapted for public +purposes.</p> + + +<div class="figleft">Fig. 12.<br /><img src="images/fig_12.jpg" alt="" /></div> + +<p><br /><b>15. Fishery or Sea-coast Barometers.</b>—Fig. 12 gives a representation of +these coast and fishery barometers. The frame is of<span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span> solid oak, firmly +screwed together. The scales are very legibly engraved on porcelain by +Negretti and Zambra’s patent process. The thermometer is large, and easily +read; and as this instrument is exposed, it will indicate the actual +temperature sufficiently for practical purposes. The barometer tube is +three-tenths of an inch in diameter of bore, exhibiting a good column of +mercury; and the cistern is of such capacity, in relation to the tube, +that the change of height in the surface of the mercury in the cistern +corresponding to a change of height of three inches of mercury in the +tube, is less than one-hundredth of an inch, and therefore, as the +readings are only to be made to this degree of accuracy, this small error +is of no importance. The cistern is made of boxwood, which is sufficiently +porous to allow the atmosphere to influence the mercurial column; but the +top is plugged with porous cane, to admit of free and certain play.</p> + + +<p><br /><b>16. Admiral FitzRoy’s Scale Words.</b>—The directions given on the scales of +these barometers were drawn up by Admiral FitzRoy, F.R.S. They appear to +be founded on the following considerations:—</p> + +<p>Supposing a compass diagram, with the principal points laid down, the N.E. +is the wind for which the barometer stands highest; for the S.W. wind it +is lowest. This is found to be so in the great majority of cases; but +there are exceptions to this, as to all rules. The N.E. and S.W. may +therefore be regarded as the poles of the winds, being opposite each +other. When the wind veers from the S.W. through W. and N. to N.E., the +barometer gradually rises; on the contrary, when the wind veers from N.E. +and E. to S.E., S. and S.W., the mercury falls. A similar curious law +exists in relation to the veering of the wind, and the action of the +thermometer. As the wind veers from the S.W. to W. and N., the thermometer +falls; as it veers from N.E. to E. and S., it rises, because the wind gets +from a colder to a warmer quarter. The polar winds are cold, dry, and +heavy. Those from the equatorial regions are warm, moist, and +comparatively light.</p> + +<p>These laws have been clearly developed and expressed by Professor Dové in +his work on the “Law of Storms.” The warm winds of Europe are those which +bring the greatest quantity of rain, as they blow from the ocean, and come +heavily laden with moisture. The cold winds, besides containing less +moisture, blow more from the land. The weight of the vapour of the warm +winds tends to raise the barometric column; but, at the same time, the +increased dilatation of the air tends to lower it. This latter influence +being the stronger, the barometer always falls for these winds; and in +regions where they traverse a large extent of land, retain their heat, and +become necessarily very dry, the fall in the barometer will be greater. +Admiral FitzRoy’s words for the scales of barometers for use in northern +latitudes, then, are as follows:—</p> + +<p><span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span></p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center"><i>RISE.</i></td><td><span class="spacer"> </span></td><td align="center"><i>FALL.</i></td></tr> +<tr><td align="center">FOR</td><td> </td><td align="center">FOR</td></tr> +<tr><td align="center"><span class="smcap">N. Ely.</span></td><td> </td><td align="center"><span class="smcap">S. Wly.</span></td></tr> +<tr><td align="center">NW.—N.—E.</td><td> </td><td align="center">SE.—S.—W.</td></tr> +<tr><td align="center">DRY</td><td> </td><td align="center">WET</td></tr> +<tr><td align="center">OR</td><td> </td><td align="center">OR</td></tr> +<tr><td align="center">LESS</td><td> </td><td align="center">MORE</td></tr> +<tr><td align="center">WIND.</td><td> </td><td align="center">WIND.</td></tr> +<tr><td align="center">———</td><td> </td><td align="center">———</td></tr> +<tr><td align="center">EXCEPT</td><td> </td><td align="center">EXCEPT</td></tr> +<tr><td align="center">WET FROM</td><td> </td><td align="center">WET FROM</td></tr> +<tr><td align="center"><span class="smcap">N. Ed.</span></td><td> </td><td align="center"><span class="smcap">N. Ed.</span></td></tr> +<tr><td align="center">———</td><td> </td><td align="center">———</td></tr> +<tr><td>Long foretold, long last;<br />Short notice, soon past.</td><td> </td><td>First rise after low,<br />Foretells stronger blow.</td></tr></table> + +<p>It will be perceived that the exception in each case applies to N.E. +winds. The barometer may fall with north-easterly winds, but they will be +violent and accompanied with rain, hail, or snow; again, it will rise with +these winds accompanied with rain, when they are light, and bring only +little rain. It rises, however, highest with the dry and light N.E. winds.</p> + +<p>These directions are very practically useful; they provide for +geographical position—also for elevation above the sea—since they are +not appended to any particular height of the column. They are suited to +the northern hemisphere generally, as well as around the British Isles. +The same directions are adapted to the southern hemisphere, by simply +substituting for the letter N the letter S, reading south for north, and +<i>vice versa</i>. South of the equator the cold winds come from the south; the +warm, from the north. The S.E. wind in the southern hemisphere corresponds +to the N.E. in the northern. The laws there are, while the wind veers from +S.E. through E. to N. and N.W., the barometer falls and the thermometer +rises. As the wind veers from N.W. through W. and S. to S.E., the +barometer rises and the thermometer falls.</p> + + +<p><br /><b>17. Instructions for the Sea-coast Barometer.</b>—The directions for fixing +the barometer, and making it portable when it has to be removed, should be +attended to carefully. The barometer should be suspended against a frame +or piece of wood, so that light may be seen <i>through</i> the tube. Otherwise +a piece of paper, or a <i>white place</i>, should be behind the upper or <i>scale +part</i> of the <i>tube</i>.</p> + +<p>When suspended on a hook, or stout nail, apply the milled-head key (which +will be found just below the scales) to the square brass pin at the lower +end of the instrument, and turn <i>gently</i> toward the left hand till the +screw stops; then take off the key and replace it for use, near the scale, +as it was before. The cistern bottom being thus <i>let down</i>, the mercury +will sink to its proper level quickly.</p> + +<p>In removing this barometer it is necessary to <i>slope it gradually</i>, till +the mercury<span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span> is at the top of the tube, and then, with the instrument +reversed, to screw up the cistern bottom, or bag, by the key, used +<i>gently</i>, till it stops. It will then be portable, and may be carried with +the <i>cistern</i> end <i>upwards</i>, or lying flat; but it must not be jarred, or +receive a concussion.</p> + + +<p><br /><b>18. French Sea-coast Barometer.</b>—The French have imitated this form of +barometer for coast service, and have translated Admiral FitzRoy’s +indications for the scale as follows:—</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td colspan="3" align="center"><span class="smcaplc">LA</span></td><td><span class="spacer"> </span></td> + <td colspan="3" align="center"><span class="smcaplc">LA</span></td></tr> +<tr><td colspan="3" align="center">HAUSSE</td><td> </td> + <td colspan="3" align="center">BAISSE</td></tr> +<tr><td colspan="3" align="center"><span class="smcaplc">INDIQUE.</span></td><td> </td> + <td colspan="3" align="center"><span class="smcaplc">INDIQUE.</span></td></tr> +<tr><td colspan="3" align="center">———</td><td> </td> + <td colspan="3" align="center">———</td></tr> +<tr><td colspan="3" align="center"><span class="smcap">des Vents de la</span></td><td> </td> + <td colspan="3" align="center"><span class="smcap">des Vents de la</span></td></tr> +<tr><td colspan="3" align="center"><span class="smcaplc">PARTIE DU</span></td><td> </td> + <td colspan="3" align="center"><span class="smcaplc">PARTIE DU</span></td></tr> +<tr><td colspan="3" align="center">N.E.</td><td> </td> + <td colspan="3" align="center">S.O.</td></tr> +<tr><td rowspan="2" align="center"><span class="giant">(</span></td><td align="center"><span class="smcap">du N.O.</span> á l’E</td><td rowspan="2" align="center"><span class="giant">)</span></td> + <td> </td> + <td rowspan="2" align="center"><span class="giant">(</span></td><td align="center"><span class="smcap">du S.E.</span> á l’O.</td><td rowspan="2" align="center"><span class="giant">)</span></td></tr> +<tr><td align="center"><span class="smcap">par le NORD</span>.</td><td> </td><td align="center"><span class="smcap">par le SUD</span>.</td></tr> + +<tr><td colspan="3" align="center"><span class="smcaplc">DE LA</span></td><td> </td> + <td colspan="3" align="center"><span class="smcaplc">DE</span></td></tr> +<tr><td colspan="3" align="center">SÉCHERESSE.</td><td> </td> + <td colspan="3" align="center">L’HUMIDITÉ.</td></tr> +<tr><td colspan="3" align="center">———</td><td> </td> + <td colspan="3" align="center">———</td></tr> +<tr><td colspan="3" align="center"><span class="smcap">un VENT</span></td><td> </td> + <td colspan="3" align="center"><span class="smcap">un VENT</span></td></tr> +<tr><td colspan="3" align="center"><span class="smcaplc">PLUS FAIBLE</span></td><td> </td> + <td colspan="3" align="center"><span class="smcaplc">PLUS FORT</span></td></tr> +<tr><td colspan="3" align="center"><span class="smcaplc">EXCEPTÉ S’IL PLEUT</span></td><td> </td> + <td colspan="3" align="center"><span class="smcaplc">EXCEPTÉ S’IL PLEUT</span></td></tr> +<tr><td colspan="3" align="center"><span class="smcaplc">AVEC DE FORTES BRISES</span></td><td> </td> + <td colspan="3" align="center"><span class="smcaplc">AVEC DE PETITES BRISES</span></td></tr> +<tr><td colspan="3" align="center"><span class="smcap">du N.E.</span></td><td> </td> + <td colspan="3" align="center"><span class="smcap">du N.E.</span></td></tr> +<tr><td colspan="3" align="center">———</td><td> </td> + <td colspan="3" align="center">———</td></tr> +<tr><td colspan="3">Mouvements lents,<br />Temps durable.<br /><span style="margin-left: 2em;">———</span><br />Mouvements rapides,<br />Temps variable.</td><td> </td> + <td colspan="3" align="center">Le commencement<br />de la hausse,<br />après une grande<br />baisse présage<br />un Vent violent.</td></tr></table> + + +<div class="figleft">Fig. 13.<br /><img src="images/fig_13.jpg" alt="" /></div> + +<div class="figright">Fig. 14.<br /><img src="images/fig_14.jpg" alt="" /></div> + +<p class="center"><br />MARINE BAROMETERS.</p> + +<p><b>19. The Common Form.</b>—The barometer is of great use to the mariner, who, +by using it as a “weather glass,” is enabled to foresee and prepare for +sudden changes in the weather. For marine purposes, the lower portion of +the glass tube of the barometer must be contracted to a fine bore, to +prevent oscillation in the mercurial column, which would otherwise be +occasioned by the movements of the ship. This tube is cemented to the +cistern, which is made of boxwood, and has a moveable leathern bottom, for +the purpose of rendering the instrument portable,<span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span> by screwing up the +mercury compactly in the tube. The tube is enclosed in a mahogany frame, +which admits of a variety of style in shape, finish, and display, to meet +the different fancies and means of purchasers. The frame is generally +enlarged at the upper part to receive the scales and the attached +thermometer, which are covered by plate glass. The cistern is encased in +brass for protection, the bottom portion unscrewing to give access to the +portable screw beneath the cistern. Figs. 13 and 14 illustrate this form +of barometer. Marine barometers require to be suspended, so that they may +remain in a vertical position under the changeable positions of a vessel +at sea. To effect this they are suspended in gimbals by a brass arm. The +gimbals consist of a loose ring fastened by thumb-screws to the middle +part of the frame of the barometer, in front and back. The forked end of +the arm supports this ring at the sides, also by the aid of thumb-screws. +Hence the superior weight of the cistern end is always sufficient to cause +the instrument to move on its bearing screws, so as always to maintain a +perpendicular position; in fact, it is so delicately held that it yields +to the slightest disturbance in any direction. The other end of the arm is +attached to a stout plate, having holes for screws, or fitted to slip into +a staple or bracket, by which it may be fixed to any part of the cabin of +a ship; the arm is hinged to the plate, for the purpose of turning the arm +and barometer up whenever it is desirable.</p> + +<p>Other forms of barometer (to be immediately described) have superseded +this in the British Marine, but the French still give the preference to +the wooden frames. They think the barometer can be more securely mounted +in wood, is more portable, and less liable to be broken by a sudden +concussion than if fitted in a metal frame. The English deem the ordinary +wooden barometers not sufficiently accurate, owing to the irregular +expansion of wood, arising from its hygrometric properties. Some of the +English opticians have shown that very portable, and really accurate +barometers can be made in brass frames, and therefore the preference is +now given to this latter material.</p> + + +<p><br /><b>20. The Kew Marine Barometer.</b>—The form of barometer so-called, is that +recommended by the Congress of Brussels, held in 1853, for the purpose of +devising a systematic plan of promoting meteorological observations at +sea.</p> + +<p>The materials employed in its construction are mercury, glass, iron, and +brass. The upper part of the tube is carefully calibrated to ensure +uniformity of bore, as this is a point upon which the accuracy of the +instrument to some extent depends. At sea, the barometer has never been +known to stand above 31 inches, nor below 27. These extremes have been +attained with instruments of undoubted accuracy, but they are quite +exceptional. It is not necessary, therefore, to carry the scales of marine +barometers beyond these limits, but they should not be made shorter. If +the vernier is adjusted to read upward, the scale should extend to 32 +inches, to allow room for the vernier to be set to 31 inches at least. +Cases have occurred in which this could not be done, and rare, but +valuable observations have been lost in consequence. If the scale part of +the tube be not uniform in bore, the index error<span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span> will be irregular +throughout the scale. Whether the bore of the rest of the tube varies in +diameter, is of no moment. From two to three inches below the measured +part, the bore is contracted very much, to prevent the pulsations in the +mercurial column—called “pumping”—which, otherwise, would occur at sea +from the motion of the ship. In ordinary marine barometers, this +contraction extends to the end of the tube. Below the contracted part is +inserted a pipette—or Gay Lussac air-trap—which is a little elongated +funnel with the point downwards. Its object is to arrest any air that may +work in between the glass and the mercury. The bubble of air lodges at the +shoulder, and can go up no farther. It is one of those simple contrivances +which turn out remarkably useful. If any air gets into the tube, it does +not get to the top, and therefore does not vitiate the performance of the +barometer; for the mercury itself works up and down through the funnel. +Below this, the tube should not be unnecessarily contracted.</p> + +<div class="figright">Fig. 15.<br /><img src="images/fig_15.jpg" alt="" /></div> + +<p>The open end of the tube is fixed into an iron cylinder, which forms the +cistern of the barometer. Iron has no action upon mercury, and is +therefore used instead of any other metal. One or two holes are made in +the top of the cistern, which are covered on the inside with strong +sheep-skin leather, so as to be impervious to mercury, but sufficiently +porous for the outer air to act upon the column. The cistern is of +capacity sufficient to receive the mercury which falls out of the tube +until the column stands lower than the scale reads; and when the tube is +completely full, there is enough mercury to cover the extremity so as to +prevent access of air. There is no screw required for screwing up the +mercury.</p> + +<p>The glass tube thus secured to the cistern is protected by a brass tubular +frame, into which the iron cistern fits and screws compactly. Cork is used +to form bearings for the tube. A few inches above the cistern is placed +the attached thermometer. Its bulb is enclosed in the frame, so as to be +equally affected by heat with the barometric column. The upper end of the +frame is fitted with a cap which screws on, and embraces a glass shield +which rests in a gallery formed on the frame below the scale, and serves +to protect the silvered scale, as well as the inner tube, from dust and +damp. A ring, moveable in a collar fixed on the frame above the centre of +gravity of the instrument, is attached to gimbals, and the whole is +supported by a brass arm in the usual manner; so that the instrument can +be moved round its axis to bring any source of light upon it, and will +remain vertical in all positions of the ship. The vernier reads to +five-hundredths of an inch. No words are placed upon the scale, as the old +formulary was deemed misleading. The vernier can be set with great +exactness, as light is admitted to the top of the<span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span> mercury by a front and +a back slit in the frame. The lower edge of the vernier should be brought +to the top of the mercury, so as just to shut out the light.</p> + +<p>It is evident that this form of barometer must be more reliable in its +indications than those in wooden frames. The graduations can be accurately +made, and they will be affected only by well-known alterations due to +temperature. Some think the tube is too firmly held, and therefore liable +to be broken by concussion more readily than that of an inferior +instrument. This, however, appears a necessary consequence of greater +exactness. It is an exceedingly good portable instrument, and can be put +up and taken down very readily. These barometers are preferred to marine +barometers in wood, wherever they have been used. In merchant ships, and +under careful treatment, they have been found very durable. They may be +sent with safety by railway, packed carefully in a wooden box.</p> + +<p><i>Directions for Packing.</i>—In removing this barometer it is necessary to +slope it gradually till the mercury reaches the top of the tube. It is +then portable, if carried cistern end upwards or lying flat. If carried +otherwise, it will very probably be broken by the jerking motion of the +heavy mercury in the glass tube. Of course it must not be jarred, or +receive concussion.</p> + +<p><i>Position for Marine Barometer.</i>—Admiral FitzRoy, to whose valuable +papers we are much indebted, writes in his “Barometer Manual”:—“It is +desirable to place the barometer in such a position as not to be in danger +of a side blow, and also sufficiently far from the deck above to allow for +the spring of the metal arm in cases of sudden movements of the ship.</p> + +<p>“If there is risk of the instrument striking anywhere when the vessel is +much heeled, it will be desirable to put some soft padding on that place, +or to check movement in that direction by a light elastic cord; in fixing +which, attention must be paid to have it acting only where risk of a blow +begins, not interfering otherwise with the free swing of the instrument: a +very light cord attached above, when possible, will be least likely to +interfere injuriously.”</p> + + +<p><br /><b>21. Method of verifying Marine and other Barometers.</b>—“In nearly all the +barometers which had been employed at sea till recently the index +correction varied through the range of scale readings, in proportion to +the difference of capacity between the cistern and the tube. To find the +index correction for a land barometer, comparison with a standard, at any +part of the scale at which the mercury may happen to be, is generally +considered sufficient. To test the marine barometer is a work of much more +time, since it is necessary to find the correction for scale readings at +about each half inch throughout the range of atmospheric pressure to which +it may be exposed; and it becomes necessary to have recourse to artificial +means of changing the pressure of the atmosphere on the surface of the +mercury in the cistern.</p> + +<p>“The barometers to be thus tested are placed, together with a standard, in +an air-tight chamber, to which an air-pump is applied, so that, by +partially exhausting the air, the standard can be made to read much lower +than the lowest pressure to<span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span> which marine barometers are likely to be +exposed; and by compressing the air it can be made to read higher than the +mercury ever stands at the level of the sea. The tube of the standard is +contracted similarly to that of the marine barometer, but a provision is +made for adjusting the mercury in its cistern to the zero point. Glass +windows are inserted in the upper part of the iron air-chamber, through +which the scales of the barometers may be seen; but as the verniers cannot +be moved in the usual way from outside the chamber, a provision is made +for reading the height of the mercury independent of the verniers attached +to the scales of the respective barometers. At a distance of some five or +six feet from the air-tight chamber a vertical scale is fixed. The +divisions on this scale correspond exactly with those on the tube of the +standard barometer. A vernier and telescope are made to slide on the scale +by means of a rack and pinion. The telescope has two horizontal wires, one +fixed and the other moveable by a micrometer screw, so that the difference +between the height of the column of mercury and the nearest division on +the scale of the standard, and also of all the other barometers placed by +the side of it for comparison, can be measured either with the vertical +scale and vernier or the micrometer wire. The means are thus possessed of +testing barometers for index error in any part of the scale, through the +whole range of atmospheric pressure to which they are likely to be +exposed; and the usual practice is to test them at every half inch from +27·5 to 31 inches.</p> + +<p>“In this way barometers of various other descriptions have been tested, +and some errors found to be so large that a few barometers read half an +inch and upwards too high, while others read as much too low. In some +cases those which were correct in one part of the scale were found to be +from half an inch to an inch wrong in other parts. These barometers were +of an old and ordinary, not to say inferior, construction. In some the +mercury would not descend lower than about 29 inches, owing to a fault +very general in the construction of many common barometers till lately in +frequent use:—the <i>cistern was not large enough</i> to hold the mercury +which descended from the tube in a <i>low atmospheric pressure</i>.</p> + +<p>“When used on shore, this contraction of the tube causes the marine +barometer to be <i>sometimes</i> a little behind an ordinary land barometer, +the tube of which is not contracted. The amount varies according to the +rate at which the mercury is rising or falling, and ranges from 0·00 to +0·02 of an inch. As the motion of the ship at sea causes the mercury to +pass more rapidly through the contracted tube, the readings are almost the +same there as they would be if the tube were not contracted, and in no +case do they differ enough to be of importance in maritime use.”</p> + +<p>The cistern of this marine barometer is generally made an inch and a +quarter in diameter, and the scale part of the tube a quarter of an inch +in bore. The inches on the scale, instead of being true, are shortened by +·04 of an inch, in order to avoid the necessity of applying a correction +due to the difference of capacity of the tube and cistern. This is done +with much perfection, and the errors of the instruments, when compared +with a standard by the apparatus used at Kew and<span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span> Liverpool Observatories, +are determined to the thousandth of an inch, and are invariably very +uniform and small. The error so determined includes the correction due to +capillarity, capacity, and error of graduation, and forms a constant +correction, so that only one variable correction, that due to temperature, +need be applied, when the barometer is suspended near the water line of +the ship, to make the observations comparable with others. With all the +advantages of this barometer, however, it has recently been superseded, to +some extent, because it was found to require more care than could +ordinarily be expected to be given to it by the commander of a ship. +Seamen do not exactly understand the value of such nice accuracy as the +thousandth part of an inch, but prefer an instrument that reads only to a +hundredth part.</p> + + +<p class="center"><br />22. THE FITZROY MARINE BAROMETER.</p> + +<p>Admiral FitzRoy deemed it desirable to construct a form of barometer as +practically useful as possible for marine purposes. One that should be +less delicate in structure than the Kew barometer, and not so finely +graduated. One that could be set at a glance and read easily; that would +be more likely to bear the common shocks unavoidable in a ship of war. +Accordingly, the Admiral has devised a barometer, which he has thus +described:—</p> + +<p>“This marine barometer, for Her Majesty’s service, is adapted to <i>general</i> +purposes.</p> + +<p>“It differs from barometers hitherto made in points of detail, rather than +principle:—1. The glass tube is packed with vulcanised india-rubber, +which checks vibration from concussion; but does not hold it rigidly, or +prevent expansion. 2. It does not oscillate (or pump), though extremely +sensitive. 3. The scale is porcelain, <i>very legible</i>, and not liable to +change. 4. There is no iron anywhere (<i>to rust</i>). 5. Every part can be +unscrewed, examined, or cleaned, by any careful person. 6. There is a +<i>spare</i> tube, fixed in a cistern, filled with boiled mercury, and <i>marked</i> +for adjustment in this, or <i>any similar</i> instrument.</p> + +<p>“These barometers are graduated to hundredths, and they will be found +accurate to <i>that</i> degree, namely the second decimal of an inch.</p> + +<p>“They are packed with vulcanised caoutchouc, in order that (by this, and +by a peculiar strength of glass tube) guns may be fired near these +instruments without causing injury to them by ordinary concussion.</p> + +<p>“It is hoped that all such instruments, for the public service at sea, +will be quite similar, so that any spare tube will fit <i>any</i> barometer.</p> + +<div class="figright">Fig. 16.<br /><img src="images/fig_16.jpg" alt="" /></div> + +<p>“<i>To Shift a Tube.</i>—Incline the barometer slowly, and then take it down, +after allowing the mercury to fill the upper part. Lay the instrument on a +table, unscrew the outer cap at the joining just below the cistern swell, +then unscrew the tube <i>and</i> cistern, by turning the cistern gently, +against the sun, or to <i>the left</i>, and draw out the tube very carefully +<i>without bending it in the least</i>, <i>turning</i> it a little, if required, as +moved. Then insert the new tube very cautiously, screw in, and adjust to +the<span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span> diamond-cut mark for 27 inches. Attach the cap, and suspend the +barometer for use.</p> + +<p>“If the mercury does not immediately quit the top of the tube, tap the +cistern end rather sharply. In a well-boiled tube, with a good vacuum, the +mercury hangs, at times, so adhesively as to deceive, by causing a +supposition of some defect.</p> + +<p>“In about ten minutes the mercurial column should be nearly right; but as +local temperature affects the brass, as well as the mercury, slowly and +unequally, it may be well to defer any <i>exact comparisons with other +instruments</i> for some few hours.”</p> + +<p>Messrs. Negretti and Zambra are the makers of these barometers for the +Royal Navy. Fig. 16 is an illustration.</p> + +<p>The tube is fixed to a boxwood cistern, which is plugged with very porous +cane at the top, to allow of the ready influence of a variation in +atmospheric pressure upon the mercury. Round the neck of the cistern is +formed a brass ring, with a screw thread on its circumference. This screws +into the frame, and a mark on the tube is to be adjusted to 27 inches on +the scale, the cistern covering screwed on, and the instrument is ready to +suspend. The frame and all the fittings are brass, without any iron +whatever; because the contact of the two metals produces a galvanic +action, which is objectionable. The spare tube is fitted with +india-rubber, and ready at any time to replace the one in the frame. The +ease with which a tube can be replaced when broken is an excellent feature +of the instrument. The spare tube is carefully stowed in a box, which can +also receive the complete instrument when not in use. All the parts are +made to a definite gauge; the frames are, therefore, all as nearly as +possible similar to each other, and the tubes—like rifle bullets—are +adjustible to any frame. If, then, the tube in use gets broken, the +captain can replace it by the other; but, as it is securely packed with +india-rubber, there is very little liability of its being broken by fair +usage. Every person who knows the importance of the barometer on board +ship, will acknowledge that the supplementary tube is a decided +improvement. Many instruments of this description are afloat in the Royal +Navy, and in a short time it may be expected that all the frames and tubes +of barometers in the public service at sea will be similar in size and +character; so that should a captain have the misfortune to get both his +tubes broken, he would be able to borrow another from any ship he fell in +with that had one to spare, which would be perfectly accurate, because it +would have been verified before it was sent out.</p> + + +<p><br /><b>23. Admiral FitzRoy’s Words for the Scale.</b>—The graduation of inches and +decimals are placed in this barometer on the right-hand side of the tube; +and on a<span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span> similar piece of porcelain, on the left-hand, are engraved, as +legibly as they are expressed succinctly, the following words, of +universal application in the interpretation of the barometer movements:—</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center"><i>RISE</i></td><td><span class="spacer"> </span></td> + <td align="center"><i>FALL</i></td></tr> +<tr><td align="center"><span class="smcaplc">FOR</span></td><td> </td> + <td align="center"><span class="smcaplc">FOR</span></td></tr> +<tr><td align="center">COLD</td><td> </td> + <td align="center">WARM</td></tr> +<tr><td align="center">DRY</td><td> </td> + <td align="center">WET</td></tr> +<tr><td align="center"><span class="smcaplc">OR</span></td><td> </td> + <td align="center"><span class="smcaplc">OR</span></td></tr> +<tr><td align="center">LESS</td><td> </td> + <td align="center">MORE</td></tr> +<tr><td align="center">WIND.</td><td> </td> + <td align="center">WIND.</td></tr> +<tr><td align="center">———</td><td> </td> + <td align="center">———</td></tr> +<tr><td align="center"><span class="smcaplc">EXCEPT</span></td><td> </td> + <td align="center"><span class="smcaplc">EXCEPT</span></td></tr> +<tr><td align="center"><span class="smcaplc">WET FROM</span></td><td> </td> + <td align="center"><span class="smcaplc">WET FROM</span></td></tr> +<tr><td align="center"><span class="smcaplc">COOLER SIDE.</span></td><td> </td> + <td align="center"><span class="smcaplc">COOLER SIDE.</span></td></tr></table> + +<p>Reverting to the explanation of the words on the “Coast” barometers (at +<a href="#Page_14">page 14</a>), and comparing and considering them as given for northern +latitudes, and as they must be altered for southern latitudes, it will be +perceived, that for all <i>cold</i> winds the barometer rises; and falls for +<i>warm</i> winds. The mercury also falls for <i>increased</i> strength of wind; and +rises as the wind <i>lulls</i>. Likewise before or with rain the column of +mercury falls; but it rises with fine dry weather. Putting these facts +together, and substituting for the points of the compass the terms “cold” +and “warm,” the appropriateness of the words on the scale of this +barometer is readily perceived. These concise and practical indications of +the movements in the barometer are applicable for instruments intended for +use in any region of the world, and are in perfect accordance with the +laws of winds and weather deduced by Dové and other meteorologists. There +is nothing objectionable in them, and being founded upon experience and +the deductions made from numerous recorded observations of the weather in +all parts of the world, as well as confirmed by the theories of science, +they may consequently be considered as generally reliable. They involve no +conjecture, but express succinctly scientific principles.</p> + + +<p><br /><b>24. Trials of the FitzRoy Marine Barometer under Fire of Guns.</b>—Some of +the first barometers made by Messrs. Negretti and Zambra on Admiral +FitzRoy’s principle were severely tried under the heaviest naval gun +firing, on board H.M.S. <i>Excellent</i>; and under all the circumstances, they +withstood the concussion. The purpose of the trials was “to ascertain +whether the <i>vulcanized india-rubber packing</i> round the glass tube of a +<i>new marine barometer</i> did check the vibration caused by firing, and +whether guns might be fired close to these instruments without causing +injury to them.” In the first and second series of experiments, a marine +barometer on Admiral FitzRoy’s plan was tried against a marine barometer +on the Kew principle, both instruments being new, and treated<span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span> in all +respects similarly. They were “hung over the gun, under the gun, and by +the side of the gun, the latter both inside and outside a bulkhead,—in +fact, in all ways that they would be tried in action with the bulkheads +cleared away.” The result was that the Kew barometer was broken and +rendered useless, while the new pattern barometer was not injured in the +least. In a third series of experiments, Mr. Negretti being present, five +of the new pattern barometers were subjected to the concussion produced by +firing a 68-pounder gun with shot, and 16 lbs. charge of powder. They were +suspended from a beam immediately under the gun, then from a beam +immediately over the gun, and finally they were suspended by the arm to a +bulkhead, at a distance of only 3 ft. 6 in. from the axis of the gun; and +the result was, according to the official report, “that all these +barometers, however suspended, would stand, without the slightest injury, +the most severe concussion that they would ever be likely to experience in +any sea-going man-of-war.” These trials were conducted under the +superintendence of Captain Hewlett, C.B., and the guns were fired in the +course of his <i>usual</i> instructions. His reports to Admiral FitzRoy, giving +all the particulars of the trials, are published in the “Ninth Number of +Meteorological Papers,” issued by the Board of Trade.<small><a name="f2.1" id="f2.1" href="#f2">[2]</a></small></p> + + +<p class="center"><br />25. NEGRETTI AND ZAMBRA’S FARMER’S BAROMETER AND DOMESTIC WEATHER-GLASS.</p> + +<p>It is a well-known fact that the barometer is as much, or even more +affected by a change of wind as it is by rain; and the objection raised +against a simple barometer reading, as leaving the observer in doubt +whether to expect wind or rain, is removed by the addition of the +Hygrometer, an instrument indicating the comparative degree of dryness or +dampness of the air;—a most important item in the determination of the +coming weather.</p> + +<p>The farmer should not be content to let his crops lie at the mercy, so to +speak, of the weather, when he has within his command instruments which +may be the means of preventing damage to, and in cases total loss of, his +crops.</p> + +<p>The farmer hitherto has had to depend for his prognostication of the +weather on his own unassisted “Weather Wisdom;” and it is perfectly +marvellous how expert he has become in its use. Science now steps in, not +to ignore this experience, but on the contrary, to give it most valuable +assistance by extending it, and enabling it to predict, with an accuracy +hitherto unknown, the various changes that take place in this most +variable of climates.</p> + +<p>To the invalid, the importance of predicting with tolerable accuracy the +changes<span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span> that are likely to occur in the weather, cannot be over-rated. +Many colds would be prevented, if we could know that the morning so balmy +and bright, would subside into a cold and cheerless afternoon. Even to the +robust, much inconvenience may be prevented by a due respect to the +indications of the hygrometer and the barometer, and the delicate in +health will do well to regard its warnings.</p> + +<div class="figleft">Fig. 17.<br /><img src="images/fig_17.jpg" alt="" /></div> + +<p><i>Description of the Instrument.</i>—The farmer’s barometer, as figured in +the margin, consists of an upright tube of mercury inverted in a cistern +of the same fluid; this is secured against a strong frame of wood, at the +upper end of which is fixed the scale, divided into inches and tenths of +an inch. On either side of the barometer, or centre tube, are two +thermometers—that on the left hand has its bulb uncovered and freely +exposed, and indicates the temperature of the air at the place of +observation; that on the right hand has its bulb covered with a piece of +muslin, from which depend a few threads of soft lamp cotton; this cotton +is immersed in the small cup situated just under the thermometer, this +vessel being full of water; the water rises by capillary attraction to the +muslin-covered bulb, and keeps it in a constantly moist state.</p> + +<p>These two thermometers, which we distinguish by the names “Wet Bulb” and +“Dry Bulb,” form the Hygrometer; and it is by the simultaneous reading of +these two thermometers, and noting the difference that exists between +their indications, that the humidity in the atmosphere is determined.</p> + +<p>Admiral FitzRoy’s words (see <a href="#Page_22">p. 22</a>) are placed upon the scale of the +barometer, as the value of a reading depends, not so much on the actual +height of the mercury in the tube, as it does on whether the column is +rising, steady, or falling.</p> + +<p>The moveable screw at the bottom of the cistern is for the purpose of +forcing the mercury to the top of the tube when the instrument is being +carried from place to place, and it must always be unscrewed to its utmost +limit when the barometer is hung in its proper place. After this it should +never be touched.</p> + +<p>The manner in which the Hygrometer acts is as follows: It is a pretty +well-known fact that water or wine is often cooled by a wet cloth being +tied round the bottle, and then being placed in a current of air. The +evaporation that takes place in the progressive drying of the cloth causes +the temperature to fall considerably below that of the surrounding +atmosphere, and the contents of the bottle are thus cooled. In the same +manner, then, the covered wet bulb thermometer will be found <i>invariably</i> +to read lower than the uncovered one; and the greater the dryness of the +air, the greater will be the difference<span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span> between the indications of the +two thermometers; and the more moisture that exists in the air, the more +nearly they will read alike.</p> + +<p>The cup must be kept filled with pure water, and occasionally cleaned out, +to remove any dirt. The muslin, or cotton-wick, should also be renewed +every few weeks. The hygrometer may be had separate from the barometer, if +the combined instruments cannot be sufficiently exposed to the external +air, this being essential for the successful use of the hygrometer.</p> + +<p>This farmer’s weather-glass, then, consists of three distinct instruments: +the barometer, the thermometer, and the hygrometer. He has thus at command +the three instrumental data necessary for the prediction of the weather. +And now to describe—</p> + +<p><i>How to Use the Instrument.</i>—The observations should be taken twice a +day, say at 9 <span class="smcaplc">A.M.</span> and 3 <span class="smcaplc">P.M.</span>; and should be entered on a slip of paper, +or a slate hung up by the barometer. The observer will then be able to see +the different values of the readings from time to time, and to draw his +conclusions therefrom.</p> + +<p>The thermometer on the left hand should first be read, and a note made of +its indication, which is the temperature of the air. The wet bulb +thermometer should now be read, and also noted; and the difference should +be taken of these two readings. Next read the barometer by moving the +small index at the side of the tube until it is on a level with the top of +the mercury. Having noted the number of inches at which the column stands, +compare with the last observation, and see immediately whether the +barometer is rising, steady, or falling.</p> + +<p>Now, having taken the observations as above, we naturally ask the +question, <i>What are we to predict from them?</i></p> + +<p>And, probably, the best way of answering this query will be by giving an +example. We will suppose that our readings yesterday were as +follows:—Temperature, 70°; Wet Bulb, 69°; Difference, 1°; =very moist +air. Barometer, 29·5, and that rain has fallen.</p> + +<p>To-day, we read:—Temperature, 60°; Wet Bulb, 55°; Difference, 5°; =dryer +air. Barometer, 30. We may safely predict that the rain will cease, and +probably we may have wind from the northward.</p> + +<p>In spring or autumn, if the barometric height be steady any where between +29·5 and 30 inches, with the temperature about 60°, fresh to moderate +south-westerly winds, with cloudy sky, will probably characterize the +weather; the indications of the hygrometer being then specially +serviceable in enabling us to foretell rain; but if the mercury become +steady at about 30·5 inches, with temperature about 40°, north-easterly +winds, dry air, and clear sky, may be confidently expected.</p> + +<p>Many cases will doubtless suggest themselves to the observer where these +figures do not occur, and where he might find a difficulty in interpreting +the indications of his instruments. We have, therefore, drawn up some +concise rules for his guidance; and although they will not prove +absolutely infallible guides to this acknowledged most difficult problem, +still, they will be found of much service in foretelling the weather, when +added to an intelligent observation of ordinary atmospheric <span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span>phenomena, as +force and direction of wind, nature of any particular season, and the time +of year.</p> + + +<p class="center"><br />26. RULES FOR FORETELLING THE WEATHER.</p> + +<p class="center"><br />A RISING BAROMETER.</p> + +<div class="blockquot"><p>A “Rapid” rise indicates unsettled weather.</p> + +<p>A “Gradual” rise indicates settled weather.</p> + +<p>A “Rise,” with dry air, and cold increasing in summer, indicates wind +from northward; and if rain has fallen, better weather is to be +expected.</p> + +<p>A “Rise,” with moist air and a low temperature, indicates wind and +rain from northward.</p> + +<p>A “Rise,” with southerly wind, indicates fine weather.</p></div> + +<p class="center"><br />A STEADY BAROMETER,</p> + +<div class="blockquot"><p>With dry air and a seasonable temperature, indicates a continuance of +very fine weather.</p></div> + +<p class="center"><br />A FALLING BAROMETER.</p> + +<div class="blockquot"><p>A “Rapid” fall indicates stormy weather.</p> + +<p>A “Rapid” fall, with westerly wind, indicates stormy weather from +northward.</p> + +<p>A “Fall,” with a northerly wind, indicates storm, with rain and hail +in summer, and snow in winter.</p> + +<p>A “Fall,” with increased moisture in the air, and the heat increasing, +indicates wind and rain from southward.</p> + +<p>A “Fall,” with dry air, and cold increasing (in winter), indicates +snow.</p> + +<p>A “Fall,” after very calm and warm weather, indicates rain with +squally weather.</p></div> + + +<p><br /><b>27. Causes which may bring about a Fall or a Rise in the Barometer.</b><small><a name="f3.1" id="f3.1" href="#f3">[3]</a></small>—As +heat produces rarefaction, a sudden rise of temperature in a distant +quarter may affect the weight of the atmosphere over our heads, by +producing an aerial current outwards, to supply the place of the lighter +air which has moved from its former position; in which case the barometer +will fall. Now such a movement in the atmosphere is likely to bring about +an intermixture of currents of air of different temperatures, and from +this intermixture rain is likely to result.</p> + +<p>On the other hand, as cold produces condensation, any sudden fall of +temperature causes the column of air over the locality to contract and +sink to a lower level, whilst other air rushes in from above to supply the +void; and, accordingly, the barometer rises. Should this air, as often +happens, proceed from the north, it will contain in general but little +moisture; and hence, on reaching a warmer latitude, will take up the +vapour of the air, so that dry weather will result.</p> + +<p>It is generally observed, that wind causes a fall in the instrument; and, +indeed, in those greater movements of the atmosphere which we denominate +storms or<span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span> hurricanes, the depression is so considerable as to forewarn +the navigator of his impending danger. It is evident, that a draught of +air in any direction must diminish the weight of the column overhead, and +consequently cause the mercury in the barometer to sink.</p> + +<p>The connection, therefore, of a sinking of the barometric column with rain +is frequently owing to the wind causing an intermixture of the aerial +currents which, by their motion, diminish the weight of the atmosphere +over our heads; whilst a steady rise in the column indicates the absence +of any great atmospheric changes in the neighbourhood, and a general +exemption from those causes which are apt to bring about a precipitation +of vapour.</p> + + +<p><br /><b>28. Use of the Barometer in the management of Mines.</b>—The inflammable and +suffocating gases, known to coal-miners as fire-damp and choke-damp, are +specifically heavier than air; and as they issue from the fissures of the +mine, or are released from the coal, the atmospheric pressure tends to +drive them into the lowest and least ventilated galleries. Consequently a +greatly reduced atmospheric pressure will favour a sudden outflow or +advance of gas; whence may result cases of explosion or suffocation. It +has been found that these accidents occur for the most part about the time +of a low barometric column. A reliable barometer should, therefore, be +systematically consulted by those entrusted with the management or control +of coal-mines, so that greater vigilance and caution may be enjoined on +the miners whenever the mercury falls low, especially after it has been +unusually high for some days.</p> + + +<p><br /><b>29. Use of the Barometer in estimating the Height of Tides.</b>—The pressure +of the atmosphere affects the height of the tide, the water being in +general higher as the barometer is lower. The expressions of seamen, that +“frost nips the tide,” and “fog nips the tide,” are explained by the high +barometer which usually accompanies frost and fog. M. Daussy, Sir J. C. +Ross, and others, have established that a rise of one inch in the +barometer will have a corresponding fall in the tide of about one foot. +Therefore navigators and pilots will appreciate the following suggestion +of Admiral FitzRoy:—</p> + +<p>“Vessels sometimes enter docks, or even harbours, where they have scarcely +a foot of water more than their draught; and as docking, as well as +launching large ships, requires a close calculation of height of water, +the state of the barometer becomes of additional importance on such +occasions.”</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span></p> +<h2><a name="CHAPTER_II" id="CHAPTER_II"></a>CHAPTER II.</h2> +<p class="center"><span class="large">SYPHON TUBE BAROMETERS.</span></p> + +<p><br /><b>30. Principle of.</b>—If some mercury, or any other fluid, be poured into a +tube of glass, bent in the form of <big><strong>∪</strong></big>, and open at both ends, it will rise +to the same height in both limbs, the tube being held vertically. If +mercury be poured in first, and then water upon it at one end, these +liquids will not come to the same level; the water will stand much higher +than the mercury. If the height of the mercury, above the line of meeting +of the fluids, be one inch, that of the water will be about +thirteen-and-a-half inches. The explanation of this is, that the two +columns balance each other. The pressure of the atmosphere in each limb is +precisely similar; but the one column stands so much higher than the +other, because the fluid of which it is composed is so much lighter, bulk +for bulk, than the other. If one end of the tube be hermetically closed, +the other limb be cut off within a few inches of the bend, and the tube +carefully filled with mercury; by placing it in a vertical position, the +mercury will fall, if the closed limb be long enough, until it is about +thirty inches higher than that in the exposed limb, where it will remain. +Here the atmosphere presses upon the short column; but not upon the long +one. It is this pressure, therefore, which maintains the difference of +level. In fact, it forms a barometer without a cistern, the short limb +answering the purpose of a cistern. The first barometers on this principle +were devised by the celebrated philosopher, Dr. Hook, as described in the +next section.</p> + + +<p class="center"><br />31. DIAL, OR WHEEL BAROMETERS.</p> + +<p>The familiar household “Weather Glasses” are barometers on the syphon +principle. The portions of the two limbs through which the mercury will +rise and fall with the varying pressure of the atmosphere are made of +precisely the same diameter; while the part between them is contracted. On +the mercury, in the exposed limb, rests a round float of ivory or glass; +to this a string is attached and passed over and around a brass pulley, +the other end carrying another lighter weight. The weight resting on the +mercury rises and falls with it. On the spindle of the pulley, which +passes through the frame and centre of the dial-plate, is fixed a light +steel hand, which revolves as the pulley turns round. When the mercury +falls for a decrease of atmospheric pressure, it rises by the same +quantity in the short tube, and pushes up the float, the counterpoise +falls, and thus moves the hand or pointer<span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span> to the left. When the pressure +increases, the pointer is drawn in a similar manner to the right.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center">Fig. 18.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 19.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 20.</td></tr> +<tr><td align="center"><img src="images/fig_18.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_19.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_20.jpg" alt="" /></td></tr></table> + +<p>The dials are generally made of metal silvered over or enamelled, but +porcelain may be used. If the circumference of the pulley, or “wheel,” be +two inches, it will revolve once for an alteration of level amounting to +two inches in each tube, or four inches in the height of the barometric +column; and as the dial may be from twenty to thirty-six inches in +circumference, five to nine inches on the graduated scale corresponds to +one inch of the column; and hence the sub-divisions are distinctly +perceptible, and a vernier is not necessary.</p> + +<p>The motion of the pointer alone is visible; and a mahogany, or rosewood, +frame, supports, covers, and renders the instrument ornamental and +portable. In the back of the frame is a hinged door, which covers the +cavity containing the tube and fixtures. The dial is covered by a glass in +a brass rim, similar to a clock face. A brass index, working over the +dial, moveable by a key or button, may be applied, and will serve to +register the position of the hand when last observed. These instruments +are usually fitted with a thermometer, and a spirit level; the latter for +the purpose of getting the instrument perfectly vertical. They sometimes +have, in addition, a hygrometer, a sympiesometer, an aneroid, a mirror, or +a clock, &c., singly or combined. The frame admits of much variety of +style and decoration. It may be carved or inlaid. The usual adjustment of +scale is suited for localities<span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span> at no considerable elevation above the +sea. Accordingly, being commercial articles, they have been found +frequently quite out of place. When intended for use at high elevations, +they should have a special adjustment of scale. As household instruments +they are serviceable, and ornamental. But the supply-and-demand principle +upon which they are sold, has entailed upon those issued by inferior +makers a generally bad adjustment of scale. The illustrations are those of +ordinary designs.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center">Fig. 21.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 22.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 23.</td></tr> +<tr><td align="center"><img src="images/fig_21.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_22.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_23.jpg" alt="" /></td></tr></table> + +<p>Dial barometers required for transmission to distant parts, as India and +the Colonies, are furnished with a steel stop-cock, to render them +portable more effectually than can be done by the method of <i>plugging</i> the +tube.</p> + +<div class="figleft">Fig. 24.<br /><img src="images/fig_24.jpg" alt="" /></div> + + + +<p class="center"><br />32. STANDARD SYPHON BAROMETER.</p> + +<p>Fig. 24 represents the most accurate form of the Gay Lussac barometer. The +short limb is closed at the top, after the mercury is introduced, and a +small lateral<span class="pagenum"><a name="Page_31" id="Page_31">[Pg 31]</a></span> puncture is made at <i>a</i>, which is covered over with a +substance which permits the access of air, but prevents the escape of any +mercury when the instrument is packed for travelling. The bent part of the +tube is contracted to a capillary bore; and just above this, in the long +limb, is placed the air-trap, already described (see <a href="#Page_17">p. 17</a>), and here +illustrated (fig. 25). <span class="figright">Fig. 25.<br /><img src="images/fig_25.jpg" alt="" /></span> When reversed, as it must be for portability, the +capillary attraction keeps the mercury in the long branch. Should the +mercury of the short column get detached, some small quantity of air <i>may</i> +pass; but it will be arrested at the pipette, and will not vitiate the +length of the barometric column. It can be easily expelled by gently +shaking or tapping the instrument before suspending it for observation. In +the illustration, the zero of the scale is placed at Z, near the middle of +the tube; and the graduations extend above and below. In making an +observation, it is necessary to take the reading ZA on the long branch, +and ZB on the short one. The sum of the two gives the height of the +barometer. The zero of the scale in some instruments is placed low down, +so as to require the difference of the two readings to be taken. A +thermometer is attached to the frame as usual.</p> + +<p>These instruments can be very accurately graduated, and are very exact in +their indications, provided great care has been exercised in selecting the +tubes, which must be of the same calibre throughout the parts destined to +measure the variations of atmospheric pressure. They should be suspended +so as to insure their hanging vertically.</p> + +<p>The syphon barometer does not require correction for capillarity nor for +capacity, as each surface of the mercury is equally depressed by capillary +attraction, and the quantity of mercury which falls from the long limb of +the tube occupies the same length in the short one. The barometric height +must, however, be corrected for temperature, as in the cistern barometer. +Tables containing the temperature corrections to be applied to barometer +readings for scales engraved on the glass tube, or on brass or wood +frames, are published.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_32" id="Page_32">[Pg 32]</a></span></p> +<h2><a name="CHAPTER_III" id="CHAPTER_III"></a>CHAPTER III.</h2> +<p class="center"><span class="large">BAROGRAPHS, OR SELF-REGISTERING BAROMETERS.</span></p> + +<p><br /><b>33. Milne’s Self-Registering Barometer.</b>—For a long time a good and +accurate self-recording barometer was much desired. This want is now +satisfactorily supplied, not by one, but by several descriptions of +apparatus. The one first to be described was the design of Admiral Sir A. +Milne, who himself constructed, in 1857, we believe, the original +instrument, which he used with much success. Since that time several of +these instruments have been made, and have performed satisfactorily. The +barometer tube is a syphon of large calibre, provided with a Gay Lussac +pipette, or air-trap; and fitted with a float, a wheel, and a pointer, as +in the “Dial” barometer. The float is attached to a delicate watch-chain, +which passes over the wheel and is adequately counterpoised. Behind the +indicating extremity of the pointer or hand is a projecting point, which +faces the frame of the instrument, and is just within contact with the +registering paper. A clock is applied, and fitted with auxiliary +mechanism, so as to be able to move the mounted paper with regularity +behind the pointer, and at designed equal intervals of time to release a +system of levers and springs, so as to cause the marker to impress a dot +on the paper, either by puncture or pencil-mark. The paper is ruled with +horizontal lines for the range of the mercurial column, and parallel arcs +of circles for the hours. Thus the barometer is rendered self-recording, +by night or day, for a week or more; hence the great value of the +instrument. The clock, index, and registering mechanism are protected from +dust and interference by a glass front, hinged on and locked. As the +temperature of the mercury is not registered, there is fixed to the frame +a Sixe’s thermometer to record the maximum and minimum temperatures, which +should be noted at least every twenty-four hours.</p> + +<p>Admiral FitzRoy has suggested the name “Atmoscope” for Admiral Milne’s +barometer; and he has also termed it a “Barograph.” This latter word +appears to be applicable to all kinds of self-registering barometers +hitherto designed. Of the arrangement under consideration Admiral FitzRoy +writes:—“It shows the alterations in tension, or the pulsations, so to +speak, of atmosphere, on a large scale, by hourly marks; and the diagram +expresses, to a practised observer, what the ‘indicator card’ of a +steam-cylinder shows to a skilful engineer, or a stethescope to a +physician.”</p> + + +<div class="figright">Fig. 26.<br /><img src="images/fig_26tmb.jpg" alt="" /><br /><a href="images/fig_26.jpg"><small>Larger Image</small></a></div> + +<p><br /><b>34. Modification of Milne’s Barometer.</b>—The great difficulty to be +overcome in Milne’s barometer, is to adjust the mechanism for obtaining +registration so that the action of the striker upon the pointer should not +in the slightest degree<span class="pagenum"><a name="Page_33" id="Page_33">[Pg 33]</a></span> move it from its true position. A different mode +of registration, capable of recording accurately the least appreciable +movement of the mercurial column, has been effected. In this instrument +the registering paper is carried upon a cylinder or drum. By reference to +the illustration, Fig. 26, the details of construction will be readily +understood. It should, however, be mentioned, that it is not a picture of +the outward appearance of the instrument. The position of the barometer +should be behind the clock; it is represented on one side merely for the +purpose of clearly illustrating the arrangement and principles. The +instrument has a large syphon barometer tube, in which the mercurial +column is represented. On the mercury at <i>A</i>, in its open end, rests a +glass float, attached to a watch-chain, or suitable silken cord, the other +end of which is connected to the top of the arched head on the short arm +of a lever-beam. The long arm of the beam is twice the length of the short +arm, for the following reason. As the mercury falls in the long limb, it +rises through an equal space in the short limb of the tube, and <i>vice +versa</i>. But the barometric column is the difference of height of the +mercury in the two limbs; hence the rise or fall of the float through +half-an-inch will correspond to a decrease or an increase of the +barometric column of one inch. In order, then, to record the movements of +the barometric column, and not those of the float, the arm of the beam +connected with the float is only half the radius of the other arm. Both +arms of the beam carry circular-arched heads, which are similar portions +of the complete circles, the centre of curvature being the fulcrum, or +axis. This contrivance maintains the leverage on each extremity of the +beam always at the same distance from the fulcrum. From the top of the +large arched head a piece of watch-chain descends, and is attached to the +marker, <i>B</i>, which properly counterpoises the float, <i>A</i>, and is capable +of easy movement along a groove in a brass bar, so as to indicate the +barometric height on an ivory scale, <i>C</i>, fixed on the same vertical +framing. On the opposite side of the marker, <i>B</i>, is formed a metallic +point, which faces the registration sheet and is nearly in contact with +it. The framing, which carries the scale and marker, is an arrangement of +brass bars, delicately adjusted and controlled by springs, so as to permit +of a quick horizontal motion, in a small arc, being communicated to it by +the action of the hammer, <i>E</i>, of the clock, whereby the point of the +marker is caused to impress a<span class="pagenum"><a name="Page_34" id="Page_34">[Pg 34]</a></span> dot upon the paper. The same clock gives +rotation to the hollow wooden cylinder, <i>D</i>, upon which is mounted the +registering paper. The clock must be rewound when a fresh paper is +attached to the cylinder, which may be daily, weekly, or monthly, +according to construction; and the series of dots impressed upon the paper +shows the height of the barometric column every hour by day and night. The +space traversed by the marker is precisely equal to the range of the +barometric column.</p> + +<div class="figleft">Fig. 27.<br /><img src="images/fig_27.jpg" alt="" /></div> + +<p><br /><b>35. King’s Self-Registering Barometer.</b>—Mr. Alfred King, Engineer of the +Liverpool Gas-light Company, designed, so long ago as 1854, a barometer to +register, by a continuous pencil-tracing, the variations in the weight of +the atmosphere; and a highly-satisfactory self-recording barometer, on his +principle and constructed under his immediate superintendence, has quite +recently been erected at the Liverpool Observatory.</p> + +<p>Fig. 27 is the front elevation of this instrument. <i>A</i>, the barometer +tube, is three inches in internal diameter, and it floats freely (not +being fixed as usual) in the fixed cistern, <i>B</i>, guided by +friction-wheels, <i>W</i>. The top end of the tube is fastened to a peculiar +chain, which passes over a grooved wheel turning on finely-adjusted +friction rollers. The other end of the chain supports the frame, <i>D</i>, +which carries the tracing pencil. The frame is suitably weighted and +guided, and faces the cylinder, <i>C</i>, around which the tracing paper is +wrapped, and which rotates once in twenty-four hours by the movement of a +clock. Mr. Hartnup, Director of the Liverpool Observatory, in his Annual +Report, 1868, says:—“For one inch change in the mercurial column the +pencil is moved through five inches, so that the horizontal lines on the +tracing, which are half an inch apart, represent one-tenth of an inch +change in the barometer. The vertical lines are hour lines, and being +nearly three-quarters of an inch apart, it will be seen that the smallest +appreciable change in the barometer, and the time of its occurrence, are +recorded.”</p> + +<p>“It has been remarked by persons in the habit of reading barometers with +large<span class="pagenum"><a name="Page_35" id="Page_35">[Pg 35]</a></span> tubes, that, in squally weather, sudden and frequent oscillations +of the mercurial column are sometimes seen. Now, to register these small +oscillations must be a very delicate test of the sensitiveness of a +self-registering barometer, as the time occupied by the rise and fall of +the mercury in the tube in some cases does not exceed one minute.” Mr. +Hartnup affirms that the tracing of this instrument exhibits such +oscillations whenever the wind blows strong and in squalls.</p> + +<p>As the barometer in this instrument is precisely similar to the “Long +Range Barometer” invented by Mr. McNeild (and which will be found +described at page 48), it may be desirable to quote the following, from +Mr. Hartnup’s Report:—“Mr. King constructed a small model instrument to +illustrate the principle. This instrument was entrusted to my care for +examination, and it was exhibited to the scientific gentlemen who visited +the Observatory in 1854, during the meeting of the British Association for +the Advancement of Science.”</p> + + +<p><br /><b>36. Syphon, with Photographic Registration.</b>—A continuous self-registering +barometer has been constructed, in which photography is employed. Those +who may wish to adopt a similar apparatus, or thoroughly to understand the +arrangements and mode of observation, should consult the detailed +description given in the <i>Greenwich Magnetical and Meteorological +Observations</i>, 1847. As the principles are applicable to photographic +registration of magnetic and electric as well as meteorologic variations +in instrumental indications, it would be beside our purpose to describe +fully the apparatus.</p> + +<p>The barometer is a large syphon tube; the bore of the upper and lower +extremities, through which the surfaces of the mercury rise and fall, is +1<span style="font-size: 0.8em;"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">10</span> inch in diameter. The glass float in the open limb is attached to a +wire, which moves a delicately-supported light lever as it alters its +elevation. The fulcrum of the lever is on one side of the wire; the +extremity on the other side, at four times this distance from the fulcrum, +carries a vertical plate of opaque mica, having a small aperture. Through +this hole the light of a gas-jet shines upon photographic paper wrapped +round a cylinder placed vertically, and moved round its axis by a clock +fixed with its face horizontal. The cylinder is delicately supported, and +revolves in friction rollers. A bent wire on the axis is embraced by a +prong on the hour hand of the time-piece; therefore the cylinder is +carried round once in twelve hours. It might be arranged for a different +period of rotation.</p> + +<p>As the cylinder rotates, the paper receives the action of the light, and a +photographic trace is left of the movements of the barometer four times +the extent of the oscillations of the float, or twice the length of the +variations in the barometric column. Certain chemical processes are +required in the preparation of the paper, and in developing the trace. The +diagram which we give on the next page, with the explanation, taken from +Drew’s <i>Practical Meteorology</i>, will enable the above description to be +better understood:</p> + +<p> <span class="pagenum"><a name="Page_36" id="Page_36">[Pg 36]</a></span></p> +<p class="center">Fig. 28.</p> +<div class="figcenter"><img src="images/fig_28.jpg" alt="" /></div> +<p> </p> + +<p>“<i>Q e</i> is a lever whose fulcrum is <i>e</i>, the counterpoise <i>f</i> nearly +supporting it; <i>s</i> is an opaque plate of mica, with a small aperture at +<i>p</i>, through which the light passes, having before been refracted by a +cylindrical lens into a long ray, the portion only of which opposite the +aperture <i>p</i> impinges on the paper; <i>d</i> is a wire supported by a float on +the surface of the mercury; <i>G H</i> is the barometer; <i>p</i>, the vertical +cylinder charged with photographic paper; <i>r</i>, the photographic trace; +<i>I</i>, the timepiece, carrying round the cylinder by the projecting arm <i>t</i>. +It is evident that the respective distances of the float and the aperture +<i>p</i> from the fulcrum may be regulated so that the rise and fall of the +float may be multiplied to any extent required.” When <i>only</i> the lower +surface of the mercury in a syphon barometer is read, as in the instrument +just described, a correction for temperature is strictly due to the height +of the quicksilver in the <i>short</i> tube; but this in so short a column will +rarely be sensible.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_37" id="Page_37">[Pg 37]</a></span></p> +<h2><a name="CHAPTER_IV" id="CHAPTER_IV"></a>CHAPTER IV.</h2> +<p class="center"><span class="large">MOUNTAIN BAROMETERS.</span></p> + +<p><br /><b>37. The Syphon Tube Mountain Barometer, on Gay Lussac’s principle</b>, +constructed as described at <a href="#Page_31">page 31</a>, and fixed in a metallic tubular +frame, forms a simple and light travelling instrument. The graduations are +made upon the frame, and it is suspended for reading by a ring at the top, +from beneath an iron tripod stand, which is usually supplied with it. +Considerable care is requisite in adjusting the verniers, so as to keep +the instrument steady and vertical. A drawback to the convenience of this +barometer is the movement of the mercury in the short limb, which is +generally not confined, and hence has every facility for becoming quickly +oxidised in travelling. To remedy this, Messrs. Negretti and Zambra so +construct the Mountain Syphon Barometer that by a simple half turn of a +screw the mercury can be confined for portability, while the lower limb +can be taken out for cleaning whenever found requisite.</p> + + +<p><br /><b>38. Mountain Barometer on Fortin’s principle.</b>—This barometer, with +Fortin’s cistern, as arranged by Messrs. Negretti and Zambra, is an +elegant, manageable, and very accurate instrument for travelling purposes, +and well adapted for careful measurement of heights. The cistern is made +large enough to receive all the mercury that will fall from the tube at +the highest attainable elevation. The screw at the bottom confines the +mercury securely for carriage, and serves to adjust the surface of the +mercury to the zero of the scale when making an observation. The vernier +reads to ·002 of an inch, and slides easily on the brass frame, which is +made as small in diameter as is compatible with the size of the tube. The +tube in this barometer should be altogether without contractions, so that +the mercury will readily fall when it is set up for observation. It must +be carefully calibrated, and its internal diameter ascertained, in order +that correction may be made for capillarity. This correction, however, +should be combined with the error of graduation, and form a permanent +index error, ascertainable at any time by comparison with an acknowledged +standard barometer.</p> + +<p>The barometer is supported in the tripod stand (furnished as part of the +instrument) when used for observation. It is suspended by placing two +studs, in the ring on the frame, in slots formed on the top of the stand, +so that it hangs freely and<span class="pagenum"><a name="Page_38" id="Page_38">[Pg 38]</a></span> vertically in gimbals. To the metal top of +the stand, mahogany legs are hinged. To make the barometer portable, it +must be lifted out of the stand, sloped gently until the mercury reaches +the top, turning the screw at the bottom meanwhile; then invert and screw +until the mercury is made tight. The inverted instrument packs in the +stand, the legs being formed to fit round the frame; and receptacles are +scooped out for the cistern, thermometer, gimbals, and vernier; so that +the instrument is firmly surrounded by the wooden legs, which are held +fast together by brass rings passed over them.</p> + +<div class="figleft">Fig. 29.<br /><img src="images/fig_29.jpg" alt="" /></div> + +<p><br /><b>39. Newman’s Mountain Barometer.</b>—Fig. 29 is an illustration of the +mountain barometer known as Newman’s. The cistern consists of two separate +compartments;—the top of the lower and the bottom of the upper, being +perfectly flat, are pivoted closely together at the centres, so that the +lower can move through a small arc, when turned by the hand. This movement +is limited by two stops. The top of the lower compartment and the bottom +of the upper have each a circular hole, through which the mercury +communicates. When the instrument is required for observation, the cistern +is turned close up to the stop marked “<i>open</i>” or “<i>not portable</i>.” When +it is necessary to pack it for travelling, the mercurial column must be +allowed to fill the tube by sloping the barometer gently; then invert it, +and move the cistern to the stop marked “<i>shut</i>” or “<i>portable</i>.” In this +condition, the upper compartment is completely filled with mercury, and +consequently that in the tube cannot move about, so as to admit air or +endanger the tube. Nor can the mercury pass back to the lower compartment, +as the holes are not now coincident, and the contact is made too perfect +to allow the mercury to creep between the surfaces. The tube does not +enter the lower compartment, which is completely full of mercury when the +instrument is arranged for observation. The spare capacity of the upper +cistern is sufficient to receive the mercury which descends from the tube +to the limit of the engraved scale, which in these barometers generally +extends only to about 20 inches. A lower limit could of course be given by +increasing the size of the cisterns, which it is not advisable to do +unless for a special purpose. This barometer may be had mounted in wood, +or in brass frame. If in wood, it has a brass shield, which slides round +the scale part of the frame, so as to be easily brought in front of the +tube and scale as a protection in travelling; the vernier screw, in this +case, being placed at the top of the instrument. When the scale is +graduated with true inches, the neutral point, the capacity and +capillarity corrections should be marked on the frame. The graduated +scales, however, placed on these barometers in brass frames, are usually +artificial inches, like the Kew plan of graduation; the advantage being +that one simple correction only is required, viz. one for index error and +capillarity combined, which can always be readily determined by comparison +with a standard barometer; moreover, as no adjustment of cistern is<span class="pagenum"><a name="Page_39" id="Page_39">[Pg 39]</a></span> +required in reading, the instrument can be verified by artificial pressure +throughout the scale, by the plan practised at Kew, Liverpool, &c., and +already described (see <a href="#Page_18">p. 18</a>).</p> + + +<p class="center"><br />40. NEGRETTI & ZAMBRA’S PATENT MOUNTAIN AND OTHER BAROMETERS.</p> + +<div class="figright">Fig. 30.<br /><img src="images/fig_30.jpg" alt="" /></div> + +<p>This invention is intended to make mountain and other barometers of +standard accuracy stronger, more portable, and less liable to derangement, +when being carried about, than heretofore, by dispensing with the ordinary +flexible cistern containing the mercury at the bottom of the instrument, +and adapting in lieu thereof a rigid cistern constructed of glass and +iron. The cistern is composed of a glass cylinder, which is secured in a +metallic tube or frame. In order to render the cistern mercury-tight at +top and bottom, metal caps are screwed into the tube or frame, and bear +against leather washers placed between them and the edges of the glass +cylinder. The upper cap of the cistern is tapped with a fine threaded +screw to receive the iron plug or socket, into which the barometer tube is +securely fixed. The whole length of this plug has a fine screw cut upon it +by which the cistern can be screwed up or down. At the side of this plug +or socket, extending from the lower end to within half an inch of the top, +is cut a groove for admitting the air to the surface of the mercury within +the cistern when the barometer is in use. An ivory point is screwed into +the under surface of the plug, carrying the barometer tube. This ivory +point is very carefully adjusted by measurement to be the zero point of +the instrument, from which the barometer scale of inches is divided. The +surface of the mercury in the cistern is adjusted to the zero point by +screwing the cistern up or down until the ivory point and its reflected +image are in contact.</p> + +<p><span class="pagenum"><a name="Page_40" id="Page_40">[Pg 40]</a></span>The instrument (fig. 30) is shown in a state of adjustment, ready to take +an observation; but <i>when it is desired to render it portable, it must be +inclined, until mercury from the cistern fills the tube; the cistern must +then be screwed up on the socket</i>, so as to bring the face of the upper +cap against the under side of the shoulder of the cover immediately above +it; the instrument may then be carried without being liable to +derangement.</p> + +<p><i>Precautions necessary in using the Mountain Barometer.</i>—On removing the +barometer from its case after a journey, allow it to remain with its scale +end downward, whilst the cistern is unscrewed to the extent of <i>one turn +of the screw</i>, after which slightly shake the cistern; the mercury in it +will then completely fill the end of the barometer tube, should any +portion of it have escaped therefrom.</p> + +<p>The barometer is then inverted, and if it be desired to make an +observation, suspend it vertically from its stand by the ring at top. The +cistern must then be unscrewed, until the surface of the mercury is +brought just level with the extreme end of the ivory or zero point fixed +to the iron plug on which the glass cistern moves up and down.</p> + +<p>Should the elevation of the place where the barometer is to be used be +considerably above the sea level, it will be well—after suspending it +from the stand—to unscrew the cistern several turns, <i>holding the +barometer in an oblique position</i>, as at great heights the mercury will +fall considerably quicker than the cistern can be unscrewed, thereby +filling it to overflowing; but by partly unscrewing the cistern first, +room is given for the reception of a fall of mercury to the extent of +several inches.</p> + +<p>The cistern must not be unscrewed when the <i>Instrument is</i> <span class="smcaplc">INVERTED</span> <i>more +than</i> two turns of the screw, otherwise the mercury will flow out through +the groove.</p> + +<p>It is found safer when travelling to carry the barometer in a horizontal +position, or with its cistern end uppermost.</p> + +<p><i>To clean the Barometer.</i>—Should at any time the mercury in the cistern +become oxidised, and reading from its surface be difficult, it can be +readily cleaned by removing the cistern and its contained mercury from the +barometer frame by unscrewing it <i>when in a horizontal position</i>; this +precaution is necessary that the mercury in the tube may not escape, and +thereby allow air to enter. The cistern must then be emptied, and with a +dry clean leather, or silk handkerchief, well cleaned.</p> + +<p>The operation of cleaning being performed, return the cistern to the +frame, and screw it until the face is brought up against the under side of +the shoulder, still keeping the instrument <i>horizontal</i>. The cistern is +now ready for re-filling, to do which stand the barometer on end <i>head +downwards</i>, and remove the small screw at bottom; through the aperture +thus opened, pour in mercury, passing it through a paper funnel with a +very small aperture. It is well to pass the mercury through a very small +funnel two or three times before returning it to the barometer cistern, as +by this process all particles of dust or oxide adhere to the paper, and +are effectually removed.</p> + +<p><span class="pagenum"><a name="Page_41" id="Page_41">[Pg 41]</a></span>Should any small quantity of the mercury be lost during the operation of +cleaning, it is of no importance so long as sufficient remains to allow of +adjustment to the zero point. This latter constitutes one of the great +advantages of this new instrument over the ordinary barometer; for, in the +majority of cases, after an instrument has been compared carefully with a +standard, should mercury be lost, there is no means of correcting the +error unless a standard barometer be at hand; the new barometer is, in +this respect, independent, a little mercury more or less being +unimportant.</p> + + +<p><br /><b>41. Short Tube Barometer.</b>—This is simply a tube shorter, as may be +required, than that necessary to show the atmospheric pressure at the sea +level. It is convenient for balloon purposes, and for use at mountain +stations, being of course a special construction.</p> + + +<p><br /><b>42. Method of Calculating Heights by the Barometer.</b>—The pressure of the +atmosphere being measured by the barometer, it is evident that as the +instrument is carried up a high mountain or elevated in a balloon, the +length of the column must decrease as the atmospheric pressure decreases, +in consequence of a stratum of air being left below. The pressure of air +arises from its weight, or the attraction of gravitation upon it, and +therefore the quantity of air below the barometer cistern cannot influence +the height of the column. Hence it follows that a certain relation must +exist between the difference of the barometric pressure at the foot and at +the top of a hill or other elevation, and the difference of the absolute +heights above the sea. Theoretical investigation, abundantly confirmed by +practical results, has determined that the strata of air decrease in +density in a geometrical proportion, while the elevations increase in an +arithmetical one. Hence we have a method of determining differences of +level, by observations made on the density of the air by means of the +barometer. It is beyond our purpose to explain in detail the principles +upon which this method is founded, or to give its mathematical +investigation. We append Tables, which will be useful to practical +persons,—surveyors, engineers, travellers, tourists, &c.,—who may carry +a barometer as a travelling companion.</p> + +<p>Table I. is calculated from the formula, height in feet = 60,200 (log. +29·922 - log. B) + 925; where 29·922 is the mean atmospheric pressure at +32° F., and the mean sea-level in latitude 45°; and B is any other +barometric pressure; the 925 being added to avoid minus signs in the +Table.</p> + +<p>Table II. contains the correction necessary for the mean temperature of +the stratum of air between the stations of observation; and is computed +from Regnault’s co-efficient for the expansion of air, which is ·002036 of +its volume at 32° for each degree above that temperature.</p> + +<p>Table III. is the correction due to the difference of gravitation in any +other latitude, and is found from the formula, <i>x</i> = 1 + ·00265 cos. 2 +lat.</p> + +<p><span class="pagenum"><a name="Page_42" id="Page_42">[Pg 42]</a></span>Table IV. is to correct for the diminution of gravity in ascending from +the sea-level.</p> + +<p>To use these Tables: The barometer readings at the upper and lower +stations having been corrected and reduced to temperature 32° F., take out +from Table I. the numbers opposite the corrected readings, and subtract +the lower from the upper. Multiply this difference successively by the +factors found in Tables II. and III. The factor from Table III. may be +neglected unless precision is desired. Finally, add the correction taken +from Table IV.</p> + +<p class="center"><span class="smcap">Table I.</span></p> +<p class="center"><i>Approximate Height due to Barometric Pressure.</i></p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td class="btlr" align="center">Inches.</td> + <td class="btrdoub" align="center">Feet.</td> + <td class="btr" align="center">Inches.</td> + <td class="btrdoub" align="center">Feet.</td> + <td class="btr" align="center">Inches.</td> + <td class="btr" align="center">Feet.</td></tr> +<tr><td class="btlr" align="center">31·0</td> + <td class="btrdoub" align="center"><span style="margin-left: 1.5em;">0</span></td> + <td class="btr" align="center">28·2</td> + <td class="btrdoub" align="center">2475</td> + <td class="btr" align="center">25·4</td> + <td class="btr" align="center">5209</td></tr> +<tr><td class="blr" align="center">30·9</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">84</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="brdoub" align="center">2568</td> + <td class="br" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="br" align="center">5312</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">169</span></td> + <td class="br" align="center">28·0</td> + <td class="brdoub" align="center">2661</td> + <td class="br" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="br" align="center">5415</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">254</span></td> + <td class="br" align="center">27·9</td> + <td class="brdoub" align="center">2754</td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="br" align="center">5519</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">339</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center">2848</td> + <td class="br" align="center">25·0</td> + <td class="br" align="center">5623</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">425</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center">2942</td> + <td class="br" align="center">24·9</td> + <td class="br" align="center">5728</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">511</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center">3037</td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="br" align="center">5833</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">597</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center">3132</td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="br" align="center">5939</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">683</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center">3227</td> + <td class="br" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="br" align="center">6045</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">770</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="brdoub" align="center">3323</td> + <td class="br" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="br" align="center">6152</td></tr> +<tr><td class="blr" align="center">30·0</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">857</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="brdoub" align="center">3419</td> + <td class="br" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="br" align="center">6259</td></tr> +<tr><td class="blr" align="center">29·9</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">944</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="brdoub" align="center">3515</td> + <td class="br" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="br" align="center">6366</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center">1032</td> + <td class="br" align="center">27·0</td> + <td class="brdoub" align="center">3612</td> + <td class="br" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="br" align="center">6474</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center">1120</td> + <td class="br" align="center">26·9</td> + <td class="brdoub" align="center">3709</td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="br" align="center">6582</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center">1208</td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center">3806</td> + <td class="br" align="center">24·0</td> + <td class="br" align="center">6691</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center">1296</td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center">3904</td> + <td class="br" align="center">23·9</td> + <td class="br" align="center">6800</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center">1385</td> + <td class="br" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center">4002</td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="br" align="center">6910</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="brdoub" align="center">1474</td> + <td class="br" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center">4100</td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="br" align="center">7020</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="brdoub" align="center">1563</td> + <td class="br" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center">4199</td> + <td class="br" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="br" align="center">7131</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="brdoub" align="center">1653</td> + <td class="br" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="brdoub" align="center">4298</td> + <td class="br" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="br" align="center">7242</td></tr> +<tr><td class="blr" align="center">29·0</td> + <td class="brdoub" align="center">1743</td> + <td class="br" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="brdoub" align="center">4398</td> + <td class="br" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="br" align="center">7353</td></tr> +<tr><td class="blr" align="center">28·9</td> + <td class="brdoub" align="center">1833</td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="brdoub" align="center">4498</td> + <td class="br" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="br" align="center">7465</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center">1924</td> + <td class="br" align="center">26·0</td> + <td class="brdoub" align="center">4598</td> + <td class="br" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="br" align="center">7577</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center">2015</td> + <td class="br" align="center">25·9</td> + <td class="brdoub" align="center">4699</td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="br" align="center">7690</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center">2106</td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center">4800</td> + <td class="br" align="center">23·0</td> + <td class="br" align="center">7803</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center">2198</td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center">4902</td> + <td class="br" align="center">22·9</td> + <td class="br" align="center">7917</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center">2290</td> + <td class="br" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center">5004</td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="br" align="center">8032</td></tr> +<tr><td class="bblr" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="bbrdoub" align="center">2382</td> + <td class="bbr" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="bbrdoub" align="center">5106</td> + <td class="bbr" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="bbr" align="center">8147</td></tr></table> + +<p> <span class="pagenum"><a name="Page_43" id="Page_43">[Pg 43]</a></span></p> +<p class="center"><span class="smcap">Table I.</span>—<i>continued</i>.</p> +<p class="center"><i>Approximate Height due to Barometric Pressure.</i></p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td class="btlr" align="center">Inches.</td> + <td class="btrdoub" align="center">Feet.</td> + <td class="btr" align="center">Inches.</td> + <td class="btrdoub" align="center">Feet.</td> + <td class="btr" align="center">Inches.</td> + <td class="btr" align="center">Feet.</td></tr> +<tr><td class="btlr" align="center">22·6</td> + <td class="btrdoub" align="center"><span style="margin-left: .5em;">8262</span></td> + <td class="btr" align="center">18·9</td> + <td class="btrdoub" align="center">12937</td> + <td class="btr" align="center">15·2</td> + <td class="btr" align="center">18632</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">8378</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center">13076</td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="br" align="center">18805</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">8495</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center">13215</td> + <td class="br" align="center">15·0</td> + <td class="br" align="center">18979</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">8612</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center">13355</td> + <td class="br" align="center">14·9</td> + <td class="br" align="center">19154</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">8729</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center">13496</td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="br" align="center">19330</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">8847</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center">13638</td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="br" align="center">19507</td></tr> +<tr><td class="blr" align="center">22·0</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">8966</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="brdoub" align="center">13780</td> + <td class="br" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="br" align="center">19685</td></tr> +<tr><td class="blr" align="center">21·9</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">9085</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="brdoub" align="center">13923</td> + <td class="br" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="br" align="center">19865</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">9205</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="brdoub" align="center">14067</td> + <td class="br" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="br" align="center">20046</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">9325</span></td> + <td class="br" align="center">18·0</td> + <td class="brdoub" align="center">14212</td> + <td class="br" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="br" align="center">20228</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">9446</span></td> + <td class="br" align="center">17·9</td> + <td class="brdoub" align="center">14358</td> + <td class="br" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="br" align="center">20412</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">9567</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center">14505</td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="br" align="center">20597</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">9689</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center">14652</td> + <td class="br" align="center">14·0</td> + <td class="br" align="center">20783</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">9811</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center">14800</td> + <td class="br" align="center">13·9</td> + <td class="br" align="center">20970</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">9934</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center">14949</td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="br" align="center">21159</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="brdoub" align="center">10058</td> + <td class="br" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center">15099</td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="br" align="center">21349</td></tr> +<tr><td class="blr" align="center">21·0</td> + <td class="brdoub" align="center">10182</td> + <td class="br" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="brdoub" align="center">15250</td> + <td class="br" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="br" align="center">21541</td></tr> +<tr><td class="blr" align="center">20·9</td> + <td class="brdoub" align="center">10307</td> + <td class="br" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="brdoub" align="center">15402</td> + <td class="br" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="br" align="center">21734</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center">10432</td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="brdoub" align="center">15554</td> + <td class="br" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="br" align="center">21928</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center">10558</td> + <td class="br" align="center">17·0</td> + <td class="brdoub" align="center">15707</td> + <td class="br" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="br" align="center">22124</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center">10684</td> + <td class="br" align="center">16·9</td> + <td class="brdoub" align="center">15861</td> + <td class="br" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="br" align="center">22321</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center">10812</td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center">16016</td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="br" align="center">22520</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center">10940</td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center">16172</td> + <td class="br" align="center">13·0</td> + <td class="br" align="center">22720</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="brdoub" align="center">11069</td> + <td class="br" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center">16329</td> + <td class="br" align="center">12·9</td> + <td class="br" align="center">22922</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="brdoub" align="center">11198</td> + <td class="br" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center">16487</td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="br" align="center">23126</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="brdoub" align="center">11328</td> + <td class="br" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center">16646</td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="br" align="center">23331</td></tr> +<tr><td class="blr" align="center">20·0</td> + <td class="brdoub" align="center">11458</td> + <td class="br" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="brdoub" align="center">16806</td> + <td class="br" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="br" align="center">23538</td></tr> +<tr><td class="blr" align="center">19·9</td> + <td class="brdoub" align="center">11589</td> + <td class="br" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="brdoub" align="center">16967</td> + <td class="br" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="br" align="center">23746</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center">11721</td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="brdoub" align="center">17129</td> + <td class="br" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="br" align="center">23956</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center">11853</td> + <td class="br" align="center">16·0</td> + <td class="brdoub" align="center">17292</td> + <td class="br" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="br" align="center">24168</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center">11986</td> + <td class="br" align="center">15·9</td> + <td class="brdoub" align="center">17456</td> + <td class="br" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="br" align="center">24381</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center">12120</td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="brdoub" align="center">17621</td> + <td class="br" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="br" align="center">24596</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center">12254</td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="brdoub" align="center">17787</td> + <td class="br" align="center">12·0</td> + <td class="br" align="center">24813</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="brdoub" align="center">12389</td> + <td class="br" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="brdoub" align="center">17954</td> + <td class="br" align="center">11·9</td> + <td class="br" align="center">25032</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·2</span></td> + <td class="brdoub" align="center">12525</td> + <td class="br" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="brdoub" align="center">18122</td> + <td class="br" align="center"><span style="margin-left: 1em;">·8</span></td> + <td class="br" align="center">25253</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="brdoub" align="center">12662</td> + <td class="br" align="center"><span style="margin-left: 1em;">·4</span></td> + <td class="brdoub" align="center">18291</td> + <td class="br" align="center"><span style="margin-left: 1em;">·7</span></td> + <td class="br" align="center">25476</td></tr> +<tr><td class="bblr" align="center">19·0</td> + <td class="bbrdoub" align="center">12799</td> + <td class="bbr" align="center"><span style="margin-left: 1em;">·3</span></td> + <td class="bbrdoub" align="center">18461</td> + <td class="bbr" align="center"><span style="margin-left: 1em;">·6</span></td> + <td class="bbr" align="center">25700</td></tr></table> + + +<p> <span class="pagenum"><a name="Page_44" id="Page_44">[Pg 44]</a></span></p> +<p class="center"><span class="smcap">Table</span> II.</p> +<p class="center"><i>Correction due to Mean Temperature of the Air.</i></p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td class="btlr" align="center">Mean<br />Temp.</td> + <td class="btrdoub" align="center">Factor.</td> + <td class="btr" align="center">Mean<br />Temp.</td> + <td class="btrdoub" align="center">Factor.</td> + <td class="btr" align="center">Mean<br />Temp.</td> + <td class="btr" align="center">Factor.</td></tr> +<tr><td class="btlr" align="center"><span style="margin-left: .35em;">10°</span></td> + <td class="btrdoub" align="center">0·955</td> + <td class="btr" align="center"><span style="margin-left: .35em;">35°</span></td> + <td class="btrdoub" align="center">1·006</td> + <td class="btr" align="center"><span style="margin-left: .35em;">60°</span></td> + <td class="btr" align="center">1·057</td></tr> +<tr><td class="blr" align="center">11</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·957</span></td> + <td class="br" align="center">36</td> + <td class="brdoub" align="center">1·008</td> + <td class="br" align="center">61</td> + <td class="br" align="center">1·059</td></tr> +<tr><td class="blr" align="center">12</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·959</span></td> + <td class="br" align="center">37</td> + <td class="brdoub" align="center">1·010</td> + <td class="br" align="center">62</td> + <td class="br" align="center">1·061</td></tr> +<tr><td class="blr" align="center">13</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·961</span></td> + <td class="br" align="center">38</td> + <td class="brdoub" align="center">1·012</td> + <td class="br" align="center">63</td> + <td class="br" align="center">1·063</td></tr> +<tr><td class="blr" align="center">14</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·963</span></td> + <td class="br" align="center">39</td> + <td class="brdoub" align="center">1·014</td> + <td class="br" align="center">64</td> + <td class="br" align="center">1·065</td></tr> +<tr><td class="blr" align="center">15</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·965</span></td> + <td class="br" align="center">40</td> + <td class="brdoub" align="center">1·016</td> + <td class="br" align="center">65</td> + <td class="br" align="center">1·067</td></tr> +<tr><td class="blr" align="center">16</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·967</span></td> + <td class="br" align="center">41</td> + <td class="brdoub" align="center">1·018</td> + <td class="br" align="center">66</td> + <td class="br" align="center">1·069</td></tr> +<tr><td class="blr" align="center">17</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·969</span></td> + <td class="br" align="center">42</td> + <td class="brdoub" align="center">1·020</td> + <td class="br" align="center">67</td> + <td class="br" align="center">1·071</td></tr> +<tr><td class="blr" align="center">18</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·971</span></td> + <td class="br" align="center">43</td> + <td class="brdoub" align="center">1·022</td> + <td class="br" align="center">68</td> + <td class="br" align="center">1·073</td></tr> +<tr><td class="blr" align="center">19</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·974</span></td> + <td class="br" align="center">44</td> + <td class="brdoub" align="center">1·024</td> + <td class="br" align="center">69</td> + <td class="br" align="center">1·075</td></tr> +<tr><td class="blr" align="center">20</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·976</span></td> + <td class="br" align="center">45</td> + <td class="brdoub" align="center">1·026</td> + <td class="br" align="center">70</td> + <td class="br" align="center">1·077</td></tr> +<tr><td class="blr" align="center">21</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·978</span></td> + <td class="br" align="center">46</td> + <td class="brdoub" align="center">1·029</td> + <td class="br" align="center">71</td> + <td class="br" align="center">1·079</td></tr> +<tr><td class="blr" align="center">22</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·980</span></td> + <td class="br" align="center">47</td> + <td class="brdoub" align="center">1·031</td> + <td class="br" align="center">72</td> + <td class="br" align="center">1·081</td></tr> +<tr><td class="blr" align="center">23</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·982</span></td> + <td class="br" align="center">48</td> + <td class="brdoub" align="center">1·033</td> + <td class="br" align="center">73</td> + <td class="br" align="center">1·083</td></tr> +<tr><td class="blr" align="center">24</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·984</span></td> + <td class="br" align="center">49</td> + <td class="brdoub" align="center">1·035</td> + <td class="br" align="center">74</td> + <td class="br" align="center">1·086</td></tr> +<tr><td class="blr" align="center">25</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·986</span></td> + <td class="br" align="center">50</td> + <td class="brdoub" align="center">1·037</td> + <td class="br" align="center">75</td> + <td class="br" align="center">1·088</td></tr> +<tr><td class="blr" align="center">26</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·988</span></td> + <td class="br" align="center">51</td> + <td class="brdoub" align="center">1·039</td> + <td class="br" align="center">76</td> + <td class="br" align="center">1·090</td></tr> +<tr><td class="blr" align="center">27</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·990</span></td> + <td class="br" align="center">52</td> + <td class="brdoub" align="center">1·041</td> + <td class="br" align="center">77</td> + <td class="br" align="center">1·092</td></tr> +<tr><td class="blr" align="center">28</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·992</span></td> + <td class="br" align="center">53</td> + <td class="brdoub" align="center">1·043</td> + <td class="br" align="center">78</td> + <td class="br" align="center">1·094</td></tr> +<tr><td class="blr" align="center">29</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·994</span></td> + <td class="br" align="center">54</td> + <td class="brdoub" align="center">1·045</td> + <td class="br" align="center">79</td> + <td class="br" align="center">1·096</td></tr> +<tr><td class="blr" align="center">30</td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">·996</span></td> + <td class="br" align="center">55</td> + <td class="brdoub" align="center">1·047</td> + <td class="br" align="center">80</td> + <td class="br" align="center">1·098</td></tr> +<tr><td class="blr" align="center">31</td> + <td class="brdoub" align="center">0·998</td> + <td class="br" align="center">56</td> + <td class="brdoub" align="center">1·049</td> + <td class="br" align="center">81</td> + <td class="br" align="center">1·100</td></tr> +<tr><td class="blr" align="center">32</td> + <td class="brdoub" align="center">1·000</td> + <td class="br" align="center">57</td> + <td class="brdoub" align="center">1·051</td> + <td class="br" align="center">82</td> + <td class="br" align="center">1·102</td></tr> +<tr><td class="blr" align="center">33</td> + <td class="brdoub" align="center">1·002</td> + <td class="br" align="center">58</td> + <td class="brdoub" align="center">1·053</td> + <td class="br" align="center">83</td> + <td class="br" align="center">1·104</td></tr> +<tr><td class="bblr" align="center">34</td> + <td class="bbrdoub" align="center">1·004</td> + <td class="bbr" align="center">59</td> + <td class="bbrdoub" align="center">1·055</td> + <td class="bbr" align="center">84</td> + <td class="bbr" align="center">1·106</td></tr></table> + + +<p class="center"><br /><span class="smcap">Table</span> III.</p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td class="btlr" align="center">Latitude.</td> + <td class="btrdoub" align="center">Factor.</td> + <td class="btr" align="center">Latitude.</td> + <td class="btrdoub" align="center">Factor.</td> + <td class="btr" align="center">Latitude.</td> + <td class="btr" align="center">Factor.</td></tr> +<tr><td class="btlr" align="center">80°</td> + <td class="btrdoub" align="center">0·99751</td> + <td class="btr" align="center">50</td> + <td class="btrdoub" align="center">0·99954</td> + <td class="btr" align="center">20</td> + <td class="btr" align="center">1·00203</td></tr> +<tr><td class="blr" align="center">75</td> + <td class="brdoub" align="center">0·99770</td> + <td class="br" align="center">45</td> + <td class="brdoub" align="center">1·00000</td> + <td class="br" align="center">15</td> + <td class="br" align="center">1·00230</td></tr> +<tr><td class="blr" align="center">70</td> + <td class="brdoub" align="center">0·99797</td> + <td class="br" align="center">40</td> + <td class="brdoub" align="center">1·00046</td> + <td class="br" align="center">10</td> + <td class="br" align="center">1·00249</td></tr> +<tr><td class="blr" align="center">65</td> + <td class="brdoub" align="center">0·99830</td> + <td class="br" align="center">35</td> + <td class="brdoub" align="center">1·00090</td> + <td class="br" align="center"><span style="margin-left: .5em;">5</span></td> + <td class="br" align="center">1·00261</td></tr> +<tr><td class="blr" align="center">60</td> + <td class="brdoub" align="center">0·99868</td> + <td class="br" align="center">30</td> + <td class="brdoub" align="center">1·00132</td> + <td class="br" align="center"><span style="margin-left: .5em;">0</span></td> + <td class="br" align="center">1·00265</td></tr> +<tr><td class="bblr" align="center">55</td> + <td class="bbrdoub" align="center">0·99910</td> + <td class="bbr" align="center">25</td> + <td class="bbrdoub" align="center">1·00170</td> + <td class="bbr" align="center"> </td> + <td class="bbr" align="center"> </td></tr></table> + +<p> <span class="pagenum"><a name="Page_45" id="Page_45">[Pg 45]</a></span></p> +<p class="center"><span class="smcap">Table</span> IV.</p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td class="btlr" align="center">Height in<br />Thousand Feet.</td> + <td class="btrdoub" align="center">Correction<br />Additive.</td> + <td class="btr" align="center">Height in<br />Thousand Feet.</td> + <td class="btr" align="center">Correction<br />Additive.</td></tr> +<tr><td class="btlr" align="center"><span style="margin-left: .5em;">1</span></td> + <td class="btrdoub" align="center"><span style="margin-left: .5em;">3</span></td> + <td class="btr" align="center">14</td> + <td class="btr" align="center">44</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: .5em;">2</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">5</span></td> + <td class="br" align="center">15</td> + <td class="br" align="center">48</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: .5em;">3</span></td> + <td class="brdoub" align="center"><span style="margin-left: .5em;">8</span></td> + <td class="br" align="center">16</td> + <td class="br" align="center">52</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: .5em;">4</span></td> + <td class="brdoub" align="center">11</td> + <td class="br" align="center">17</td> + <td class="br" align="center">56</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: .5em;">5</span></td> + <td class="brdoub" align="center">14</td> + <td class="br" align="center">18</td> + <td class="br" align="center">60</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: .5em;">6</span></td> + <td class="brdoub" align="center">17</td> + <td class="br" align="center">19</td> + <td class="br" align="center">65</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: .5em;">7</span></td> + <td class="brdoub" align="center">20</td> + <td class="br" align="center">20</td> + <td class="br" align="center">69</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: .5em;">8</span></td> + <td class="brdoub" align="center">23</td> + <td class="br" align="center">21</td> + <td class="br" align="center">74</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: .5em;">9</span></td> + <td class="brdoub" align="center">26</td> + <td class="br" align="center">22</td> + <td class="br" align="center">78</td></tr> +<tr><td class="blr" align="center">10</td> + <td class="brdoub" align="center">30</td> + <td class="br" align="center">23</td> + <td class="br" align="center">83</td></tr> +<tr><td class="blr" align="center">11</td> + <td class="brdoub" align="center">33</td> + <td class="br" align="center">24</td> + <td class="br" align="center">88</td></tr> +<tr><td class="blr" align="center">12</td> + <td class="brdoub" align="center">37</td> + <td class="br" align="center">25</td> + <td class="br" align="center">93</td></tr> +<tr><td class="bblr" align="center">13</td> + <td class="bbrdoub" align="center">41</td> + <td class="bbr" align="center">26</td> + <td class="bbr" align="center">98</td></tr></table> + +<p><span class="smcap">Example 1.</span> On October 21st, 1852, when Mr. Welsh ascended in a balloon, at +3h. 30m. p.m., the barometer, corrected and reduced, was 18·85, the air +temperature 27°, while at Greenwich, 159 feet above the sea, the barometer +at the same time was 29·97 inches, air temperature 49°, the balloon not +being more than 5 miles S.W. from over Greenwich; required its elevation.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td colspan="6"> </td><td align="center">Feet.</td></tr> + +<tr><td>Barometer</td> + <td>in Balloon</td> + <td> </td> + <td>18·85,</td> + <td>Table I.</td> + <td align="center">=</td> + <td align="right">13007</td></tr> +<tr><td align="center">"</td> + <td>at Greenwich</td> + <td> </td> + <td>29·97</td> + <td align="center">"</td> + <td> </td> + <td class="botbor" align="right">883</td></tr> +<tr><td colspan="6"> </td> + <td align="right">12124</td></tr> +<tr><td colspan="6">Mean Temperature, 38°, Table II. Factor</td> + <td align="right" class="botbor">1·012</td></tr> +<tr><td colspan="6"> </td> + <td align="right" class="botbor">12269·</td></tr> +<tr><td colspan="6">Latitude 51½°, Factor from Table III.</td> + <td align="right" class="botbor">·99941</td></tr> +<tr><td colspan="6"> </td> + <td align="right">12262</td></tr> +<tr><td colspan="6">Correction from Table IV.</td> + <td align="right" class="botbor">38</td></tr> +<tr><td colspan="6"> </td> + <td align="right">12300</td></tr> +<tr><td colspan="6">Elevation of Greenwich</td> + <td align="right" class="botbor">159</td></tr> +<tr><td colspan="6"><span style="margin-left: 1.75em;">"</span><span style="margin-left: 2.75em;">Balloon</span></td> + <td align="right" class="botbor2">12459</td><td>feet.</td></tr></table> + +<p>The following examples, from the balloon ascents of J. Glashier, Esq., +F.R.S., will serve for practice.<small><a name="f4.1" id="f4.1" href="#f4">[4]</a></small></p> + +<p><span class="pagenum"><a name="Page_46" id="Page_46">[Pg 46]</a></span>2. Ascended from Wolverhampton, 18th August, 1862, at 2h. 38m. p.m.; +barometer (in all cases corrected and reduced to 32° F) was 14·868, the +temperature of the air 26°; at the same time, at Wrottesley Hall, 531 feet +above the sea, in latitude 52½° N, the barometer was 29·46, and the +temperature of the air 65°·4; find the elevation of the balloon above the +sea.</p> + +<p class="right">Height, 18,959 feet.</p> + +<p>3. From the same place an ascent was made 5th September, 1862, when at 1h. +48m. p.m. barometer was 11·954, air O°; at Wrottesley Hall 29·38, air 56°.</p> + +<p class="right">Height, 23,923 feet.</p> + +<p>4. From the Crystal Palace a balloon ascent was made 20th August, 1862. At +6h. 47m. p.m. barometer was 25·55, air 50°·5; and at the same time at +Greenwich Observatory, at 159 feet above the sea, the barometer was 29·81, +air 63°.</p> + +<p class="right">Height, 4,406 feet.</p> + +<p>5. From the same place an ascent was made 8th September, 1862. At 5 p.m., +the balloon being over Blackheath, barometer was 25·60, and the air 49°·5, +while at Greenwich, barometer was 29·92, air 66°·4.</p> + +<p class="right">Height, 4,461 feet.</p> + + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_47" id="Page_47">[Pg 47]</a></span></p> +<h2><a name="CHAPTER_V" id="CHAPTER_V"></a>CHAPTER V.</h2> +<p class="center"><span class="large">SECONDARY BAROMETERS.</span></p> + +<p><br /><b>43. Desirability of Magnifying the Barometer Range.</b>—The limits within +which the ordinary barometric column oscillates, do not exceed four inches +for extreme range, while the ordinary range is confined to about two +inches; hence it has often been felt that the public utility of the +instrument would be greatly enhanced if by any means the scale indications +could be increased in length. This object was sought to be obtained by +bending the upper part of the tube from the vertical, so that the inches +on the scale could be increased in length in proportion to the secant of +the angle it made with the vertical. This was called “the diagonal +barometer.” The upper part of the tube has also been formed into a spiral, +and the scale, placed along it, is thus greatly enlarged.</p> + +<p>But these methods of enlarging the indications cannot be so successfully +accomplished, nor so cheaply nor so elegantly, as is done by the principle +employed in the dial barometer. Hence they are not in use.</p> + + +<div class="figleft">Fig. 31.<br /><img src="images/fig_31.jpg" alt="" /></div> + +<p><br /><b>44. Howson’s Long Range Barometer.</b>—Very recently quite a novel design has +been patented by Mr. Howson, for a long range barometer. The construction +requires neither distortion of the tube, nor mechanism for converting a +short scale into a long one; but the mercury itself rises and falls, +through an extended range, naturally, and in simple obedience to the +varying pressure of the atmosphere. The tube is fixed, but its cistern is +sustained by the mere pressure of the atmosphere. Looking at the +instrument, it seems a perfect marvel. It appears as though the cistern +with the mercury in it must fall to the ground. The bore of the tube is +wide, about an inch across. A long glass rod is fixed to the bottom of the +glass cistern, where a piece of cork or some elastic substance is also +placed. The tube is filled with mercury; the glass rod is plunged into the +tube as it is held top downwards, until the cork gets close up to the tube +and fits tightly against it. The pressure against the cork simply prevents +the mercury from coming out while the instrument is being inverted. When +it is inverted, the mercury partly falls, and forms an ordinary barometric +column. When the top is held, the cistern and glass rod, instead of +falling away, remain perfectly suspended. There is no material support to +the cistern; the tube only is fixed, the cistern hangs to it. Glass is +many times lighter than mercury. When the glass rod is introduced, it +displaces an equal volume of mercury. The glass rod, being so much lighter +than mercury, floats and sustains the additional weight of the cistern by +its buoyancy. In the mean time, the atmosphere is acting upon the mercury, +keeping up the ordinary barometric column. Supposing there is a rise in +the ordinary barometer, the<span class="pagenum"><a name="Page_48" id="Page_48">[Pg 48]</a></span> atmosphere presses some more mercury up the +tube. This mercury is taken out of the cistern, which of course becomes +lighter, and therefore the rod and cistern float up a little higher, which +thus causes the column of mercury to rise still more. The increased +pressure and buoyancy thus acting together, increase the ascent in the +barometric column, as shown by the fixed scale. One inch in the barometer +might be represented by two or more inches in this instrument, according +to construction. Supposing there was a decrease of pressure, the mercury +would fall, come into the cistern, make it heavier, and increase the fall +somewhat. Friction guides, at the top of the rod, prevent it coming into +contact with the side of the tube when vertically suspended. The +illustration, Fig. 31, shows the appearance of the instrument as framed in +wood by the makers, Messrs. Negretti and Zambra.</p> + + +<p><br /><b>45. McNeild’s Long Range Barometer.</b>—A barometer designed by a gentleman +named McNeild is on a directly opposite principle to the one just +described. The tube is made to float on the mercury in the cistern. It is +filled with mercury, inverted in the usual manner, then allowed to float, +being held vertically by glass friction points or guides. By this +contrivance, the ordinary range of the barometer is greatly increased. One +inch rise or fall in the standard barometer may be represented by four or +five inches in this instrument, so that it shows small variations in +atmospheric pressure very distinctly. As the mercury falls in the tube +with a decrease of pressure, the surface of the mercury in the cistern +rises, and the floating tube rises also, which causes an additional +descent in the column, as shown by fixed graduations on the tube. With an +increase of pressure, some mercury will leave the cistern and rise in the +tube, while the tube itself will fall, and so cause an additional ascent +of mercury. This barometer is identical in principle with King’s Barograph +(see <a href="#Page_34">p. 34</a>).</p> + +<p>The construction of Howson’s and McNeild’s Barometers has been assigned to +Messrs. Negretti and Zambra. These instruments are usually made for +domestic purposes with a scale of from three to five, and for public use +from five to eight times the scale of the ordinary standard. Their +sensitiveness is consequently increased in an equal proportion, and they +have the additional advantage of not being affected by differences of +level in the cistern. However, these novelties have not been sufficiently +tried to determine their practical value for strictly scientific<span class="pagenum"><a name="Page_49" id="Page_49">[Pg 49]</a></span> +purposes; but as weather-glasses, for showing minute changes, they are +superior to the common barometer.</p> + + +<p><br /><b>46. The Water-glass Barometer.</b>—If a Florence flask, having a long neck, +have a small quantity of water poured into it, and then be inverted and so +supported that the open end dips into a vessel containing water, a small +column of water will be confined in the neck of the bottle, the pressure +of which, upon the surface of the exposed water, will be equal to the +difference between the atmospheric pressure and the elasticity of the +confined air in the body of the bottle. As the pressure of the atmosphere +varies, this column will alter in height. But the elasticity of the +confined air is also subject to variations, owing to changes of +temperature. It follows, then, that the oscillations of the column are +dependent on alterations of temperature and atmospheric pressure. Such an +arrangement has been called “the Water-glass Barometer,” and bears about +the same relative value to the mercurial barometer, as an exponent of +weather changes, that a cat-gut hygrometer bears to a thermometric +hygrometer, as an indicator of relative moisture.</p> + + +<p class="center"><br />47. SYMPIESOMETER.</p> + +<div class="figleft">Fig. 32.<br /><img src="images/fig_32.jpg" alt="" /></div> + +<p>Nevertheless the instrument now about to be described, depending upon +similar principles, but scientifically constructed and graduated, is a +very useful and valuable substitute for the mercurial barometer. It +consists of a glass tube, varying, according to the purposes for which the +instrument is required, from six to twenty-four inches in length. The +upper end is closed, and formed into a bulb; the lower is turned up, +formed into a cistern, and open at top, through a pipette, or cone. A +plug, moveable by a catch from below, can be made to close this opening, +so as to render the instrument portable.</p> + +<p>The upper portion of the tube is filled with air; the lower portion, and +part of the cistern, with sulphuric acid, coloured so as to render it +plainly visible. Formerly, hydrogen and oil were used. It was found, +however, that, by the process known to chemists as <i>osmosis</i>, this light +gas in time partially escaped, and the remainder became mixed with air, +the consequence being that the graduations were no longer correct. They +are more durable as at present constructed. The liquid rises and falls in +the tube with the variations of atmospheric pressure and temperature +acting together. If the pressure were constant, the confined air would +expand and contract for temperature only, and the instrument would act as +a thermometer. In fact, the instrument is regarded as such in the +manufacture; and the thermometric<span class="pagenum"><a name="Page_50" id="Page_50">[Pg 50]</a></span> scales are ascertained and engraved on +the scale. A good mercurial thermometer is also mounted on the same frame. +If, therefore, at any time the mercurial and the air thermometers do not +read alike, it must evidently be due to the atmospheric pressure acting +upon the air in the tube; and it is further evident that, under these +circumstances, the position of the top of the liquid may be marked to +represent the barometric pressure at the time. In this manner a scale of +pressure is ascertained by comparison with a standard barometer, extending +generally from 27 to 31 inches.</p> + +<p>When made correctly, these instruments agree well with the mercurial +barometer for a number of years, and their subsequent adjustment is not a +matter of much expense.</p> + +<p>For use at sea, the liquid column is contracted at the bend. The +sympiesometer is very sensitive, and feels the alterations in the +atmospheric pressure sooner than the ordinary marine barometer.</p> + +<p>The scale is usually on silvered brass, mounted on a mahogany or rosewood +frame, protected in front by plate glass. It is generally furnished with a +revolving register, to record the observation, in order that it may be +known whether the pressure has increased or decreased in the interval of +observation.</p> + +<p>Small pocket sympiesometers are sometimes fitted with ivory scales, and +protected by a neat velvet-lined pasteboard or morocco case.</p> + +<p><i>How to take an Observation.</i>—In practice, the indications of the +atmospheric pressure are obtained from the sympiesometer by noting, first, +the temperature of the mercurial thermometer; secondly, adjusting the +pointer of the pressure scale to the same degree of temperature on the +scale of the air column; thirdly, reading the height of the liquid on the +sliding scale.</p> + +<p><i>Directions for Use.</i>—The sympiesometer should be carried and handled so +as to keep the top always upwards, to prevent the air mechanically mixing +with the liquid. Care should also be taken to screen it from casual rays +of the sun or cabin fire.</p> + + +<p class="center"><br />48. ANEROIDS.</p> + +<p>The beautiful and highly ingenious instrument called by the name +<i>Aneroid</i>, is no less remarkable for the scientific principles of its +construction and action, than for the nicety of its mechanism. It is a +substitute, and perhaps the best of all substitutes, for the mercurial +barometer. As its name implies, it is constructed “without fluid.” It was +invented by M. Vidi of Paris. In the general form in which it is made it +consists of a brass cylindrical case about four inches in diameter and one +and a half inch deep, faced with a dial graduated and marked similarly to +the dial-plate of a “wheel-barometer,” upon which the index or pointer +shows the atmospheric pressure in inches and decimals of an inch in +accordance with the mercurial barometer. Within the case, for ordinary +sizes, is placed a flat metal box, generally not more than half an inch +thick and about two inches or a little more in diameter, from which nearly +all the air is exhausted. The top and bottom of this box is corrugated in +concentric circles, so as to yield inwardly to external pressure, and +return when the pressure is removed. The<span class="pagenum"><a name="Page_51" id="Page_51">[Pg 51]</a></span> pressure of the atmosphere, +acting externally, continually changes, while the elastic pressure of the +small quantity of air within can only vary by its volume being increased +or decreased, or by change of temperature. Leaving out of consideration, +for the moment, the effect of temperature, we can readily perceive that as +the pressure is lessened upon the outside of the box, the elastic force of +the air within will force out the top and bottom of the box; and when the +outer pressure is increased they will be forced in. Thus with the varying +pressure of the atmosphere, the top and bottom of the box approach to and +recede from each other by a small quantity; but the bottom being fixed, +nearly all this motion takes place on the top. Thus the top of the box is +like an elastic cushion, which rises and falls according as the +compressing force lessens or increases. To the eye these expansions and +contractions would not be perceptible, so small is the motion. But they +are rendered very evident by a nice mechanical arrangement. To the box is +attached a strong piece of iron, kept pressed upon it by a spring at one +extremity; so that as the top of the box rises, the motion is made +sensible at the point held by the spring, and when the top descends the +spring draws the piece of iron into close contact with it. This piece of +iron acts as a lever, having its fulcrum at one extremity, the power at +the centre of the box-top, and the other extremity controlled by the +spring. Thus it is evident that the small motion of the centre of the +box-top is much increased at the spring extremity. The motion thus +obtained is communicated to a system of levers; and, by the intervention +of a piece of watch-chain and a fine spring passing round the arbour, +turns the index to the right or left, according as the external pressure +increases or decreases. Thus, when by increase of pressure the vacuum box +is compressed, the mechanism transfers the movement to the index, and it +moves to the right; when the vacuum box bulges out under diminished +pressure, the mechanical motion is reversed, and the index moves to the +left. As the index traverses the dial, it shows upon the scale the +pressure corresponding with that which a good mercurial barometer would at +the same time and place indicate; that is, supposing it correctly +adjusted.</p> + +<p>A different and more elegant arrangement has since been adopted. A broad +curved spring is connected to the top of the vacuum box, so as to be +compressed by the top of the box yielding inward to increased pressure, +and to relax itself and the box as the pressure is lessened. The system of +levers is connected to this spring, which augments and transfers the +motion to the index, in the manner already described. Increase of pressure +causes the levers to slacken the piece of watch-chain connected with them +and the arbour of the index. The spring now uncoils, winds the chain upon +the arbour, and turns the index to the right. Decrease of pressure winds +the chain off the barrel, tightens the spiral spring, which thus turns the +index to the left. The graduations of the aneroid scale are obtained by +comparisons with the correct standard reading of a mercurial barometer, +under the normal and reduced atmospheric pressure. Reduced pressure is +obtained by placing both instruments under the receiver of an air pump.</p> + +<div class="figleft">Fig. 33.<br /><img src="images/fig_33.jpg" alt="" /></div> + +<p><span class="pagenum"><a name="Page_52" id="Page_52">[Pg 52]</a></span>Fig. 33 represents the latest improved mechanism of an aneroid. The outer +case and the face of the instrument are removed, but the hand is attached +by its collet to the arbour. <i>A</i> is the corrugated box, which has been +exhausted of air through the tube, <i>J</i>, and hermetically sealed by +soldering. <i>B</i> is a powerful curved spring, resting in gudgeons fixed on +the frame-plate, and attached to a socket behind, <i>F</i>, in the top of the +box. A lever, <i>C</i>, joined to the stout edge of the spring, is connected, +by the bent lever at <i>D</i>, with the chain, <i>E</i>, the other end of which is +coiled round, and fastened to the arbour, <i>F</i>. As the box, <i>A</i>, is +compressed by the weight of the atmosphere increasing, the spring, <i>B</i>, is +tightened, the lever, <i>C</i>, depressed, and the chain, <i>E</i>, uncoiled from +<i>F</i>, which is thereby turned so that the hand, <i>H</i>, moves to the right. In +the mean while the spiral spring, <i>G</i>, coiled round <i>F</i>, and fixed at one +extremity to the frame-work and by the other to <i>F</i>, is compressed. When, +therefore, the pressure decreases, <i>A</i> and <i>B</i> relax, by virtue of their +elasticity; <i>E</i> slackens, <i>G</i> unwinds, turning <i>F</i>, which carries <i>H</i> to +the left. Near <i>J</i> is shown an iron pillar, cast as part of the stock of +the spring, <i>B</i>. A screw works in this pillar through the bottom of the +plate, by means of which the spring, <i>B</i>, may be so adjusted to the box, +<i>A</i>, as to set the hand, <i>H</i>, to read on the scale according to the +indications of a mercurial barometer. The lever, <i>C</i>, is composed of brass +and steel, soldered together, and adjusted by repeated trials to correct +for the effects of temperature.</p> + +<p>A thermometer is sometimes attached to the aneroid, as it is convenient +for indicating the temperature of the air. As regards the instrument +itself, no correction for temperature can be applied with certainty. It +should be set to read with the mercurial barometer at 32° F. Then the +readings from it are supposed to require no correction.</p> + +<p>In considering the effects of temperature upon the aneroid, they are found +to be somewhat complex. There is the effect of expansion and contraction +of the various metals of which the mechanism is composed; and there is the +effect on the elasticity of the small portion of air in the box. An +increase of temperature produces greater, a diminution less elasticity in +this air. The compensation for effects of temperature is adjusted by the +process of “trial and error,” and only a few makers do it well. It is very +often a mere sham. Admiral FitzRoy writes, in his <i>Barometer Manual</i>, “The +known expansion and contraction of metals under varying temperatures, +caused doubts as to the accuracy of the aneroid under such changes; but +they were partly removed by introducing into the vacuum box a small +portion of gas, as a compensation for the effects of heat or cold. The gas +in the box, changing its bulk on a change of temperature, was intended to +compensate for the effect on the metals<span class="pagenum"><a name="Page_53" id="Page_53">[Pg 53]</a></span> of which the aneroid is made. +Besides which, a further and more reliable compensation has lately been +effected by a combination of brass and steel bars.”</p> + +<p>“Aneroid barometers, if often compared with good mercurial columns, are +similar in their indications, and valuable; but it must be remembered that +they are not independent instruments, that they are set originally by a +barometer, require adjustment occasionally, and may deteriorate in time, +though slowly.”</p> + +<p>“The aneroid is quick in showing the variation of atmospheric pressure; +and to the navigator who knows the difficulty, at times, of using +barometers, this instrument is a great boon, for it can be placed +anywhere, quite out of harm’s way, and is not affected by the ship’s +motion, although faithfully giving indication of increased or diminished +pressure of air. In ascending or descending elevations, the hand of the +aneroid may be seen to move (like the hand of a watch), showing the height +above the level of the sea, or the difference of level between places of +comparison.”</p> + +<p>In the admiral’s <i>Notes on Meteorology</i>, he says, “The aneroid is an +excellent <i>weather glass</i>, if well made. Compensation for heat or cold has +lately been introduced by efficient mechanism. In its <i>improved</i> +condition, when the cost may be about £5, it is fit for measuring heights +as far as 5,000 feet with approximate accuracy; but even at the price of +£3, as a <i>weather-glass</i> only, it is exceedingly valuable, because it can +be carried anywhere; and if now and then compared with a good barometer, +it may be relied on sufficiently. I have had one in constant use for ten +years, and it appears to be as good now as at first. For a ship of war +(considering concussion by the fire of guns), for boats, or to put in a +drawer, or on a table, I believe there is nothing better than it for use +as a common weather-glass.”</p> + +<p>Colonel Sir H. James, R.E., in his <i>Instructions for taking Meteorological +Observations</i>, says of the aneroid, “This is a most valuable instrument; +it is extremely portable. I have had one in use for upwards of ten years, +and find it to be the best form of barometer, as a “weather-glass,” that +has been made.”</p> + +<p>One of the objects of Mr. Glaisher’s experiments in balloons was “to +compare the readings of an aneroid barometer with those of a mercurial +barometer up to five miles.” In the comparisons the readings of the +mercurial barometer were corrected for index-error and temperature. The +aneroid readings, says Mr. Glaisher, “prove all the observations made in +the several ascents may be safely depended upon, and also that an aneroid +barometer can be made to read correctly to pressures below twelve inches.” +As one of the general conclusions derived from his experiments he states, +“that an aneroid barometer read correctly to the first place, and probably +to the second place of decimals, to a pressure as low as seven inches.” +The two aneroids used by Mr. Glaisher were by Messrs. Negretti and Zambra.</p> + +<p>Aneroids are now manufactured almost perfectly compensated for +temperature. Such an instrument therefore ought to show the same pressure +in the external air at a temperature say of 40°, as it would in a room +where the temperature at the same time may be 60°; provided there is no +difference of elevation. To test it thoroughly would require an +examination and a comparison with barometer readings<span class="pagenum"><a name="Page_54" id="Page_54">[Pg 54]</a></span> reduced to 32° F., +conducted through a long range of temperature and under artificially +reduced pressure. A practical method appears to be to compare the aneroid +daily, or more often, for a few weeks with the readings of a mercurial +barometer reduced to 32°; and if the error so found be constant, the +object of the compensation may be assumed to be attained, particularly if +the temperature during the period has varied greatly.</p> + +<p><i>Directions for using the Aneroid.</i>—Aneroids are generally suspended with +the dial vertical; but if they be placed with the dial horizontal, the +indications differ a few hundredths of an inch in the two positions. +Hence, if their indications are registered, they should be kept in the +same position.</p> + +<p>The aneroid will not answer for exact scientific purposes, as it cannot be +relied upon for a length of time. Its error of indication changes slowly, +and hence the necessity of its being set from time to time with the +reading of a good barometer. To allow of this being done, at the back of +the outer case is the head of a screw in connection with the spring +attached to the vacuum box. By applying a small turnscrew to this screw, +the spring of the vacuum box may be tightened or relaxed, and the index +made to move correspondingly to the right or left on the dial. By this +means, besides being enabled to correct the aneroid at any time, “if the +measure of a height rather greater than the aneroid will commonly show be +required, it may be <i>re-set</i> thus: When at the upper station (<i>within its +range</i>), and having noted the reading carefully, touch the screw behind so +as to bring back the hand a few inches (if the instrument will admit), +then read off and start again. <i>Reverse the operation when descending.</i> +This may add some inches of measure <i>approximately</i>.”—<i>FitzRoy.</i></p> + + +<div class="figleft">Fig. 34.<br /><img src="images/fig_34.jpg" alt="" /></div> + +<p><br /><b>49. Small Size Aneroids.</b>—The patent for the Aneroid having expired, +Admiral FitzRoy urged upon Messrs. Negretti & Zambra the desirability of +reducing the size at which it had hitherto been made, as well as of +improving its mechanical arrangement, and compensation for temperature. +They accordingly engaged skilful workmen, who, under their directions, and +at their expense, by a great<span class="pagenum"><a name="Page_55" id="Page_55">[Pg 55]</a></span> amount of labour and experiment, succeeded +in reducing its dimensions to two inches in diameter, and an inch and a +quarter thick. The exact size and appearance of this aneroid are shown in +fig. 34. The compensation is carefully adjusted, and the graduations of +the dial ascertained under reduced pressure, so that they are not quite +equal, but more accurate.</p> + +<div class="figright">Fig. 35.<br /><img src="images/fig_35.jpg" alt="" /></div> + +<p><br /><b>50. Watch Aneroid.</b>—Subsequently the aneroid has been further reduced in +size and it can now be had from an inch and a quarter to six inches in +diameter. The smallest size can be enclosed in watch cases, fig. 35, or +otherwise, so as to be adapted to the pocket. By a beautifully simple +contrivance, a milled rim is adjusted to move round with hand pressure, +and carry a fine index or pointer, outside and around the scale engraved +on the dial, or face, for the purpose of marking the reading, so that the +subsequent increase or decrease of pressure may be readily seen. These +very small instruments are found to act quite as correctly as the largest, +and are much more serviceable. Besides serving the purpose of a +weather-glass in the house or away from home, if carried in the pocket, +they are admirably suited to the exigencies of tourists and travellers. +They may be had with scale sufficient to measure heights not exceeding +8,000 feet; with a scale of elevation in feet, as well as of pressure in +inches, engraved on the dial. The scale of elevation, which is for the +temperature of 50°, was computed by Professor Airy, the Astronomer Royal, +who kindly presented it to Messrs. Negretti and Zambra, at the same time +suggesting its application. Moderate-sized aneroids, fitted in leathern +sling cases, are also good travelling instruments, and will be found +serviceable to pilots, fishermen, and for use in coasting and small +vessels, where a mercurial barometer cannot be employed, because requiring +too much space.</p> + +<p>Admiral FitzRoy, in a communication to the <i>Mercantile Marine Magazine</i>, +December, 1860, says:—“Aneroids are now made more portable, so that a +pilot or chief boatman may carry one in his pocket, as a railway guard +carries his timekeeper; and, thus provided, pilots cruising for expected +ships would be able to caution strangers arriving, if bad weather were +impending, or give warning to coasters or fishing boats. Harbours of +Refuge, however excellent and important, are not always accessible, even +when most wanted, as in snow, rain, or darkness, when neither land, nor +buoy, nor even a lighthouse-light can be seen.”</p> + + +<p><br /><span class="pagenum"><a name="Page_56" id="Page_56">[Pg 56]</a></span><b>51. Measurement of Heights by the Aneroid.</b>—For measuring heights not +exceeding many hundred feet above the sea-level by means of the aneroid, +the following simple method will suffice:—</p> + +<p>Divide the difference between the aneroid readings at the lower and upper +stations by ·0011; the quotient will give the approximate height in feet.</p> + +<p>Thus, supposing the aneroid to read at the</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>Lower Station</td><td> </td><td>30·385</td><td>inches.</td></tr> +<tr><td>Upper Station</td><td> </td><td class="botbor">30·025</td></tr> +<tr><td> </td><td>Difference</td><td class="botbor2">·360</td></tr></table> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td rowspan="2">Divided gives</td><td class="botbor">·360</td><td rowspan="2">= 327 feet.</td></tr> +<tr><td>·0011</td></tr></table> + +<p>As an illustration of the mode in which the aneroid should be used in +measuring heights, the following example is given:—</p> + +<p>A gentleman who ascended Helvellyn, August 12th, 1862, recorded the +following observations with a pocket aneroid by Negretti and Zambra:—</p> + +<p>Near 10 a.m., at the first milestone from Ambleside, found by survey to be +188 feet above the sea, the aneroid read 29·89 inches; about 1 p.m., at +the summit of Helvellyn, 26·81; and at 5 p.m., at the milestone again, +29·76. The temperature of the lower air was 57°, of the upper, 54°. Hence +the height of the mountain is deduced as follows:—</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td colspan="3"> </td> + <td align="center">Inches.</td></tr> +<tr><td>Reading at</td> + <td>10 a.m.</td> + <td><span class="spacer"> </span></td> + <td>29·89</td></tr> +<tr><td align="center">"</td> + <td>5 p.m.</td> + <td> </td> + <td class="botbor">29·76</td></tr> +<tr><td> </td> + <td>Mean</td> + <td> </td> + <td>29·825</td> + <td><span class="spacer2"> </span></td> + <td>Table I.<small><a name="f5.1" id="f5.1" href="#f5">[5]</a></small></td> + <td align="right">1010</td></tr> +<tr><td colspan="2">Upper Reading</td> + <td> </td> + <td class="botbor">26·81</td> + <td> </td> + <td align="center">"</td> + <td align="right" class="botbor">3796</td></tr> +<tr><td> </td> + <td>Difference</td> + <td colspan="4"> </td> + <td align="right">2786</td></tr> +<tr><td colspan="6">Mean Temperature 55°·5, gives in Table II.</td> + <td align="right" class="botbor">1·048</td></tr> +<tr><td colspan="6"> </td> + <td align="right">2920</td></tr> +<tr><td colspan="6">Lat. 55° N., gives in Table III.</td> + <td align="right" class="botbor">·9991</td></tr> +<tr><td colspan="6"> </td> + <td align="right">2917</td></tr> +<tr><td colspan="6"><span style="margin-left: 8em;">Table IV.</span></td> + <td align="right" class="botbor">5</td></tr> +<tr><td colspan="6"><span style="margin-left: 4em;">Difference of height</span></td> + <td align="right">2922</td></tr> +<tr><td colspan="6">Height of lower station</td> + <td align="right" class="botbor">188</td></tr> +<tr><td colspan="6"><span style="margin-left: 2em;">"</span><span style="margin-left: 1.5em;">Helvellyn</span></td> + <td align="right" class="botbor2">3110</td></tr> +<tr><td colspan="6">In Sir J. Herschell’s <i>Physical Geography</i> it is given as</td> + <td align="right">3115</td><td>ft.</td></tr></table> + +<p><span class="pagenum"><a name="Page_57" id="Page_57">[Pg 57]</a></span>So near an agreement is attributable to the excellence of the aneroid, and +the careful accuracy of the observer.</p> + + +<p class="center"><br />52. METALLIC BAROMETER.</p> + +<p>This instrument, the invention of M. Bourdon, has a great resemblance to +the aneroid, but is much simpler in arrangement. The inventor has applied +the same principle to the construction of metallic steam-pressure gauges. +We are here, however, only concerned with it as constructed to indicate +atmospheric pressure. It consists of a long slender flattened metallic +tube, partially exhausted of air, and hermetically closed at each end, +then fixed upon its centre, and bent round so as to make the ends face +each other. The transverse section of this tube is an elongated ellipse. +The principle of action is this: interior pressure tends to straighten the +tube, external pressure causes it to coil more. Hence as the atmospheric +pressure decreases, the ends of the tube become more apart.</p> + +<p>This movement is augmented and transferred by a mechanical arrangement of +small metallic levers to a radius bar, which carries a rack formed on the +arc of its circle. This moves a pinion, upon the arbour of which a light +pointer, or “hand,” is poised, which indicates the pressure upon a dial. +When the pressure increases, the ends of the tube approach each other, and +the pointer moves from left to right over the dial. The whole mechanism is +fixed in a brass case, having a hole at the back for adjusting the +instrument to the mercurial barometer by means of a key, which sets the +pointer without affecting the levers. The dial is generally open to show +the mechanism, and is protected by a glass, to which is fitted a moveable +index.</p> + +<p>This barometer is very sensitive, and has the advantage of occupying +little space, although it has not yet been made so small as the aneroid. +Both these instruments admit of a great variety of mounts to render them +ornamental. The metallic barometer can be constructed with a small clock +in its centre, so as to form a novel and beautiful drawing-room ornament.</p> + +<p>Admiral FitzRoy writes, “Metallic barometers, by Bourdon, have not yet +been tested in very moist, hot, or cold air for a sufficient time. They +are dependent, or secondary instruments, and liable to deterioration. For +limited employment, when sufficiently compared, they may be very useful, +especially in a few cases of electrical changes, <i>not foretold or shown by +mercury</i>, which these seem to indicate remarkably.”</p> + +<p>They are not so well adapted for travellers, nor for measurements of +considerable elevations, as aneroids.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_58" id="Page_58">[Pg 58]</a></span></p> +<h2><a name="CHAPTER_VI" id="CHAPTER_VI"></a>CHAPTER VI.</h2> +<p class="center"><span class="large">INSTRUMENTS FOR ASCERTAINING TEMPERATURE.</span></p> + +<p><br /><b>53. Temperature</b> is the energy with which heat affects our sensation of +feeling.</p> + +<p>Bodies are said to possess the same temperature, when the amounts of heat +which they respectively contain act outwardly with the same intensity of +transfer or absorption, producing in the one case the sensation of warmth, +in the other that of coldness. Instruments used for the determination and +estimation of temperatures are called <i>Thermometers</i>.</p> + +<p>Experience proves that the same body always occupies the same space at the +same temperature; and that for every increase or decrease of its +temperature, it undergoes a definite dilatation or contraction of its +volume. Provided, then, a body suffers no loss of substance or peculiar +change of its constituent elements or atoms, while manifesting changes of +temperature it will likewise exhibit alterations in volume; the latter +may, therefore, be taken as exponents of the former. The expansion and +contraction of bodies are adopted as arbitrary measures of changes of +temperature; and any substance will serve for a thermometer in which these +changes of volume are sensible, and can be rendered measureable.</p> + + +<p><br /><b>54. Thermometric Substances.</b>—Thermometers for meteorological and domestic +purposes are constructed with liquids, and generally either mercury or +alcohol, because their alterations of volume for the same change of +temperature are greater than those of solids; while being more manageable, +they are preferred to gases. Mercury is of all substances the best adapted +for thermometric purposes, as it maintains the liquid state through a +great alteration of heat, has a more equable co-efficient of expansion +than any other fluid, and is peculiarly sensitive to changes of +temperature. The temperature of solidification of mercury, according to +Fahrenheit’s scale of temperature, is -40°; and its temperature of +ebullition is about 600°. Sulphuric ether, nitric acid, oil of sassafras, +and other limpid fluids, have been employed for thermometers.</p> + + +<p><br /><b>55. Description of the Thermometer.</b>—The ordinary thermometer consists of +a glass tube of very fine bore, having a bulb of thin glass at one +extremity, and closed at the other. The bulb and part of the tube contains +mercury; the rest of the tube is a vacuum, and affords space for the +expansion of the liquid. This arrangement renders very perceptible the +alterations in volume of the mercury due to changes of temperature. It is +true, the glass expands and contracts also; but only by about +one-twentieth of the extent of the mercury. Regarding the bulb, then, as +unalterable in size, all the changes in the bulk of the fluid must take +place<span class="pagenum"><a name="Page_59" id="Page_59">[Pg 59]</a></span> in the tube, and be exhibited by the expansion and contraction of +the column, which variations are made to measure changes of temperature.</p> + + +<p class="center"><br />56. STANDARD THERMOMETER.</p> + +<div class="figright">Fig. 36<br /><img src="images/fig_36.jpg" alt="" /><br /></div> + +<p>The peculiarities in the construction of thermometers will be best +understood by describing the manufacture of a <i>Standard Thermometer</i>, +which is one of the most accurate make, and the scale of which is divided +independently of any comparison with another thermometer. Fig. 36 is an +illustration of such an instrument, on a silvered brass scale.</p> + +<p><i>Selection of Tube.</i>—In selecting the glass tube, much care is requisite +to ascertain that its bore is perfectly uniform throughout. As received +from the glass-house, the tubes are generally, in their interior, portions +of very elongated cones, so that the bore is wider at one end than at the +other. With due care, however, a proper length of tube can be selected, in +which there is no appreciable difference of bore. This is ascertained by +introducing into the tube a length of mercury of about a half or a third +of an inch, and accurately measuring it in various positions in the tube. +To accomplish this, the workman blows a bulb at one end of the tube, and +heats the bulb a little to drive out some of the air. Then, placing the +open end in mercury, upon cooling the elasticity of the enclosed air +diminishes, and the superior pressure of the atmosphere drives in some +mercury. The workman stops the process so soon as he judges sufficient +mercury has entered. By cooling or heating the bulb, as necessary, the +mercury is made to pass from one end of the tube to the other. Should the +length of this portion of mercury alter in various parts of the bore, the +tube must be rejected. If it is, as nearly as possible, one uniform +length, the tube is set aside for filling.</p> + +<p>The <i>bulb</i> is never blown by the breath, but by an elastic caoutchouc ball +containing air, so that the introduction of moisture is avoided. The +spherical form is to be preferred; for it is best adapted to resist the +varying pressure of the atmosphere. The bulbs should not be too large, or +the mercury will take some time to indicate sudden changes of temperature. +Cylindrical bulbs are sometimes desirable, as they offer larger surfaces +to the mercury, and enable thermometers to be made more sensitive.</p> + +<p>The <i>mercury</i>, with which the bulb is to be filled, should be quite pure, +and freed from moisture and air by recent boiling.</p> + +<p><i>Filling the Tube.</i>—The filling is effected by heating the bulb with the +flame of a spirit-lamp, while the open end is embedded in mercury. Upon +allowing the bulb to cool, the atmospheric pressure drives some mercury +into it; and the process of heating and cooling is thus continued until +sufficient mercury is introduced. The mercury is next boiled in the tube, +to expel any air or moisture that may be present. In order to close the +tube and exclude all air, the artist ascertains that the tube<span class="pagenum"><a name="Page_60" id="Page_60">[Pg 60]</a></span> contains +the requisite quantity of mercury; then, by holding the bulb over the +spirit flame, he causes the mercury to fill the whole of the tube, and +dexterously removing it from the source of heat, he, at the same instant, +closes it with the flame of a blow-pipe. If any air remain in the tube, it +is easily detected; for if the instrument be inverted, the mercury will +fall to the extremity of the tube, if there is a perfect vacuum, unless +the tube be so finely capillary that its attraction for the mercury is +sufficient to overcome the force of gravity, in which case the mercury +will retain its position in every situation of the instrument. If, +however, the mercury fall and does not reach quite to the extremity of the +bore, some air is present, which must be removed.</p> + +<p><i>The Graduation.</i>—The thermometer is now prepared for graduation, the +first part of which process is the determination of two fixed points. +These are given by the temperatures of melting ice and of the vapour of +boiling water. Melting ice has always the same temperature in every place +and under all circumstances; provided only that the water from which the +ice is congealed is free from salts. The temperature of the vapour of +boiling water depends upon the pressure of the atmosphere, but is always +constant for the same pressure.</p> + +<p>The fixed point corresponding to the temperature of melting ice is called +the <i>freezing point</i>. It is obtained by keeping the bulb and the part of +the tube occupied by mercury immersed in melting ice, until the mercury +contracts to a certain point, where it remains stationary. This position +of the end of the mercury is then marked upon the tube.</p> + +<p>The <i>boiling point</i> is not so easily determined, for the barometer must be +consulted about the same time. The boiling apparatus is generally +constructed of copper. It consists of a cylindrical boiler, heated from +the base by a spirit lamp or charcoal fire. An open tube two or three +inches in diameter and of suitable length enters the top of the boiler. +This tube is enveloped by another fixed to the top of the boiler but not +opening into it, and so that the two tubes are about an inch apart. The +object of the outer tube is to protect the inner tube from the cold +temperature of the air. The outer tube has an opening at the top for the +admission of the thermometer, and a hole near the bottom for the escape of +steam through a spout. When the water is made to boil, the steam rises in +the inner tube, fills the space between the tubes, and escapes at the +spout. The thermometer is then passed down into the inner cylinder, and +held securely from the top by means of a piece of caoutchouc. The tubes or +cylinders should be of sufficient length to prevent the thermometer +entering the water. This is necessary because the temperature of boiling +water is influenced by any substance which it holds in chemical solution; +and, moreover, its temperature increases with the depth, owing to the +pressure of the upper stratum. The thermometer being thus surrounded with +steam, the mercury rises in the tube. As it does so, the tube should be +depressed so as always to keep the top of the mercury just perceptible. +When the temperature of the vapour is attained, the mercury ceases to +rise, and remains stationary. The position of<span class="pagenum"><a name="Page_61" id="Page_61">[Pg 61]</a></span> the end of the mercury is +now marked upon the tube, and the “<i>boiling-point</i>” is obtained.</p> + + +<p><br /><b>57. Methods of ascertaining the exact Boiling Temperature.</b>—The normal +boiling temperature of water all nations have tacitly agreed to fix under +a normal barometric pressure of 29·922 inches of mercury, having the +temperature of melting ice, in the latitude of 45°, and at the sea-level. +If the atmospheric pressure at the time or place of graduating a +thermometer does not equal this, the boiling temperature will be higher or +lower according as the pressure is greater or less. Hence a reading must +be taken from a reliable barometer, which must also be corrected for +errors and temperature, and reduced for latitude, in order to compare the +actual atmospheric pressure at the time with the assumed normal pressure. +Tables of vapour tension, as they are termed, have been computed from +accurate experimental investigations and theory,—giving the temperatures +of the vapour of water for all probable pressures; Regnault’s, the most +recent, is considered the most accurate; and his investigations are based +upon the standard pressure given above, and are for the same latitude. His +Table, therefore, will give the temperature on the thermometric scale +corresponding to the pressure.</p> + +<p>The Commissioners appointed by the British Government to construct +standard weights and measures, decided that the normal boiling-point, +212°, on the thermometer should represent the temperature of steam +generated under an atmospheric pressure equal in inches of mercury, at the +temperature of freezing water, to 29·922 + (cos. 2 latitude × ·0766) + +(·00000179 × height in feet above the sea-level). Hence, at London, lat. +51°30´ N., we deduce 29·905 as the barometric pressure representing the +normal boiling point of water,—the trifling correction due to height +being neglected. If then, in the latitude of London, the barometric +pressure, at the time of fixing the boiling point, be not 29·905 inches, +that point will be higher or lower, according to the difference of the +pressure from the normal. Near the sea-level about 0·59 inch of such +difference is equivalent to 1° Fahrenheit in the boiling point.</p> + +<p>Suppose, then, the atmospheric pressure at London to be 30·785 inches, the +following calculation gives the corresponding boiling temperature for +Fahrenheit’s scale:—</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>Observed</td><td>pressure</td><td><span class="spacer"> </span></td><td align="right">30·785</td></tr> +<tr><td>Normal</td><td align="center">"</td><td> </td><td align="right" class="botbor">29·905</td></tr> +<tr><td colspan="2">Difference</td><td> </td><td align="right" class="botbor2">·880</td></tr></table> + +<p>As 0·59 is to 0·88, so is 1° to 1°·5.</p> + +<p>That is, the water boils at 1°·5 above its normal temperature; so that, in +this case, the normal temperature to be placed on the scale, viz. 212°, +must be 1°·5 lower than the mark made on the tube at the height at which +the mercury stood under the influence of the boiling water.</p> + +<p><span class="pagenum"><a name="Page_62" id="Page_62">[Pg 62]</a></span>The temperature of the vapour of boiling water may be found, at any time +and place, as follows:—Multiply the atmospheric pressure by the factor +due to the latitude, given in the annexed Table V., and with the result +seek the temperature in Table VI.</p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td colspan="2" align="center"><span class="smcap">Table V.</span></td> + <td colspan="4" align="center"><span class="smcap">Table VI.</span></td></tr> +<tr><td class="btlr" align="center">Latitude.</td> + <td class="btrdoub2" align="center">Factor.</td> + <td class="btr" align="center">Temperature<br />of Vapour.</td> + <td class="btrdoub" align="center">Tension.</td> + <td class="btr" align="center">Temperature<br />of Vapour.</td> + <td class="btr" align="center">Tension.</td></tr> +<tr><td class="btlr" align="center">Degrees.</td> + <td class="btrdoub2" align="center"> </td> + <td class="btr" align="center">Degrees.</td> + <td class="btrdoub" align="center">Inches.</td> + <td class="btr" align="center">Degrees.</td> + <td class="btr" align="center">Inches.</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: .5em;">0</span></td> + <td class="brdoub2" align="center">0·99735</td> + <td class="br" align="center">179</td> + <td class="brdoub" align="center">14·934</td> + <td class="br" align="center">197</td> + <td class="br" align="center">22·036</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: .5em;">5</span></td> + <td class="brdoub2" align="center">0·99739</td> + <td class="br" align="center">180</td> + <td class="brdoub" align="center">15·271</td> + <td class="br" align="center">198</td> + <td class="br" align="center">22·501</td></tr> +<tr><td class="blr" align="center">10</td> + <td class="brdoub2" align="center">0·99751</td> + <td class="br" align="center">181</td> + <td class="brdoub" align="center">15·614</td> + <td class="br" align="center">199</td> + <td class="br" align="center">22·974</td></tr> +<tr><td class="blr" align="center">15</td> + <td class="brdoub2" align="center">0·99770</td> + <td class="br" align="center">182</td> + <td class="brdoub" align="center">15·963</td> + <td class="br" align="center">200</td> + <td class="br" align="center">23·456</td></tr> +<tr><td class="blr" align="center">20</td> + <td class="brdoub2" align="center">0·99797</td> + <td class="br" align="center">183</td> + <td class="brdoub" align="center">16·318</td> + <td class="br" align="center">201</td> + <td class="br" align="center">23·946</td></tr> +<tr><td class="blr" align="center">25</td> + <td class="brdoub2" align="center">0·99830</td> + <td class="br" align="center">184</td> + <td class="brdoub" align="center">16·680</td> + <td class="br" align="center">202</td> + <td class="br" align="center">24·445</td></tr> +<tr><td class="blr" align="center">30</td> + <td class="brdoub2" align="center">0·99868</td> + <td class="br" align="center">185</td> + <td class="brdoub" align="center">17·049</td> + <td class="br" align="center">203</td> + <td class="br" align="center">24·952</td></tr> +<tr><td class="blr" align="center">35</td> + <td class="brdoub2" align="center">0·99910</td> + <td class="br" align="center">186</td> + <td class="brdoub" align="center">17·425</td> + <td class="br" align="center">204</td> + <td class="br" align="center">25·468</td></tr> +<tr><td class="blr" align="center">40</td> + <td class="brdoub2" align="center">0·99954</td> + <td class="br" align="center">187</td> + <td class="brdoub" align="center">17·808</td> + <td class="br" align="center">205</td> + <td class="br" align="center">25·993</td></tr> +<tr><td class="blr" align="center">45</td> + <td class="brdoub2" align="center">1·00000</td> + <td class="br" align="center">188</td> + <td class="brdoub" align="center">18·197</td> + <td class="br" align="center">206</td> + <td class="br" align="center">26·527</td></tr> +<tr><td class="blr" align="center">50</td> + <td class="brdoub2" align="center">1·00046</td> + <td class="br" align="center">189</td> + <td class="brdoub" align="center">18·594</td> + <td class="br" align="center">207</td> + <td class="br" align="center">27·070</td></tr> +<tr><td class="blr" align="center">55</td> + <td class="brdoub2" align="center">1·00090</td> + <td class="br" align="center">190</td> + <td class="brdoub" align="center">18·998</td> + <td class="br" align="center">208</td> + <td class="br" align="center">27·623</td></tr> +<tr><td class="blr" align="center">60</td> + <td class="brdoub2" align="center">1·00132</td> + <td class="br" align="center">191</td> + <td class="brdoub" align="center">19·409</td> + <td class="br" align="center">209</td> + <td class="br" align="center">28·185</td></tr> +<tr><td class="blr" align="center">65</td> + <td class="brdoub2" align="center">1·00170</td> + <td class="br" align="center">192</td> + <td class="brdoub" align="center">19·828</td> + <td class="br" align="center">210</td> + <td class="br" align="center">28·756</td></tr> +<tr><td class="blr" align="center">70</td> + <td class="brdoub2" align="center">1·00203</td> + <td class="br" align="center">193</td> + <td class="brdoub" align="center">20·254</td> + <td class="br" align="center">211</td> + <td class="br" align="center">29·335</td></tr> +<tr><td class="blr" align="center">75</td> + <td class="brdoub2" align="center">1·00230</td> + <td class="br" align="center">194</td> + <td class="brdoub" align="center">20·688</td> + <td class="br" align="center">212</td> + <td class="br" align="center">29·922</td></tr> +<tr><td class="blr" align="center">80</td> + <td class="brdoub2" align="center">1·00249</td> + <td class="br" align="center">195</td> + <td class="brdoub" align="center">21·129</td> + <td class="br" align="center">213</td> + <td class="br" align="center">30·515</td></tr> +<tr><td class="bblr" align="center"> </td> + <td class="bbrdoub2" align="center"> </td> + <td class="bbr" align="center">196</td> + <td class="bbrdoub" align="center">21·578</td> + <td class="bbr" align="center">214</td> + <td class="bbr" align="center">31·115</td></tr></table> + +<p><i>How to use the Tables.</i>—When the <i>temperature</i> is known to decimals of a +degree, take out the tension for the degree, and multiply the difference +between it and the next tension by the decimals of the temperature, and +add the product to the tension, for the degree.</p> + +<p>Required the tension corresponding to 197°·84.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center">°</td></tr> + +<tr><td>197</td><td> </td><td>=</td><td align="right" class="botbor">22·036</td><td><span class="spacer"> </span></td> + <td>·465 × ·84</td><td>=</td><td align="right">·391</td></tr> + +<tr><td>198</td><td> </td><td>=</td><td align="right" class="botbor">22·501</td><td> </td> + <td>197°</td><td>=</td><td align="right" class="botbor">22·036</td></tr> + +<tr><td> </td><td>Difference</td><td> </td><td align="right" class="botbor2">·465</td><td> </td> + <td>197·84</td><td>=</td><td align="right" class="botbor2">22·427</td></tr></table> + +<p>When the <i>tension</i> is given, take the difference between it and the next +less tension in the Table, and divide this difference by the difference +between the next less and<span class="pagenum"><a name="Page_63" id="Page_63">[Pg 63]</a></span> next greater tensions. The quotient will be the +decimals to add to the degree opposite the next less tension.</p> + +<p>Thus, for 23·214 inches, required the temperature.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>Given</td> + <td align="right">23·214</td> + <td><span class="spacer2"> </span></td> + <td> </td><td> </td> + <td>Next</td><td>greater</td> + <td><span class="spacer2"> </span></td> + <td align="right">23·456</td></tr> +<tr><td> </td> + <td align="right" class="botbor">22·974</td> + <td> </td><td> </td><td> </td> + <td>Next</td><td>less</td> + <td> </td> + <td class="botbor" align="right">22·974</td></tr> +<tr><td> </td> + <td align="right">·240</td> + <td colspan="4"> </td> + <td>Difference</td> + <td> </td> + <td align="right">·482</td></tr> +<tr><td rowspan="2" colspan="3"> </td> + <td rowspan="2">And </td> + <td class="botbor">·240</td> + <td rowspan="2" colspan="2"> </td> + <td rowspan="2">=</td> + <td rowspan="2" align="right">·5</td></tr> +<tr><td>·482</td></tr> +<tr><td colspan="7"><span style="margin-left: 1em;">Temperature opposite next less</span></td> + <td> </td> + <td align="right" class="botbor">199·0</td></tr> +<tr><td colspan="7"><span style="margin-left: 1em;">Temperature required</span></td> + <td> </td> + <td align="right" class="botbor2">199·5</td></tr></table> + +<p>A similar method of interpolation in taking out numerical quantities is +applicable to almost all tables; and should be practised with all those +given in this work.</p> + +<p><i>Example.</i>—Thus, in Liverpool, lat. 53° 30´ N., the barometer reading +29·876 inches, its attached thermometer 55°, and the correction of the +instrument being + ·015 (including index error, capillarity and capacity), +what temperature should be assigned for the boiling point marked on the +thermometer?</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>Observed barometer</td> + <td><span class="spacer2"> </span></td> + <td align="right">29·876</td></tr> +<tr><td>Correction</td> + <td> </td> + <td align="right" class="botbor">+<span class="spacer2"> </span>·015</td></tr> +<tr><td> </td> + <td> </td> + <td align="right">29·891</td></tr> +<tr><td>Correction for temperature</td> + <td> </td> + <td align="right" class="botbor">-<span class="spacer2"> </span>·074</td></tr> +<tr><td>Reduced reading</td> + <td> </td> + <td align="right">29·817</td></tr> +<tr><td>Factor from Table V.</td> + <td> </td> + <td align="right" class="botbor">1·00077</td></tr> +<tr><td> </td> + <td> </td> + <td align="right">208719</td></tr> +<tr><td> </td> + <td> </td> + <td><span style="margin-left: 1.75em;">208719</span></td></tr> +<tr><td> </td> + <td> </td> + <td class="botbor"><span style="margin-left: .25em;">29817</span></td></tr> +<tr><td>Equivalent for lat. 45°</td> + <td> </td> + <td align="right" class="botbor2">29·83995909</td></tr></table> + +<p>In Table VI., 29·84 gives temperature 211°·86.</p> + + +<p><br /><b>58. Displacement of the Freezing Point.</b>—Either the prolonged effect of +the atmospheric pressure upon the thin glass of the bulbs of thermometers, +or the gradual restoration of the equilibrium of the particles of the +glass after having been greatly disturbed by the operation of boiling the +mercury, seems to be the cause of the freezing points of standard +thermometers reading from a few tenths to a degree higher in the course of +some years, as has been repeatedly observed. To obviate this small error, +it is our practice to place the tubes aside for about six months before +fixing the freezing point, in order to give time for the glass to regain +its former state<span class="pagenum"><a name="Page_64" id="Page_64">[Pg 64]</a></span> of aggregation. The making of accurate thermometers is a +task attended with many difficulties, the principal one being the +liability of the zero or freezing point varying constantly, so much so, +that a thermometer that is perfectly correct to-day, if immersed in +boiling water, will be no longer accurate; at least, it will take some +time before it again settles into its normal state. Then, again, if a +thermometer is recently blown, filled, and graduated immediately, or, at +least, before some months have elapsed, though every care may have been +taken with the production of the instrument, it will require some +correction; so that the instrument, however carefully made, should from +time to time be plunged into finely-pounded ice, in order to verify the +freezing point.</p> + + +<p><br /><b>59. The Scale.</b>—The two fixed points having been determined, it is +necessary to apply the scale. The thermometers in general use in the +United Kingdom, the British Colonies, and North America are constructed +with Fahrenheit’s scale. Fahrenheit was a philosophical instrument maker +of Amsterdam, who, about the year 1724, invented the scale which has given +his name to the thermometer. The freezing point is marked 32°, the boiling +point 212°, so that the intermediate space is divided into 180 equal +parts, called degrees. “The principle which dictated this <i>peculiar +division</i> of the scale is as follows:—When the instrument stood at the +greatest cold of Iceland, or 0 degree, it was computed to contain 11124 +equal parts of quicksilver, which, when plunged in melting snow, expanded +to 11156 parts; hence the intermediate space was divided into 32 equal +portions, and 32 was taken as the freezing point of water: when the +thermometer was plunged in boiling water, the quicksilver was expanded to +11336; and therefore 212° was marked as the boiling point of that fluid. +In <i>practice</i>, Fahrenheit determined the divisions of his scale from two +fixed points, the freezing and boiling of water. <i>The theory</i> of the +division, if we may so speak, was derived from the lowest cold observed in +Iceland, and the expansions of a given portion of mercury” (<i>Professor +Trail</i>).</p> + +<p>The divisions of the scale can be carried beyond the fixed points, if +requisite, by equal graduations. Fahrenheit’s scale is very convenient in +some respects. The meteorological observer is seldom troubled with +negative signs, as the zero of the scale is much below freezing. Again, +the divisions are more numerous, and consequently smaller, than on other +scales in use; and the further subdivision into tenths of degrees, seems +to give all the minuteness usually required.</p> + +<p><i>Celcius</i>, a Swede, in 1742, proposed zero for the freezing point, and 100 +for the boiling point, all temperatures below zero being distinguishable +by the sign (—) minus. This scale is known as the <i>centigrade</i>, and is in +use in France, Sweden, and the southern part of Europe. It has the +advantage of the decimal notation, with the embarrassment of the negative +sign.</p> + +<p><i>Reaumur</i>, a Frenchman, proposed zero for the freezing point, and 80° for +the boiling point, an arrangement inferior to the centigrade. It is, +however, in use in Spain, Switzerland, and Germany.</p> + +<p><span class="pagenum"><a name="Page_65" id="Page_65">[Pg 65]</a></span>It is merely a simple arithmetical operation to change the indications of +any one of these scales into the equivalents on the others. To facilitate +such conversions, tables are convenient, when a large number of +observations are under discussion; and they can be easily formed or +obtained.</p> + +<p>In the absence of such tables, the following formulæ will insure accuracy +of method, and save thinking, when occasional conversions are wanted to be +made:—F. stands for Fahrenheit, C. for Centigrade, and R. for Reaumur.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center">Given.</td><td><span class="spacer"> </span></td> + <td align="center">Required.</td><td><span class="spacer"> </span></td> + <td> </td> + <td colspan="2" align="center">Solution.</td></tr> +<tr><td align="center">F.</td><td> </td> + <td align="center">C.</td><td> </td> + <td>=</td> + <td> </td> + <td>(F.-32) <span style="font-size: 0.8em;"><sup>5</sup></span>⁄<span style="font-size: 0.6em;">9</span></td></tr> +<tr><td align="center">F.</td><td> </td> + <td align="center">R.</td><td> </td> + <td>=</td> + <td> </td> + <td>(F.-32) <span style="font-size: 0.8em;"><sup>4</sup></span>⁄<span style="font-size: 0.6em;">9</span></td></tr> +<tr><td align="center">C.</td><td> </td> + <td align="center">F.</td><td> </td> + <td>=</td> + <td><span style="font-size: 0.8em;"><sup>9</sup></span>⁄<span style="font-size: 0.6em;">5</span></td> + <td>C. + 32</td></tr> +<tr><td align="center">C.</td><td> </td> + <td align="center">R.</td><td> </td> + <td>=</td> + <td><span style="font-size: 0.8em;"><sup>4</sup></span>⁄<span style="font-size: 0.6em;">5</span></td> + <td>C.</td></tr> +<tr><td align="center">R.</td><td> </td> + <td align="center">F.</td><td> </td> + <td>=</td> + <td><span style="font-size: 0.8em;"><sup>9</sup></span>⁄<span style="font-size: 0.6em;">5</span></td> + <td>R. + 32</td></tr> +<tr><td align="center">R.</td><td> </td> + <td align="center">C.</td><td> </td> + <td>=</td> + <td><span style="font-size: 0.8em;"><sup>5</sup></span>⁄<span style="font-size: 0.6em;">4</span></td> + <td>R.</td></tr></table> + +<p><i>Example.</i>—Convert 25° of Fahrenheit’s scale into the corresponding +temperature on the Centigrade scale.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>Here</td><td>C. =</td><td colspan="3"> (25 - 32) <span style="font-size: 0.8em;"><sup>5</sup></span>⁄<span style="font-size: 0.6em;">9</span></td></tr> +<tr><td rowspan="2"> </td><td rowspan="2">C. = -</td><td class="botbor" align="center">35</td><td rowspan="2">= -3·9</td></tr> +<tr><td align="center">9</td></tr></table> + +<p>or nearly 4° <i>below</i> zero of the Centigrade scale. The algebraical sign +must be carefully attended-to in the calculations.</p> + + +<p><br /><b>60. The method of testing Thermometers</b> for meteorological purposes is very +simple. Such thermometers are seldom required to read above 120°. In these +the freezing point having been determined, the divisions of the scale are +ascertained by careful comparisons, with a standard thermometer, in water +of the requisite temperature. “For the freezing point, the bulbs, and a +considerable portion of the tubes of the thermometers, are immersed in +pounded ice. For the higher temperatures, the thermometers are placed in a +cylindrical glass vessel containing water of the required heat: the scales +of the thermometers intended to be tested, together with the Standard with +which they are to be compared, are read through the glass. In this way the +scale readings may be tested at any required degree of temperature, and +the usual practice is to test them at every ten degrees from 32° to 92° of +Fahrenheit.”—<i>FitzRoy.</i></p> + + +<p><br /><b>61. Porcelain Scale Plates.</b>—Thermometer scales of brass, wood, or ivory, +either by atmospheric influence or dipping in sea-water, are very liable +to become soiled and discoloured, so much so that after a very little time +the divisions are rendered nearly invisible. To obviate this +inconvenience, Messrs. Negretti and Zambra were the first to introduce +into extensive use thermometer and barometer scale-plates made of +porcelain, having the divisions and figures engraved thereon by means of +fluoric acid, and permanently burnt-in and blackened, so as always to +present a clear legible scale. That these scales have been found superior +to all others, may be inferred from the fact that all the thermometers now +supplied to the various government departments are provided with such +scales.</p> + +<p><span class="pagenum"><a name="Page_66" id="Page_66">[Pg 66]</a></span>They can be adapted to replace any of the old forms of brass or zinc +scales, the divisions and figures of which have become obliterated or +indistinct.</p> + + +<p><br /><b>62. Enamelled Tubes.</b>—Nearly all thermometer tubes are now made with +enamelled backs. This contrivance of enamelling the backs of the tubes +enables the makers to use finer threads of mercury than had before been +found practicable; for were it not for the great contrast between the dark +thread of mercury and the white enamel on the glass, many of the +thermometers now in use would be positively illegible. The enamelling of +thermometers is an invention of Messrs. Negretti and Zambra. It is +necessary to state this, as many persons, from interested motives, are +anxious to ignore to whom the credit of the invention is due.</p> + + +<p><br /><b>63. Thermometers of extreme Sensitiveness.</b>—Thermometers for delicate +experiments are no novelty. Thermometers have been made with very delicate +bulbs to contain a very small quantity of mercury. Such instruments have +also been made with spiral or coiled tubular bulbs, but the thickness of +glass required to keep these coils or spirals in shape, and in fact to +prevent their falling to pieces, served to nullify the effect sought to be +produced, viz. instantaneous action; and where a small thin bulb was +employed, the indicating column was generally so fine that it was +positively invisible except by the aid of a powerful lens. Messrs. +Negretti and Zambra have now introduced a new form of thermometer, which +combines sensitiveness and quickness of action, together with a good +visible column. The bulb of this thermometer is of the gridiron form. Care +has been taken in constructing the bulb, so that the objections attending +spirals and other forms have been overcome; for whilst the reservoir or +bulb is made of glass so thin that it is only by a spirit lamp and not a +glass blower’s blowpipe that it can be formed, yet it is still so rigid +(owing to its peculiar configuration) that no variations in its +indications can be detected, whether it be held in a horizontal, vertical, +or oblique position, nor will any error be detected if it be stood on its +own bulb. They have made thermometers with bulbs or reservoirs formed of +about nine inches of excessively thin cylindrical glass, whose outer +diameter is not more than a twentieth of an inch; so that, owing to the +large surface presented, the indications are positively instantaneous. +This form of thermometer was constructed expressly to meet the +requirements of scientific balloon ascents, to enable thermometrical +readings to be taken at the precise elevation. It was contemplated to +procure a metallic thermometer, but on the production of this perfect +instrument the idea was abandoned.</p> + + +<p class="center"><br />64. VARIETIES OF THERMOMETERS.</p> + +<p>Fig. 37 is an illustration of boxwood scale thermometers for general use +and common purposes.</p> + +<p>Fig. 38, Negretti and Zambra’s Travelling Thermometer; it is fixed in a +plated metal (silver or otherwise) case, similar to a pencil-case, and has +the scale divided upon its stem.</p> + +<p><span class="pagenum"><a name="Page_67" id="Page_67">[Pg 67]</a></span>Fig. 39, Thermometer mounted on a slab of glass, upon which the scale is +etched, the back being either oak, mahogany, or ebony.</p> + +<p>Fig. 40, Portable Thermometer, in a bronzed brass or German silver +revolving case.</p> + +<p>Fig. 41, Pocket Thermometer, on ivory or metallic scale, in morocco or +papier-mâché case.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center">Fig. 37.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 38.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 39.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 40.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 41.</td><td><span class="spacer2"> </span></td></tr> +<tr><td align="center"><img src="images/fig_37.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_38.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_39.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_40.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_41.jpg" alt="" /></td><td> </td></tr></table> + + +<p>Fig. 42, an Ornamental Drawing-room Thermometer, on ebony or ivory stand, +with glass shade.</p> + +<p>Fig. 43, representation of highly carved or engine-turned design for +thermometer mounts, in ivory or wood, for the drawing-room. Some have the +addition of a sundial or compass at the top; they may also be formed for a +watch-stand.</p> + +<p>Fig. 44, <b>Bath Thermometer</b>, having a float to admit of its being kept in +the water.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center">Fig. 42.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 43.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 44.</td><td><span class="spacer2"> </span></td></tr> +<tr><td align="center"><img src="images/fig_42.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_43.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_44.jpg" alt="" /></td><td> </td></tr></table> + +<p><span class="pagenum"><a name="Page_68" id="Page_68">[Pg 68]</a></span>Fig. 45, Thermometer with ivory scale in glass cylinder, mounted on oak +bracket with metal top, for out-door use; as at a window.</p> + +<p>Fig. 46, Thermometer for the window, on patent porcelain or glass scale, +with oak bracket and convenient brass supports, for placing the instrument +at any angle.</p> + +<p>Fig. 47, <b>Chemical Thermometer</b>, on boxwood scale, jointed near the bulb on +a brass hinge, ranging from 300° to 600°.</p> + +<p>Fig. 48, <b>Chemical Thermometer</b>, for acids, graduated on its own stem, +suitable for insertion in the tubulure of retorts; they are also made +insulated in glass cylinder to protect the graduated stem; ranging from 0° +to 600°.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center">Fig. 45.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 46.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 47.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 48.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 49.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 50.</td><td><span class="spacer2"> </span></td></tr> +<tr><td align="center"><img src="images/fig_45.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_46.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_47.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_48.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_49.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_50.jpg" alt="" /></td><td> </td></tr></table> + + +<p><br /><b>65. Superheated Steam Thermometer.</b>—The great advantage gained by the use +of superheated steam in marine and other steam-engines being now generally +admitted by engineers, reliable thermometers, reading to 600° at least, +are of the utmost importance. To meet this want, Messrs. Negretti and +Zambra have constructed for the purpose a substantial form of thermometer, +on their patent porcelain scales, in strong and convenient metal +mountings, with perforated protection to the bulb. The scales cannot be +deteriorated by steam, heat, oil, or dirt; and an occasional wiping will +be all that is necessary to keep the divisions and figures clean and +visible for any length of time; while careful calibration of the +thermometer tubes ensures the most accurate indications attainable. These +thermometers are illustrated by figs. 49 & 50. A similar,<span class="pagenum"><a name="Page_69" id="Page_69">[Pg 69]</a></span> but cheaper, +construction is given to thermometers to be used with hot air, or hot +water, apparatus.</p> + + +<p><br /><b>66. Thermometer for Sugar Boiling</b> is protected by a metallic frame; and is +usually from three to four feet long, the graduations being confined to a +space of about twelve inches at the upper part of the instrument, allowing +the bulb and greater part of the tube to be immersed in the boiling sugar. +The graduations extend to 270° or further. An index is sometimes attached +to the scale, which may be set to any degree of heat required to be +maintained.</p> + + +<p class="center"><br />67. EARTH THERMOMETER.</p> + +<p>The Earth Thermometer is for ascertaining the temperature of the soil at +various depths. It is protected by a brass frame, pointed and strengthened +at the end to facilitate insertion into the ground, as in fig. 51.</p> + +<div class="figright">Fig. 51.<br /><img src="images/fig_51.jpg" alt="" /></div> + +<p><i>Utility of a Knowledge of the Temperature of the Soil.</i>—The temperature +of the soil is an important element in the consideration of climate, as it +concerns the vegetable kingdom.</p> + +<p>Dr. Daubeny, in his <i>Lectures on Climate</i>, gives the following statement +with respect to some temperatures which have been observed just beneath +the earth’s surface, in different parts of the globe:—</p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td class="btr" align="center">Country.</td> + <td class="btr" align="center">Temperature.</td> + <td class="bt" align="center">Authority.</td></tr> +<tr><td class="btr">Tropics, often</td> + <td class="btr">162-184°</td> + <td class="bt">Humboldt.</td></tr> +<tr><td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="br">Egypt</td> + <td class="br">133-144</td> + <td class="dent">Edwards & Colin.</td></tr> +<tr><td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="br">Orinoco</td> + <td class="br">In white sand, 140</td> + <td class="dent">Humboldt.</td></tr> +<tr><td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="br">Chili</td> + <td class="br">113-118, among dry grass</td> + <td class="dent">Boussingault.</td></tr> +<tr><td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="br">Cape of Good Hope</td> + <td class="br">150, under the soil of a bulb garden</td> + <td class="dent">Herschell.</td></tr> +<tr><td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="br">Bermuda</td> + <td class="br">142, thermometer barely covered in earth</td> + <td class="dent">Emmet.</td></tr> +<tr><td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="br">China</td> + <td class="br">Water of the fields, 113; adjacent sand,<br />much higher; blackened sides of the boat<br />at midday, 142-150</td> + <td class="dent">Meyer.</td></tr> +<tr><td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="bbr">France</td> + <td class="bbr">118-122, and in one instance 127</td> + <td class="bb">Arago.</td></tr></table> + +<p>“The importance of this to vegetation may be estimated by the following +considerations:—</p> + +<p>“It is known that every plant requires a certain amount of heat, varying +in<span class="pagenum"><a name="Page_70" id="Page_70">[Pg 70]</a></span> the case of each species, for the renewal of its growth, at the +commencement of the season.</p> + +<p>“Now when this degree of heat has spurred into activity those parts that +are above ground, and caused them to elaborate the sap, it is necessary +that the subterranean portions should at the same time be excited by the +heat of the ground to absorb the materials which are to supply the plant +with nourishment. Unless the latter function is provided for, the aerial +portions of the plant will languish from want of food to assimilate. +Indeed, it is even advisable that the roots should take the start of the +leaves, in order to have in readiness a store of food for the latter to +draw upon.” In another place the professor remarks:—“It has been +calculated by Mr. Raikes, from experiments made at Chat Moss, that the +temperature of the soil when drained averages 10° more than it does when +undrained; and this is not surprising, when we find that 1 lb. of water +evaporated from 1,000 lbs. of soil will depress the whole by 10°, owing to +the latent heat which it absorbs in its conversion into vapour.”</p> + + +<p class="center"><br />68. MARINE THERMOMETER.</p> + +<div class="figleft">Fig. 52.<br /><img src="images/fig_52.jpg" alt="" /></div> + +<p>This instrument is a special construction to meet the requirements of +navigation. It consists of a carefully constructed thermometer divided on +its stem to degrees, which are sufficiently large to admit of subdivision +into tenths of degrees by estimation, and ranging from 0° to 130°. The +scale is porcelain, having the degrees etched upon it, and burnt-in a +permanent black. The instrument is made to slide into a japanned metallic +case, for handy use and protection. It is therefore adapted for almost any +ordinary purpose; and cannot be injuriously affected by any chemical +action arising from air or sea-water. A set of these thermometers consists +of six, carefully packed in a neat box; two having japanned metallic cases +(fig. 52), the others being designed for use without the case, or to +replace a breakage.</p> + +<p>This thermometer is employed in the Royal Navy, and for the observations +made at sea for the Board of Trade.</p> + +<p>The thermometer is now considered a necessary instrument on board ship. +Not only is it of invaluable utility in connection with the barometer as a +guide to the weather, but its indications are of service in showing the +presence of a warm or cold current in the sea; many of the great oceanic +currents being characterised by the warmth or coldness of their waters. In +seas visited by icebergs, the habitual use of the thermometer would +indicate their proximity, as the water is rendered colder for some +distance around by the thawing of huge masses of ice. The water over a +shoal in the sea is generally colder than the surface-water of the +surrounding ocean; which may result from the cold water being brought to +the surface by the current of water encountering the shoal. With this fact +navigators are well acquainted; and therefore a fall in the sea-water +thermometer may forebode that shallow water is at hand. It has been +ascertained that fish<span class="pagenum"><a name="Page_71" id="Page_71">[Pg 71]</a></span> inhabit regions of the oceans and seas having the +peculiar temperature suitable to their habits. The better and firmer sort +of fish are found where cold waters exist. Those taken in warmer belts or +streams of water, even in the same latitude, are far inferior in +condition, and less approved by the palate. The fish of the Mediterranean, +a warm sea, are generally poor and scarce. Fish taken in the cold waters +between the American shore and the Gulf Stream are much esteemed; while in +and on the other side of the stream they are said to be tasteless, and of +no flavour. Between the coasts of China and the warm waters of the +Japanese current, the seas abound with excellent fish; but in the warm +waters of the current and beyond, they are never seen in such shoals.</p> + +<p>In fact, it is clearly ascertained that fishes are adapted to climates, +like birds and beasts. It has been even affirmed, after careful +investigation, that herrings, which abound in the British Seas, and form a +most important branch of our fisheries, can only be found in a temperature +varying from 54° to 58°. Hence the thermometer, if brought into use by the +fishermen, would guide them to the spots where they may with the best +chance cast their nets on dark nights, when other indications are not +perceptible.</p> + +<p>This thermometer in its metallic case is perfectly suited for dipping +overboard, or placing in a bucket of water just taken from the sea, to +ascertain its temperature.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_72" id="Page_72">[Pg 72]</a></span></p> +<h2><a name="CHAPTER_VII" id="CHAPTER_VII"></a>CHAPTER VII.</h2> +<p class="center"><span class="large">SELF-REGISTERING THERMOMETERS.</span></p> + +<p><br /><b>69. Importance of Self-Registering Thermometers.</b>—Heat being apparently +the most effective agent in producing meteorological phenomena, the +determination of the highest temperature of the day, and the lowest during +the night, is a prime essential to enable an estimate of the climate of +any place to be formed. To observe these extremes by means of the ordinary +thermometer would be impracticable, from the constant watchfulness which +would be necessary. Hence, the utility and importance of self-recording +thermometers are evident. A thermometer constructed to <i>register</i> the +highest temperature is usually called a <i>maximum thermometer</i>; one to show +the lowest temperature is termed a <i>minimum thermometer</i>; and if made to +record both extremes of temperature, it is designated a +<i>maximum-and-minimum thermometer</i>. We will, for the sake of method, +describe the instruments in use in this order.</p> + +<p>It would carry us beyond our scope to explain in detail the methods of +dealing with temperature observations; but we may remark that half the sum +of the maximum and minimum temperature of each day of twenty-four hours, +is not what meteorologists designate the <i>mean daily temperature</i>, +although it very frequently approximates to it. The mean temperature of +the day is understood to be the average of twenty-four consecutive hourly +readings of a thermometer; and meteorology now supplies formulæ whereby +this result can be deduced from two or three observations only in a day. +But we would observe that the actual mean temperature of any place has not +such an important influence upon life, either animal or vegetable, as the +abruptness and magnitude of the variations of temperature. Climate, +therefore, should be estimated more by the range of the thermometer than +by the average of its indications. The Registrar General’s returns prove +that with a wide range of the thermometer, the mortality greatly +increases; and it is now becoming apparent to meteorologists that the +daily range of the thermometer marks the effects of temperature on the +health of men, and the success of crops, better than any other +meteorological fact of which we take cognizance. Now that self-registering +thermometers are constructed with mercury, the most appropriate of all +thermometric substances, not only for maxima, but likewise for minima +temperatures, the determination of the diurnal range of temperature is +rendered more certain, and observations at different places are more +strictly comparable.</p> + + +<p class="center"><br /><span class="pagenum"><a name="Page_73" id="Page_73">[Pg 73]</a></span>MAXIMA THERMOMETERS.</p> + +<p><br /><b>70. Rutherford’s Maximum Thermometer.</b>—The maximum thermometer, invented +by Dr. John Rutherford, differs from an ordinary thermometer in having a +small cylinder of steel, porcelain, or aluminium, moving freely in the +tube beyond the mercury, so as to form an index. The stem of the +thermometer is fixed horizontally on the frame, which must be suspended in +the same position, as represented in fig. 53. The instrument is set by +holding it bulb downward, so as to allow the index to fall by its own +gravity into contact with the mercury. Increase of heat produces expansion +of the mercury, which consequently pushes forward the index. When the +temperature decreases, the mercury recedes from the index, leaving it so +that the extremity which was in contact with the mercury indicates upon +the scale the highest temperature since the instrument was last set.</p> + +<p> </p> +<p class="center">Fig. 53.</p> +<div class="figcenter"><img src="images/fig_53.jpg" alt="" /></div> +<p> </p> + +<p>As it is easily constructed and is comparatively cheap, it is still +employed for ordinary purposes. Its disadvantages are, firstly, its +liability of soon getting out of order by the index becoming embedded in +the mercury, or fixed by oxidation, thus rendering it altogether useless; +secondly, the ease with which the index can be displaced by the wind +moving the instrument, or other accidental disturbance, so as to cause it +to give erroneous indications occasionally; and thirdly, its consequent +total unfitness for use at sea.</p> + +<p>In the part of the tube beyond the mercury, a small quantity of air is +enclosed for the purpose of preventing the metal flowing freely in the +tube. This necessitates the construction of a larger bulb, which renders +the thermometer less sensitive. Moreover, as it frequently happens that +some mercury passes the index, particles of air insinuate themselves in +the metal, and cause separations in the column, which very often can be +removed only by a maker. To facilitate this re-adjustment, a small chamber +is left at the end of the tube, and the mercury being expanded into it by +heat until the index and air bubbles are forced into it, if possible, upon +the cooling down again, by a little management, the mercury will contract, +leaving the air and index behind. Yet sometimes the index cannot be moved +in the least from its place of fixture, so that the instrument must be +virtually reconstructed.</p> + + +<p><br /><b>71. Phillip’s Maximum Thermometer.</b>—A maximum thermometer, better perhaps +in its action than Rutherford’s, has been suggested by Professor John +Phillips, of Oxford. A small portion of air is introduced into an ordinary +thermometer, so as to cut off about half an inch of the mercurial thread +near its end in the tube. This forms a maximum thermometer, when the stem +is arranged horizontally. The isolated portion is pushed forward by +expansion, and is left in this position when the<span class="pagenum"><a name="Page_74" id="Page_74">[Pg 74]</a></span> mercury contracts. The +end remote from the bulb shows on the scale the maximum temperature.</p> + +<p>When made with a capillary tube so fine that the attraction arising from +capillarity overcomes the force of gravity, and prevents the mercury +falling to the end of the tube when the instrument is inverted, it forms a +very serviceable thermometer, quite portable and suitable for use on board +ship. In such a tube a smart shake from a swing of the hand is required to +bring the detached portion back to the column, so as to set the instrument +for future observation; no ordinary motion will move it. When the +thermometer has not this peculiarity, the mercury will flow to the end, if +held bulb downward; and in this state it is not at all a satisfactory +instrument, as the air is likely to be displaced, and a great deal of tact +is requisite to again get it to divide the column suitably. It has been +found in practice that the air bubble at different temperatures assumes +different lengths, and if very small it disappears in a few years by +oxidation and by diffusion with the mercury, so that the instrument +becomes defective and uncertain in action,—results which led to the +construction of the self-registering mercurial maximum thermometer, +invented and patented by Messrs. Negretti and Zambra. It has been before +the public about twelve years; we may therefore, now, safely speak of its +merits.</p> + + +<p><br /><b>72. Negretti and Zambra’s Patent Maximum Thermometer</b> consists of a glass +tube containing mercury fitted on an engraved scale, as shown in fig. 54. +The part of the thermometer tube above the mercury is entirely free from +air; and at the point <span class="smcaplc">A</span> in the bend above the bulb, is inserted and fixed +with the blow-pipe a small piece of solid glass, or enamel, which acts as +a valve, allowing mercury to pass on one side of it when heat is applied, +but not allowing it to return when the thermometer cools. When mercury has +been once made to pass the contraction, which nothing but the expansive +force of heat can effect, and has risen in the tube, the upper end of the +column registers the maximum temperature. To return the mercury to the +bulb, we must apply a force equal to that which raised it in the tube; the +force employed is gravity, assisted when necessary by a little agitation +of the instrument.</p> + +<p> </p> +<p class="center">Fig. 54.</p> +<div class="figcenter"><img src="images/fig_54.jpg" alt="" /></div> +<p> </p> + +<p>The degrees are generally divided on the stems of these thermometers, but +their frames of course bear a scale as well. The makers have various +styles of framing in wood, metal, porcelain, and even glass. Each material +is eligible according to requirements. Porcelain scales, having the marks +<i>etched</i> upon them by acid and permanently blackened and baked in,—by a +process for which the<span class="pagenum"><a name="Page_75" id="Page_75">[Pg 75]</a></span> inventors have a separate patent,—will be found +very serviceable, as they do not corrode or tarnish by exposure to any +kind of weather; while any amount of dust and dirt can readily be cleaned +off.</p> + +<p>The chief recommendation of this thermometer is its simplicity of +construction, enabling it to be used with confidence and safety. Of no +other maximum thermometer can it be said that it is impossible to derange +or put it out of order; hence, as regards durability, it surpasses all +others. Nothing short of actual breakage can cause it to fail. Hence it is +the most easily portable of all self-registering thermometers, an +advantage which renders it suitable for travellers, and for transmission +abroad. In the year 1852, the British Meteorological Society reported this +thermometer to be “the best which has yet been constructed for maximum +temperature, and particularly for sun observations.” Since then eleven +years have elapsed, and it is still without a rival.</p> + +<p><i>Directions for use.</i> In using this thermometer for meteorological +observations, it should be suspended by means of two brass plates <span class="smcaplc">B</span>, <span class="smcaplc">C</span>, +attached for that purpose, in such manner that it hangs raised up a little +at <span class="smcaplc">C</span>, and so placed that it is in the shade, with the air passing freely +to it from all sides; then, on an increase of heat, the mercury will pass +up the tube as in an ordinary thermometer, and continue doing so as long +as the heat increases. On a decrease of heat, the contraction of mercury +will take place <i>below</i> the <i>bend</i> in the tube, leaving the whole column +of mercury in the tube, thus registering the highest temperature, and +showing such till the instrument is disturbed.</p> + +<p>To prepare the instrument for future observations, remove and hold it +perpendicularly, with the bulb downward, and then shake it. The mercury +will then descend in the tube, and indicate the temperature of the air at +that time; and, when again suspended, is prepared for future observation.</p> + +<p>After the temperature has attained a maximum, there will be, with a +decrease of heat, a slight contraction of mercury in the tube—as well as +of that in the bulb—and hence doubts have arisen as to the accuracy of +the registration; but calculation shows, and critical trial has proved, +that the greatest daily range of temperature will not produce an error +large enough to be appreciable on the scale.</p> + +<p>A very great advantage of this thermometer is that the mercury may be +allowed to flow to the end of the tube without the maximum temperature +attained during an experiment being lost. It can be employed with the bulb +uppermost. All that is necessary for reading the maximum temperature is to +slope the instrument so that the mercury flows gently towards the bulb. It +will then stop at the contraction so as to show the maximum temperature on +the scale. Afterwards the mercury is driven into the bulb by agitating the +instrument while held in the hand. Hence the instrument is invaluable as a +registering thermometer on board ship, as its indications are in no way +affected by the motions and tremors of the vessel.</p> + +<p>For physiological experiments, such as taking the temperature of the +mouth<span class="pagenum"><a name="Page_76" id="Page_76">[Pg 76]</a></span> in fever, this thermometer is the only one that can be used with +certainty, as it can be held in any position, without losing the maximum +temperature attained.</p> + + +<p class="center"><br />MINIMA THERMOMETERS.</p> + +<p><br /><b>73. Rutherford’s Alcohol Minimum Thermometer</b>, fig. 55, consists of a glass +tube, the bulb and part of the bore of which is filled with perfectly pure +spirits of wine, in which moves freely a black glass index. A slight +elevation of the thermometer, bulb uppermost, will cause the glass index +to flow to the surface of the liquid, where it will remain, unless +violently shaken. On a <i>decrease</i> of temperature the alcohol recedes, +taking with it the glass index; on an <i>increase</i> of temperature the +alcohol alone ascends in the tube, leaving the end of the index <i>farthest</i> +from the bulb indicating the minimum temperature.</p> + +<p> </p> +<p class="center">Fig. 55.</p> +<div class="figcenter"><img src="images/fig_55.jpg" alt="" /></div> +<p> </p> + +<p><i>Directions for using, &c.</i>—Having caused the glass index to flow to the +end of the column of spirit, by slightly tilting the thermometer, bulb +uppermost, suspend the instrument (in the shade with the air passing +freely to it on all sides) by the two brass plates attached for that +purpose,—in such manner that the bulb is about half an inch lower than +the upper, or the end of the thermometer farthest from the bulb; then, on +a decrease of temperature, the spirits of wine will descend, carrying with +it the glass index; on an increase of temperature, however, the spirits of +wine will ascend in the tube, leaving that end of the small glass index +farthest from the bulb indicating the minimum temperature. To reset the +instrument, simply raise the bulb end of the thermometer a little, as +before observed, and the index will again descend to the end of the +column, ready for future observation.</p> + +<p><i>Precautions.</i>—1. By no means jerk or shake an alcohol minimum +thermometer <i>when resetting</i> it, for by so doing it is liable to +disarrange the instrument, either by causing the index to leave the +spirit, or by separating a portion of the spirit from the main column.</p> + +<p>2. As alcohol thermometers have a tendency to read lower by age, owing to +the volatile nature of the fluid allowing particles in the form of vapour +to rise and lodge in the tube, it becomes necessary to compare them +occasionally with a mercurial thermometer whose index error is known; and +if the difference be more than a few tenths of a degree, examine well the +upper part of the tube to see if any alcohol is hanging in the bore +thereof; if so, the detached portion of it can be joined to the main +column by swinging the thermometer with a pendulous motion, <i>bulb +downwards</i>.</p> + +<p>3. The spirit column is sometimes much separated by jolting in travelling. +If the instrument is in such a condition when received, it should be held +by the right<span class="pagenum"><a name="Page_77" id="Page_77">[Pg 77]</a></span> hand, bulb downward, and the frame tapped smartly, but +cautiously, against the palm of the left hand. The broken thread of spirit +will soon begin to join, and by continuing the operation a sufficient time +all the bubbles will disappear, and the thermometer become as good as +ever.</p> + + +<p><br /><b>74. Horticultural Minimum Thermometer.</b>—This instrument, represented in +fig. 56, is a special construction of Rutherford’s minimum thermometer to +meet the requirements of horticulturists. It is desirable, if not +essential, that gardeners should have the means of ascertaining to what +temperature stoves and greenhouses descend on cold nights, especially in +winter. This thermometer is mounted on a strong cast zinc frame, with the +divisions and figures of the scale raised.</p> + +<p> </p> +<p class="center">Fig. 56.</p> +<div class="figcenter"><img src="images/fig_56.jpg" alt="" /></div> +<p> </p> + +<p>The sunk surface of the frame is painted dark; the figures and division a +bright colour, so that observations can be made without a close inspection +of the instrument.</p> + +<p>The directions for using are the same as those given in the preceding +section. It may be used as an ordinary thermometer, by simply hanging it +from the top loop, in which position, the coloured liquid will always +indicate the present temperature.</p> + +<p>It was a source of annoyance with the ordinary boxwood and flat metal +scales, that after a time, exposure to a damp warm atmosphere favoured the +growth of confervæ upon them, and obliterated the divisions; the plan of +raising the figures and divisions of the scale has been found to prevent +the destruction of the instrument in this way.</p> + + +<p><br /><b>75. Baudin’s Alcohol Minimum Thermometer.</b>—This instrument resembles +Rutherford’s thermometer in appearance; its indications are given by the +expansion and contraction of alcohol, and its minimum temperature is +likewise registered by a glass index being pulled back and left behind by +the alcohol, as in Rutherford’s instrument. There is, however, a great +improvement in Baudin’s instrument; for whilst Rutherford’s thermometer +can only register in a horizontal position, Baudin’s can be used either +horizontally or vertically, as necessity may require. This important +change is effected in the following manner:—Instead of the index in the +thermometer being loose and free to run up and down according to the +position in which the instrument is held, as in Rutherford’s, the index in +the new instrument is made to fit the bore of the tube as nearly tight as +possible, so much so that in holding the thermometer even upside down, or +shaking it, the index will not shift from its position; but, inasmuch as a +minimum thermometer with an immoveable index could not be set when +required for observation, and would consequently be<span class="pagenum"><a name="Page_78" id="Page_78">[Pg 78]</a></span> useless, the inventor +has introduced behind the index a piece of solid glass, about +one-and-a-half inch in length, which moves freely in the alcohol. The +addition of the weight of this piece of glass on the top of the index, +when turned upside down, forces the index down to the edge of the alcohol; +and it is there left, as in the case of the ordinary Rutherford’s +thermometer. It is, therefore, by turning the thermometer upside down, and +letting the moveable piece of glass fall on the index, that the index is +driven to the end of the alcohol; after this operation the thermometer is +hung up either horizontally or vertically, and will then be ready for use.</p> + +<p>The index, although immoveable <i>per se</i>, is by the alcohol drawn back, as +in the ordinary minimum, and its indications are read off on the scale +from the top of the index.</p> + + +<p><br /><b>76. Mercurial Minima Thermometers desirable.</b>—Alcohol does not expand +equally for equal increments of heat, consequently errors are likely to +exist in the scale indications unless the graduations are very +accurately—not necessarily equally—made. On this account, as well as +from the volatility of alcohol, and the intervention of gaseous partitions +in the tube, a good and thoroughly reliable minimum thermometer was for a +long time a desideratum. It was desirable to obtain a thermometer which +should register the lowest temperature by mercury, the fluid in general +use for meteorological thermometers. Several instruments have recently +been invented to meet this requirement, which are suitable and +satisfactory for land purposes, but one well adapted for use on board ship +is still very much wanted.</p> + +<p>For very low temperatures, alcohol thermometers will always be required; +as mercury freezes at -40° F, and contracts very irregularly much before +this point, while alcohol has never yet been frozen.</p> + +<div class="figleft">Fig. 57.<br /><img src="images/fig_57.jpg" alt="" /></div> + +<p><br /><b>77. Negretti and Zambra’s Patent Mercurial Minimum Thermometer</b>, +represented by fig. 57, has a cylindrical bulb of large size, which, at +first sight, might induce the idea that the instrument would not be +sufficiently sensitive; but as length is given to the cylinder instead of +increasing its diameter, it will be found as sensitive as a globular bulb +of the same diameter, and much more so than an ordinary alcohol +thermometer.</p> + +<p>The reason for having the bulb large is to allow the internal diameter of +the thermometer tube to be larger than that generally used for +thermometrical purposes, so that a steel index, pointed at both ends, may +move freely within when required.</p> + +<p>The tube is blown, filled and regulated in the usual way, 60° of +temperature being about half-way up the tube. A small cylindrical bulb is +then formed at the upper end of the tube, and then is introduced a steel +needle pointed at both ends, that in contact with the mercury being +abrupt, the other more prolonged. The open<span class="pagenum"><a name="Page_79" id="Page_79">[Pg 79]</a></span> extremity of the tube is now +drawn out into a fine capillary tube, and the bulb of the instrument +warmed so as to cause the mercury to fill the tube completely. When the +mercury reaches the capillary tube, the flame of a blow-pipe is applied; +the glass is dexterously melted, the superfluous part taken away, and the +tube left hermetically closed. During this operation, the steel index has +been embedded in the heated mercury. As the instrument cools, if held +upright, the mercury will recede and expose the needle, which will then +follow the descending column simply by its own gravity. In this condition +the thermometer resembles Rutherford’s maximum, being a tube of mercury +with a steel index floating on its surface; but it possesses these +important advantages: it is quite free from air, so that the mercury can +move with perfect freedom; and the index is pointed at both ends, to allow +the mercury to pass, instead of being ground flat to prevent it.</p> + +<div class="figright">Fig. 58.<br /><img src="images/fig_58.jpg" alt="" /></div> + +<p><i>To use the Thermometer</i>, it is suspended perpendicularly (figure 57) with +the steel index resting on the surface of the mercurial column. As the +mercury in the cylinder contracts, that in the tube descends, and the +index, of its own gravity, follows it; on the contrary, as the mercury +expands and rises in the tube, it passes the index on one side, and in +rising, exerts a lateral pressure on the needle, and jams it to one side +of the tube, where it remains firmly fixed, leaving the upper point of the +needle indicating the minimum temperature. In this thermometer, the +reading is always from the upper point of the needle, and not from the +mercury itself.</p> + +<p><i>To extricate the Needle</i> from the mercury, a magnet is used, when, if the +needle is embedded only a few degrees, it can readily be withdrawn without +altering the position of the instrument. Should the magnet not be +sufficient for the purpose, we simply turn the thermometer on its support +from the upright position, slightly elevating the bulb (fig. 58 (<b>2</b>)). The +mercury and index will then flow into the small reservoir. Should the +index not freely leave the tube with the mercury, assist it with a magnet, +and when the mercury and index are in the upper bulb (figure <b>2</b>), apply a +magnet outside, which will attract and hold fast the index; and whilst +thus holding it, again bring the thermometer to the upright position, when +the mercury will immediately fall back into the tube, leaving the index +attached to the magnet (figure <b>4</b>), with which it is guided down to the +surface of the mercury, ready for another observation.</p> + +<p>Care must be taken not to withdraw the magnet until the index is in +contact with mercury; for, if released before touching, it might plunge +too deeply, and give a false indication. The rule for re-setting it will +be to bring the needle-point in contact with the mercury, and then +withdraw the magnet, having previously ascertained that no particles of +mercury are attached to the index.</p> + +<p>It may sometimes, though rarely, happen, that from the time a<span class="pagenum"><a name="Page_80" id="Page_80">[Pg 80]</a></span> minimum +temperature is registered by the index, and by the time an observation is +made, the mercury may have risen so high in the tube as to completely pass +the index, as shown (figure <b>3</b>). Should it so happen, the space which the +index occupies will readily be observed, as it will be pressed to one side +of the tube, causing a different appearance in that part, although the +point of the needle may not be seen. If such be the case, apply a magnet +to the spot where you see the index is fixed: this will hold the needle +firmly. Then, by slightly tilting the thermometer bulb uppermost, the +mercury will flow into the top bulb, leaving the index attached to the +magnet, and quite uncovered. Having taken the reading, draw the needle +into the top bulb, and hold it there whilst you adjust the thermometer by +again bringing it to the upright position.</p> + +<p>By contracting the bore of this thermometer, at the bend of the tube, +sufficiently to keep the mercury from flowing out of its bulb with too +much freedom by motion, the instrument becomes perfectly safe for +transmission abroad.</p> + + +<p><br /><b>78. Negretti & Zambra’s Second Patent Mercurial Minimum Thermometer.</b>—In +this thermometer a principle is used that has been long known to +scientific men, viz. the affinity of mercury for platinum. If mercury be +placed in contact with platinum under ordinary circumstances, no effect +will take place; but if the mercury is once made to attack the platinum, +the amalgamation is permanent and the contact perfect, so much so, that +the principle was made use of in constructing standard barometers. A ring +of platinum was fused round the end of the tube, dipping into the mercury; +and the contact between the platinum and mercury became so perfect that +air could not creep down the tube and up the bore, as in ordinary +barometer tubes. This principle of adhesion or affinity of mercury for +platinum has been brought into play for the purpose of arresting the +mercury after it has reached the minimum temperature in a thermometer. +This thermometer is made as follows:—behind the bulb is placed a +supplementary chamber; in the space or neck between the bulb of the +thermometer and the chamber, is placed a small piece of platinum; this may +be of any shape or size, but the smaller the better. This is not to fit in +the neck; it must, on the contrary, be rather loose; it may be fastened in +position or not. The instrument is represented by fig. 59.</p> + +<p> </p> +<p class="center">Fig. 59.</p> +<div class="figcenter"><img src="images/fig_59.jpg" alt="" /></div> +<p> </p> + +<p><i>Directions for using.</i>—Having suspended the thermometer in a horizontal +position, the mercury is made to stand in exact contact with the platinum +plug by slightly elevating the bulb end of the instrument. The thermometer +is now ready for observation. On a decrease of temperature, the mercury +will endeavour to contract first from the easier passage, viz. behind the +bulb; but in consequence of the adhesion of the<span class="pagenum"><a name="Page_81" id="Page_81">[Pg 81]</a></span> mercury to the platinum, +it cannot recede from here, it is therefore forced to contract from the +indicating tube, and will continue to do so as long as the temperature +decreases; and as no indices are employed in this thermometer, the extreme +end of the mercurial column will show “how cold it has been.” On an +increase of temperature the mercury will glide over the platinum plug and +expand by the easier passage into the supplementary chamber, and there +remain until a decrease of temperature again takes place, when the mercury +that had gone into the supplementary chamber will be the first to recede, +until it reaches the platinum plug, its further progress being arrested; +it will then fall in the indicating tube, and there remain until re-set.</p> + + +<p><br /><b>79. Casella’s Mercurial Minimum Thermometer.</b>—The general form and +arrangement of this instrument is shown in fig. 60. A tube with large +bore, <i>a</i>, has at the end a <i>flat glass diaphragm</i> formed by the abrupt +junction of a small chamber, <i>b c</i>, the inlet to which at <i>b</i> is larger +than the bore of the indicating tube. The result of this is that on +setting the thermometer, as described below, the contracting force of the +mercury in cooling withdraws the fluid in the indicating stem only; whilst +on its expanding with heat, the long column does not move, the increased +bulk of mercury finding an easier passage into the small pear-shaped +chamber attached.</p> + +<p> </p> +<p class="center">Fig. 60.</p> +<div class="figcenter"><img src="images/fig_60.jpg" alt="" /></div> +<p> </p> + +<p>We believe that a small speck of air must be confined in the chamber, <i>b +c</i>, to act as a spring to start the mercury from the chamber in the act of +setting the thermometer. Were this air not present, the mercury would so +adhere to the glass that no amount of shaking could induce it to flow from +the chamber.</p> + +<p><i>To set the Instrument</i>, place it in a horizontal position, with the back +plate, <i>d</i>, suspended on a nail, and the lower part supported on a hook, +<i>e</i>. The bulb end may now be gently raised or lowered, causing the mercury +to flow slowly until the bent part, <i>a</i>, <i>is full</i> and the chamber, <i>b c</i>, +<i>quite empty</i>. At this point the flow of mercury in the long stem of the +tube is arrested, <i>and indicates the exact temperature</i> of the bulb or air +at the time. On an increase of temperature the mercury will expand into +the small chamber, <i>b c</i>; and a return of cold will cause its recession +from this chamber only, until it reaches the diaphragm, <i>b</i>. Any further +diminution of heat withdraws the mercury down the bore to whatever degree +the cold may attain, where it remains until farther withdrawn by increased +cold, or till re-set for future observation.</p> + + +<p class="center"><br /><span class="pagenum"><a name="Page_82" id="Page_82">[Pg 82]</a></span>MAXIMA AND MINIMA THERMOMETERS.</p> + +<p><br /><b>80. Rutherford’s</b> arrangement for obtaining a complete instrument for the +registration of heat and cold was simply mounting a maximum thermometer +and a minimum thermometer upon the same frame or slab. Thus constructed, +they are often called “day and night” thermometers, though somewhat +inappropriately; for in temperate climates the temperature of the night +sometimes exceeds that of the day, notwithstanding the reverse is the +general law of temperature. Fig. 61 will explain the arrangement of +Rutherford’s day and night thermometer.</p> + +<p> </p> +<p class="center">Fig. 61.</p> +<div class="figcenter"><img src="images/fig_61.jpg" alt="" /></div> +<p> </p> + +<div class="figleft">Fig. 62.<br /><img src="images/fig_62.jpg" alt="" /></div> + +<p><br /><b>81. Sixe’s Self-Registering Thermometer.</b>—The very ingenious and certainly +elegant instrument about to be described was invented by James Sixe, of +Colchester. It consists of a long cylindrical bulb, united to a tube of +more than twice its length, bent round each side of it in the form of a +syphon, and terminated in a smaller, oval-shaped bulb. Figure 62 gives a +representation of this instrument. The lower portion of the syphon is +filled with mercury; the long bulb, the other parts of the tube, and part +of the small bulb, with highly rectified alcohol. A steel index moves in +the spirit in each limb of the syphon. The two indices are terminated at +top and bottom with a bead of glass, to enable them to move with the least +possible friction, and without causing separation of the spirit, or +allowing mercury to pass easily. They would, from their weight, always +rest upon the mercury; but each has a fine hair tied to its upper +extremity and bent against the interior of the tube, which acts as a +spring with sufficient elasticity to keep the index supported in the +spirit in opposition to gravity.</p> + +<p>The instrument acts as follows:—A rise of temperature causes the spirit +in the long bulb to expand and press some of the mercury into the other +limb of the syphon, into which it rises also from its own expansion, and +carries the index with it, until the greatest temperature is attained. The +lower end of this index then indicates upon the engraved scale the maximum +temperature. As the temperature falls the spirit and the mercury contract, +and in returning towards the bulb the second index is met and carried up +by the mercury until the lowest temperature occurs, when it is left to +indicate upon the scale the minimum temperature. The limb of the syphon +adjoining the bulb requires, therefore, a descending scale of<span class="pagenum"><a name="Page_83" id="Page_83">[Pg 83]</a></span> +thermometric degrees; the other limb, an ascending scale. The graduations +must be obtained by comparisons with a standard thermometer under +artificial temperatures, which should be done in this way for every 5°, in +order to correct for the inequality in the bore of the tube, and the +irregular expansion of the spirit. The instrument is set for observation +by bringing the indices into contact with the mercury, by means of a small +magnet, which attracts the steel through the glass, so that it is readily +drawn up or down. They should be drawn nearly to the top of the limbs when +it is desired to remove the instrument, which should be carefully carried +in the vertical position; for should it be inverted, or laid flat, the +spirit may get among the mercury, and so break up the column as to require +the skill of a maker to put it in order again. For transmission by +ordinary conveyances, it requires that attention be given to keep it +vertical. The entanglement of a small portion of mercury with the indices +is sometimes a source of annoyance in this instrument, for the readings +are thereby rendered somewhat incorrect. Small breakages in the mercury, +either from intervening bubbles of spirit or adhesion to the indices, may +generally be rectified by cautiously tapping the frame of the instrument, +so as to cause the mercury to unite by the assistance thus given to its +superior gravity.</p> + +<p>These thermometers, when carefully made and adjusted to a standard +thermometer, are strongly recommended for ordinary purposes, where strict +scientific accuracy is not required. This is also the only fluid +thermometer applicable for determining the temperature of the sea at +depths.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_84" id="Page_84">[Pg 84]</a></span></p> +<h2><a name="CHAPTER_VIII" id="CHAPTER_VIII"></a>CHAPTER VIII.</h2> +<p class="center"><span class="large">RADIATION THERMOMETERS.</span></p> + +<p><br /><b>82. Solar and Terrestrial Radiation considered.</b>—The surface of the earth +absorbs the heat of the sun during the day, and radiates heat into space +during the night. The envelope of gases and vapour, which we call the +atmosphere, exerts highly important functions upon these processes. Thanks +to the researches of Professor Tyndall, we are now enabled to understand +these functions much more clearly than heretofore. His elaborate, patient, +and remarkably sagacious series of experiments upon radiant heat, have +satisfactorily demonstrated that <i>dry</i> air is as transparent to radiant +heat as the vacuum itself; while air <i>perfectly saturated</i> with aqueous +vapour absorbs more than five per cent. of radiant heat, estimated by the +thermal unit adopted for the galvanometer indications of the effect upon a +thermo-electric pile.</p> + +<p>Aqueous vapour, in the form of fog or mist, as is well known, gives to our +sensation a feeling of cold, and interferes with the healthy action of the +skin and the lungs; the cause being its property of absorbing heat from +our person.</p> + +<p>Air containing moisture in an invisible state likewise exerts a remarkable +influence in radiating and absorbing heat. By reason of these properties, +aqueous vapour acts as a kind of blanket upon the ground, and maintains +upon it a higher temperature than it would otherwise have. “Regarding the +earth as a source of heat, no doubt at least ten per cent. of its heat is +intercepted within ten feet of the surface.” Thus vapour—whether +transparent and invisible, or visible, as cloud, fog, or mist—is +intimately connected with the important operations of solar and +terrestrial radiation. Cloudy, or humid days, diminish the effect upon the +soil of solar radiation; similar nights retard the radiation from the +earth. A dry atmosphere is the most favourable for the direct transmission +of the sun’s rays; and the withdrawal of the sun from any region over +which the air is dry, must be followed by very rapid cooling of the soil. +“The removal, for a single summer night, of the aqueous vapour from the +atmosphere which covers England, would be attended by the destruction of +every plant which a freezing temperature could kill. In Sahara, where ‘the +soil is fire and the wind is flame,’ the refrigeration at night is often +painful to bear. Ice has been formed in this region at night. In +Australia, also, the <i>diurnal range</i> of temperature is very great, +amounting, commonly, to between 40 and 50 degrees. In short, it may be +safely predicted, that wherever the air is <i>dry</i>, the daily thermometric +range will be great. This, however, is quite different from saying that +when the air is <i>clear</i>, the thermometric range will be great. Great +clearness to light is perfectly compatible with great opacity to heat; the +atmosphere may be charged with aqueous vapour while a deep blue sky is +overhead; and on such occasions the terrestrial<span class="pagenum"><a name="Page_85" id="Page_85">[Pg 85]</a></span> radiation would, +notwithstanding the ‘clearness,’ be intercepted.” The great range of the +thermometer is attributable to the absence of that protection against gain +or loss of heat which is afforded when aqueous vapour is present in the +air; and during such weather the rapid abstraction of moisture from the +surface of plants and animals is very deleterious to their healthy +condition. “The nipping of tender plants by frost, even when the air of +the garden is some degrees above the freezing temperature, is also to be +referred to chilling by radiation.” Hence the practice of gardeners of +spreading thin mats, of bad radiating material, over tender plants, is +often attended with great benefit.</p> + +<p>By means of the process of terrestrial radiation ice is artificially +formed in Bengal, “where the substance is never formed naturally. Shallow +pits are dug, which are partially filled with straw, and on the straw flat +pans containing water which had been boiled is exposed to the clear +firmament. The water is a very powerful radiant, and sends off its heat +into space. The heat thus lost cannot be supplied from the earth—this +source being cut off by the non-conducting straw. Before sunrise a cake of +ice is formed in each vessel.... To produce the ice in abundance, the +atmosphere must not only be clear, but it must be comparatively free from +aqueous vapour.”</p> + +<p>Considering, therefore, the important consequences attending both +terrestrial and solar radiation, it appears to us that observations from +radiation thermometers are of much more utility in judging of climate than +is usually supposed. These observations are very scanty; and what few are +upon record are not very reliable, principally from bad exposure of the +instruments, while the want of uniformity in construction may be another +cause. Herschell’s actinometer and Pouillet’s pyrheliometer, instruments +for ascertaining the absolute heating effect of the sun’s rays, should, +however, be more generally employed by meteorologists. In comparing +observations on radiation it should be kept in mind, that “the difference +between a thermometer which, properly confined [or shaded], gives the true +temperature of the night air, and one which is permitted to radiate freely +towards space, must be greater at high elevations than at low ones;”<small><a name="f6.1" id="f6.1" href="#f6">[6]</a></small> +because the higher the place, the less the thickness of the vapour-screen +to intercept the radiation.</p> + + +<p><br /><b>83. Solar Radiation Thermometer.</b>—“As the interchange of heat between two +bodies by radiation depends upon the relative temperature which they +respectively possess, the earth, by the rays transmitted from the sun +during the day, must be continually gaining an accession of heat, which +would be far from being counterbalanced by the opposite effect of its own +radiation into space. Hence, from sunrise till two or three hours after +mid-day, the earth goes on gradually increasing in temperature, the +augmentation being greatest where the surface consists of materials +calculated, from their colour and texture, to absorb heat, and where it is +deficient in<span class="pagenum"><a name="Page_86" id="Page_86">[Pg 86]</a></span> moisture, which, by its evaporation, would have a tendency +to diminish it.”<small><a name="f7.1" id="f7.1" href="#f7">[7]</a></small> It is, therefore, important to have instruments for +measuring the efficacy of solar radiation, apart from those for exhibiting +the temperature of the place in the shade.</p> + +<p> </p> +<p class="center">Fig. 63.</p> +<div class="figcenter"><img src="images/fig_63.jpg" alt="" /></div> +<p> </p> + +<p>Fig. 63 shows the arrangement of Negretti & Zambra’s maximum thermometer, +for registering the greatest heat of the sun’s direct rays, hence called a +<i>solar radiation thermometer</i>. It has a blackened bulb, the scale divided +on its own stem, and the divisions protected by a glass shield. In use it +should be placed nearly horizontally, resting on Y supports of wood or +metal, with its bulb in the full rays of the sun, resting on grass, and, +if possible, so that lateral winds should not strike the bulb; and at a +sufficient distance from any wall, so that it does not receive any +<i>reflected</i> heat from the sun. Some observers place the thermometer as +much as two feet from the ground. It would be very desirable if one +uniform plan could be recognized: that of placing the instrument as +indicated in the figure appears to be most generally adopted, and the +least objectionable.</p> + + +<p><br /><b>84. Vacuum Solar Radiation Thermometer.</b>—In order that the heat absorbed +by the blackened bulb of the solar radiation thermometer may not in part +be carried off by the currents of air which would come into contact with +it, the instrument has been improved by Messrs. Negretti and Zambra into +the <i>vacuum solar radiation thermometer</i>, as illustrated by fig. 64.</p> + +<p> </p> +<p class="center">Fig. 64.</p> +<div class="figcenter"><img src="images/fig_64.jpg" alt="" /></div> +<p> </p> + +<p>This consists of a blackened-bulb radiation thermometer, enclosed in a +glass tube and globe, from which all air is exhausted. Thus protected from +the loss of heat which would ensue if the bulb were exposed, its +indications are from 20° to 30° higher than when placed side by side with +a similar instrument with the bulb exposed to the passing air. At times +when the air has been in rapid motion, the difference between the reading +of a thermometer giving the true temperature of the<span class="pagenum"><a name="Page_87" id="Page_87">[Pg 87]</a></span> air in the shade, and +an ordinary solar radiation thermometer, has been 20° only, whilst the +difference between the air temperature and the reading of a radiation +thermometer in vacuo has been as large as 50°. It is also found that the +readings are almost identical at distances from the earth varying from six +inches to eighteen inches. By the use of this improvement, it is hoped +that the amounts of solar radiation at different places may be rendered +comparable; hitherto they have not been so; the results found at different +places cannot be compared, as the bulbs of the thermometers are under very +different circumstances as to exposure and currents of air. Important +results are anticipated from this arrangement. The observations at +different places are expected to present more agreement. Observers would +do well to note carefully the effect of any remarkable degree of intensity +in the solar heat upon particular plants, crops, fruit or other trees.</p> + + +<p><br /><b>85. Terrestrial Radiation Thermometer</b> is an alcohol minimum thermometer, +with the graduations etched upon the stem, and protected by a glass +shield, as shown in figure 65, instead of being mounted on a frame. The +bulb is transparent; that is to say, the spirit is not coloured.</p> + +<p> </p> +<p class="center">Fig. 65.</p> +<div class="figcenter"><img src="images/fig_65.jpg" alt="" /></div> +<p> </p> + +<p>In use, it should be placed with its bulb fully exposed to the sky, +resting on grass, the stem being supported by little forks of wood. The +precautions required with this thermometer are similar to those for +ordinary spirit thermometers, explained at <a href="#Page_76">page 76</a>.</p> + +<div class="figright">Fig. 66.<br /><img src="images/fig_66.jpg" alt="" /></div> + +<p><br /><b>86. Æthrioscope.</b>—The celebrated experimental philosopher, Sir John +Leslie, was the inventor of this instrument, the purpose of which is to +give a comparative idea of the radiation proceeding from the surface of +the earth towards the sky. It consists, as represented in fig. 66, of two +glass bulbs united by a vertical glass tube, of so fine a bore that a +little coloured liquid is supported in it by its own adhesion, there being +air confined in each of the bulbs. The bulb, <i>A</i>, is enclosed in a highly +polished brass sphere, <i>D</i>, made in halves and screwed together. The bulb, +<i>B</i>, is blackened and placed in the centre of a metallic cup, <i>C</i>, which +is well gilt on the inside, and which may be covered by a top, <i>F</i>. The +brass coverings defend both bulbs from solar radiation, or any +adventitious source of heat.<span class="pagenum"><a name="Page_88" id="Page_88">[Pg 88]</a></span> When the top is on, the liquid remains at +zero of the scale. On removing the top and presenting the instrument to a +clear sky, either by night or by day, the bulb, <i>B</i>, is cooled by +terrestrial radiation, while the bulb, <i>A</i>, retains the temperature of the +air. The air confined in <i>B</i>, therefore, contracts; and the elasticity of +that within <i>A</i> forces the liquid up the tube, to a height proportionate +to the intensity of the radiation. Such is the sensitiveness of the +instrument, that the smallest cloud passing over it checks the rise of the +liquid. Sir John Leslie says:—“Under a clear blue sky, the <i>æthrioscope</i> +will sometimes indicate a cold of fifty millesimal degrees; yet, on other +days, <i>when the air seems equally bright</i>, the effect is hardly 30°.” This +anomaly, according to Dr. Tyndall, is simply due to the difference in the +quantity of aqueous vapour present in the atmosphere. The presence of +invisible vapour intercepts the radiation from the æthrioscope, while its +absence opens a door for the escape of this radiation into space.</p> + +<div class="figleft">Fig. 67.<br /><img src="images/fig_67.jpg" alt="" /></div> + +<p><br /><b>87. Pouillet’s Pyrheliometer.</b>—“This instrument is composed of a shallow +cylinder of steel, <i>A</i>, fig. 67, which is filled with mercury. Into the +cylinder a thermometer, <i>D</i>, is introduced, the stem of which is protected +by a piece of brass tubing. We thus obtain the temperature of the mercury. +The flat end of the cylinder is to be turned towards the sun, and the +surface, <i>B</i>, thus presented is coated with lamp black. There is a collar +and screw, <i>C</i>, by means of which the instrument may be attached to a +stake driven into the ground, or into the snow, if the observations are +made at considerable heights. It is necessary that the surface which +receives the sun’s rays should be perpendicular to the rays; and this is +secured by appending to the brass tube which shields the stem of the +thermometer, a disk, <i>E</i>, of precisely the same diameter as the steel +cylinder. When the shadow of the cylinder accurately covers the disk, we +are sure that the rays fall, as perpendiculars, on the upturned surface of +the cylinder.</p> + +<div class="figright">Fig. 68.<br /><img src="images/fig_68.jpg" alt="" /></div> + +<p>“The observations are made in the following manner:—First, the instrument +is permitted, not to receive the sun’s rays, but to radiate its own heat +for five minutes against an unclouded part of the firmament; the decrease +of the temperature of the mercury consequent on this radiation is then +noted. Next, the instrument is turned towards the sun, so that the solar +rays fall perpendicularly upon it for five minutes; the augmentation of +heat is now noted. Finally, the instrument is turned again towards the +firmament, away from the sun, and allowed to radiate for another five +minutes, the sinking of the thermometer being noted as before. In order to +obtain the whole heating power<span class="pagenum"><a name="Page_89" id="Page_89">[Pg 89]</a></span> of the sun, we must add to his observed +heating power the quantity lost during the time of exposure, and this +quantity is the mean of the first and last observations. Supposing the +letter <i>R</i> to represent the augmentation of temperature by five minutes’ +exposure to the sun, and that <i>t</i> and <i>t¹</i> represent the reductions of +temperature observed before and after, then the whole force of the sun, +which we may call <i>T</i>, would be thus expressed:—<i>T = R + ½(t + t¹)</i>.</p> + + +<p>“The surface on which the sun’s rays here fall is known; the quantity of +mercury within the cylinder is also known; hence we can express the effect +of the sun’s heat upon a given area, by stating that it is competent, in +five minutes, to raise so much mercury so many degrees in +temperature.”—<i>Dr. Tyndall’s “Heat considered as a Mode of Motion.”</i></p> + + +<p><br /><b>88. Sir John Herschell’s Actinometer</b>, for ascertaining the absolute +heating effect of the solar rays, in which <i>time</i> is considered one of the +elements of observation, is illustrated by fig. 68. The actinometer +consists of a large cylindrical thermometer bulb, with a scale +considerably lengthened, so that minute changes may be easily seen. The +bulb is of transparent glass filled with a deep blue liquid, which is +expanded when the rays of the sun fall direct on the bulb. To take an +observation, the actinometer is placed in the shade for one minute and +read off; it is then exposed for one minute to sunshine, and its +indication recorded; it is finally restored to the shade, and its reading +noted. The mean of the two readings in the shade, subtracted from that in +the sun, gives the actual amount of expansion of the liquid produced by +the sun’s rays in one minute of time. For further information, see <i>Report +of the Royal Society on Physics and Meteorology</i>; or <i>Kæmtz’s +Meteorology</i>, translated by C. V. Walker; or the <i>Admiralty Manual of +Scientific Instructions</i>.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_90" id="Page_90">[Pg 90]</a></span></p> +<h2><a name="CHAPTER_IX" id="CHAPTER_IX"></a>CHAPTER IX.</h2> +<p class="center"><span class="large">DEEP-SEA THERMOMETERS.</span></p> + +<p><br /><b>89. On Sixe’s Principle.</b>—Thermometers for ascertaining the temperature of +the sea at various depths are constructed to register either the maximum +or minimum temperature, or both. The principle of each instrument is that +of Sixe. There are very few parts of the ocean in which the temperature +below is greater than at the surface, except in the Polar Seas, where it +is generally found to be a few degrees warmer at considerable depths than +at the surface. When the instrument is required to register only one +temperature, it can be made narrower and more compact—a great advantage +in sounding; and with less length of bulb and glass tube, so that the +liability of error is diminished. Hence, the minimum is the most generally +useful for deep-sea soundings. These thermometers must be sufficiently +strong to withstand the pressure of the ocean at two or three miles of +depth, where there may be a force exerted to compress them exceeding three +or four hundred atmospheres (of 15 lbs. to the square inch).</p> + +<p>Many have been the contrivances for obtaining correct deep-sea +indications. Thermometers and machines of various sorts have been +suggested, adopted, and eventually abandoned as only approximate +instruments. The principal reason for such instruments failing to give +correct or reliable indications, has been that the weight or pressure on +the bulbs at great depths has interfered with the correct reading of the +instruments. Thermometers have been enclosed in strong water-tight cases +to resist the pressure; but this contrivance has only had the tendency to +retard the action, so much so as to throw a doubt on the indications +obtained by the instrument so constructed.</p> + +<p>The thermometers constructed by Messrs. Negretti and Zambra for this +purpose do not differ materially from those usually made under the +denomination of Sixe’s thermometers, except in the following most +important particular:—The usual Sixe’s thermometers have a central +reservoir or cylinder containing alcohol; this reservoir, which is the +only portion of the instrument likely to be affected by pressure, has +been, in Negretti and Zambra’s new instrument, superseded by a strong +outer cylinder of glass, containing mercury and rarefied air; by this +means the portion of the instrument susceptible of compression, has been +so strengthened that no amount of pressure can possibly make the +instrument vary. This instrument has been tested in every possible manner, +and the results have been highly satisfactory, so much so as to place +their reliability beyond any possible doubt.</p> + +<div class="figright">Fig. 69.<br /><img src="images/fig_69.jpg" alt="" /></div> + +<p><span class="pagenum"><a name="Page_91" id="Page_91">[Pg 91]</a></span>The scales are made of porcelain, and are firmly secured to a back of oak, +which holds in a recess the bulb with its protecting shield, and is +rounded off so as to fit easily and firmly in a stout cylindrical copper +case, in which the thermometer is sent down when sounding (see fig. 69). +The lid of the case is made to fit down closely, and water-tight. At the +bottom of the case is a valve opening upward; and the lid has a similar +valve. These allow the water to pass through the case as the instrument +sinks, so that the least amount of obstruction is offered to the descent. +At the lower end of the case is a stout brass spring, to protect the +instrument from a sudden jar if it should touch the bottom while +descending rapidly. As the instrument is drawn up, the valves close with +the weight of water upon them, and it arrives at the surface filled with +water brought up from its lowest position. The deep-sea thermometers used +in the Royal Navy are of this pattern.</p> + + +<p><br /><b>90. Johnson’s Metallic Deep-Sea Thermometer.</b>—The objection to the +employment of mercurial thermometers for ascertaining the temperature of +the ocean at depths, arising from the compression of the bulbs, which was +of such serious consequence previous to the modification made in the +construction of the instrument by Messrs. Negretti and Zambra, led to the +construction of a metallic thermometer altogether free from liability of +disturbance from compression by the surrounding water; which, however, is +certainly not so sensitive to changes of temperature as mercury. This +instrument is the invention of Henry Johnson, Esq., F.R.A.S., and is thus +described by him:—</p> + +<p>“During the year 1844 some experiments were made by James Glaisher, Esq., +F.R.S., on the temperature of the water of the Thames near Greenwich at +the different seasons of the year; when that gentleman found that the +indications of temperature were greatly affected by the pressure on the +bulbs of the thermometers. At a depth of 25 feet this pressure would be +nearly equal to the presence of three-fourths of an atmosphere. These +observations demonstrate the importance of using in deep-sea soundings an +instrument free from liability of disturbance from compression by the +surrounding water, and have ultimately led to the construction of the +thermometer now to be described.</p> + +<p>“The instrument is composed of solid metals of considerable specific +gravity, viz. of brass and steel, the specific gravity of these metals +being 8·39 and 7·81 respectively. They are therefore not liable to +compression by the water, which under a pressure of 1,120 atmospheres, or +at a depth of 5,000 fathoms in round numbers, acquires a density or +specific gravity of 1·06. In the construction of this instrument, +advantage has been taken of the well-known difference in the ratios of +expansion and contraction by heat and cold of brass and steel, to form +compound bars of thin bars of these metals riveted together; and which +will be found to assume<span class="pagenum"><a name="Page_92" id="Page_92">[Pg 92]</a></span> a slight curve in one direction when heat has +expanded the brass more than the steel, and a slight one in the contrary +direction when cold has contracted the brass more than the steel.</p> + +<div class="figleft">Fig. 70.<br /><img src="images/fig_70.jpg" alt="" /></div> + +<p>“The indications of the instrument record the motions under changes of +temperature of such compound bars; in which the proportion of brass, the +more dilatable metal, is two-thirds, and of steel one-third.</p> + +<p>“Upon one end of a narrow plate of metal about a foot long, <i>a</i>, are fixed +three scales of temperature, <i>h</i>, which ascend from 25° to 100° F., and +which are shown more clearly in the drawing detached from the instrument. +Upon one of these scales the present temperature is shown by the pointer, +<i>e</i>, which turns upon a pivot in its centre. The register index, <i>g</i>, to +the maximum temperature, and the index, <i>f</i>, to the minimum temperature, +are moved along the other scales by the pin upon the moving pointer, at +<i>e</i>, where they are retained by stiff friction. At equal distances from +the centre of the pointer are two connecting pieces, <i>d d</i>, by which it is +attached to the free ends of two compound bars, <i>b b</i>, and its movements +correspond with the movements of the compound bars under variations of +temperature. The other ends of the bars are fastened by the plate, <i>c</i>, to +the plate, <i>a</i>, on which the scales of temperature are fixed. The +connection of the bars with both sides of the centre of the pointer +prevents disturbance of indication by lateral concussion. The case of the +instrument has been improved at the suggestion of Admiral FitzRoy, and now +presents to the water a smooth cylindrical surface, with rounded ends, and +without projection of fastenings.</p> + +<p>“In surveying expeditions, this instrument would be found useful in giving +notice of variation of depth of water, and of the necessity for taking +soundings. A diminution of the temperature of water has been observed by +scientific voyagers to accompany diminution of depth, as on nearing land, +or approaching hidden rocks or shoals. Attention would also thus be +attracted to the vicinity of icebergs.”</p> + +<div class="figright">Fig. 71.<br /><img src="images/fig_71.jpg" alt="" /></div> + +<p>This thermometer might easily be modified to serve for several other +important purposes, such as the determination of the temperature of +intermittent hot springs, and mud volcanoes.</p> + +<p>The principle of this thermometer is not altogether new; but the duplicate +arrangement of the bars, which effectually prevents the movement of the +indices by any shaking, and the application are certainly novel. Professor +Trail, in the <i>Library of Useful Knowledge</i>, writes:—“In 1803, Mr. James +Crighton, of Glasgow, published a new<span class="pagenum"><a name="Page_93" id="Page_93">[Pg 93]</a></span> ‘metallic thermometer,’ in which +the unequal expansion of zinc and iron is the moving power. A bar is +formed by uniting a plate of zinc (fig. 71), <i>c d</i>, 8 inches long, 1 inch +broad, and ¼ inch thick, to a plate of iron, <i>a b</i>, of the same length. +The lower extremity of the compound bar is firmly attached to a mahogany +board at <i>e e</i>; a pin, <i>f</i>, fixed to its upper end, plays in the forked +opening in the short arm of the index, <i>g</i>. When the temperature is +raised, the superior expansion of the zinc, <i>c d</i>, will bend the whole +bar, as in the figure; and the index, <i>g</i>, will move along the graduated +arc, from right to left, in proportion to the temperature. In order to +convert it into a <i>register thermometer</i>, Crighton applied two slender +hands, <i>h h</i>, on the axis of the index; these lie below the index, and are +pushed in opposite directions by the stud, <i>i</i>,—a contrivance seemingly +borrowed from the instrument of Fitzgerald,” a complicated metallic +thermometer, described by the Professor previously.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_94" id="Page_94">[Pg 94]</a></span></p> +<h2><a name="CHAPTER_X" id="CHAPTER_X"></a>CHAPTER X.</h2> +<p class="center"><span class="large">BOILING-POINT THERMOMETERS.</span></p> + +<p><br /><b>91. Ebullition.</b>—The temperature at which a fluid <i>boils</i> is called the +<i>boiling-point</i> of that particular fluid. It is different for different +liquids; and, moreover, in the same liquid it varies with certain changes +of circumstance. Thus the same liquid in various states of purity would +have its boiling temperature altered in a slight degree. There is also an +intimate connection with the pressure under which a fluid is boiled, and +its temperature of ebullition. Liquids boiled in the open air are +subjected to the atmospheric pressure, which is well known to vary at +different times and places; and the boiling-point of the liquid exhibits +corresponding changes. When the pressure is increased on the surface of +any fluid, the temperature of ebullition rises; and with a decrease of +pressure, the boiling goes on at a lower degree of heat.</p> + +<p>In the case of water, we commonly state the boiling-point to be 212° F.; +but it is only so at the level of the sea, under the mean pressure of the +atmosphere, represented, in the latitude of London, by a column of 29·905 +inches of mercury, at a temperature of 32° F., and when the water is fresh +and does not contain any matter chemically dissolved in it. When steam is +generated and confined in a boiler, the pressure upon the boiling water +may be several times greater than that of the atmosphere. Experimentally +it has been found, that if the pressure in the boiler be 25 lbs. on the +square inch, the temperature of the boiling water, and of the steam +likewise, is raised to 241°; while under the exhausted receiver of an +air-pump, water will boil at 185°, when the pressure is reduced to 17 +inches of mercury.</p> + + +<p><br /><b>92. Relation between the Boiling-Point and Elevation.</b>—Now, as the +atmospheric pressure is diminished by ascent, as shown by the fall of +mercury in the barometer, it follows that in elevated localities water, or +any other fluid, heated in the open air, will boil at a temperature lower +than at the sea-level. Therefore, there must be some relation between the +height of a hill, or mountain, and the temperature at which a fluid will +boil at that height. Hence, the thermometer, as used to determine the +boiling-point of fluids, is also an indicator of the atmospheric pressure; +and may be used as a substitute for the barometer in measuring elevations.</p> + +<p>If the atmospheric pressure were constant at the sea-level, and always the +same for definite heights, we might expect the boiling-points of fluids +also to be in exact accordance with height; and the relation once +ascertained, we could readily, by means of the thermometer and boiling +water, determine an unknown height, or for a known elevation assert the +boiling temperature of a liquid. However, as the atmospheric pressure is +perpetually varying at the same place, within certain limits, so there +are, as it were, sympathetic changes in the boiling temperatures of +fluids.<span class="pagenum"><a name="Page_95" id="Page_95">[Pg 95]</a></span> It follows from this, that heights can never be accurately +measured, either by the barometer or the boiling-point thermometer, by +simply observing at the places whose elevations are required. To determine +a height with any approach to accuracy, it is necessary that a similar +observation should be made at the same time at a lower station, not very +remote laterally from the upper, and that they should be many times +repeated. When such observations have been very carefully conducted, the +height of the upper station above the lower may be ascertained with great +precision, as has been repeatedly verified by subsequent trigonometrical +measurement of elevations so determined. If the lower station be at the +sea-level, of course the absolute height of the upper is at once obtained.</p> + + +<p><br /><b>93. Mountain Thermometer; sometimes called Hypsometric Apparatus.</b>—We have +now to examine the construction of the boiling-point thermometer, and its +necessary appendages, as adapted for the determination of heights.</p> + +<div class="figleft">Fig. 72.<br /><img src="images/fig_72.jpg" alt="" /></div> + +<div class="figright">Fig. 73.<br /><img src="images/fig_73.jpg" alt="" /></div> + +<p>Messrs. Negretti and Zambra’s arrangement of the instrument is shown in +figures 72 and 73.</p> + +<p>The thermometer is made with an elongated bulb, so as to be as sensitive +as possible. The scale, about a foot long, is graduated on the stem, and +ranges from 180° to 214°, each degree being sufficiently large to show the +divisions of tenths of a degree. A sliding metallic vernier might perhaps +with advantage be attached to the stem, which would enable the observer to +mark hundredths of a degree; which, however, he can pretty well do by +estimation. The boiler is so contrived as to allow, not only the bulb, but +the stem also of the thermometer, to be surrounded by the steam. The +arrangement is readily understood by reference to the accompanying +diagram, fig. 73.</p> + +<p><i>C</i>, is a copper boiler, supported by a tripod stand so as to allow a +spirit-lamp, <i>A</i>, made of metal to be placed underneath. The flame from +the lamp may be surrounded by a fine wire gauze, <i>B</i>, which will prevent +it being extinguished when experimenting in the external air. <i>E E E</i>, is +a three-drawn telescope tube, proceeding from the boiler, and open also at +top. Another tube, similarly constructed, envelops this, as shown by <i>D D +D</i>. This tube is screwed to the top of the boiler, and has two openings, +one at the top to admit the thermometer, the other low<span class="pagenum"><a name="Page_96" id="Page_96">[Pg 96]</a></span> down, <i>G</i>, to give +vent to the steam. As the steam is generated, it rises in the inner tube, +passes down between the tubes, and flows away at <i>G</i>. The thermometer is +passed down, supported by an india-rubber washer, fitting steam tight, so +as to leave the top of the mercury, when the boiling-point is attained, +sufficiently visible to make the observation. The telescopic movement, and +the mode of supporting the thermometer, enable the observer always to keep +the bulb near the water, and the double tube gives all the protection +required to obtain a steady boiling-point. Some boiling-point thermometers +are constructed with their scales altogether exposed to the air, which may +be very cold, and consequently may contract to some extent the thread of +mercury outside the boiler. The steam, having the same temperature as the +boiling water, keeps the tube, throughout nearly its whole length, at the +same degree of heat, in the apparatus described. The whole can be packed +in a tin case very compactly and securely for travelling, as in fig. 72.</p> + +<p><i>Directions for Using.</i>—When the apparatus is required for practical use, +sufficient water must be poured into the boiler to fill it about one +third, through an opening, <i>F</i>, which must be afterwards closed by the +screw plug. Then apply the lighted lamp. In a short time steam will issue +from <i>G</i>; and the mercury in the thermometer, kept carefully immersed, +will rise rapidly until it attains a stationary point, which is the +boiling temperature. The observation should now be taken and recorded with +as much accuracy as possible, and the temperature of the external air must +be noted at the same time by an ordinary thermometer.</p> + +<p>The water employed should be pure. Distilled water would therefore be the +best. If a substance is held mechanically suspended in water, it will not +affect the boiling-point. Thus, muddy water would serve equally as well as +distilled water. However, as it cannot be readily ascertained that nothing +is dissolved chemically when water is dirty, we are only correct when we +employ pure water.</p> + + +<p><br /><b>94. Precautions to ensure correct Graduation.</b>—Those who possess a +boiling-point thermometer should satisfy themselves that it has been +correctly graduated. To do this, it is advisable to verify it with the +reading of a standard barometer reduced to 32° F. The table of “Vapour +Tension” (given at <a href="#Page_62">p. 62</a>) will furnish the means of comparison. Thus, if +the reduced reading of the barometer, corrected also for latitude, be +29·922, the thermometer should show 212° as the boiling-point of water at +the same time and place; if 29·745, the thermometer should read 211·7; and +so on as per table. In this way the error of the chief point of the scale +can be obtained. Other parts of the scale may be checked with a standard +thermometer, by subjecting both to the same temperature, and comparing +their indications. The graduations as fixed by some makers are not always +to be trusted; and this essential test should be conducted with the utmost +nicety and care.</p> + +<p>Admiral FitzRoy writes, in his <i>Notes on Meteorology</i>:—“Each degree of +the boiling-point thermometer is equivalent to about 550 <i>feet of ascent</i>, +or one-tenth to<span class="pagenum"><a name="Page_97" id="Page_97">[Pg 97]</a></span> 55 feet; therefore, the smallest error in the graduation +of the thermometer itself will affect the height deduced materially.</p> + +<p>“In the thermometer which is graduated from 212° (the boiling-point) to +180°, similarly to those intended for the purpose of measuring heights, +there must have been a starting point, or zero, from which to begin the +graduation. I have asked an optician in London how he fixed that zero, the +boiling-point. ‘By boiling water at my house,’ he replied. ‘Where is your +house?’ In such a part of the town, he answered. I said: ‘What height is +it above the sea?’ to which he replied, ‘I do not know;’ and when I asked +the state of the barometer when he boiled the water, whether the mercury +was high or low, he said that he had not looked at it! Now, as this +instrument is intended to measure heights and to decide differences of +some hundred, if not thousand feet upwards, at least one should endeavour +to ascertain a reliable starting point. From inquiries made, I believe +that the determination of the boiling-point of ordinary thermometers has +been very vague, not only from the extreme difficulties of the process +itself (which are well known to opticians), but from the radical errors of +not allowing for the pressure of the atmosphere at the time of +graduation—which may be much, even an inch higher or lower, than the +mean, or any <i>given height</i>—while the elevation of the place above the +level of the sea is also unnoticed. Then there is another source of error, +a minor one, perhaps: the inner limit, the 180° point, is fixed only by +comparison with another thermometer; it may be right, or it may be very +much out, as may be the intermediate divisions; for the difficulty of +ascertaining degree by degree is great: and it must be remembered that the +measurement of a very high mountain depends upon those inner degrees from +200° down to 180°, thereabouts. Hence, the difficulty of making a reliable +observation by boiling water seems to be greater than has been generally +admitted.”</p> + + +<p><br /><b>95. Method of Calculating Heights from Observations with the Mountain +Thermometer.</b>—Having considered how to make observations with the proper +care and accuracy, it becomes necessary to know how to deduce the height +by calculation. That a constant intimate relation exists between the +boiling temperature of water and the pressure of the air, we have already +learned. This knowledge is the result of elaborate experiments made by +several scientific experimentalists, who have likewise constructed formulæ +and tables for the conversion of the boiling temperatures into the +corresponding pressures of vapour, or, which is equivalent, of the +atmosphere, when the operation is performed in the open air. As might be +expected, there is not a perfect accord in the results arrived at by +different persons. Regnault is the most recent, and his experiments are +considered the most reliable.</p> + +<p>From Regnault’s table of vapour tension, we can obtain the pressure in +inches of mercury at 32°, which corresponds to the observed boiling-point; +or <i>vice versa</i>, if required. From the pressure, the height may be deduced +by the method for finding heights by means of the barometer.</p> + +<p><span class="pagenum"><a name="Page_98" id="Page_98">[Pg 98]</a></span>The following table expresses very nearly the elevation in feet +corresponding to a fall of 1° in the temperature of boiling water:—</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center">Boiling Temperatures<br />between.</td><td><span class="spacer"> </span></td> + <td align="center">Elevation in Feet<br />for each Degree.</td></tr> +<tr><td><span style="margin-left: 1em;">214° and 210—</span></td><td> </td><td align="center">520</td></tr> +<tr><td><span style="margin-left: 1em;">210 and 200—</span></td><td> </td><td align="center">530</td></tr> +<tr><td><span style="margin-left: 1em;">200 and 190</span></td><td> </td><td align="center">550</td></tr> +<tr><td><span style="margin-left: 1em;">190 and 180</span></td><td> </td><td align="center">570</td></tr></table> + +<p>These numbers agree very well with the results of theory and actual +observation. The assumption is that the boiling-point will be diminished +1° for each 520 feet of ascent until the temperature becomes 210°, then +530 feet of elevation will lower it one degree until the water boils at +200°, and so on; the air being at 32°.</p> + +<p>Let <i>H</i> represent the vertical height in feet between two stations; <i>B</i> +and <i>b</i>, the boiling-points of water at the lower and upper stations +respectively; <i>f</i>, the factor found in the above table. Then</p> + +<p class="center"><i>H</i> = <i>f</i> (<i>B</i> - <i>b</i>)</p> + +<p>Further, let <i>m</i> be the mean temperature of the stratum of air between the +stations. Now, if the mean temperature is less than 32°, the column of air +will be shorter; and if greater, longer than at 32°. According to +Regnault, air expands <span style="font-size: 0.8em;"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">491·13</span> +or ·002036 of its volume at 32°, for each degree increase of heat. Calling the correction due to the mean +temperature of air <i>C</i>, its value will be found from the equation,</p> + +<p class="center"><i>C</i> = <i>H</i> (<i>m</i> - 32) ·002036</p> + +<p>Calling the corrected height <i>H′</i>, it will be found from the formula,</p> + +<p class="center"><i>H′</i> = <i>H</i> + <i>H</i> (<i>m</i> - 32) ·002036</p> + +<p>that is,</p> + +<p class="center"><i>H′</i> = <i>H</i> {1 + (<i>m</i> - 32) ·002036}</p> + +<p>and substituting the value of <i>H</i>,</p> + +<p class="center"><i>H′</i> = <i>f</i> (<i>B</i> - <i>b</i>) {1 + (<i>m</i> - 32) ·002036}</p> + +<p>Strictly, according to theoretical considerations, there is a correction +due to latitude, as in the determination of heights by the barometer; but +its value is so small that it is practically of no importance.</p> + +<p>If a barometer be observed at one of the stations, the table of vapour +tensions (<a href="#Page_62">p. 62</a>) will be useful in converting the pressure into the +corresponding boiling-point, or <i>vice versa</i>; so that the difference of +height may be found either by the methods employed for the boiling-point +thermometer or the barometer.</p> + +<p>In conclusion, it may be remarked that observers who have good instruments +at considerable elevations, as sites on mountains or plateaus, would +confer a benefit to science, by registering for a length of time the +barometer along with the boiling temperature of water, as accurately as +possible. Such observations would serve to<span class="pagenum"><a name="Page_99" id="Page_99">[Pg 99]</a></span> verify the accuracy of +theoretical deductions, and fix with certainty the theoretical scale with +the barometer indications.</p> + +<p><i>Example, in calculating Heights from the Observations of the +Boiling-point of Water.</i>—1. At Geneva the observed boiling-point of water +was 209°·335; on the Great St. Bernard it was 197°·64; the mean +temperature of the intermediate air was 63°·5; required the height of the +Great St. Bernard above Geneva.</p> + +<p>Method by formula:—</p> + +<p class="center"><i>H′</i> = <i>f</i> (<i>B</i> - <i>b</i>) {1 + (<i>m</i> - 32°) ·002036}</p> + +<p>In this case <i>f</i> is between 530 and 550, or 540.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td><i>B</i> =</td> + <td>209·335</td> + <td> </td> + <td><span class="spacer"> </span></td> + <td><i>m</i> =</td> + <td>63·5</td></tr> +<tr><td><i>b</i> =</td> + <td class="botbor">197·64</td> + <td colspan="3"> </td> + <td class="botbor">32</td></tr> +<tr><td> </td> + <td><span style="margin-left: .5em;">11·695</span></td> + <td colspan="3"> </td> + <td>31·5</td></tr> +<tr><td><i>f</i> =</td> + <td class="botbor"><span style="margin-left: 1.75em;">540</span></td> + <td colspan="3"> </td> + <td class="botbor"><span style="margin-left: 1em;">·002036</span></td></tr> +<tr><td> </td> + <td><span style="margin-left: .5em;">6315·3</span></td> + <td colspan="3"> </td> + <td><span style="margin-left: .5em;">0·0641340</span></td></tr> +<tr><td> </td> + <td class="botbor"><span style="margin-left: 1em;">1·064</span></td> + <td colspan="3"> </td> + <td class="botbor"><span style="margin-left: .5em;">1</span></td></tr> +<tr><td><i>H′</i> =</td> + <td class="botbor2"><span style="margin-left: .5em;">6719·5</span></td><td>feet.</td> + <td colspan="2"> </td> + <td><span style="margin-left: .5em;">1·064</span></td></tr></table> + +<p>Method by Tables supplied with boiling-point apparatus made by Messrs. +Negretti and Zambra:—</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>209·335</td> + <td>gives</td> + <td>1464</td> + <td>in Table I.</td></tr> +<tr><td>197·64</td> + <td align="center">"</td> + <td class="botbor">7736</td> + <td align="center">"</td></tr> +<tr><td colspan="2"> </td> + <td>6272</td></tr> +<tr><td align="right">63·5</td> + <td align="center">"</td> + <td class="botbor"><span style="margin-left: 1.5em;">1·07</span></td> + <td>in Table II.</td></tr> +<tr><td>Height</td> + <td> </td> + <td class="botbor2">6711</td></tr></table> + +<p><br /><b>96. Thermometers for Engineers.</b>—<i>1st. Salinometer.</i>—Under the +circumstances at which fresh water boils at 212°, sea water boils at +213°·2. The boiling temperature is raised by the chemical solution of any +substance in the water, and the more with the increase of matter +dissolved.</p> + +<p>From a knowledge of this principle, marine engineers make use of the +thermometer to determine the amount of salts held in solution by the water +in the boilers of sea-going steamers. Common sea-water contains <span style="font-size: 0.8em;"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">33</span> of +its volume of salt and other earthy matters. As evaporation proceeds, the +solution becomes proportionally stronger, and more heat is required to +produce steam. The following table from the work of Messrs. Main and +Brown, on the Marine Steam-Engine, shows the relation between the +boiling-point under the mean pressure of the atmosphere, or 80 inches of +mercury, and the proportion of matter dissolved in the water:—</p> + +<p><span class="pagenum"><a name="Page_100" id="Page_100">[Pg 100]</a></span></p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>Proportion of Salt in 100 parts of water</td> + <td align="center">0</td> + <td>Boiling-point</td> + <td>212°</td></tr> +<tr><td><span style="margin-left: 4em;">"</span><span style="margin-left: 7em;">"</span></td> + <td align="center"><span style="font-size: 0.8em;"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">33</span></td> + <td align="center">"</td> + <td>213·2</td></tr> +<tr><td><span style="margin-left: 4em;">"</span><span style="margin-left: 7em;">"</span></td> + <td align="center"><span style="font-size: 0.8em;"><sup>2</sup></span>⁄<span style="font-size: 0.6em;">33</span></td> + <td align="center">"</td> + <td>214·4</td></tr> +<tr><td><span style="margin-left: 4em;">"</span><span style="margin-left: 7em;">"</span></td> + <td align="center"><span style="font-size: 0.8em;"><sup>3</sup></span>⁄<span style="font-size: 0.6em;">33</span></td> + <td align="center">"</td> + <td>215·5</td></tr> +<tr><td><span style="margin-left: 4em;">"</span><span style="margin-left: 7em;">"</span></td> + <td align="center"><span style="font-size: 0.8em;"><sup>4</sup></span>⁄<span style="font-size: 0.6em;">33</span></td> + <td align="center">"</td> + <td>216·6</td></tr> +<tr><td><span style="margin-left: 4em;">"</span><span style="margin-left: 7em;">"</span></td> + <td align="center"><span style="font-size: 0.8em;"><sup>5</sup></span>⁄<span style="font-size: 0.6em;">33</span></td> + <td align="center">"</td> + <td>217·9</td></tr> +<tr><td><span style="margin-left: 4em;">"</span><span style="margin-left: 7em;">"</span></td> + <td align="center"><span style="font-size: 0.8em;"><sup>6</sup></span>⁄<span style="font-size: 0.6em;">33</span></td> + <td align="center">"</td> + <td>219·0</td></tr> +<tr><td><span style="margin-left: 4em;">"</span><span style="margin-left: 7em;">"</span></td> + <td align="center"><span style="font-size: 0.8em;"><sup>7</sup></span>⁄<span style="font-size: 0.6em;">33</span></td> + <td align="center">"</td> + <td>220·2</td></tr> +<tr><td><span style="margin-left: 4em;">"</span><span style="margin-left: 7em;">"</span></td> + <td align="center"><span style="font-size: 0.8em;"><sup>8</sup></span>⁄<span style="font-size: 0.6em;">33</span></td> + <td align="center">"</td> + <td>221·4</td></tr> +<tr><td><span style="margin-left: 4em;">"</span><span style="margin-left: 7em;">"</span></td> + <td align="center"><span style="font-size: 0.8em;"><sup>9</sup></span>⁄<span style="font-size: 0.6em;">33</span></td> + <td align="center">"</td> + <td>222·5</td></tr> +<tr><td><span style="margin-left: 4em;">"</span><span style="margin-left: 7em;">"</span></td> + <td align="center"><span style="font-size: 0.8em;"><sup>10</sup></span>⁄<span style="font-size: 0.6em;">33</span></td> + <td align="center">"</td> + <td>223·7</td></tr> +<tr><td><span style="margin-left: 4em;">"</span><span style="margin-left: 7em;">"</span></td> + <td align="center"><span style="font-size: 0.8em;"><sup>11</sup></span>⁄<span style="font-size: 0.6em;">33</span></td> + <td align="center">"</td> + <td>224·9</td></tr> +<tr><td><span style="margin-left: 4em;">"</span><span style="margin-left: 7em;">"</span></td> + <td align="center"><span style="font-size: 0.8em;"><sup>12</sup></span>⁄<span style="font-size: 0.6em;">33</span></td> + <td align="center">"</td> + <td>226·0</td></tr></table> + +<div class="figleft">Fig. 74.<br /><img src="images/fig_74.jpg" alt="" /></div> + +<p>When the salts in solution amount to <span style="font-size: 0.8em;"><sup>12</sup></span>⁄<span style="font-size: 0.6em;">33</span>, the water is saturated. It has +also been ascertained that, when a solution of <span style="font-size: 0.8em;"><sup>4</sup></span>⁄<span style="font-size: 0.6em;">33</span> is attained, +incrustation of the substances commences on the boiler. Hence, it is a +rule with engineers to expel some of the boiling water, when the +thermometer indicates a temperature of 216°, and introduce some more cold +water, in order to prevent incrustation, which not only injures the +boiler, but opposes the passage of heat to the water. The thermometer used +for this purpose should be very accurately graduated, and the scale must +be considerably higher than, though it need not read much below 212°.</p> + +<p><i>2nd. Pressure Gauge.</i>—The elasticity of gases augments by increase of +temperature, and <i>vice versa</i>; it follows, therefore, that when steam is +generated in a closed boiler, its temperature rises beyond the boiling +temperature of 212°, owing to the increased pressure upon the water. The +law connecting the pressure and the corresponding temperature of steam is +the same as that upon which the boiling of fluids under diminished +atmospheric pressure takes place. Hence, the indications of the +thermometer become exponents of steam pressure. Engineers are furnished, +in works on the steam-engine, with tables, from which the pressure +corresponding to a given temperature, or the converse, can be obtained by +mere inspection.</p> + +<p>Fig. 74 represents the thermometer employed as a steam-pressure gauge. It +is fitted in a brass case, with screw-plug and washers for closing the +boiler when the thermometer is not in use. The scale shows the pressure +corresponding to the temperature, from 15 to 120 lbs., above the +atmospheric pressure, which is usually taken as 15 lbs. on the square +inch.</p> + + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_101" id="Page_101">[Pg 101]</a></span></p> +<h2><a name="CHAPTER_XI" id="CHAPTER_XI"></a>CHAPTER XI.</h2> +<p class="center"><span class="large">INSTRUMENTS FOR ASCERTAINING THE HUMIDITY OF THE AIR.</span></p> + +<p><br /><b>97. Hygrometric Substances.</b>—The instruments devised for the purpose of +ascertaining the humidity of the atmosphere are termed <i>hygrometers</i>. The +earliest invented hygrometers were constructed of substances readily acted +upon by the vapour in the air, such as hair, grass, seaweed, catgut, &c., +which all absorb moisture, and thereby increase in length, and when +deprived of it by drying they contract. Toy-like hygrometers, upon the +principle of absorption, are still common as ornaments for mantel-pieces. +A useful little instrument of this class, formed from the beard of the +wild oat, is made to resemble a watch in external appearance, and is +designed to prove the dampness or dryness of beds: a moveable hand points +out on the dial the hygrometric condition of the clothes upon which the +instrument is laid.</p> + + +<div class="figright">Fig. 75.<br /><img src="images/fig_75.jpg" alt="" /></div> + +<p><br /><b>98. Saussure’s Hygrometer</b>, formerly used as a meteorologic instrument, but +now regarded as an ornamental curiosity, is represented in fig. 75. Its +action depends upon a prepared hair, fixed at one end to the frame of the +instrument, and wound round a pulley at the other. The pulley carries a +pointer which has a counterpoise sufficient to keep the hair stretched. By +this means the shrinking and lengthening of the hair cause the pointer to +traverse a graduated arc indicating the relative humidity.</p> + +<p>Such instruments, however ingenious, are not of scientific value; because +they do not admit of rigid comparison, are liable to alter in their +contractile and expansive properties, and cannot be made to indicate +precisely alike.</p> + + +<p><br /><b>99. Dew-Point.</b>—The amount of water which the air can sustain in an +invisible form increases with the temperature; but for every definite +temperature there is a limit to the amount of vapour which can be thus +diffused. When the air is cooled, the vapour present may be more than it +can sustain; part will then be condensed as dew, rain, hail or snow, +according to the meteorologic circumstances. The temperature which the air +has when it is so fully saturated with vapour that any excess will be +deposited as dew, is called the <i>dew-point</i>.</p> + + +<p><br /><b>100. Drosometer.</b>—“To measure the quantity of dew deposited each night, an +instrument is used called a <i>Drosometer</i>. The most simple process consists +in exposing to the open air bodies whose exact weight is known, and then +weighing them afresh after they are covered with dew. According to Wells, +locks of wool, weighing about eight grains, are to be preferred, which are +to be divided [formed] into spherical masses of the diameter of about two +inches.”—<i>Kœmtz.</i></p> + + +<p><br /><span class="pagenum"><a name="Page_102" id="Page_102">[Pg 102]</a></span><b>101. Humidity.</b>—The proportion existing between the amount of vapour +actually present in the air at any time, and the quantity necessary to +completely saturate it, is called <i>the degree of humidity</i>. It is usually +expressed in a centesimal scale, 0 being perfect dryness, and 100 complete +saturation.</p> + +<p>The pressure, or tension, of vapour at the dew-point temperature, divided +by the tension of vapour at the air temperature and the quotient +multiplied by 100, gives the degree of humidity. (Regnault’s Tables should +be used.)</p> + +<p>Hence the utility of instruments for determining the dew-point.</p> + + +<div class="figleft">Fig. 76.<br /><img src="images/fig_76.jpg" alt="" /></div> + +<p><br /><b>102. Leslie’s Hygrometer.</b>—This instrument consists of a glass syphon +tube, terminated with a bulb or ball at each end, turned outwards from +each other, as in fig. 76. The tube is partly filled with concentrated +sulphuric acid, tinged by carmine. One of the balls is covered smoothly +with fine muslin, and is kept continually moistened with pure water, drawn +from a vase placed near it by the capillary attraction of a few strands of +clean cotton-wick. The descent of the coloured liquid in the other stem +will mark the diminution of temperature caused by the evaporation of the +water from the humid surface. The drier the ambient air is, the more +rapidly will the evaporation go on; and the cold produced will be greater. +When the air is nearly saturated with moisture, the evaporation goes on +slowly; the cold produced is moderate, because the ball regains a large +portion of its lost heat from surrounding bodies; and the degree of +refrigeration of the ball is an index of the dryness of the air.</p> + +<p>“Should the water become frozen on the ball, this hygrometer will still +act; for evaporation goes on from the surface of ice in proportion to the +dryness of the air. Leslie estimates, that when the ball is moist, air, at +the temperature of the ball, will take up moisture equal to the +sixteen-thousandth part of its weight, for each degree of his hygrometer; +and as ice in melting requires one-seventh of the caloric consumed in +converting water into vapour, when the ball is frozen, the hygrometer will +sink more than when wet by 1° in 7°; and hence, in the frozen state, we +must increase the value of the degrees one-seventh: so that each of them +will correspond to an absorption of moisture equal to +one-fourteen-thousandth part of the weight of the air.</p> + +<p>“When this hygrometer stands at 15°, the air feels damp; from 30° to 40°, +we reckon it dry; from 50° to 60°, very dry; and from 70° upwards, we +should call it intensely dry. A room would feel uncomfortable, and would +probably be unwholesome, if the instrument in it did not reach 30°.<small><a name="f8.1" id="f8.1" href="#f8">[8]</a></small> In +thick fogs it keeps almost at the beginning of the scale. In winter, in +our climate, it ranges from 5° to<span class="pagenum"><a name="Page_103" id="Page_103">[Pg 103]</a></span> 15°; in summer often from 15° to 55°; +and sometimes attains 80° or 90°. The greatest degree of dryness ever +noticed by Leslie was at Paris, in the month of September, when the +hygrometer indicated 120°.”—<i>Professor Trail, in “Library of Useful +Knowledge.”</i></p> + +<p>In estimating the value of the indications of this hygrometer, it should +be borne in mind that the scale adopted by Leslie was <i>millesimal</i>, that +is to say, from the freezing to the boiling-point of water was divided +into a thousand parts; ten millesimal degrees are therefore equal to one +of the scale of Celsius.</p> + + +<p class="center"><br />103. DANIEL’S HYGROMETER.</p> + +<div class="figright">Fig. 77.<br /><img src="images/fig_77.jpg" alt="" /></div> + +<p>This instrument was invented about the year 1820, by Professor Daniel, the +distinguished author of <i>Meteorological Essays</i>; and it entirely +superseded all hygrometers depending upon the absorption of moisture. The +form of the instrument is shown in fig. 77.</p> + +<p>It consists of a glass tube, about one-eighth of an inch in diameter of +bore, bent twice at right angles, and terminated, at each end, in a bulb +about one inch and a quarter in diameter. In one limb of the tube is +enclosed a delicate thermometer, which descends to the centre of the +adjoining bulb, which is about three-parts filled with sulphuric ether. +All the other parts of the tube are carefully freed from air, so that they +are occupied by the vapour of the ether. This bulb is generally made of +black glass; the other is transparent, but covered with a piece of fine +muslin. The support for the tube has a thermometer attached, which shows +the temperature of the external air. The tube can be removed from the +stand, and the parts are made to pack, with a necessary phial of ether, in +a small box, which can easily be got into the pocket.</p> + +<p><i>How to use the Hygrometer.</i>—This instrument gives the dew-point by +direct observation, which must be made in the following manner:—Having +fixed the tube upon the stand, with the bulbs vertically downward, the +ether is all caused to flow into the lower ball by inclining the tube. The +temperature of the air is noted by the exposed thermometer. Then some +ether is poured, from a dropping tube fitting into the neck of the phial, +upon the muslin-covered bulb. The rapid evaporation of this ether cools +the bulb and causes condensation of the ethereal vapour in its interior. +This gives rise to rapid evaporation of the ether in the lower bulb, +whereby its temperature is greatly reduced. The air in the vicinity is +deprived of its warmth by the cold bulb, and is soon cooled to the +temperature at which it is perfectly<span class="pagenum"><a name="Page_104" id="Page_104">[Pg 104]</a></span> saturated with the vapour which it +contains. Cooled ever so little below this temperature, some aqueous +vapour will be condensed, and will form a dew upon the black-glass bulb. +At the first indication of the deposit of dew the reading of the internal +thermometer is taken: which is the dew-point.</p> + +<p>This hygrometer has undeniable disadvantages. The surface upon which the +dew condenses is small, and requires a peculiar direction of light in +which to see it well. The observer, having his attention on the bulb and +the thermometer, cannot always fix with precision the dew-point; and hence +he is recommended to note the temperature at the appearance and at the +disappearance of the dew, in order that the chance of error may be +diminished. Without doubt, the necessarily long continuance of the +observer near the instrument influences, to some extent, the observed +temperatures; and the difficulty of not being always able to procure pure +ether for the experiments is not the least of the drawbacks to the use of +the instrument. Some of these disadvantages are obviated in Regnault’s +hygrometer.</p> + + +<div class="figleft">Fig. 78.<br /><img src="images/fig_78.jpg" alt="" /></div> + +<p class="center"><br />104. REGNAULT’S CONDENSER HYGROMETER</p> + +<p>(Fig. 78) consists of a tube, <i>C</i>, made of silver, very thin, and +perfectly polished; the tube is larger at one end than the other, the +large part being 1·8 inches in depth, by 0·8 in diameter; this is fitted +tightly to a brass stand, <i>B</i>, with a telescopic arrangement for adjusting +when making an observation.</p> + +<p>The tube, <i>C</i>, has a small lateral tubulure, to which is attached an +India-rubber tube, with ivory mouth-piece; this tubulure enters <i>C</i> at +right angles near the top, and traverses it to the bottom of the largest +part.</p> + +<p>A delicate thermometer, <i>D</i>, is inserted through a cork, or India-rubber +washer, at the open end of the tube, <i>C</i>, the bulb of which descends to +the centre of its largest part.</p> + +<p><i>G</i> is an attached thermometer for taking the temperature of the air, and +<i>F</i> is a bottle containing ether.</p> + +<p><i>To use the Condenser Hygrometer</i>, a sufficient quantity of ether is +poured into the silver tube to cover the thermometer bulb: on allowing air +to pass bubble by bubble through the ether, by breathing in the tube, <i>E</i>, +an uniform temperature will be obtained; if the ether continues to be +agitated, by breathing briskly through the tube a rapid reduction of +temperature will be the result; at the moment the ether is cooled down to +the dew-point temperature, the external surface of that portion of the +silver tube containing ether will become covered with a coating of +moisture, and the degree shown by the thermometer at that instant will be +the temperature of the dew-point.</p> + +<p>This form of hygrometer, for ascertaining by direct observation the +dew-point, is so superior to Daniell’s, both from its being more certain +in its indications and<span class="pagenum"><a name="Page_105" id="Page_105">[Pg 105]</a></span> economical in use, that Messrs. Negretti and +Zambra have been induced to modify it, and reduce its price to little more +than that of a good Daniell’s Hygrometer.</p> + +<div class="figright">Fig. 79.<br /><img src="images/fig_79.jpg" alt="" /></div> + +<p><br /><b>105. Temperature of Evaporation.</b>—When the air is not saturated with +vapour, evaporation is going on with more or less activity, according as +the temperature is high or low, rising or falling. Now vapour cannot be +formed without an expenditure of heat; as we invariably find that the +process of evaporation lowers the temperature of the liquid from which the +vapour is produced, and, by communication, that of contiguous substances +also. Thus the emigrant, crossing the line under the scorching influence +of the vertical sun, wraps a wet towel round his can of water, swings it +in the breeze, to evaporate the moisture of the towel, and obtains a glass +of cool water. So also, European residents in India, during the hot +season, spread out mats in their apartments, and keep them wet, in order +that the evaporation may cool the air. This principle has been applied, +for the purpose of ascertaining the hygrometric condition of the air, in +the instrument known as Mason’s hygrometer, or psychrometer, which is now +in general use, from its simplicity, accuracy, and ease of observing.</p> + + +<p class="center"><br />106. MASON’S HYGROMETER.</p> + +<p><br /><b>The Dry and Wet Bulb Hygrometer, or Psychrometer</b>, known also as Mason’s +hygrometer (fig. 79), consists of two parallel thermometers, as nearly +identical as possible, mounted on a wooden bracket, one marked <i>dry</i>, the +other <i>wet</i>. The bulb of the wet thermometer is covered with thin muslin, +and round the neck is twisted a conducting thread of lamp-wick, which +passes into a vessel of water, placed at such a distance as to allow a +length of conducting thread, of about three inches; the cup or glass is +placed on one side, and a little beneath, so that the water within may not +affect the reading of the <i>dry bulb thermometer</i>. In observing, the eye +should be placed on a level with the top of the mercury in the tube, and +the observer should refrain from breathing whilst taking an observation.</p> + +<p>The <i>dry</i> bulb thermometer indicates the temperature of the air itself; +while the wet bulb, cooled by evaporation, shows a lower temperature +according to the rapidity of evaporation.</p> + +<p><span class="pagenum"><a name="Page_106" id="Page_106">[Pg 106]</a></span><i>To find the Dew-point.</i>—From the readings of the two thermometers, the +dew-point can be deduced by formulæ (that known as Apjohn’s is considered +the most theoretically true), or from the valuable Hygrometric Tables by +J. Glaisher, Esq., F.R.S.</p> + +<p>For practical purposes in estimating the comparative humidity, the annexed +table, which is a reduction from Mr. Glaisher’s elaborate work, will be +sufficient; it will at least serve to assist in familiarising the +inexperienced in the value of the psychrometer’s indications:—</p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td rowspan="3" class="btlr" align="center">Temperature<br />by the<br />Dry Bulb<br />Thermometer.</td> + <td class="btr" colspan="6" align="center">Difference between Dry-bulb and Wet-bulb Readings.</td></tr> +<tr><td class="btr" align="center">2°</td> + <td class="btr" align="center">4°</td> + <td class="btr" align="center">6°</td> + <td class="btr" align="center">8°</td> + <td class="btr" align="center">10°</td> + <td class="btr" align="center">12°</td></tr> +<tr><td class="btr" colspan="6" align="center">Degree of Humidity.</td></tr> +<tr><td class="btlr" align="center"><span style="margin-left: .5em;">34°</span></td> + <td class="btr" align="center">79</td> + <td class="btr" align="center">63</td> + <td class="btr" align="center">50</td> + <td class="btr" align="center">..</td> + <td class="btr" align="center">..</td> + <td class="btr" align="center">..</td></tr> +<tr><td class="blr" align="center">36</td> + <td class="br" align="center">82</td> + <td class="br" align="center">66</td> + <td class="br" align="center">53</td> + <td class="br" align="center">..</td> + <td class="br" align="center">..</td> + <td class="br" align="center">..</td></tr> +<tr><td class="blr" align="center">38</td> + <td class="br" align="center">83</td> + <td class="br" align="center">68</td> + <td class="br" align="center">56</td> + <td class="br" align="center">45</td> + <td class="br" align="center">..</td> + <td class="br" align="center">..</td></tr> +<tr><td class="blr" align="center">40</td> + <td class="br" align="center">84</td> + <td class="br" align="center">70</td> + <td class="br" align="center">58</td> + <td class="br" align="center">47</td> + <td class="br" align="center">..</td> + <td class="br" align="center">..</td></tr> +<tr><td class="blr" align="center">42</td> + <td class="br" align="center">84</td> + <td class="br" align="center">71</td> + <td class="br" align="center">59</td> + <td class="br" align="center">49</td> + <td class="br" align="center">..</td> + <td class="br" align="center">..</td></tr> +<tr><td class="blr" align="center">44</td> + <td class="br" align="center">85</td> + <td class="br" align="center">72</td> + <td class="br" align="center">60</td> + <td class="br" align="center">50</td> + <td class="br" align="center">..</td> + <td class="br" align="center">..</td></tr> +<tr><td class="blr" align="center">46</td> + <td class="br" align="center">86</td> + <td class="br" align="center">73</td> + <td class="br" align="center">61</td> + <td class="br" align="center">51</td> + <td class="br" align="center">..</td> + <td class="br" align="center">..</td></tr> +<tr><td class="blr" align="center">48</td> + <td class="br" align="center">86</td> + <td class="br" align="center">73</td> + <td class="br" align="center">62</td> + <td class="br" align="center">52</td> + <td class="br" align="center">44</td> + <td class="br" align="center">..</td></tr> +<tr><td class="blr" align="center">50</td> + <td class="br" align="center">86</td> + <td class="br" align="center">74</td> + <td class="br" align="center">63</td> + <td class="br" align="center">53</td> + <td class="br" align="center">45</td> + <td class="br" align="center">..</td></tr> +<tr><td class="blr" align="center">52</td> + <td class="br" align="center">86</td> + <td class="br" align="center">74</td> + <td class="br" align="center">64</td> + <td class="br" align="center">54</td> + <td class="br" align="center">46</td> + <td class="br" align="center">..</td></tr> +<tr><td class="blr" align="center">54</td> + <td class="br" align="center">86</td> + <td class="br" align="center">74</td> + <td class="br" align="center">64</td> + <td class="br" align="center">55</td> + <td class="br" align="center">47</td> + <td class="br" align="center">..</td></tr> +<tr><td class="blr" align="center">56</td> + <td class="br" align="center">87</td> + <td class="br" align="center">75</td> + <td class="br" align="center">65</td> + <td class="br" align="center">56</td> + <td class="br" align="center">48</td> + <td class="br" align="center">..</td></tr> +<tr><td class="blr" align="center">58</td> + <td class="br" align="center">87</td> + <td class="br" align="center">76</td> + <td class="br" align="center">66</td> + <td class="br" align="center">57</td> + <td class="br" align="center">49</td> + <td class="br" align="center">..</td></tr> +<tr><td class="blr" align="center">60</td> + <td class="br" align="center">88</td> + <td class="br" align="center">76</td> + <td class="br" align="center">66</td> + <td class="br" align="center">58</td> + <td class="br" align="center">50</td> + <td class="br" align="center">43</td></tr> +<tr><td class="blr" align="center">62</td> + <td class="br" align="center">88</td> + <td class="br" align="center">77</td> + <td class="br" align="center">67</td> + <td class="br" align="center">58</td> + <td class="br" align="center">50</td> + <td class="br" align="center">44</td></tr> +<tr><td class="blr" align="center">64</td> + <td class="br" align="center">88</td> + <td class="br" align="center">77</td> + <td class="br" align="center">67</td> + <td class="br" align="center">59</td> + <td class="br" align="center">51</td> + <td class="br" align="center">45</td></tr> +<tr><td class="blr" align="center">66</td> + <td class="br" align="center">88</td> + <td class="br" align="center">78</td> + <td class="br" align="center">68</td> + <td class="br" align="center">60</td> + <td class="br" align="center">52</td> + <td class="br" align="center">45</td></tr> +<tr><td class="blr" align="center">68</td> + <td class="br" align="center">88</td> + <td class="br" align="center">78</td> + <td class="br" align="center">68</td> + <td class="br" align="center">60</td> + <td class="br" align="center">52</td> + <td class="br" align="center">46</td></tr> +<tr><td class="blr" align="center">70</td> + <td class="br" align="center">88</td> + <td class="br" align="center">78</td> + <td class="br" align="center">69</td> + <td class="br" align="center">61</td> + <td class="br" align="center">53</td> + <td class="br" align="center">47</td></tr> +<tr><td class="blr" align="center">72</td> + <td class="br" align="center">89</td> + <td class="br" align="center">79</td> + <td class="br" align="center">69</td> + <td class="br" align="center">61</td> + <td class="br" align="center">54</td> + <td class="br" align="center">48</td></tr> +<tr><td class="blr" align="center">74</td> + <td class="br" align="center">89</td> + <td class="br" align="center">79</td> + <td class="br" align="center">70</td> + <td class="br" align="center">62</td> + <td class="br" align="center">55</td> + <td class="br" align="center">48</td></tr> +<tr><td class="blr" align="center">76</td> + <td class="br" align="center">89</td> + <td class="br" align="center">79</td> + <td class="br" align="center">71</td> + <td class="br" align="center">63</td> + <td class="br" align="center">55</td> + <td class="br" align="center">49</td></tr> +<tr><td class="blr" align="center">78</td> + <td class="br" align="center">89</td> + <td class="br" align="center">79</td> + <td class="br" align="center">71</td> + <td class="br" align="center">63</td> + <td class="br" align="center">56</td> + <td class="br" align="center">50</td></tr> +<tr><td class="blr" align="center">80</td> + <td class="br" align="center">90</td> + <td class="br" align="center">80</td> + <td class="br" align="center">71</td> + <td class="br" align="center">63</td> + <td class="br" align="center">56</td> + <td class="br" align="center">50</td></tr> +<tr><td class="blr" align="center">82</td> + <td class="br" align="center">90</td> + <td class="br" align="center">80</td> + <td class="br" align="center">72</td> + <td class="br" align="center">64</td> + <td class="br" align="center">57</td> + <td class="br" align="center">51</td></tr> +<tr><td class="blr" align="center">84</td> + <td class="br" align="center">90</td> + <td class="br" align="center">80</td> + <td class="br" align="center">72</td> + <td class="br" align="center">64</td> + <td class="br" align="center">57</td> + <td class="br" align="center">51</td></tr> +<tr><td class="bblr" align="center">86</td> + <td class="bbr" align="center">90</td> + <td class="bbr" align="center">80</td> + <td class="bbr" align="center">72</td> + <td class="bbr" align="center">64</td> + <td class="bbr" align="center">58</td> + <td class="bbr" align="center">52</td></tr></table> + +<p><span class="pagenum"><a name="Page_107" id="Page_107">[Pg 107]</a></span>The total quantity of aqueous vapour which at any temperature can be +diffused in the air being represented by 100, the per-centage of vapour +actually present will be found in the table opposite the temperature of +the dry thermometer, and under the difference between the dry-bulb and +wet-bulb temperatures. The degree of humidity for intermediate +temperatures and differences to those given in the table can be easily +estimated sufficiently accurately for most practical purposes.</p> + +<p>The difference between the two thermometer readings taken from the reading +of the wet bulb, gives the dew-point very nearly, when the air is at any +temperature between freezing and 80°. This simple rule will be found +serviceable to horticulturists, since it will enable them to estimate the +chilling effect of dew or hoar-frost on tender plants.</p> + +<p><i>Use as an Indicator of Weather.</i>—In our climate, the usual difference +between the thermometer readings,—in the open air, shaded from the sun, +reflected heat, and currents of air,—ranges from one to twelve degrees. +In hot and dry climates, as India and Australia, the range out of doors +has been found as much as 30°, occasionally.</p> + +<p>When the moisture is frozen, the bulb should be wetted afresh, and the +reading taken just before it again freezes; but the observation then is of +little value, and for general purposes need not be taken, as the air is +known to be dry in frosty weather.</p> + +<p>The muslin or cotton rag should be washed once or twice a week by pouring +water over the bulb; and it should be replaced by a fresh piece at least +once a month. Accuracy depends very much upon keeping the wet bulb clean, +and not <i>too</i> wet.</p> + +<p>In connection with the barometer, this hygrometer is very useful, not only +on land, but especially at sea, where other kinds of hygrometers cannot be +practically used. A fall in the barometer is indicative of coming wind or +rain: if the hygrometer shows increasing dampness by the difference of the +readings becoming smaller,—rain may therefore be anticipated. On the +contrary, if the hygrometer shows continuing or increasing dryness, a +stronger wind is probable, without rain.</p> + +<p><i>Domestic Uses.</i>—Mason’s hygrometer is useful in regulating the moisture +of the air of apartments; a difference in the thermometer readings of from +5° to 8° being considered healthy. Many complaints require that the +temperature and humidity of the air which the invalid breathes should be +carefully regulated. Hence it is a valuable household instrument. In a +room, it should be placed away from the fire as much as possible, but not +exposed to draughts of air.</p> + +<p>Figs. 80 and 81 show cheap arrangements of the instrument for domestic +purposes. Other arrangements are given to the instrument to make it +suitable for exhibiting the hygrometrical state of the air in hot-houses, +conservatories, malting-houses, warehouses, manufactories, &c.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td align="center">Fig. 80.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 81.</td><td><span class="spacer2"> </span></td> + <td align="center">Fig. 82.</td><td><span class="spacer2"> </span></td></tr> +<tr><td align="center"><img src="images/fig_80.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_81.jpg" alt="" /></td><td> </td> + <td align="center"><img src="images/fig_82.jpg" alt="" /></td><td> </td></tr></table> + +<p>Fig. 82 shows the instrument arranged on brass tripod stand, with folding +legs and metal cover, to render it portable.</p> + + +<p><br /><span class="pagenum"><a name="Page_108" id="Page_108">[Pg 108]</a></span><b>107. Self-Registering Hygrometer.</b>—A maximum thermometer and a minimum +thermometer, each fitted up as a wet-bulb thermometer, record the highest +and lowest temperature of evaporation during the interval of observation. +Negretti’s mercurial maximum, and an alcohol minimum, answer best.</p> + + +<p><br /><b>108. Causes of Dew.</b>—“The aqueous vapour of our atmosphere is a powerful +radiant; but it is diffused through air which usually exceeds its own mass +more than one hundred times. Not only, then, its own heat, but the heat of +the large quantity of air which surrounds it, must be discharged by the +vapour, before it can sink to its point of condensation. The retardation +of chilling due to this cause enables good solid radiators, at the earth’s +surface, to outstrip the vapour in their speed of refrigeration; and +hence, upon these bodies, aqueous vapour may be condensed to liquid, or +even congealed to hoar-frost, while at a few feet above the surface it +still maintains its gaseous state.”<small><a name="f9.1" id="f9.1" href="#f9">[9]</a></small> The amount of moisture so deposited +will vary with different atmospheric conditions. If the sky be decidedly +cloudy or misty, the heat radiated from the earth will be partly restored +by counter-radiation from the visible vapour; the cooling of the earth’s +surface will, therefore, take place slowly, and little dew will be +deposited. On the other hand, if the air contain transparent vapour, and +the sky appear clear, the counter-radiation will be less, the earth will +cool rapidly, and the deposit of dew will be copious; provided the night +be comparatively calm, for, when the wind blows, the circulating air +supplies heat to the radiating substances, and prevents any considerable +chilling.</p> + +<p>The dew which falls in tropical countries greatly exceeds in abundance +what we experience in our climate; because the air is there, from the +great heat, capable of<span class="pagenum"><a name="Page_109" id="Page_109">[Pg 109]</a></span> sustaining a large amount of vapour in the +transparent state, and the conditions most favourable for a maximum +reduction of temperature by radiation are present. At those places, or +upon those substances which cool the lowest and most readily, the dew +falls most copiously.</p> + +<p> </p> +<p class="center">Fig. 83.</p> +<div class="figcenter"><img src="images/fig_83.jpg" alt="" /></div> +<p> </p> + +<p><br /><b>109. Plan of Exposing Thermometers</b>, &c.—Figure 83 is an illustration of a +convenient slab for supporting thermometers in an exposed position +attached to a stand (such as <a href="#glaisher">Glaisher’s, described in Chapter XVI.</a>) for +ordinary scientific observations. It has a projecting ledge, <i>B</i>, to carry +off rain from the instruments, the slab, <i>A</i>, being erected vertically. +The hygrometer is placed at <i>E</i>, with the vase of water at <i>F</i>. An alcohol +minimum thermometer is represented at <i>C</i>, in the position most favourable +to its certain action; and at <i>D</i> is shown one of Negretti & Zambra’s +maximum thermometers, the position of which may be more nearly horizontal +than there exhibited, although a slight depression of the bulb-end of the +frame is desirable, but not necessary, as this thermometer can be used in +any position.</p> + + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_110" id="Page_110">[Pg 110]</a></span></p> +<h2><a name="CHAPTER_XII" id="CHAPTER_XII"></a>CHAPTER XII.</h2> +<p class="center"><span class="large">INSTRUMENTS USED FOR MEASURING THE RAINFALL.</span></p> + +<p><br />The instruments in use for measuring the quantity of rain which falls on a +given spot are of very simple construction. Perhaps the simplest is:—</p> + + +<p><br /><b>110. Howard’s Rain-Gauge.</b>—It consists of a copper funnel, a stout glass +or stone bottle, and a measuring glass. The bottle is to be placed upon +the ground, with the funnel resting on its neck. A brass band or cylinder +fixed upon the outer surface of the funnel envelops the neck of the +bottle, and the pipe of the funnel extends nearly to the bottom of the +bottle; so that loss by evaporation is avoided as much as possible. The +receiving space of the funnel is formed by a brass ring, five inches in +diameter, very accurately turned. The measuring vessel enables the +observer to note the rainfall in inches, tenths, and hundredths of an +inch.</p> + +<div class="figleft">Fig. 84.<br /><img src="images/fig_84.jpg" alt="" /></div> + +<p><br /><b>111. Glaisher’s Rain-Gauge.</b>—The rain-gauge designed by Mr. Glaisher, the +well-known meteorologist, and used by most observers of the present day, +is arranged for the reception of the water which falls upon its receiving +surface only, and for the prevention of loss by evaporation. The rain is +first collected in a funnel, <i>B</i>, (fig. 84,) the receiving surface of +which is turned in a lathe. The conical surface of the funnel slopes to +the pipe, <i>E</i>, at an angle of 60° from the horizontal receiving surface. +The tube, <i>E</i>, is of small aperture, and is bent up, in order to retain +the last few drops of rain, so that the only opening for the escape of +vapour may be closed as long as possible. The funnel, <i>B</i>, fits upon the +cylinder, <i>A</i>, tightly in the groove, <i>D</i>. A copper can is placed inside +the cylinder, <i>A</i>, to receive the rain from the funnel. Once or twice a +day, or after a shower, this can should be taken out, and the water +measured in the glass measure, <i>C</i>, which is graduated to hundredths of an +inch, according to the calculated quantity of water, determined by the +area of<span class="pagenum"><a name="Page_111" id="Page_111">[Pg 111]</a></span> the receiving space. In use, this gauge should be partly sunk in +the ground, so that the top may be about five inches above it. Thus +situated, there will be little or no evaporation from it during any month +of the year; and the readings need not be taken daily, although desirable.</p> + + +<p><br /><b>112. Rain-Gauge with Float.</b>—In this construction the graduated glass +measure is dispensed with. The cylinder of the gauge is made less in +diameter than the funnel, and a hollow, very flattened spheroid of copper +forming a float, and carrying a vertical graduated boxwood scale which +moves through the orifice of the funnel, is placed in it. As the rain +accumulates the float rises, and the amount of rain in the gauge is read +upon the scale from the top of the gauge, a bar, having a hole at the +centre for the passage of the scale, being fixed diametrically across the +receiving space of the funnel. The gauge is provided at the bottom with a +brass cock, by which the water may be allowed to flow out of it whenever +necessary.</p> + +<p>This form of gauge is not very suitable for the measurement of small +quantities; but is admirably adapted for localities where the rainfall is +excessive.</p> + +<div class="figright">Fig. 85.<br /><img src="images/fig_85.jpg" alt="" /></div> + +<p><br /><b>113. Rain-Gauge with Side-Tube.</b>—This instrument, as represented in fig. +85, is a cylindrical vessel, mounted on a base shaped as a frustum of a +cone. This base may be filled with sand or gravel to make the instrument +stable, so that when placed upon a lawn or in a garden it may have an +ornamental appearance. The funnel for collecting the rain is larger in +diameter than the cylinder. Parallel to the cylinder, and communicating +with the lowest part of the interior and extending to its top, is a +graduated glass tube, open at both ends. The rain collected will rise as +high in this tube as in the cylinder, and its amount can therefore be read +off without any trouble. The gauge is emptied by the brass tap at the +bottom of the cylinder.</p> + + +<p><br /><b>114. Admiral FitzRoy’s Rain-Gauge.</b>—A form of rain-gauge, very well +adapted for expeditious observation at any time, has been designed by +Admiral FitzRoy, and extensively employed by his observers. It is +cylindrical in shape, with the funnel let into the top; and the rainfall +is collected in an inner and much smaller cylinder, so that a small fall +is represented by a considerable depth of water in the gauge. The amount +of rain which has fallen is ascertained by a dipping tube, similar in +principle to the dipping syphon used by gaugers for taking out specimens +of wines or spirits from casks by simply removing the bung. A short, +vertical, tubular opening provided with a cap, which is attached to the +instrument by a chain that it may not be lost, is formed in the funnel. +The measuring tube, which has a small hole at each end, should be<span class="pagenum"><a name="Page_112" id="Page_112">[Pg 112]</a></span> placed +upright in the gauge; then the thumb should be pressed over the upper +aperture, while the tube is lifted gently out, holding in the lower part a +quantity of water representing the depth of the rain in the gauge, the +upper edge of which is at the mark to be read off. The glass tube is +graduated to inches and tenths; hundredths of an inch can be readily +estimated by the eye. The marks are fixed by actual trial with a standard +gauge, and are artificial, not true, inches.</p> + + +<p><br /><b>115. Self-Registering Rain-Gauge.</b>—The rain-gauge can be combined with +clock-work and other mechanism so as to be self-recording of the amount of +rain, the time, and duration of its fall. For the details of construction +the reader is referred to the next chapter, where he will find the +instrument described in connection with Osler’s anemometer, as the +“pluviometer.” To observe and duly record the times of commencement and +termination of rain is very desirable. Scarcely any observer can attempt +to do this even approximately from personal observation. Hence the want of +a cheap and simple self-recording rain-gauge is much felt, the present +construction being too expensive for all but a few individuals.</p> + +<p>In 1862, Mr. R. Strachan estimated the duration and amount of rain in +London (Gray’s Inn Road) as follows:—</p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td class="btlr" align="center"><span class="smcap">Months.</span></td> + <td class="btr" align="center"><span class="smcap">Inches.</span></td> + <td class="btr" align="center"><span class="smcap">Days.</span></td> + <td class="btrdoub" align="center"><span class="smcap">Hours.</span></td> + <td class="btr" align="center"><span class="smcap">Months.</span></td> + <td class="btr" align="center"><span class="smcap">Inches.</span></td> + <td class="btr" align="center"><span class="smcap">Days.</span></td> + <td class="btr" align="center"><span class="smcap">Hours.</span></td></tr> +<tr><td class="btlr">January.</td> + <td class="btr" align="center">1·86</td> + <td class="btr" align="center">19</td> + <td class="btrdoub" align="center">88</td> + <td class="btr">July.</td> + <td class="btr" align="center">2·27</td> + <td class="btr" align="center">17</td> + <td class="btr" align="center">68</td></tr> +<tr><td class="blr">February.</td> + <td class="br" align="center">0·37</td> + <td class="br" align="center"><span style="margin-left: .5em;">9</span></td> + <td class="brdoub" align="center">25</td> + <td class="br">August.</td> + <td class="br" align="center">2·45</td> + <td class="br" align="center">12</td> + <td class="br" align="center">72</td></tr> +<tr><td class="blr">March.</td> + <td class="br" align="center">3·40</td> + <td class="br" align="center">22</td> + <td class="brdoub" align="center"><span style="margin-left: -.5em;">130</span></td> + <td class="br">September.</td> + <td class="br" align="center">1·70</td> + <td class="br" align="center">12</td> + <td class="br" align="center">55</td></tr> +<tr><td class="blr">April.</td> + <td class="br" align="center">2·34</td> + <td class="br" align="center">14</td> + <td class="brdoub" align="center">80</td> + <td class="br">October.</td> + <td class="br" align="center">3·23</td> + <td class="br" align="center">21</td> + <td class="br" align="center">94</td></tr> +<tr><td class="blr">May.</td> + <td class="br" align="center">3·04</td> + <td class="br" align="center">16</td> + <td class="brdoub" align="center">90</td> + <td class="br">November.</td> + <td class="br" align="center">1·12</td> + <td class="br" align="center">10</td> + <td class="br" align="center">53</td></tr> +<tr><td class="bblr">June.</td> + <td class="bbr" align="center">2·45</td> + <td class="bbr" align="center">20</td> + <td class="bbrdoub" align="center"> 83</td> + <td class="bbr">December.</td> + <td class="bbr" align="center">1·44</td> + <td class="bbr" align="center">17</td> + <td class="bbr" align="center">66</td></tr></table> + +<p>“During the year 1862, the rainfall amounted to 25·67 inches. Rain fell on +179 days, that is, on nearly every other day. The hours of rain were +estimated at 904; therefore, if the rain had fallen continuously, it would +have lasted nearly 38 days and nights.”<small><a name="f10.1" id="f10.1" href="#f10">[10]</a></small> The value of similar estimates +of the rainfall by numerous observers would be very great to meteorology.</p> + + +<p><br /><b>116. The principle of measurement</b> in all these gauges is the relation +existing between the areas of the collecting and receiving surfaces; that +is, between the area of the funnel into which the rain falls, and the area +of the cylinder which receives it. In Howard’s and Glaisher’s gauges, this +cylinder is virtually the measuring glass itself; in the others, above +described, the measuring scales show the same depth of water as in the +cylinder of the gauge.</p> + +<p>The cylinder being of less diameter than the funnel, and receiving all the +rain collected by the funnel, it follows that its contents will have an +increased depth. Now equal cylindrical volumes, having different +diameters, are to each other in<span class="pagenum"><a name="Page_113" id="Page_113">[Pg 113]</a></span> length inversely as the squares of the +diameters. Hence, if the funnel be 9 inches and the cylinder 3 inches in +diameter, a fall of 1 inch of rain will be represented in the gauge by 9 +inches; for 3² : 9² : : 1 : <i>x</i> = 9. In this case, therefore, a length of +nine inches of the measuring glass, tube, or scale, would represent an +inch of rainfall, and be divided into tenths and hundredths of the +artificial inch.</p> + + +<p><br /><b>117. Position for Rain-Gauge, &c.</b>—Rain gauges should be placed on the +ground, in any position exposed to a free fall of rain, snow, or hail, +where neither walls, buildings, nor trees shelter or cause eddies of wind. +They should be supported by a frame, or other means, to prevent them being +blown down by the wind, but so that they can be readily emptied.</p> + +<p>During snow or frost, the gauge must be watched, and its contents melted +by placing it in a warm room, either when the amount is to be measured, or +the funnel is filled up with snow. A tin vessel of equal area to the +funnel may at such times be useful as a substitute.</p> + +<p>Rain gauges are constructed of metal, usually copper, which, besides being +readily workable, is little affected by atmospheric influences. If made of +iron or zinc, they should be well japanned; if of copper, this is not so +essential. The capacity of a gauge should be sufficient to contain at +least the probable maximum fall of rain in a day at the locality. Those +required for rainy districts must be of large size.</p> + + +<p><br /><b>118. Causes of Rain.</b>—When the invisible vapour which is diffused in the +atmosphere becomes sufficiently cooled, it appears visible as mist or +cloud, and a further reduction of temperature causes its precipitation as +rain, hail, or snow. The cooling of the higher regions of the atmosphere +is doubtless the chief cause of this condensation; but the property which +aqueous vapour possesses of radiating heat may also contribute to the +result. Moreover, the law which regulates the amount of vapour which air +at any particular temperature can sustain in a transparent state, +determines that when two bodies of air at different temperatures, +saturated with vapour, intermix, some moisture must be rendered visible; +and hence, it is not only possible, but highly probable, that rain may +result from the conflict of different winds. Let us imagine two cubic +yards of air, both saturated with moisture, but having the respective +temperatures of 50 and 70 degrees, to come into contact. There will be a +tendency to equalize the temperature to a mean, which is 60°; and during +this process, some of the vapour will be condensed.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>For</td> + <td>in the air at</td> + <td>50°</td> + <td>there is</td> + <td><span class="spacer"> </span></td> + <td>110·7</td> + <td>grains of</td> + <td>vapour<small><a name="f11.1" id="f11.1" href="#f11">[11]</a></small></td></tr> +<tr><td>and</td> + <td class="center">"</td> + <td>70</td> + <td align="center">"</td> + <td> </td> + <td class="botbor">216·0</td> + <td colspan="2" align="center">"</td></tr> +<tr><td colspan="5">Total amount of vapour</td> + <td>326·7</td> + <td colspan="2" align="center">"</td></tr> +<tr><td colspan="5">But two cubic yards of air at 60° can only sustain</td> + <td class="botbor">313·2</td> + <td colspan="2" align="center">"</td></tr> +<tr><td colspan="5">Hence there will be deposited</td> + <td class="botbor2">13·5</td> + <td align="center"><span style="margin-left: 1em;">"</span></td> + <td>rain.</td></tr></table> + +<p><span class="pagenum"><a name="Page_114" id="Page_114">[Pg 114]</a></span>It may be conceded, therefore, that when a warm and moist current of air +encounters a body of cold air which may not be extremely dry, the mixture +is unable to retain the whole of the vapour in an invisible state; so that +the excess becomes visible as mist or fog, and, when the temperature has +become sufficiently lowered, rain. The British Isles are more or less +enveloped in fog, or mist, at the commencement of easterly winds, which, +with a sudden change of wind, is exhibited even in summer; while the +south-westerly winds, warm, and arriving from the ocean, deposit large +quantities of rain by the cooling effect of the land, colder by reason of +its latitude. When rain occurs with a northerly wind, it is probably due +to the deposition from an upper south-westerly current, often apparently +proved by the movements of the upper clouds.</p> + + +<p><br /><b>119. Laws of Rain-fall.</b>—Tropical countries have a dry and a wet season +during the year: <i>dry</i>, when the sun is at the opposite side of the +equator; <i>wet</i>, when the sun is overhead. With reference to the British +Isles, the statistics collected by Mr. G. J. Symons indicate that: 1st. +The stations of least rain are inland, or on the east or south-east +coasts; the stations of greatest rain are on the western coasts. 2nd. The +rain-fall is very large in the vicinity of mountain chains or groups, +unless the station happens to be some miles to the north-eastward.</p> + +<p>It may be well to illustrate these remarks by quoting<small><a name="f12.1" id="f12.1" href="#f12">[12]</a></small> the average fall +at a few places, grouping them as—</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td colspan="2" align="center">Westerly.</td><td><span class="spacer"> </span><span class="spacer"> </span></td> + <td colspan="2" align="center">Central.</td><td><span class="spacer"> </span><span class="spacer"> </span></td> + <td colspan="2" align="center">Easterly.</td></tr> +<tr><td> </td><td><small>Inches.</small></td><td> </td> + <td> </td><td><small>Inches.</small></td><td> </td> + <td> </td><td><small>Inches.</small></td></tr> +<tr><td>Bodmin</td><td align="right">43</td><td> </td> + <td>Enfield</td><td align="right">23</td><td> </td> + <td>Witham (Essex)</td><td align="right">21</td></tr> +<tr><td>Bolton (Lancashire)</td><td align="right">44</td><td> </td> + <td>Epping</td><td align="right">23</td><td> </td> + <td>Patrington (Hull)</td><td align="right">21</td></tr> +<tr><td>Coniston (Windermere)</td><td align="right">71</td><td> </td> + <td>Derby</td><td align="right">24</td><td> </td> + <td>Sunderland</td><td align="right">17</td></tr> +<tr><td>Seathwaite</td><td align="right">127</td><td> </td> + <td>York</td><td align="right">22</td><td> </td> + <td>Inveresk (Edinburgh)</td><td align="right">25</td></tr> +<tr><td>Torosay (I. of Mull)</td><td align="right">75</td><td> </td> + <td>Stirling</td><td align="right">39</td><td> </td> + <td>Pittenweem (Fife)</td><td align="right">24</td></tr> +<tr><td>Killaloe (Limerick)</td><td align="right">38</td><td> </td> + <td>Perth</td><td align="right">29</td><td> </td> + <td>Dublin</td><td align="right">22</td></tr></table> + +<p>Mr. Green, the celebrated aeronaut, has asserted from his experience, +“that whenever a fall of rain happens, and the sky is entirely overcast, +there will invariably be found to exist another stratum of cloud at a +certain elevation above the former;” and the recent scientific balloon +ascents by Mr. Glaisher have tended to confirm this theory. Mr. Glaisher +says, “It would seem to be an established fact, that whenever rain is +falling from an overcast sky, there is a second stratum above.” “It would +also seem that when the sky is overcast without rain, that there is no +stratum of cloud above, but that the sun is shining on the upper surface. +In every instance in which I have been up under these circumstances, I +have found such to be the case, agreeing in this respect also with Mr. +Green’s observations.”</p> + +<p><span class="pagenum"><a name="Page_115" id="Page_115">[Pg 115]</a></span>The amount of rain collected in a gauge placed near the surface of the +earth is larger than in any gauge placed above it; and the higher the +gauge is placed, the less water is collected. Mr. Glaisher contends that +his balloon experiments corroborate this law.</p> + + +<p><br /><b>120. Utility of Statistics of Rain-fall.</b>—The utility of knowing the +rain-fall of any locality is sufficiently obvious, and little need be said +upon the subject. The rain-gauge should be in the hands of every gardener +and farmer. In the management of out-door plants and crops, as well as in +the construction of cisterns and tanks for the supply of water, a rain +gauge is a valuable assistant. By its use, the gardener will be guided in +judging how far the supply of moisture to the earth is needed; and he will +also see how beneficial is even a hasty shower to growing plants, when he +considers that a fall of rain measuring the tenth of an inch in depth, +corresponds to the deposit of about forty hogsheads per acre. The study of +the rain-fall of a country is of considerable interest to agriculturists. +The health and increase of domestic animals, the development of the +productions of the land, as well as the daily labours of the farmer, are +dependent upon the excess or deficiency of rain. “It must be a subject of +great satisfaction and confidence to the husbandman to know at the +beginning of a summer, by the certain evidence of meteorological results +on record, that the season, in the ordinary course of things, may be +expected to be a dry and warm one; or to find, in a certain period of it, +that the average quantity of rain to be expected for the month has fallen. +On the other hand, when there is reason, from the same source of +information, to expect much rain, the man who has courage to begin his +operations under an unfavourable sky, but with good ground to conclude, +from the state of his instruments and his collateral knowledge, that a +fair interval is approaching, may often be profiting by his observations; +while his cautious neighbour who waited ‘for the weather to settle’ may +find that he has let the opportunity go by. This superiority, however, is +attainable by a very moderate share of application to the subject; and by +the keeping of a plain diary of the barometer and rain-gauge, with the +hygrometer and vane, under his daily notice.”<small><a name="f13.1" id="f13.1" href="#f13">[13]</a></small> The statistics of +rain-fall are not only valuable and interesting in a meteorological point +of view, and for agricultural purposes, but are also highly important in +connection with sanitary arrangements for towns, and engineering +operations. This is especially evident to the hydraulic engineer. As rain +is an important source of water-supply to rivers, canals, and reservoirs, +it is evident that a knowledge of the probable fall for any season or +month, at a given place, as furnished by averages of the observations of +former years, will be the data upon which the engineer will base his plans +for providing for floods or droughts; while the measurement of the actual +quantity which has just fallen, as gathered from the indications of a +series of gauges, will suggest to him the precautions to adopt either to +economise or conduct away the in-pouring waters.</p> + +<p><span class="pagenum"><a name="Page_116" id="Page_116">[Pg 116]</a></span>“When a canal is conducted across an undulating country, its course is +necessarily governed by the accidents of the ground, and it alternately +rises and falls. In this case, rising by a succession of levels, it +necessarily arrives at a certain highest level, which is called by +engineers the <i>summit level</i>. From this it again descends by a +corresponding series of levels. Now, it is evident that, supposing the +locks to be all equal in magnitude, the ascent of a vessel will require +the descent of as much water from the summit to the lowest level as would +fill a single lock; for this quantity of water must be discharged from +each lock of the series when the vessel passes through it.</p> + +<p>“The same may be said of the process by which the vessel descends along +the series of locks on the other side of the summit. It appears, +therefore, that a supply of water must always be maintained on the summit +level sufficient to fill a single lock twice for each vessel which crosses +the summit.</p> + +<p>“It happens, fortunately, that by the laws of natural evaporation, rain is +precipitated in greater quantities on elevated summits than on the +intermediate valleys, so that the moving power, in this case, accommodates +itself to the exigencies of intercommunication.”—<i>Dr. Lardner’s “Handbook +of Natural Philosophy.”</i></p> + + +<p><br /><b>121. New Form of Rain-Gauge.</b>—Since the foregoing pages were in type, a +modification of Howard’s rain-gauge has been arranged by Mr. Symons, which +is compact in design, convenient in use, and low in price. It combines the +advantages of most gauges; having solidity, and facility of measurement. +The bottle is placed in a tin case, to the bottom of which are attached +stout spikes, which, when forced into the earth, prevent its being upset +either by wind or accident. The bottle being transparent, and slits made +in the case, the fall of rain is seen at a glance, or with a race-glass, +from a window. The funnel being attached to the cover of the case is +thereby kept strictly horizontal, and the depth of rain can be accurately +measured by lifting the bottle from its case and emptying it into a +graduated glass jar.</p> + +<p>The funnel of this gauge is a very deep cone, to prevent the rain drops +outsplashing. When properly placed, the receiving surface will be twelve +inches above the ground, which experience has shown to be the most +advantageous height.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_117" id="Page_117">[Pg 117]</a></span></p> +<h2><a name="CHAPTER_XIII" id="CHAPTER_XIII"></a>CHAPTER XIII.</h2> +<p class="center"><span class="large">APPARATUS EMPLOYED FOR REGISTERING THE DIRECTION, PRESSURE, AND VELOCITY OF THE WIND.</span></p> + +<div class="figright">Fig. 86.<br /><img src="images/fig_86.jpg" alt="" /></div> + +<p><br /><b>122. The Vane.</b>—The instrument by which the wind’s direction is most +generally noted, is the vane, or weather-cock, and all that need be said +of it here is that the points north, east, south and west, usually +attached to it, should indicate the <i>true</i> and not the <i>magnetic</i> +directions; and that care should be taken to prevent its setting fast. +Very complicated instruments are required for ascertaining the pressure +and velocity of the wind, and these are called <i>Anemometers</i>. The simplest +is <i>Lind’s</i>.</p> + +<p><br /><b>123. Lind’s Anemometer, or Wind-Gauge</b> (fig. 86), invented so late as 1775, +for showing the pressure of the wind, consists of a glass syphon, the +limbs parallel to each other, and each limb the same diameter. One end of +the syphon is bent at right angles to the limb, so as to present a +horizontal opening to the wind. A graduated scale, divided to inches and +tenths, is attached to the syphon tube, reading either way from a zero +point in the centre of the scale. The whole instrument is mounted on a +spindle, surmounted by a vane, and is moved freely in any direction by the +wind, always presenting the open end towards the quarter from which the +wind blows. To use the instrument, it is simply filled up to the zero +point with water, and then exposed to the wind; the difference in the +level of the water gives the force of the wind in inches and tenths, by +adding together the amount of depression in one limb, and elevation in the +other, the <i>sum of the two</i> being the height of a column of water which +the wind is capable of sustaining at that time.</p> + +<p class="center"><br /><span class="pagenum"><a name="Page_118" id="Page_118">[Pg 118]</a></span><span class="smcap">Table</span>,</p> + +<p>Showing the Force of Wind on a square foot, for different heights of the +column of Water in Lind’s Wind-Gauge.</p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td class="btlr" align="center">Inches.</td> + <td class="btr" align="center">Force in lbs.</td> + <td class="btr" align="center">Common designation<br />of such Wind.</td></tr> +<tr><td class="btlr" align="center">6</td> + <td class="btr" align="center">31·75</td> + <td class="btr">A Hurricane.</td></tr> +<tr><td class="blr" align="center">5</td> + <td class="br" align="center">26·04</td> + <td class="br">A violent Storm.</td></tr> +<tr><td class="blr" align="center">4</td> + <td class="br" align="center">20·83</td> + <td class="br">A great Storm.</td></tr> +<tr><td class="blr" align="center">3</td> + <td class="br" align="center">15·62</td> + <td class="br">A Storm.</td></tr> +<tr><td class="blr" align="center">2</td> + <td class="br" align="center">10·42</td> + <td class="br">A strong Wind.</td></tr> +<tr><td class="blr" align="center">1</td> + <td class="br" align="center"><span style="margin-left: .5em;">5·21</span></td> + <td class="br">A high Wind.</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·5</span></td> + <td class="br" align="center"><span style="margin-left: .5em;">2·60</span></td> + <td class="br">A brisk Wind.</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1em;">·1</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·52</span></td> + <td class="br">A fresh Breeze.</td></tr> +<tr><td class="blr" align="center"><span style="margin-left: 1.5em;">·05</span></td> + <td class="br" align="center"><span style="margin-left: 1em;">·26</span></td> + <td class="br">A gentle Breeze.</td></tr> +<tr><td class="bblr" align="center">0.</td> + <td class="bbr" align="center"><span style="margin-left: -.5em;">0.</span></td> + <td class="bbr">A Calm.</td></tr></table> + + +<p><br /><b>124. Modification of Lind’s Gauge.</b>—<i>Sir W. Snow Harris</i> has effected a +modification of Lind’s anemometer, with a view of obtaining a hand +instrument for use at sea more especially. At present the force of the +wind is estimated at sea by an arbitrary scale, suggested by Sir F. +Beaufort, the late hydrographer; 0 being calm, 12 the strongest hurricane, +and the intermediate numerals giving the varying strength of the wind. +There has been a long-felt want of instrumental means for obtaining this +data at sea, if merely for the sake of checking occasionally personal +estimations, which may vary considerably among different observers. +Harris’s wind gauge is intended to be held by hand, while facing the wind, +and keeping it in proper position by attending to a spirit-level attached. +When in position, and held firmly, the tube has to be opened to the wind +by pressure of the thumb acting upon jointed levers, controlled by +springs. The pressure of the wind moves the enclosed liquid; and by +withdrawing the thumb, the tube is closed so as to keep the liquid in its +position; the reading is then taken from its scale, either in pounds on +the square foot, miles per hour, or the ordinary designations of wind, as +light, fresh, strong, &c.</p> + +<div class="figright">Fig. 87.<br /><img src="images/fig_87.jpg" alt="" /></div> + +<p><br /><b>125. Robinson’s Anemometer.</b>—<i>Dr. Robinson</i>, of Armagh, is the inventor of +a very successful anemometer, which determines the horizontal velocity of +the wind. It was first used in 1850, in the meteorological and tidal +observations made on the coast of Ireland under the direction of the Rev. +Dr. Lloyd. No meteorological observatory should be without this valuable +instrument, which is essential in determining the average velocity of the +wind of a locality as distinguished from<span class="pagenum"><a name="Page_119" id="Page_119">[Pg 119]</a></span> the most frequent wind of the +same place. It is represented in fig. 87. Four hollow hemispherical cups, +<i>A A</i>, are extended upon conjugate diameters, or arms, with their +diametrical planes placed vertically, and facing the same way upon a +vertical axis, <i>B</i>, which has at its lower extremity an endless screw, +<i>D</i>. The axis is supported at <i>C</i> so as to turn with as little friction as +possible. The endless screw is placed in gear with a train of wheels and +pinions. Each wheel carries an index over a stationary dial in front; or +the index is fixed, and the graduations are placed upon the wheels +themselves.</p> + +<p>Dr. Robinson has proved, both by theory and experiment, that the centre of +any one of the cups so mounted and set in motion by the wind, revolves +with one-third of the wind’s velocity. If, therefore, the diametrical +distance between the centres of the cups be one foot, the circle described +by the centres in one revolution is 3·1416 feet, and the velocity of the +wind will be three times this, or 9·42 feet, which must be referred to +time for the absolute rate. The instrument is sometimes made with the +centres of the cups 1·12 feet apart, so that the circle described is +<span style="font-size: 0.8em;"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">1500</span> of a mile in circumference. Hence, to produce one revolution of the +cups, the wind must travel three times as fast, or <span style="font-size: 0.8em;"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">500</span> of a mile. +Therefore, 500 revolutions will be produced by one mile of wind; so that +the dials may be graduated to register the velocity in miles and tenths of +miles. The simplest arrangement is with five dials, recording respectively +10, 100, 1,000, 10,000 and 100,000 revolutions.</p> + +<p><i>Directions for using Robinson’s Anemometer.</i>—The dials read off in the +same manner as the register of a gas meter, commencing with the dial +farthest from the endless screw.</p> + +<p>“The figures on the first dial indicate so many hundreds of thousands of +revolutions; those on the second dial so many tens of thousands; those on +the third, thousands; those on the fourth, hundreds; and those on the +fifth so many tens.</p> + +<p>“The instrument should be read every morning at 9 o’clock; and, usually, +it will only be necessary to read the first three dials. The figures can +be entered as they are read off. Should the index point <i>between</i> two +figures, the less of the two is to be taken.</p> + +<p>“For example, if the first dial points to 7, or between 7 and 8; while the +second dial indicates 4; and the third, 5; the entry to be made is 745 +(indicative of 745 <i>thousand</i> revolutions).</p> + +<p>“Every time the index of the first dial is found to have passed zero (0), +a cross or star is to be prefixed to the next (a lower) reading.</p> + +<p><span class="pagenum"><a name="Page_120" id="Page_120">[Pg 120]</a></span>“To ascertain how many <i>thousands</i> of revolutions have been made during +the month, it will simply be necessary to subtract the first reading from +the last, and prefix to the three figures thus obtained a figure +corresponding to the number of stars in the column. For every <i>thousand</i> +revolutions there are two miles of wind: we have therefore only to +multiply by 2 to find how many miles of wind have passed during the month.</p> + +<p>“Two entries must be made for the last day of each month (the one being +written under the other), so as to bring the readings down to 9 <span class="smcaplc">A.M.</span> on +the 1st of the following month. The same entry which ends one month, will +therefore begin the next. This repetition of one entry is necessary, in +order to prevent losing a day’s wind.</p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td><span style="margin-left: 1em;">“The accompanying example of the</span></td><td><span class="spacer"> </span></td><td align="right">687</td></tr> +<tr><td>readings of an Anemometer for 13 days</td><td> </td><td align="right">773</td></tr> +<tr><td>will illustrate the method of making</td><td> </td><td align="right">822</td></tr> +<tr><td>the entries, &c.</td><td> </td><td align="right">855</td></tr> +<tr><td><span style="margin-left: 1em;">“In this instance, the first read-</span></td><td> </td><td align="right">900</td></tr> +<tr><td>ing (687) is less than the last (793).</td><td> </td><td align="right">953</td></tr> +<tr><td>When the first reading is greater than</td><td> </td><td align="right">990</td></tr> +<tr><td>the last, it will be necessary to borrow</td><td> </td><td align="right">*066</td></tr> +<tr><td>1,000 in making the subtractions,</td><td> </td><td align="right">197</td></tr> +<tr><td>and then deduct one from the number</td><td> </td><td align="right">323</td></tr> +<tr><td>of stars. Thus, if the first reading</td><td> </td><td align="right">414</td></tr> +<tr><td>of the series on the margin had</td><td> </td><td align="right">597</td></tr> +<tr><td>been 887, the result would have been</td><td> </td><td align="right">712</td></tr> +<tr><td>906 instead of 1106.</td><td> </td><td align="right" class="botbor">793</td></tr> +<tr><td colspan="2"> </td><td align="right">1106</td><td> thousands of revolutions.</td></tr> +<tr><td colspan="2"> </td><td class="botbor" align="right">2</td></tr> +<tr><td> </td><td class="br" align="right">13</td><td class="botbor" align="right"> 2212</td><td> miles of wind in period.</td></tr> +<tr><td colspan="2"> </td><td align="right">170</td><td> miles of wind per day, on an average.</td></tr></table> + +<p>“The foregoing directions are all which require to be regularly attended +to. But it may be interesting at times to find the velocity of the wind +during a period of a few minutes. This may be ascertained by observing the +difference of two readings of all the dials, with an interval of some +minutes between them, when a very brief calculation will suffice; but +perhaps the simplest method is the following:—</p> + +<div class="figright">Fig. 88.<br /><img src="images/fig_88.jpg" alt="" /></div> + +<p>“Take two readings, with an interval of 12 minutes between them. The +difference of these readings, divided by 10, is the velocity of the wind +in miles per hour. Thus—if the reading of the five dials (from left to +right) at noon is 15206, and at 12 minutes past 12 is 15348, the velocity +of the wind is 14·2 miles per hour.”—<i>Admiral FitzRoy, F.R.S.</i></p> + +<p><span class="pagenum"><a name="Page_121" id="Page_121">[Pg 121]</a></span>A lever and clutch are sometimes fitted to this anemometer, as in fig. 88, +for throwing the train out of gear when not required to register. It may +also be connected with clock-work so as to be self-recording, by causing +the mechanism to impress a mark upon prepared paper moved by the +apparatus, at certain intervals of time.</p> + +<p>This anemometer should be fixed in an exposed situation, as high above +ground as may be convenient for reading. It may be made very portable, by +the arms which carry the cups being fitted to unscrew or to fold down. +When fitted in gimbals, it can be used at sea with much advantage.</p> + +<p>The pressure of the wind has been experimentally proved to vary as the +square of the velocity; the relation being <i>V²</i> = 200 × <i>P</i>. From this +formula, therefore, the pressure can be calculated corresponding to the +observed velocity.</p> + + +<p><br /><b>126. Whewell’s Anemometer.</b>—This apparatus, the invention of the +celebrated Dr. W. Whewell, registers the horizontal motion of the air with +the direction. Its mechanism may be described in general terms, as +follows:—</p> + +<p>A horizontal brass plate is attached to a vertical spindle, which passes +through the axis of a fixed cylinder, being supported by a bearing at the +lower end, and working in a collar at the upper. A vane is attached, by +which the plate is moved about according to the direction of the wind. A +fly, having eight fans, each fixed at an angle of 45° with the axle, is +placed upon the plate so that the axle is in the line of direction of the +vane. An endless screw on the axle turns a vertical wheel having one +hundred teeth, the axle to which has also an endless screw working into a +horizontal wheel, having a like number of teeth, and which communicates +motion to a vertical screw fifteen inches long. On this screw is placed a +moveable nut, which carries a pencil. Round the cylinder is wrapped daily +a paper divided for the points of the compass. The wind acting upon the +vane will cause the plate to turn; and the screw which carries the pencil +will travel with it, so that the pencil will mark upon the paper the +direction of the wind. The fly will also be set in motion, and thereby the +nut upon the screw will descend, so that the attached pencil will trace a +vertical line upon the paper. When the fans on the axle are 2·3 inches +from axis to end, and 1·9 inches wide, and the thread of the screw such +that forty-five revolutions will cause the nut to descend two inches, +75·85 miles of wind will cause the pencil to descend through a vertical +space of two inches; but the actual trace upon the paper will be longer in +proportion to the magnitude of change of azimuth, or direction, of the +wind.</p> + + +<p><br /><span class="pagenum"><a name="Page_122" id="Page_122">[Pg 122]</a></span><b>127. Osler’s Anemometer, and Pluviometer.</b>—Mr. Follet Osler is the +inventor of a self-recording apparatus which registers the direction and +pressure of the wind, and the amount and duration of rain, upon the same +sheet of paper. His apparatus has met with very much approbation, and has +been erected in many observatories. The mechanism may be modified in +various ways, and the following is a description of the simplest and most +recent arrangement.</p> + +<p> </p> +<p class="center">Fig. 89.</p> +<div class="figcenter"><img src="images/fig_89.jpg" alt="" /></div> +<p> </p> + +<p>The instrument, of which fig. 89 is a diagram rather than a picture, +consists, first, of a vane, <i>V</i>, of a wedge-shape form, which is found to +answer better than a flat vane; for the latter is always in a neutral +line, and therefore is not sufficiently<span class="pagenum"><a name="Page_123" id="Page_123">[Pg 123]</a></span> sensitive. A wind-mill governor +has been substituted for the vane to get the direction of the wind, with +advantage. At the lower end of the tube, <i>T T</i>, is a small pinion, working +in a rack, <i>r</i>, which moves backwards and forwards as the wind presses the +vane. To this rack a pencil, <i>x</i>, is attached, which marks the direction +of the wind on a properly ruled paper, placed horizontally beneath, and so +adjusted as to progress at the rate of half an inch per hour, by means of +a simple contrivance connecting it with a good clock. The paper is shown +in the illustration upon the table of the instrument.</p> + +<p>The pressure plate, <i>F</i>, for ascertaining the force of the wind, is one +foot square, placed immediately beneath, and at right angles with the +vane; it is supported by light bars, running horizontally on friction +rollers, and communicating with flattened springs, 1, 2, 3, so that the +plate, when affected by the pressure of the wind, acts upon them, and they +transfer such action to a copper chain passing down the interior of the +direction tube, and over a pulley at the bottom. A light copper wire +connects this chain with the spring lever, <i>y y</i>, carrying a pencil which +records the pressure upon the paper below. Mr. Osler much prefers a spring +to any other means for ascertaining the force of the wind, because it is +of the highest importance to have as little matter in motion as possible, +otherwise the momentum acquired will cause the pressure plate to give very +erroneous indications. The pressure plate is as light as is consistent +with strength. It is kept before the wind by the vane, and is urged out by +three or more springs, so that with light winds one only is compressed, +and two, or more, according to the strength of the wind.</p> + +<p>The <i>pluviometer</i> is placed on the right in the figure, <i>P P</i> being the +plane of the roof of the building. The rain funnel, <i>R</i>, exposes an area +of about 200 square inches. The water collected in it is conveyed by a +tube through the roof of the building into a glass vessel, <i>G</i>, so +adjusted and graduated as to indicate a quarter of an inch of rain for +every 200 square inches of surface, <i>i. e.</i> 50 cubic inches. <i>G</i> is +supported by spiral springs, <i>b b</i>, which are compressed by the +accumulating rain. A glass tube, open at both ends, is cemented into the +bottom of <i>G</i>, and over it is placed a larger one closed at the top like a +bell glass. The smaller tube thus forms the long leg of a syphon, and the +larger tube acts as the short leg. The water, having risen to the level of +the top of the inner tube, drops over into a little copper tilt, <i>t</i>, in +the globe, <i>S</i>, beneath the reservoir. This tilt is divided into two equal +partitions by a slip of copper, and placed upon an axis not exactly +balanced, but so that one end or the other preponderates. The water then +drops into the end of the tilt which happens to be uppermost, and when +quite full it falls over, throwing the water into the globe, <i>S</i>, from +which it flows away by the waste pipe. In this way an imperfect vacuum is +produced in the globe, quite sufficient to produce a draught in the small +tube of the syphon, or the long leg; and the whole contents of the +reservoir, <i>G</i>, immediately run off, and the spiral springs, <i>b b</i>, +elevate the reservoir to its original position. To produce this action, a +quarter of an inch of rain must have fallen. The registration is easily +understood. A spring lever, <i>z</i>,<span class="pagenum"><a name="Page_124" id="Page_124">[Pg 124]</a></span> carrying a pencil, is attached by a +cord, <i>c</i>, to <i>S</i>. This spring always keeps the cord tight, so that as the +apparatus descends during the fall of rain, the spring advances the pencil +more and more from the zero of the scale upon the paper beneath, until a +quarter of an inch has fallen, when the pencil is drawn back to zero by +the ascent of the reservoir.</p> + +<p>The clock movement carries the registering paper forward by one of the +wheels working into a rack attached to the frame.</p> + +<p>The adjustment of the instrument should be carefully made at its first +erection. The scale for pressure should be established experimentally, by +applying weights of 2, 4, 6, &c., lbs., to move the pressure plate.</p> + +<p>The registration trace for twenty-four hours is readily understood. The +direction is recorded on the centre part; the pressure on one side, and +the rain on the other. Lines parallel to the length of the paper show no +rain, steady wind, and constant pressure. On the rain trace, a line +parallel to the width of the paper shows that the pencil had been drawn +back to zero, a quarter of an inch of rain having fallen. The hour lines +are in the direction of the width of the paper.</p> + +<p>At the International Exhibition 1862, Messrs. Negretti and Zambra +exhibited an improved Osler’s anemometer, having combined with it +Robinson’s cups, so that the pressure and velocity appear on the same +sheet, on which a line an inch in length is recorded at every ten miles; +thus the complete instrument shows continuously the direction, pressure, +and velocity of the wind.</p> + + +<p><br /><b>128. Beckley’s Anemometer.</b>—Mr. R. Beckley, of the Kew Observatory, has +devised a self-registering anemometer, which consists of three principal +parts: Robinson’s cups for the determination of velocity; a double fan, or +wind-mill governor, for obtaining the direction; and a clock to move a +cylinder, around which registration paper is wrapped. The paper records +the time, velocity, and direction of the wind for twenty-four hours, when +it must be replaced. It has a cast-iron tubular support, or pedestal to +carry the external parts—the cups and the fans,—which must be erected +upon the roof of the building upon which it is desired to mount the +instrument.</p> + +<p>The fans keep their axis at right angles to the wind; and with any change +of direction they move, carrying with them an outer brass tube, which +rests upon friction balls on the top of the pedestal, and is attached to a +tubular shaft passing through the interior of the pedestal, and +terminating with a mitre wheel. The mitre wheel, working with other cogged +wheels, communicates the motion of the direction shaft to a cylinder +carrying a pencil, to record the direction.</p> + +<p>The shaft carrying the cups is supported upon friction balls, placed in a +groove formed on the top of the direction shaft, and passing through the +interior of that shaft, comes out below the mitre wheel, where it is +terminated in an endless screw, or worm.</p> + +<p>Upon the wind moving the cups, motion is given to the innermost shaft,<span class="pagenum"><a name="Page_125" id="Page_125">[Pg 125]</a></span> +thence to the worm-wheel, whence motion is given to a pencil which +registers the velocity.</p> + +<p>De la Rue’s metallic paper is used in registration, it having the property +of receiving a trace from a brass pencil. The pencils can, therefore, be +made in the most convenient form. Mr. Beckley forms each pencil of a strip +of brass wrapped round a cylinder, making a very thin threaded screw, so +that the contact of the pencil cylinder and the clock cylinder is a mere +point of the metallic thread. The pencil cylinders are placed side by side +upon the cylinder turned by the clock, and require no spring or other +appliance to keep them to their work, but always make contact with the +registration paper by their own gravity. They therefore require no +attention, and being as long as the trace which they make, they will last +a long time.</p> + +<p>The velocity pencil has only one turn on the cylinder, and its pitch is +equal to a scale of fifty miles upon the paper. The direction pencil has +likewise one turn on its cylinder, its pitch being equal to a scale of the +cardinal points of the compass upon the paper.</p> + +<p>The clock gives a uniform motion of half an inch per hour to the cylinder +upon which the paper is fastened.</p> + +<p>The registering mechanism of the instrument is very compact, requiring +only a space of about 18 inches by 8 inches.</p> + +<p>In the Report of the British Association for 1858, Mr. Beckley has given a +detailed description of his anemometer, with drawings of all the parts.</p> + + +<p><br /><b>129. Self-Registering Lind’s Anemometer.</b>—A Lind’s wind-gauge, designed to +register the maximum pressure, was exhibited at the International +Exhibition 1862, by Mr. E. G. Wood. The bend of the syphon is contracted +to obtain steadiness. On the leeward limb a hole is drilled corresponding +in size with the contracted portion of the tube. The edge of the hole +corresponds with the zero of the scale. On the pressure of the wind +increasing, as much of the water as would have risen above the aperture +flows away, and therefore the quantity left indicates the greatest +pressure of the wind since the last setting of the instrument, which is +done by filling it with water up to the zero point.</p> + + +<p><br /><b>130. Anemometric Observations.</b>—To illustrate the value of anemometric +observations, we quote from a paper by Mr. Hartnup, on the results +obtained from Osler’s Anemometer, at the Liverpool Observatory. The six +years’ observations, ending 1857, gave for the yearly average of the +winds: North-easterly, on 60 days, at 7·8 miles per hour; North-westerly, +on 112 days, at 15·4 miles per hour; South-easterly, on 115 days, at 11·0 +miles per hour; South-westerly, on 77 days, at 13·8 miles per hour; and +one day calm. From the same observations, the average variation in the +strength of the wind during the 24 hours is:—11 miles per hour, the +minimum force, occurring at 1½ a.m.; until 6 a.m. it remains much the +same, being then 11·3 miles per hour; at 10 a.m. it is 13·4 miles per +hour; at 1½ p.m.<span class="pagenum"><a name="Page_126" id="Page_126">[Pg 126]</a></span> the wind is at its maximum strength, being 14·8 miles +per hour; at 5 p.m. it is again 13·4 miles per hour, and at 9 p.m. 11·3 +miles per hour. Hence it appears that the wind falls to its minimum force +much more gradually than it rises to its maximum; that the decrease and +increase are equal and contrary, so that the curve is symmetrical; and +that generally the force of wind is less at night than during the day.</p> + +<p>“There is evidence,” says Admiral FitzRoy, “in Mr. Hartnup’s very valuable +anemometrical results, which seems to prove that to his observatory, in a +valley, with buildings and hills to the north-eastward, the real polar +current does not blow from N.E., but nearer S.E. By his reliable digest of +winds experienced there, it appears that those most prevalent were from +W.N.W. and S.S.E. But in England, generally, the <i>prevailing</i> winds are +<i>believed</i> to be westerly, inclining to south-westerly, and +north-easterly; while of all winds, the south-easterly is about the +rarest.</p> + +<p>“At Lord Wrottesley’s observatory, in Staffordshire, about 530 feet above +the sea, there appears to be considerably less strength of wind at any +given time, when a gale is blowing <i>generally</i>, than occurs simultaneously +at places along the sea-coast: whence the inference is, that undulations +of the land’s surface and hills, diminish the strength of wind materially +by frictional resistance.</p> + +<p>“All the synoptic charts hitherto advanced at the Board of Trade exhibit a +marked diminution of force inland compared with that on the sea-coast. +Indeed, the coast itself offers similar evidence, in its stunted, sloping +trees, and comparative barrenness.”<small><a name="f14.1" id="f14.1" href="#f14">[14]</a></small></p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_127" id="Page_127">[Pg 127]</a></span></p> +<h2><a name="CHAPTER_XIV" id="CHAPTER_XIV"></a>CHAPTER XIV.</h2> +<p class="center"><span class="large">INSTRUMENTS FOR INVESTIGATING ATMOSPHERIC ELECTRICITY.</span></p> + +<div class="figright">Fig. 90.<br /><img src="images/fig_90.jpg" alt="" /></div> + +<p><br /><b>131. Atmospheric Electroscope.</b>—The simplest instrument for ascertaining +at any time the electric condition of the atmosphere is an electroscope +composed of two equal pieces of gold leaf, suspended from a brass support, +and insulated, as well as protected from the movement of the air, by a +glass covering. Fig. 90 represents such an instrument. The cap of the +brass support is fitted for the reception, in the vertical direction, of a +metallic rod, not less than two or three feet in length. The top of the +rod carries a clip. The instrument acts according to the law, that bodies +similarly electrified repel each other; but when dissimilarly electrified, +they attract each other. To make an observation, the instrument is placed +in the open air, and a lighted piece of cigar fusee, or touch-paper, is +fixed in the clip. The electricity of the air is collected by the +substance undergoing combustion, and conducted by the rod to the gold +leaf; and the pieces, being similarly electrified, separate more or less +according to the amount of electricity present. The kind is determined by +the effect of either an excited stick of sealing-wax or rod of glass upon +the electrified gold leaf. A rod of glass, when rubbed briskly with a silk +handkerchief or piece of woollen cloth, becomes positively electrified, or +excited, as it is termed. A stick of sealing-wax, similarly treated, +acquires the negative state. If, therefore, an excited glass rod be +presented to the cap of the instrument, and it cause the pieces of gold +leaf to diverge still further, the electric state of the air must be +analogous to that of the glass, that is, <i>positive</i>; if they approach, it +is <i>negative</i>. On the contrary, if a stick of sealing-wax be used, the +pieces will be repelled more apart if they have acquired negative +electricity from the air; and they will converge if they have a positive +charge.</p> + +<p>By means of this very simple instrument, meteorological observers can +readily ascertain the electric condition of the lower air at any time.</p> + +<p><span class="pagenum"><a name="Page_128" id="Page_128">[Pg 128]</a></span><span class="smcap">Note.</span>—A book containing +strips of gold leaf is sent with the Electrometer to replace the gold leaves when torn or broken in use.</p> + +<p>To mount fresh gold leaves, unscrew the brass plate to which is attached +the rod supporting the leaves; then moisten with the breath the flat piece +of brass, and press it gently down on one strip of gold, whilst the book +is only partly opened; the second leaf is attached in the same manner.</p> + + +<p><br /><b>132. Volta’s Electrometer</b> is similar to the instrument just described, +except that instead of gold leaf two light pieces of straw, or two pith +balls, are freely suspended from the conductor; the amount of the electric +charge being estimated from the degrees of divergence, shown by a +graduated arc.</p> + + +<p><br /><b>133. Peltier’s Electrometer</b> is a much superior instrument in point of +sensibility. A tall glass tube an inch or more in diameter, is connected +to a glass receiver, mounted on a base fitted with levelling screws. At +the top of the tube is formed a globe from four to five inches in +diameter, which is thickly gilt on the exterior, so as to form a good +conducting surface. A wire passes from the ball down the tube into the +receiver, where it is bent up, and ends in a steel point over the centre +of the base. A bent wire, carrying a small magnetic needle, is balanced on +the steel point, so that the magnet, with the fine wire, arranges itself +horizontally in the direction of the magnetic meridian. If any cloud or +portion of air in the neighbourhood be in an electrical state, it will act +by induction upon the gilt ball, and the needle will be deflected from its +north and south direction.</p> + +<p>A graduated circle indicates the number of degrees of the deflection, +which will be greater or less according to the tension of the electricity. +To ascertain whether the electricity is positive or negative, a stick of +shellac or glass must be employed, as already described.</p> + +<div class="figleft">Fig. 91.<br /><img src="images/fig_91.jpg" alt="" /></div> + +<p><br /><b>134. Bohnenberger’s Electroscope</b> may be fitted with a metallic conductor, +and used with great advantage for observing atmospheric electricity. “The +principal parts of the instrument, as improved by Becquérel, are the +following:—<i>A B</i>, fig. 91, is a small dry galvanic pile of from 500 to +800 pairs, about a quarter of an inch in diameter; when the plates are +pressed together, such a pile will be from 2 to 2½ inches in length. +The wires, which are bent so as to stand above the pile, terminate in two +plates, <i>P</i> and <i>M</i>, which are the poles of the pile. These plates, which +are 2 inches by ½ an inch, are parallel and opposite to each other. It +is convenient for their opposite sides to be slightly convex, for them to +be gilded or coated with platinum, and for them to run on the polar wires, +by the latter being made to pass through a small hole in them. One of +these plates will always be in a state of positive,<span class="pagenum"><a name="Page_129" id="Page_129">[Pg 129]</a></span> and the other of +negative, electricity; between them suspend the very fine gold leaf, <i>D +G</i>, which is attached to the conductor, <i>C D</i>, of copper wire. If the leaf +hang exactly between the two plates, it is equally attracted by each, and +will therefore be in a state of repose. The apparatus should be protected +by a bell-glass, fitting exactly, and having an opening at the top through +which the copper wire, <i>C D</i>, passes; the wire, however, is insulated by +its being contained in a glass tube, which is made to adhere to the +bell-glass by means of a small portion of shellac or gum-lac. Screw on a +metal ball or plate, to impart to it the electricity you wish to test, +which will be conveyed by the copper wire to the gold leaf, and the latter +will immediately move towards the plate which has the opposite polarity. +This electroscope is, beyond doubt, one of the most delicate ever +constructed, and is well adapted to show small quantities of positive and +negative electricity.</p> + +<p>“To ensure the susceptibility of electroscopes and electrometers placed +under bell-glasses, precautions should be taken to render the air they +contain as dry as possible, which may be effected by enclosing in a +suitable vessel a little melted chloride of calcium beneath the glass.”</p> + +<p>The galvanic pile employed in this electroscope is that invented by +Zamboni. “It differs from the common hydro-electric batteries principally +in this, that the presence of the electromotive liquid is dispensed with, +and that in its place is substituted some moist substance of low +conducting power, generally paper. The electromotors in these piles are +composed for the most part of Dutch gold (copper) and silver (zinc) paper +pressed one on the other, with their paper sides together, out of which +discs are cut with a diameter of from a quarter of an inch to an inch. +More powerful pairs of plates may be obtained by using only the silver +paper and smearing its paper side with a thin coat of honey, on which some +finely pulverized peroxide of manganese has been sprinkled, and all the +sides similarly coated are presented one way. Powerful pairs of plates may +also be made by pasting pure gold leaf on the paper side of zinc-paper. +These plates are then to be arranged, just as in the ordinary voltaic +pile, one above the other, so that the similar metallic surfaces may all +lie one way; press them tightly together; tie them with pretty stout silk +threads, and press them into a glass tube of convenient size. The metal +rims of the tubes, which must be well connected with the outermost pairs +of plates, form the poles of the pile, the negative pole being in the +extreme zinc surface, and the positive in the extreme copper or manganese +surface.</p> + +<p>“The electromotive energy called into action in these dry piles is less +than that excited in the moist or hydro-electric piles, principally on +account of the imperfect conduction of the paper. The accumulation of +electricity at their poles also goes on less rapidly, and consequently the +electrical tension continues for a long while unaltered; whereas, in all +moist piles, even in the most constant of them, the tension is maintained, +comparatively speaking, for but a short time, on account of<span class="pagenum"><a name="Page_130" id="Page_130">[Pg 130]</a></span> the chemical +action and decomposition of the electromotive fluid—causes of disturbance +which do not exist in the dry pile.”<small><a name="f15.1" id="f15.1" href="#f15">[15]</a></small></p> + + +<p><br /><b>135. Thomson’s Electrometer.</b>—Professor W. Thomson, of Glasgow, has +devised an atmospheric electrometer, which is likely to become eminently +successful, in the hands of skilful observers. It is mainly a torsion +balance combined with a Leyden-jar. The index is an aluminium needle +strung on a fine platinum wire, passing through its centre of gravity, and +stretched firmly between two points. The needle and wire are carefully +insulated from the greater part of the instrument, but are in metallic +communication with two small plates fixed beside the two ends of the +needle, and termed the repelling plates. A second pair of larger plates +face the repelling plates, on the opposite side of the needle, but +considerably farther from it. These plates are in connection with the +inner coating of a Leyden-jar, and are termed the attracting plates. The +whole instrument is enclosed in a metal cage, to protect the glass +Leyden-jar and the delicate needle.</p> + +<p>The Leyden-jar should be charged when the instrument is used. Its effect +is two-fold: it increases greatly the sensibility of the instrument, and +enables the observer to distinguish between positive and negative +electrification.</p> + +<p>The air inside the jar is kept dry by pumice-stone, slightly moistened +with sulphuric acid; by which means very perfect insulation is maintained.</p> + +<p>Electrodes, or terminals, are brought outside the instrument, by which the +Leyden-jar can be charged, and the needle system connected with the body, +the electric state of which is to be tested.</p> + +<p>For the purpose of testing the electric state of the atmosphere, the +instrument is provided with a conductor and support for a burning match, +or, preferably, with an arrangement termed a water-dropping collector; by +either of which means the electricity of the air is conveyed to the needle +system.</p> + +<p>The needle abuts upon the repelling plates when not influenced by +electricity, in which position it is at zero. It can always be brought +back to zero by a torsion-head, turning one end of the platinum wire, but +insulated from it, and provided with a graduated circle, so that the +magnitude of the arc, that the torsion-head is moved through to bring the +needle to zero, measures the force tending to deflect it.</p> + +<p>The action of the instrument is as follows:—The Leyden-jar is to be +highly charged, say negatively; and the repelling plates are to be +connected with the earth. The needle will then be deflected against a +stop, under the combined influence of attraction from the Leyden-jar, or +attracting plates, and repulsion from the repelling plates due to the +positive charge induced on the needle and its plates by the Leyden-jar +plates. The platinum wire must then be turned round by the torsion-head so +as to bring back the needle to zero; and the number of degrees of torsion +required will measure the force with which the needle is attracted. Next, +let the needle<span class="pagenum"><a name="Page_131" id="Page_131">[Pg 131]</a></span> plates be disconnected from the earth, and connected with +the insulated body, the electric state of which is to be tested. In +testing the atmosphere, the conductor and lighted match, or water-dropping +apparatus, must be applied.</p> + +<p>If the electricity of the body be positive, it will augment the positive +charge in the needle plates, induced by the Leyden-jar plates; and +consequently the needle will be more deflected than by the action of the +jar alone. If the electricity of the body be negative, it will tend to +neutralize the positive charge; and the needle will be less deflected. +Hence the kind of electricity present in the air becomes at once apparent, +without the necessity of an experimental test. The platinum wire must then +be turned till the needle is brought to zero, and the number of degrees +observed; which is a measure of the intensity of the electrification.</p> + +<p>Any loss of charge from the Leyden-jar which may from time to time occur, +reducing the sensibility inconveniently, may be made good by additions +from a small electrophorus which accompanies the instrument.<small><a name="f16.1" id="f16.1" href="#f16">[16]</a></small></p> + +<p>The instrument may be made self-recording by the aid of clockwork and +photography. To effect this, a clock gives motion to a cylinder, upon +which photographic paper is mounted. The needle of the electrometer is +made to carry a small reflector; and rays from a properly adjusted source +of light are thrown by the reflector, through a small opening, upon the +photographic paper. It is evident, that as the cylinder revolves, a trace +will be left upon the paper, showing the magnitude of, and variations in, +the deflection of the needle.</p> + + +<p><br /><b>136. Fundamental Facts regarding Atmospheric Electricity.</b>—The <i>general</i> +electrical condition of the atmosphere is <i>positive</i> in relation to the +surface of the earth and ocean, becoming more and more positive as the +altitude increases. When the sky is overcast, and the clouds are moving in +different directions, it is subject to great and sudden variations, +changing rapidly from positive to negative, and the reverse. During fog, +rain, hail, sleet, snow, and thunderstorms, the electrical state of the +air undergoes many variations. The intensity of the electricity increases +with hot weather following a series of wet days, or of wet weather coming +after a continuance of dry days. The atmospheric electricity, in fact, +seems to depend for its intensity and kind upon the direction and +character of the prevailing wind, under ordinary circumstances. It has an +annual and a diurnal variation. There is a greater diurnal change of +tension in winter than in summer. By comparing observations from month to +month, a gradual increase of tension is perceived from July to February, +and a decrease from February to July. The intensity seems to vary with the +temperature. The diurnal variation exhibits two periods of greatest and +two of least intensity. In summer, the <i>maxima</i> occur about 10 a.m. and 10 +p.m.; the <i>minima</i> about 2 a.m. and noon. In winter, the <i>maxima</i> take +place near 10 a.m. and 8 p.m.; the <i>minima</i> near 4 a.m. and 4 p.m.</p> + +<p>The researches of Saussure, Beccaria, Crosse, Quétèlet, Thompson, and<span class="pagenum"><a name="Page_132" id="Page_132">[Pg 132]</a></span> +FitzRoy have tended to show that during the prevalence of polar currents +of air positive electricity is developed, and becomes more or less active +according to the greater or less coldness and strength of wind; but with +winds from the equatorial direction there is little evidence of sensitive +electricity, and when observable, it is of the negative kind. Storms and +gales of wind are generally attended, in places, with lightning and +thunder; and as the former are very often attributed to the conflict of +polar and equatorial winds, the difference of the electric tension of +these winds may account for the latter phenomena. It is not our intention +to enter upon the general consideration of thunderstorms; the facts which +we have given may be of service to the young observer; and finally, as it +is interesting to be able to judge of the locality of a thunderstorm, the +following simple rule will be of service, and sufficiently accurate:—Note +by a second’s watch the number of seconds which elapse from the sight of +the lightning to the commencement of the thunder; divide them by five, and +the quotient will be the distance in miles. Thus, if thunder is heard ten +seconds after the lightning was seen, the distance from the seat of the +storm will be about two miles. The interval between the flash and the roll +has seldom been observed greater than seventy-two seconds.</p> + + +<p><br /><b>137. Lightning Conductors.</b>—“The line of danger, whether from the burning +or lifting power of lightning, is the line of strong and obstructed +currents of air, of the greatest aerial friction.”<small><a name="f17.1" id="f17.1" href="#f17">[17]</a></small> Trees, church +spires, wind-mills and other tall structures, obstruct the aerial +currents, and hence their exposure to danger. The highest objects of the +landscape, especially those that are nearest the thunder cloud, will +receive the lightning stroke. The more elevated the object, the more +likely is it to be struck. Of two or more objects, equally tall and near, +the lightning is invariably found to select the best conductor of +electricity, and even to make a circuitous path to get to it. Hence the +application and evident advantage of metallic rods, called <i>lightning +conductors</i>, attached to buildings and ships. A lightning conductor should +be pointed at top, and extend some feet above the highest part of the +edifice, or mast. It should be made of copper, which is a better +conducting medium than iron, and more durable, being less corrosive. It +must be unbroken throughout its length, and extend to the bottom of the +building, and even some distance into the ground, so as to conduct the +electricity into a well or moist soil. If it be connected with the lead +and iron work in the structure of the house, it will be all the better, as +affording a larger surface, and a readier means of exit for the fluid. In +a ship, the lower end of the conductor should be led into communication +with the hull, if of iron, and with the copper sheathing, if a wooden +vessel; so that, spread over a large surface, it may escape more readily +to the water.</p> + + +<p><br /><b>138. Precautions against Lightning.</b>—Experience seems to warrant the +assumption that any building or ship, fitted with a substantial lightning +conductor,<span class="pagenum"><a name="Page_133" id="Page_133">[Pg 133]</a></span> is safe from danger during a thunderstorm. Should a house or +vessel be undefended by a conductor, it may be advisable to adopt a few +precautions against danger. In a house, the fire-place should be avoided, +because the lightning may enter by the chimney, its sooty lining being a +good conductor. “Through chimneys, lightning has a way into most houses; +and therefore, it is wise, by opening doors or windows, to give it a way +out. Wherever the aerial current is fiercest, there the danger is +greatest; and if we kept out of the way of currents or draughts, we keep +out of the way of the lightning.”<small><a name="f18.1" id="f18.1" href="#f18">[18]</a></small> Lightning evinces as it were a +preference for metallic substances, and will fly from place to place, even +out of the direct line of its passage to the earth, to enter such bodies. +It is therefore well to avoid, as much as possible, gildings, silvered +mirrors, and articles of metal. The best place is perhaps the middle of +the room, unless a draught passes, or a metallic lamp or chandelier should +be hanging from the ceiling. The neighbourhood of bad conductors, such as +glass windows, not being open, and on a thick bed of mattrasses, are safe +places. The quality of trees as lightning conductors is considered to +depend upon their height and moisture, those which are taller and +relatively more humid being struck in preference to their fellows; +therefore, it is unwise to seek shelter under tall and wet trees during a +thunderstorm. In the absence of any other shelter, it would be better to +lie down on the ground.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_134" id="Page_134">[Pg 134]</a></span></p> +<h2><a name="CHAPTER_XV" id="CHAPTER_XV"></a>CHAPTER XV.</h2> +<p class="center"><span class="large">OZONE AND ITS INDICATORS.</span></p> + +<p><br /><b>139. Nature of Ozone.</b>—During the action of a powerful electric machine, +and in the decomposition of water by the voltaic battery, a peculiar odour +is perceptible, which is considered to arise from the generation of a +substance to which the term ozone has been given, on account of its having +been first detected by smell, which, for a long time after its discovery, +was its only known characteristic. A similar odour is evolved by the +influence of phosphorus on moist air, and in other cases of slow +combustion. It is also traceable, by the smell, in air,—where a flash of +lightning has passed immediately before. Afterwards it was established +that the same element possessed an oxidising property. It was found to be +liberated at the oxygen electrode when water was decomposed by an electric +current; and has been regarded by some chemists as what is termed an +<i>allotropic</i> form of oxygen, while others speak of it as oxygen in the +<i>nascent</i> state, and some even regard it as intimately related to +chlorine. So various are the existing notions of the nature of this +obscure agent.</p> + +<p>Its oxidising property affords a ready means for its detection, even when +the sense of smell completely fails. The methods of noting the presence +and measuring the amount of ozone present in the air, are very simple; +being the free exposure to the air, defended from rain and the direct rays +of the sun, of prepared test-papers. There are two kinds of test-papers. +One kind was invented by Dr. Schonbein, the original discoverer of ozone; +and the other, which is more generally approved, by Dr. Moffat.</p> + + +<p><br /><b>140. Schonbein’s Ozonometer</b> consists of strips of paper, previously +saturated with a solution of starch and iodide of potassium, and dried. +The papers are suspended in a box, or otherwise properly exposed to the +air, for a given interval, as twenty-four hours. The presence of ozone is +shown by the test-paper acquiring a purple tint when momentarily immersed +in water. The amount is estimated by the depth of the tint, according to a +scale of ten tints furnished for the purpose, which are distinguished by +numbers from 1 to 10. The ozone decomposes the compound which iodine forms +with hydrogen, and, it is presumed, combines as oxygen with hydrogen, +while the iodine unites with the starch, giving the blue colour when +moist.</p> + + +<p><br /><b>141. Dr. Moffat’s Ozonometer</b> consists of papers prepared in a somewhat +similar manner to Schonbein’s; but they do not require immersion in water. +The <span class="pagenum"><a name="Page_135" id="Page_135">[Pg 135]</a></span>presence of ozone is shown by a brown tint, and the amount by the +depth of tint according to a scale of ten tints, which is furnished with +each box of the papers.</p> + +<p>Moffat’s have the advantage of preserving their tint for years, if kept in +the dark, or between the leaves of a book; and are simpler to use.</p> + +<div class="figright">Fig. 92.<br /><img src="images/fig_92.jpg" alt="" /></div> + +<p><br /><b>142. Sir James Clark’s Ozone Cage</b> (fig. 92), consists of two cylinders of +very fine wire gauze, one fitting into the other; the wire gauze being of +such a fineness as to permit the free ingress of air, at the same time +that it shuts out all light that would act injuriously on the test-paper, +which is suspended by a clip or hook attached to the upper part of the +inner cylinder.</p> + + +<p><br /><b>143. Distribution and Effects of Ozone.</b>—Mr. Glaisher has found that “the +amount of ozone at stations of low elevation is small; at stations of high +elevation, it is almost always present; and at other and intermediate +stations, it is generally so. The presence and amount of ozone would seem +to be graduated by the elevation, and to increase from the lowest to the +highest ground. The amount of ozone is less in towns than in the open +country at the same elevation; and less at inland than at sea-side +stations.” It seems to abound most with winds from the sea, and to be most +prevalent where the air is considered the purest and most salubrious. This +may seem, says Admiral FitzRoy, in <i>The Weather Book</i>, to point to a +connection between ozone and chlorine gas, which is in and over sea-water, +and which <i>must</i> be brought by any wind that blows from the sea. It +prevails more over the ocean and near it than over land, especially land +remote from the sea; and, says the Admiral, it affects the gastric juice, +improves digestion, and has a tanning effect. Dr. Daubeny, in his +<i>Lectures on Climate</i>, writes: “Its presence must have a sensible +influence upon the purity of the air, by removing from it fœtid and +injurious organic effluvia. It is also quite possible that ozone may play +an important part in regulating the functions of the vegetable kingdom +likewise; and although it would be premature at present to speculate upon +its specific office, yet, for this reason alone, it may be well to note +the fact of its frequency, in conjunction with the different phases which +vegetation assumes, persuaded that no principle can be generally diffused +throughout nature, as appears to be the case, with this, without having +some important and appropriate use assigned for it to fulfil.”</p> + + +<p><br /><b>144. Registering Ozonometer.</b>—Dr. E. Lancaster has contrived an +ozonometer, the object of which is to secure the constant registration of +ozone, so that the varying quantities present in the atmosphere may be +detected and registered. For this purpose, an inch of ozone paper passes +in each hour, by clock-work, beneath an opening in the cover of the +instrument.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_136" id="Page_136">[Pg 136]</a></span></p> +<h2><a name="CHAPTER_XVI" id="CHAPTER_XVI"></a>CHAPTER XVI.</h2> +<p class="center"><span class="large">INSTRUMENTS NOT DESCRIBED IN THE PRECEDING CHAPTERS.</span></p> + +<p><br /><b>145. Chemical Weather Glass.</b>—This curious instrument appears to have been +invented more than a hundred years ago, but the original maker is not +known. It is simply a glass vial about ten inches long and three quarters +of an inch in diameter, which is nearly filled, and hermetically sealed, +with the following mixture:—Two drachms of camphor, half a drachm of +nitrate of potassium, half a drachm of chlorate of ammonium, dissolved in +about two fluid ounces of absolute alcohol mixed with two ounces of +distilled water. All the ingredients should be as pure as possible, and +each vial filled separately. When the instruments are made in numbers and +filled from a common mixture, some get more than the due proportion of the +solid ingredients, and consequently such glasses do not exhibit that +uniformity of appearance and changes, that undoubtedly should accompany +similar influencing circumstances. It is in consequence of a want of +precision and fixed principle of manufacture, that these interesting +instruments are not properly appreciated, and more generally used.</p> + +<p>The glass should be kept quite undisturbed, exposed to the north, and +shaded from the sun. Camphor is soluble in alcohol, but not in water, +while both water and alcohol have different solvent powers, according to +the temperature; hence, the solid ingredients being in excess for certain +conditions of solution, depending upon temperature chiefly, and perhaps +electricity and the action of light also, appear as crystals and disappear +with the various changes that occur in the weather.</p> + +<p>The various appearances thus presented in the menstruum have been inferred +to prognosticate atmospheric changes. The following rules have been +deduced from careful study of the glass and weather:—</p> + +<p>1. During cold weather, beautiful fern-like or feathery crystallization is +developed at the top, and sometimes even throughout the liquid. This is +the normal state of the glass during winter. The crystallization increases +with the coldness; and if the structure grows downward, the cold will +continue.</p> + +<p>2. During warm and serene weather, the crystals dissolve, the upper and +greater part of the liquid becoming perfectly clear. This is the normal +state of the glass during summer. The less amount of crystallization, that +is, the greater the clear portion of the liquid (for there is always some +of the composition visible at the bottom), the greater the probability of +continued fine dry weather.</p> + +<p>3. When the upper portion is clear, and flakes of the composition rise to +the top and aggregate, it is a sign of increasing wind and stormy +weather.</p> + +<p><span class="pagenum"><a name="Page_137" id="Page_137">[Pg 137]</a></span>4. In cold weather, if the top of the liquid becomes thick and cloudy, it +denotes approaching rain.</p> + +<p>5. In warm weather, if small crystals rise in the liquid, which still +maintains its clearness, rain may be expected.</p> + +<p>6. Sharpness in the points and features of the fern-like structure of the +crystals, is a sign of fine weather; but when they begin to break up, and +are badly defined, unsettled weather may be expected.</p> + +<p>Admiral FitzRoy, in <i>The Weather Book</i>, writes of this instrument as +follows:—“Since 1825, we have generally had some of these glasses, as +curiosities rather than otherwise; for nothing certain could be made of +their variations until lately, when it was fairly demonstrated that if +fixed undisturbed in free air, not exposed to radiation, fire, or sun, but +in the ordinary light of a well-ventilated room, or, <i>preferably</i>, in the +outer air, the chemical mixture in a so-called storm-glass varies in +character with the <i>direction</i> of the wind—not its force, <i>specially</i> +(though it <i>may</i> so vary in <i>appearance</i>, only from another cause, +<i>electrical tension</i>).</p> + +<p>“As the atmospheric current veers toward, comes from, or is only +<i>approaching</i> from the polar direction, this chemical mixture—if closely, +even microscopically watched—is found to grow like <i>fir</i>, <i>yew</i>, fern +leaves, or hoar-frost—or like crystallizations.</p> + +<p>“As the wind, or great body of air, tends more from the <i>opposite</i> +quarter, the lines or spikes—all regular, hard, or crisp +features—gradually diminish, till they vanish.</p> + +<p>“Before, and in a continued southerly wind, the mixture sinks slowly +downward in the vial, till it becomes shapeless, like melting white sugar.</p> + +<p>“Before, or during the continuance of a northerly wind (polar current), +the crystallizations are beautiful (if the mixture is correct, the glass a +<i>fixture</i>, and duly <i>placed</i>); but the least motion of the liquid disturbs +them.</p> + +<p>“When the main currents meet, and turn <i>toward the west</i>, making +<i>easterly</i> winds, stars are more or less numerous, and the liquid dull, or +less clear. When, and while they <i>combine by the west</i>, making westerly +winds, the liquid is clear, and the crystallization well-defined, without +loose stars.</p> + +<p>“While <i>any hard</i> or <i>crisp</i> features are visible below, above, or at the +top of the liquid (where they form for polar winds), there is <i>plus</i> +electricity in the air; a <i>mixture</i> of polar current co-existing <i>in that +locality</i> with the opposite, or southerly.</p> + +<p>“When nothing but soft, melting, sugary substance is seen, the atmospheric +current (feeble or strong as it may be) is southerly with <i>minus</i> +electricity, unmixed with, and <i>uninfluenced</i> by, the contrary wind.</p> + +<p>“Repeated trials with a delicate galvanometer, applied to measure electric +tension in the air, have proved these facts, which are now found useful +for aiding, with the barometer and thermometer, in forecasting weather.</p> + +<p>“Temperature affects the mixture much, but not solely; as many comparisons +of winter with summer changes of temperature have fully proved.</p> + +<p><span class="pagenum"><a name="Page_138" id="Page_138">[Pg 138]</a></span>“A confused appearance of the mixture, with flaky spots, or stars, in +motion, and less clearness of the liquid, indicates south-easterly wind, +probably strong to a gale.</p> + +<p>“Clearness of the liquid, with more or less perfect crystallizations, +accompanies a combination, or a contest, of the main currents, by the +<i>west</i>, and very remarkable these differences are,—the results of these +air currents acting on each other <i>from</i> eastward, or from an entirely +opposite direction, the <i>west</i>.</p> + +<p>“The glass should be wiped clean now and then,—and once or twice a year +the mixture should be disturbed, by inverting and gently shaking the glass +vial.”</p> + +<div class="figleft">Fig. 93.<br /><img src="images/fig_93.jpg" alt="" /></div> + +<p><br /><b>146. Leslie’s Differential Thermometer.</b>—A glass tube having a large bulb +at each extremity, and bent twice at right angles, as represented in +figure 93, containing strong sulphuric acid tinged with carmine, and +supported at the centre by a wooden stand, constitutes the differential +thermometer as invented by Professor Leslie. The instrument is designed to +exhibit and measure small differences of temperature. Each leg of the +instrument is usually from three to six inches long, and the balls are +about four inches apart. The calibre of the legs is about <span style="font-size: 0.8em;"><sup>1</sup></span>⁄<span style="font-size: 0.6em;">50</span> inch, not +more; the other part of the tube may be wider. The tube is filled with the +liquid, the bulbs contain air. When both bulbs are heated alike, each +scale indicates zero. The scale is divided so that the space between the +freezing and the boiling-points of water is equal to 1,000 parts. When one +bulb is heated more than the other, the difference of temperature is +delicately shown by the descent of the coloured fluid from the heated +ball. It is uninfluenced by changes in the temperature of the atmosphere; +hence it is admirably adapted for experiments of radiant heat. The theory +of the instrument is that gases expand equally for uniform increments of +heat.</p> + + +<p><br /><b>147. Rumford’s Differential Thermometer</b> differs from that just described +in simply containing only a small bubble of liquid, which lies in the +centre of the tube, when both bulbs are similarly influenced. The bulbs +and other parts of the tube contain air. When one bulb is more heated than +the other, the bubble moves towards the one less heated; and the scale +attached to the horizontal part of the tube affords a measurement of the +difference of temperature.</p> + +<div class="figright">Fig. 94.<br /><img src="images/fig_94.jpg" alt="" /></div> + +<p><a name="glaisher" id="glaisher"></a><br /><b>148. Glaisher’s Thermometer Stand.</b>—The thermometer stand consists of a +horizontal board as a base, of a vertical board projecting upwards from +one edge of the horizontal one, and of two parallel inclined boards, +separated from each other by blocks of three inches in thickness, +connected at the top with the vertical,<span class="pagenum"><a name="Page_139" id="Page_139">[Pg 139]</a></span> and at the bottom with the +horizontal board, and the air passes freely about and between them all. To +the top of the inclined boards is connected a small projecting roof to +prevent the rain falling on the bulbs of the instrument, which are carried +on the face of the vertical board, with their bulbs projecting below it, +so that the air plays freely on the bulbs from all sides. The whole frame +revolves on an upright post firmly fixed to the ground, as shown in the +engraving, fig. 94; and in use, the inclined side is always turned towards +the sun.</p> + + +<p><br /><b>149. Thermometer Screen, for use at Sea.</b>—This screen, or shade, was +designed by Admiral FitzRoy, and has been in use for several years on +board H.M. vessels and many merchant-ships. It is about twenty-four inches +long by twelve wide and eight deep; having lattice-work sides, door, and +bottom; with perforation also at top, so contrived that the air has free +access to the interior, while the direct rays of the sun, rain, and sea +spray are effectually excluded from the thermometers mounted inside. There +is ample space for two thermometers placed side by side on brackets, at +least three inches from each other or any part of the exterior of the +screen. One thermometer should be fitted up as a “wet bulb” (see <a href="#Page_105">p. 105</a>). +A small vessel of water can easily be fixed inside the screen so as to +retain its position and contents under the usual motions of the ship; and +by means of a piece of cotton-wick, or muslin rag tied round the bulb of +the thermometer and trailing into the cup of water, keep the bulb +constantly moist.</p> + +<p>Self-registering thermometers should be protected by a similar screen. It +has been found that thermometric observations made at sea are not valuable +for scientific purposes unless the instruments have been duly protected by +such a screen.</p> + +<div class="figright">Fig. 95.<br /><img src="images/fig_95.jpg" alt="" /></div> + +<p><br /><b>150. Anemoscope</b>, or Portable Wind Vane for travellers, with compass, bar +needle, &c., shows the direct course of the wind to half a point of the +compass.</p> + + +<p><br /><b>151. Evaporating Dish, or Gauge</b> (fig. 95), for showing the amount of<span class="pagenum"><a name="Page_140" id="Page_140">[Pg 140]</a></span> +evaporation from the earth’s surface. This gauge consists of a brass +vessel, the area or evaporating surface of which is accurately determined; +and also a glass cylindrical measure, graduated into inches, tenths, and +hundredths of inches. In use, the evaporating gauge is nearly filled with +water, the quantity having been previously measured by means of the glass +cylinder; it is then placed out of doors, freely exposed to the action of +the atmosphere; after exposure, the water is again measured, and the +difference between the first and second measurement shows the amount of +evaporation that has taken place. If rain has fallen during the exposure +of the gauge, the quantity collected by it must be deducted from the +measured quantity; the amount is shown by the quantity of rain collected +in the rain gauge. The wire cage round the gauge is to prevent animals, +birds, &c., from drinking the water.</p> + + +<p><br /><b>152. Dr. Babington’s Atmidometer</b>, or instrument for measuring the +evaporation from water, <i>ice or snow</i>, consists of an oblong hollow bulb +of glass or copper, beneath which and communicating with it by a +contracted neck is a second globular bulb, duly weighted with mercury or +shot. The upper bulb is surmounted by a small glass or metal stem, having +a scale graduated to grains and half-grains; on the top of which is fixed +horizontally a shallow metal pan. The bulbs are immersed in a vessel of +water having a circular hole in the cover through which the stem rises. +Distilled water is then gradually poured into the pan above, until the +zero of the stem sinks to a level with the cover of the vessel. Thus +adjusted, as the water in the pan evaporates, the stem ascends, and the +amount of evaporation is indicated in grains. This instrument affords a +means of measuring evaporation from <i>ice or snow</i>. An adjustment for +temperature is necessary.</p> + + +<p><br /><b>153. Cloud Reflector.</b>—At the International Exhibition 1862, Mr. J. T. +Goddard exhibited a cloud mirror, for ascertaining the direction in which +the clouds are moving.</p> + +<p>The mirror is laid on a horizontal support near a window, and fastened so +that the point marked north may coincide with the south point of the +horizon,—the several points will consequently be reversed. The edge of a +conspicuous cloud is brought to the centre of the mirror, and the observer +keeps perfectly still until it passes off at the margin, where the true +point of the horizon <i>from which</i> the clouds are coming can be read off.</p> + + +<p><br /><b>154. Sunshine Recorder.</b>—Mr. Goddard also exhibited an instrument which he +calls by this name. It works by letting the sun’s rays pass through a +narrow slit, and fall on photographic paper wound round a barrel moved by +clock-work; the paper being changed daily, and the photographic impression +developed and fixed in the usual manner.<small><a name="f19.1" id="f19.1" href="#f19">[19]</a></small></p> + + +<p class="center"><br /><span class="pagenum"><a name="Page_141" id="Page_141">[Pg 141]</a></span>155. SET OF PORTABLE INSTRUMENTS.</p> + +<p>In a small box, 8 in. by 8 in. by 4 in., a complete set of meteorological +instruments have been packed. The lid of the box, by an ingenious +arrangement, is made to take off and hang up; on it are permanently fixed +for observation, a maximum and minimum, and a pair of dry and wet bulb +thermometers. The interior of the box contains a maximum thermometer in +vacuo for solar radiation, and a minimum for terrestrial purposes, one of +Negretti and Zambra’s small pocket aneroid barometers, pedometer for +measuring distances, pocket compass, clinometer, and lastly a rain gauge. +This latter instrument consists of an accurately turned brass ring having +an india rubber body fastened to it to receive the rain, which is measured +off by a small graduated glass, also contained in the box. Gentlemen +travelling will find this compact observatory all that can be desired for +meteorological observations.</p> + + +<p class="center"><br />156. IMPLEMENTS.</p> + +<p>The practical meteorologist will find the following articles very useful, +if not necessary. They scarcely require description; an enumeration will +therefore suffice:—<i>Weather Diagrams</i>, or prepared printed and ruled +forms, whereon to exhibit graphically the readings of the various +instruments to render their indications useful in foretelling weather, +&c.;—<i>Meteorological Registers</i>, or Record Books, for recording all +observations, and the deductions;—<i>Cloud Pictures</i>, by which the clouds +can be readily referred to their particular classification, very necessary +to the inexperienced and learners;—Cyclone Glasses, or Horns, outline +Maps with Wind-markers, are also useful, especially in forecasting +weather.</p> + + +<div class="figleft">Fig. 96.<br /><img src="images/fig_96.jpg" alt="" /></div> + +<div class="figright">Fig. 97.<br /><img src="images/fig_97.jpg" alt="" /></div> + +<p class="center"><br />157. HYDROMETER.</p> + +<p>A simple kind of hydrometer is very much used at sea, as “a sea-water +test;” and as the observations are usually recorded in a meteorological +register or the ship’s log-book, it may not be altogether out of place to +give a description of it here.</p> + +<p>It is constructed of glass. If made of brass, the corrosive action of +salt-water soon renders the instrument erroneous in its indications. The +shapes usually given to the instruments are shown in figs. 96 and 97. A +globular bulb is blown, and partly filled with mercury or small shot, to +make the instrument float steadily in a vertical position. From the neck +of the bulb the glass is expanded into an oval or a cylindrical shape, to +give the instrument sufficient volume for flotation; finally, it is +tapered off to a narrow upright stem which encloses an ivory scale, and is +closed at the top. The divisions on the scale read downward, so as to +measure the length of the stem which stands above the surface of any +liquid in which the hydrometer is floated. The denser the fluid, the +higher will the instrument rise; the rarer, the lower it will sink.</p> + +<p><span class="pagenum"><a name="Page_142" id="Page_142">[Pg 142]</a></span>The indications depend upon the hydrostatic principle, that floating +bodies displace a quantity of the fluid which sustains them equal to their +own weight. According, therefore, as the specific gravities of fluids +differ from each other, so will vary the quantities of the fluids +displaced by the same body when floated successively in each.</p> + +<p>The specific gravity of distilled water, at the temperature of 62° <i>F</i>, +being taken as unity, the depth to which the instrument sinks when gently +immersed in such water is the zero of the scale. The graduations extend +from 0 to 40; the latter being the mark which will be level with the +surface when the instrument is placed in water, the specific gravity of +which is 1·040. In recording observations, the last two figures +only—being the figures on the scale—are written down. Sea-water usually +ranges from 1·020 to 1·036.</p> + +<p>A small tin, copper, or glass cylinder is useful for containing the water +to be tested. It should be wider than the hydrometer, and always filled to +the brim. If fitted to a stand, which is supported by gimbals, it will be +very convenient. Water in a bucket, basin, or other wide vessel, acquires +motion at sea, and the eye cannot be brought low enough (on account of the +edges) to read off the scale accurately.</p> + +<p>Errors of observation may occur with the hydrometer, if it be put into +water without being clean, or without being carefully wiped. The +instrument is extremely accurate if correctly used. It should be kept free +from contact with the sides of the vessel; and all dust, smears, or +greasiness, should be scrupulously avoided, by carefully wiping it with a +clean cloth before and after use.</p> + +<p>Whenever the temperature of the water tested differs from 62°, a +correction to the reading is necessary, for the expansion or contraction +of the glass, as well as the water itself, in order to reduce all +observations to one generally adopted standard.</p> + +<p>Negretti and Zambra’s hydrometer, with thermometer in the stem, shows the +density and temperature in one instrument.</p> + +<p>For the following Tables we are indebted to the kindness of Admiral +FitzRoy:—</p> + +<p><span class="smcap">Table</span> for reducing observations made with a <span class="smcap">Brass Hydrometer</span>, assuming the +linear expansion of brass to be 0·000009555 for 1° F. The correction is +additive for all temperatures above 62°, and subtractive for temperatures +below 62°.</p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td class="btlr" align="center"><i>t°</i></td> + <td class="btrdoub" align="center">Correction.</td> + <td class="btr" align="center"><i>t°</i></td> + <td class="btrdoub" align="center">Correction.</td> + <td class="btr" align="center"><i>t°</i></td> + <td class="btrdoub" align="center">Correction.</td> + <td class="btr" align="center"><i>t°</i></td> + <td class="btr" align="center">Correction.</td></tr> +<tr><td class="btlr" align="center">32</td> + <td class="btrdoub" align="center">-0·0014</td> + <td class="btr" align="center">48</td> + <td class="btrdoub" align="center">-0·0010</td> + <td class="btr" align="center">64</td> + <td class="btrdoub" align="center">+0·0002</td> + <td class="btr" align="center">80</td> + <td class="btr" align="center">+0·0020</td></tr> +<tr><td class="blr" align="center">33</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0014</span></td> + <td class="br" align="center">49</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0009</span></td> + <td class="br" align="center">65</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0003</span></td> + <td class="br" align="center">81</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0021</span></td></tr> +<tr><td class="blr" align="center">34</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0014</span></td> + <td class="br" align="center">50</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0009</span></td> + <td class="br" align="center">66</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0004</span></td> + <td class="br" align="center">82</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0023</span></td></tr> +<tr><td class="blr" align="center">35</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0014</span></td> + <td class="br" align="center">51</td> + <td class="brdoub" align="center">-0·0008</td> + <td class="br" align="center">67</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0005</span></td> + <td class="br" align="center">83</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0024</span></td></tr> +<tr><td class="blr" align="center">36</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0014</span></td> + <td class="br" align="center">52</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0008</span></td> + <td class="br" align="center">68</td> + <td class="brdoub" align="center">+0·0006</td> + <td class="br" align="center">84</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0026</span></td></tr> +<tr><td class="blr" align="center">37</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0014</span></td> + <td class="br" align="center">53</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0007</span></td> + <td class="br" align="center">69</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0007</span></td> + <td class="br" align="center">85</td> + <td class="br" align="center">+0·0027</td></tr> +<tr><td class="blr" align="center">38</td> + <td class="brdoub" align="center">-0·0014</td> + <td class="br" align="center">54</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0006</span></td> + <td class="br" align="center">70</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0008</span></td> + <td class="br" align="center">86</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0029</span></td></tr> +<tr><td class="blr" align="center">39</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0013</span></td> + <td class="br" align="center">55</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0006</span></td> + <td class="br" align="center">71</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0009</span></td> + <td class="br" align="center">87</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0030</span></td></tr> +<tr><td class="blr" align="center">40</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0013</span></td> + <td class="br" align="center">56</td> + <td class="brdoub" align="center">-0·0005</td> + <td class="br" align="center">72</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0010</span></td> + <td class="br" align="center">88</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0032</span></td></tr> +<tr><td class="blr" align="center">41</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0013</span></td> + <td class="br" align="center">57</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0004</span></td> + <td class="br" align="center">73</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0011</span></td> + <td class="br" align="center">89</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0033</span></td></tr> +<tr><td class="blr" align="center">42</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0013</span></td> + <td class="br" align="center">58</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0003</span></td> + <td class="br" align="center">74</td> + <td class="brdoub" align="center">+0·0013</td> + <td class="br" align="center">90</td> + <td class="br" align="center">+0·0035</td></tr> +<tr><td class="blr" align="center">43</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0012</span></td> + <td class="br" align="center">59</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0003</span></td> + <td class="br" align="center">75</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0014</span></td> + <td class="br" align="center">91</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0036</span></td></tr> +<tr><td class="blr" align="center">44</td> + <td class="brdoub" align="center">-0·0012</td> + <td class="br" align="center">60</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0002</span></td> + <td class="br" align="center">76</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0015</span></td> + <td class="br" align="center">92</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0038</span></td></tr> +<tr><td class="blr" align="center">45</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0011</span></td> + <td class="br" align="center">61</td> + <td class="brdoub" align="center">-0·0001</td> + <td class="br" align="center">77</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0016</span></td> + <td class="br" align="center">93</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0040</span></td></tr> +<tr><td class="blr" align="center">46</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0011</span></td> + <td class="br" align="center">62</td> + <td class="brdoub" align="center"><span style="margin-left: .25em;">0·0000</span></td> + <td class="br" align="center">78</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0018</span></td> + <td class="br" align="center">94</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0041</span></td></tr> +<tr><td class="bblr" align="center">47</td> + <td class="bbrdoub" align="center">-0·0010</td> + <td class="bbr" align="center">63</td> + <td class="bbrdoub" align="center">+0·0001</td> + <td class="bbr" align="center">79</td> + <td class="bbrdoub" align="center">+0·0019</td> + <td class="bbr" align="center">95</td> + <td class="bbr" align="center">+0·0043</td></tr></table> + +<p><span class="pagenum"><a name="Page_143" id="Page_143">[Pg 143]</a></span><span class="smcap">Table</span> for reducing +observations made with a <span class="smcap">Glass Hydrometer</span>, assuming the +linear expansion of glass to be 0·00000463 for 1° F. The correction is +additive for temperatures above 62°, and subtractive for temperatures below 62°.</p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td class="btlr" align="center"><i>t°</i></td> + <td class="btrdoub" align="center">Correction.</td> + <td class="btr" align="center"><i>t°</i></td> + <td class="btrdoub" align="center">Correction.</td> + <td class="btr" align="center"><i>t°</i></td> + <td class="btrdoub" align="center">Correction.</td> + <td class="btr" align="center"><i>t°</i></td> + <td class="btr" align="center">Correction.</td></tr> +<tr><td class="btlr" align="center">32</td> + <td class="btrdoub" align="center">-0·0019</td> + <td class="btr" align="center">48</td> + <td class="btrdoub" align="center">-0·0012</td> + <td class="btr" align="center">64</td> + <td class="btrdoub" align="center">+0·0002</td> + <td class="btr" align="center">80</td> + <td class="btr" align="center">+0·0023</td></tr> +<tr><td class="blr" align="center">33</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0019</span></td> + <td class="br" align="center">49</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0011</span></td> + <td class="br" align="center">65</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0003</span></td> + <td class="br" align="center">81</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0024</span></td></tr> +<tr><td class="blr" align="center">34</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0018</span></td> + <td class="br" align="center">50</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0011</span></td> + <td class="br" align="center">66</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0004</span></td> + <td class="br" align="center">82</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0026</span></td></tr> +<tr><td class="blr" align="center">35</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0018</span></td> + <td class="br" align="center">51</td> + <td class="brdoub" align="center">-0·0010</td> + <td class="br" align="center">67</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0005</span></td> + <td class="br" align="center">83</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0027</span></td></tr> +<tr><td class="blr" align="center">36</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0018</span></td> + <td class="br" align="center">52</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0009</span></td> + <td class="br" align="center">68</td> + <td class="brdoub" align="center">+0·0007</td> + <td class="br" align="center">84</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0029</span></td></tr> +<tr><td class="blr" align="center">37</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0017</span></td> + <td class="br" align="center">53</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0008</span></td> + <td class="br" align="center">69</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0008</span></td> + <td class="br" align="center">85</td> + <td class="br" align="center">+0·0031</td></tr> +<tr><td class="blr" align="center">38</td> + <td class="brdoub" align="center">-0·0017</td> + <td class="br" align="center">54</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0008</span></td> + <td class="br" align="center">70</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0009</span></td> + <td class="br" align="center">86</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0032</span></td></tr> +<tr><td class="blr" align="center">39</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0017</span></td> + <td class="br" align="center">55</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0007</span></td> + <td class="br" align="center">71</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0010</span></td> + <td class="br" align="center">87</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0034</span></td></tr> +<tr><td class="blr" align="center">40</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0016</span></td> + <td class="br" align="center">56</td> + <td class="brdoub" align="center">-0·0006</td> + <td class="br" align="center">72</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0012</span></td> + <td class="br" align="center">88</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0036</span></td></tr> +<tr><td class="blr" align="center">41</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0016</span></td> + <td class="br" align="center">57</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0005</span></td> + <td class="br" align="center">73</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0013</span></td> + <td class="br" align="center">89</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0037</span></td></tr> +<tr><td class="blr" align="center">42</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0015</span></td> + <td class="br" align="center">58</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0004</span></td> + <td class="br" align="center">74</td> + <td class="brdoub" align="center">+0·0014</td> + <td class="br" align="center">90</td> + <td class="br" align="center">+0·0039</td></tr> +<tr><td class="blr" align="center">43</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0015</span></td> + <td class="br" align="center">59</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0003</span></td> + <td class="br" align="center">75</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0016</span></td> + <td class="br" align="center">91</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0041</span></td></tr> +<tr><td class="blr" align="center">44</td> + <td class="brdoub" align="center">-0·0014</td> + <td class="br" align="center">60</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0002</span></td> + <td class="br" align="center">76</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0017</span></td> + <td class="br" align="center">92</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0042</span></td></tr> +<tr><td class="blr" align="center">45</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0014</span></td> + <td class="br" align="center">61</td> + <td class="brdoub" align="center">-0·0001</td> + <td class="br" align="center">77</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0018</span></td> + <td class="br" align="center">93</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0044</span></td></tr> +<tr><td class="blr" align="center">46</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0013</span></td> + <td class="br" align="center">62</td> + <td class="brdoub" align="center"><span style="margin-left: .25em;">0·0000</span></td> + <td class="br" align="center">78</td> + <td class="brdoub" align="center"><span style="margin-left: 1em;">·0020</span></td> + <td class="br" align="center">94</td> + <td class="br" align="center"><span style="margin-left: 1em;">·0046</span></td></tr> +<tr><td class="bblr" align="center">47</td> + <td class="bbrdoub" align="center">-0·0013</td> + <td class="bbr" align="center">63</td> + <td class="bbrdoub" align="center">+0·0001</td> + <td class="bbr" align="center">79</td> + <td class="bbrdoub" align="center">+0·0021</td> + <td class="bbr" align="center">95</td> + <td class="bbr" align="center">+0·0048</td></tr></table> + + +<p class="center"><br />158. NEWMAN’S SELF-REGISTERING TIDE-GAUGE.</p> + +<p>At places where the phenomena of the tides are of much maritime +importance, a continuous series of observations upon the rise and fall, +and times of change, is essentially necessary as a basis for the +construction of good tide tables; and as such observations should also be +accompanied with the registration of atmospheric phenomena, we have no +hesitation in inserting a description of an accurate self-registering +tide-gauge.</p> + +<p>The tide-gauge, as shown in the illustration, consists of a cylinder, <i>A</i>, +which is made to revolve on its axis once in twenty-four hours by the +action of the clock, <i>B</i>. A chain, to which is attached the float, <i>D</i>, +passes over the wheel, <i>C</i>, and on the axis of this wheel, <i>C</i> (in about +the middle of it) is a small toothed wheel, placed so as to be in contact +with a larger toothed wheel carrying a cylinder, <i>E</i>, over which passes +another smaller chain. This chain, passing along the upper surface of the +cylinder, <i>A</i>, and round a second cylinder, <i>F</i>, at its further end, is +acted on by a spring so as to be kept in a constant state of tension. In +the middle of this chain a small tube is fixed for carrying a pencil, +which, being gently pressed down by means of a small weight on the top of +it, performs the duty of marking on paper placed round the cylinder the +progress of the rise or fall of the tide as the cylinder revolves, and as +it is drawn by the chain forward or backward by the rise or fall of the +float. The paper is prepared with lines equidistant from each other, to +correspond with the hours of the clock, crossed by others showing the +number of feet of rise and fall.</p> + +<p><span class="pagenum"><a name="Page_144" id="Page_144">[Pg 144]</a></span></p> +<div class="figcenter"><img src="images/page_144tmb.jpg" alt="" /><br /> +<a href="images/page_144.jpg"><small>Larger Image</small></a></div> + +<p>The cylinder while in action revolves from left to right to a spectator +facing the clock, and the pencil is carried horizontally along the top of +the cylinder; and the large wheel being made to revolve by the rise and +fall of the float, turns the wheel<span class="pagenum"><a name="Page_145" id="Page_145">[Pg 145]</a></span> with the small cylinder, <i>E</i>, +attached to it. If the tide is <i>falling</i>, the small chain is wound round +the cylinder, <i>E</i>, and the pencil is drawn towards the large wheel; but if +the tide is <i>rising</i>, the small chain is wound on to the cylinder, <i>F</i>, by +means of the spring contained in it, which constantly keeps it in a state +of tension. Thus, by means of the rise and fall of the tide, a lateral +progress is given to the pencil, while the cylinder is made to revolve on +its axis by the clock, so that a line is traced on the paper showing the +exact state of the tide continuously, without further attention than is +necessary to change the paper once every day, and to keep the pencil +carefully pointed; or a metallic pencil may be used, which will require +little, if any, attention.</p> + +<p>A good self-registering tide-gauge is a valuable and important acquisition +wherever tidal observations are required, and the only perfectly efficient +instrument of this kind is that invented by the late Mr. John Newman, of +Regent Street, London. It is now in action in several parts of the world, +silently and <i>faithfully</i> performing its duty, requiring no other kind of +attention than that of a few minutes daily, and thus admitting the +employment of the person on any other service whose duty it would +otherwise have been to have registered the tide. It has done much by its +faithful records in contributing to the construction of good tide tables +for many places; for those unavoidable defects dependent on merely +watching the surface on a divided scale are set aside by it, all erroneous +conclusions excluded, and a true delineation of Nature’s own making is +preserved by it for the theorist.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_146" id="Page_146">[Pg 146]</a></span></p> +<h2>ADDENDA.</h2> + + +<p>1. French barometers are graduated to millimetres. An English inch is +equal to 25·39954 millimetres. Hence, 30 inches on the English barometer +scales correspond to 762 millimetres on the French barometer scales. +Conversions from one scale to another can be effected by the following +formulæ:—</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>(1) Inches = millimetres divided by</td><td><span class="spacer2"> </span></td><td>25·39954</td></tr> +<tr><td>(2) Millimetres = inches multiplied by</td><td> </td><td>25·39954</td></tr></table> + +<p>Of course, a table of equivalent values should be drawn up and employed, +when a large number of observations are to be converted from one scale to +the other.</p> + + +<p><br />2. In Germany, barometers are sometimes graduated with old French inches +and lines,—the vernier generally indicating the tenth of a line.</p> + +<p class="center"><span class="smcap">Old French Lineal Measure.</span></p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td colspan="4"> </td> + <td colspan="2" align="center"><small>English Inches.</small></td></tr> +<tr><td align="right">1</td> + <td>douzième, or point</td> + <td colspan="3"> </td> + <td><span style="margin-left: .5em;">0·0074</span></td></tr> +<tr><td align="right">12</td> + <td>points</td> + <td>=</td> + <td>1 ligne</td> + <td>=</td> + <td><span style="margin-left: .5em;">0·0888</span></td></tr> +<tr><td align="right">12</td> + <td>lignes</td> + <td>=</td> + <td>1 pouce</td> + <td>=</td> + <td><span style="margin-left: .5em;">1·065765</span></td></tr> +<tr><td align="right">12</td> + <td>pouces</td> + <td>=</td> + <td>1 pied</td> + <td>=</td> + <td>12·7892</td></tr> +<tr><td align="right">1</td> + <td>pied</td> + <td>=</td> + <td>324·7 millimetres.</td></tr></table> + +<p>“The Germans indicate inches by putting two accents after the number; +lines, by putting three accents; 27″ 3′″·85, means 27 inches 3 lines 85 +hundredths of a line; more frequently, they give the height in lines, and +the preceding number becomes 327′″·85.”—<i>Kaemtz.</i></p> + + +<p><br />3. <i>Rule for finding Diameter of Bore of a Barometer Tube.</i></p> + +<p>“If the maker has not taken care to measure the interior diameter +directly, it may be deduced from the exterior diameter. The exterior +diameter is first measured by calipers, and, by deducting from this +diameter 0·1 of an inch for tubes from ·3 to ·5 of an inch in external +diameter, we have an approximation to the interior diameter of the +tube.”—<i>Kaemtz.</i></p> + + +<p><br /><span class="pagenum"><a name="Page_147" id="Page_147">[Pg 147]</a></span>4. <span class="smcap">Wind Scales.</span></p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td colspan="3" align="center" class="botbor">Sea Scale.</td><td><span class="spacer"> </span></td><td> </td><td><span class="spacer"> </span></td> + <td align="center" class="botbor">Wind.</td><td><span class="spacer"> </span></td><td> </td><td><span class="spacer"> </span></td> + <td colspan="3" align="center" class="botbor">Land Scale.</td></tr> +<tr><td><span style="margin-left: .5em;">0</span></td><td align="center">to</td><td><span style="margin-left: .5em;">3</span></td><td> </td> + <td>=</td><td> </td> + <td align="center">Light</td><td> </td> + <td>=</td><td> </td> + <td align="right">0</td><td align="center">to</td><td>1</td></tr> +<tr><td><span style="margin-left: .5em;">3</span></td><td align="center">"</td><td><span style="margin-left: .5em;">5</span></td><td> </td> + <td>=</td><td> </td> + <td align="center">Moderate</td><td> </td> + <td>=</td><td> </td> + <td align="right">1</td><td align="center">"</td><td>2</td></tr> +<tr><td><span style="margin-left: .5em;">5</span></td><td align="center">"</td><td><span style="margin-left: .5em;">7</span></td><td> </td> + <td>=</td><td> </td> + <td align="center">Fresh</td><td> </td> + <td>=</td><td> </td> + <td align="right">2</td><td align="center">"</td><td>3</td></tr> +<tr><td><span style="margin-left: .5em;">7</span></td><td align="center">"</td><td><span style="margin-left: .5em;">8</span></td><td> </td> + <td>=</td><td> </td> + <td align="center">Strong</td><td> </td> + <td>=</td><td> </td> + <td align="right">3</td><td align="center">"</td><td>4</td></tr> +<tr><td><span style="margin-left: .5em;">8</span></td><td align="center">"</td><td>10</td><td> </td> + <td>=</td><td> </td> + <td align="center">Heavy</td><td> </td> + <td>=</td><td> </td> + <td align="right">4</td><td align="center">"</td><td>5</td></tr> +<tr><td>10</td><td align="center">"</td><td>12</td><td> </td> + <td>=</td><td> </td> + <td align="center">Violent</td><td> </td> + <td>=</td><td> </td> + <td align="right">5</td><td align="center">"</td><td>6</td></tr> +<tr><td> </td></tr> +<tr><td colspan="3" align="center" class="botbor">Pressure<br />in Pounds<br />(Avoirdupois)</td><td colspan="3"> </td> + <td align="center" class="botbor">(Land Scale).</td><td colspan="3"> </td> + <td colspan="3" align="center" class="botbor">Velocity in<br />Miles<br />(Hourly).</td></tr> +<tr><td colspan="3" align="center"><span style="margin-left: .5em;">½</span></td><td> </td> + <td>=</td><td> </td> + <td align="center">1</td><td> </td> + <td>=</td><td> </td> + <td colspan="3" align="center">10</td></tr> +<tr><td colspan="3" align="center"><span style="margin-left: .5em;">5</span></td><td> </td> + <td>=</td><td> </td> + <td align="center">2</td><td> </td> + <td>=</td><td> </td> + <td colspan="3" align="center">32</td></tr> +<tr><td colspan="3" align="center">10</td><td> </td> + <td>=</td><td> </td> + <td align="center">3</td><td> </td> + <td>=</td><td> </td> + <td colspan="3" align="center">45</td></tr> +<tr><td colspan="3" align="center">21</td><td> </td> + <td>=</td><td> </td> + <td align="center">4</td><td> </td> + <td>=</td><td> </td> + <td colspan="3" align="center">65</td></tr> +<tr><td colspan="3" align="center">26</td><td> </td> + <td>=</td><td> </td> + <td align="center">5</td><td> </td> + <td>=</td><td> </td> + <td colspan="3" align="center">72</td></tr> +<tr><td colspan="3" align="center">32</td><td> </td> + <td>=</td><td> </td> + <td align="center">6</td><td> </td> + <td>=</td><td> </td> + <td colspan="3" align="center">80</td></tr></table> + + +<p><br />5. Letters to Denote the State of the Weather.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td><i>b</i></td><td>denotes</td><td>blue sky, whether with clear or hazy atmosphere.</td></tr> +<tr><td><i>c</i></td><td align="center">"</td><td>cloudy, that is detached opening clouds.</td></tr> +<tr><td><i>d</i></td><td align="center">"</td><td>drizzling rain.</td></tr> +<tr><td><i>f</i></td><td align="center">"</td><td>fog.</td></tr> +<tr><td><i>h</i></td><td align="center">"</td><td>hail.</td></tr> +<tr><td><i>l</i></td><td align="center">"</td><td>lightning.</td></tr> +<tr><td><i>m</i></td><td align="center">"</td><td>misty, or hazy so as to interrupt the view.</td></tr> +<tr><td><i>o</i></td><td align="center">"</td><td>overcast, gloomy, dull.</td></tr> +<tr><td><i>p</i></td><td align="center">"</td><td>passing showers.</td></tr> +<tr><td><i>q</i></td><td align="center">"</td><td>squally.</td></tr> +<tr><td><i>r</i></td><td align="center">"</td><td>rain.</td></tr> +<tr><td><i>s</i></td><td align="center">"</td><td>snow.</td></tr> +<tr><td><i>t</i></td><td align="center">"</td><td>thunder.</td></tr> +<tr><td><i>u</i></td><td align="center">"</td><td>ugly, threatening appearance of sky.</td></tr> +<tr><td><i>v</i></td><td align="center">"</td><td>unusual visibility of distant objects.</td></tr> +<tr><td><i>w</i></td><td align="center">"</td><td>wet, that is dew.</td></tr></table> + +<p>A letter repeated denotes much, as <i>r r</i>, heavy rain; <i>f f</i>, dense fog; + +and a figure attached denotes duration in hours, as 14 <i>r</i>, 14 hours rain.</p> + +<p>By the combination of these letters, all the ordinary phenomena of the +weather may be recorded with certainty and brevity.</p> + +<p><span class="smcap">Examples.</span>—<i>b c</i>, blue sky with less proportion of cloud. 2 <i>r r l l t</i>, +heavy rain for two hours, with much lightning, and some thunder.</p> + +<p>The above methods of recording the force of wind and state of weather +were<span class="pagenum"><a name="Page_148" id="Page_148">[Pg 148]</a></span> originally proposed by Admiral Sir Francis Beaufort. They are now in +general use at sea, and by many observers on land.</p> + + +<p><br />6. Table of Expansion by Heat from 32° to 212° F.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>Platinum</td><td><span class="spacer"> </span></td> + <td>0·0008842</td> + <td>of the length.</td></tr> +<tr><td>Glass, Flint</td><td> </td> + <td>0·0008117</td> + <td><span style="margin-left: 2em;">"</span></td></tr> +<tr><td><span style="margin-left: 1em;">"</span><span style="margin-left: 1.3em;">with Lead</span></td><td> </td> + <td>0·0008622</td> + <td><span style="margin-left: 2em;">"</span></td></tr> +<tr><td>Brass</td><td> </td> + <td>0·0018708</td> + <td><span style="margin-left: 2em;">"</span></td></tr> +<tr><td>Mercury</td><td> </td> + <td>0·0180180</td> + <td><span style="margin-left: 2em;">"</span></td></tr> +<tr><td>Water</td><td> </td> + <td>0·0433200,</td> + <td>from 39° to 212°</td></tr> +<tr><td>Alcohol</td><td> </td> + <td>0·1100</td> + <td><span style="margin-left: 1em;">"</span><span style="margin-left: .8em;">32° to 174°</span></td></tr> +<tr><td>Nitric Acid</td><td> </td> + <td>0·1100</td></tr> +<tr><td>Sulphuric Acid</td><td> </td> + <td>0·0600</td></tr></table> + + +<p><br />7. Table of Specific Gravity of Bodies at 32° F. except water, which is +taken at 39°·4.</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td>Water</td><td><span class="spacer"> </span></td> + <td colspan="2"> </td> + <td><span style="margin-left: .5em;">1·000</span></td></tr> +<tr><td>Alcohol, pure</td><td> </td> + <td colspan="2"> </td> + <td><span style="margin-left: .5em;">0·791</span></td></tr> +<tr><td><span style="margin-left: 1.5em;">"</span><span style="margin-left: 1.5em;">proof</span></td><td> </td> + <td colspan="2"> </td> + <td><span style="margin-left: .5em;">0·916</span></td></tr> +<tr><td>Mercury</td><td> </td> + <td colspan="2"> </td> + <td>13·596</td></tr> +<tr><td>Glass</td><td> </td> + <td><span style="margin-left: 1em;">3</span></td><td>to</td><td><span style="margin-left: .5em;">2·7</span></td></tr> +<tr><td>Brass</td><td> </td> + <td>7·8</td><td>to</td><td><span style="margin-left: .5em;">8·54</span></td></tr> +<tr><td>Platinum</td><td> </td> + <td>21</td><td>to</td><td>22·00</td></tr></table> + +<p>Weight of a cubic foot of water, at the temperature of comparison, 62·425 +lbs. avoirdupois.</p> + +<p>The pound avoirdupois contains 7,000 grains.</p> + +<p>Air is 813·67 times lighter than water.</p> + +<p>The linear expansions are the mean values of the results of various +experimentalists. The specific gravities are as given in Professor +Rankine’s <i>Applied Mechanics</i>.</p> + + +<p><br />8. Important Temperatures. Under the circumstances of—</p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td colspan="4"> </td><td align="center">°</td></tr> +<tr><td>Water</td><td><span class="spacer2"> </span></td> + <td align="center">boiling at</td><td><span class="spacer"> </span></td> + <td align="right">212</td></tr> +<tr><td>Mercury</td><td> </td> + <td align="center">boils at</td><td> </td> + <td align="right">660</td></tr> +<tr><td>Sulphuric Acid</td><td> </td> + <td align="center">"</td><td> </td> + <td align="right">590</td></tr> +<tr><td>Oil of Turpentine</td><td> </td> + <td align="center">"</td><td> </td> + <td align="right">560</td></tr> +<tr><td>Nitric Acid</td><td> </td> + <td align="center">"</td><td> </td> + <td align="right">242</td></tr> +<tr><td>Alcohol</td><td> </td> + <td align="center">"</td><td> </td> + <td align="right">174</td></tr> +<tr><td>A Saturated Solution of Salt</td><td> </td> + <td align="center">"</td><td> </td> + <td align="right">218</td></tr> +<tr><td>Vital Heat</td> + <td colspan="3"> </td> + <td align="right">96</td></tr> +<tr><td>Olive Oil begins to solidify</td> + <td colspan="3"> </td> + <td align="right">36</td></tr> +<tr><td>Fresh Water freezes</td> + <td colspan="3"> </td> + <td align="right">32</td></tr> +<tr><td>Sea Water freezes</td> + <td colspan="3"> </td> + <td align="right">28</td></tr> +<tr><td>Mercury freezes</td> + <td colspan="3"> </td> + <td align="right">-39</td></tr></table> + + +<p class="center"><br /><span class="pagenum"><a name="Page_149" id="Page_149">[Pg 149]</a></span> +9. TABLE OF METEOROLOGICAL ELEMENTS, FORMING EXPONENTS OF THE CLIMATE OF LONDON.</p> + +<table border="0" cellpadding="0" cellspacing="0" summary="table"> +<tr><td align="center" class="btlr">1841<br />to<br />1861.<br /><br />Months.</td> + <td align="center" class="btr">Mean<br />Height of<br />Barometer,<br />reduced<br />to 32° F.,<br />at the mean<br />sea-level.</td> + <td align="center" class="btr">Mean<br />Monthly<br />Range of<br />Barometer.</td> + <td align="center" class="btr">Mean<br />of all the<br />Highest<br />Temp’s.</td> + <td align="center" class="btr">Mean<br />of all the<br />Lowest<br />Temp’s.</td> + <td align="center" class="btr">Mean<br />Temp.</td> + <td align="center" class="btr">Mean<br />Temp.<br />of Dew-point.</td> + <td align="center" class="btr">Mean<br />Degree of<br />Humidity.</td> + <td align="center" class="btr">Mean<br />Number of<br />Rainy Days.</td> + <td align="center" class="btr">Average<br />Rainfall.</td> + <td align="center" class="btr">Average<br />Amount<br />of Cloud<br />(10=<br />overcast).</td> + <td align="center" class="btr">Prevalent<br />Winds.</td> + <td align="center" class="btr">Sun<br />above the<br />Horizon on Middle<br />Day.</td> + <td align="center" class="btr"><span class="smcap">Remarks.</span></td></tr> +<tr><td class="btlr"> </td> + <td align="center" class="btr">Inches.</td> + <td align="center" class="btr">Inches.</td> + <td align="center" class="btr">°</td> + <td align="center" class="btr">°</td> + <td align="center" class="btr">°</td> + <td align="center" class="btr">°</td> + <td class="btr"> </td> + <td class="btr"> </td> + <td align="center" class="btr">Inches.</td> + <td class="btr"> </td> + <td class="btr"> </td> + <td align="center" class="btr">Hours.</td> + <td class="btr"> </td></tr> +<tr><td class="blr">Jan.</td> + <td class="br" align="center">29·932</td> + <td class="br" align="center">1·44</td> + <td class="br" align="center">43·2</td> + <td class="br" align="center">33·7</td> + <td class="br" align="center">38·3</td> + <td class="br" align="center">35·4</td> + <td class="br" align="center">89</td> + <td class="br" align="center">11</td> + <td class="br" align="center">1·8</td> + <td class="br" align="center">7·7</td> + <td class="br" align="center">W. to N.</td> + <td class="br" align="center">8½</td> + <td class="br">The majority of the nights are frosty.</td></tr> +<tr><td class="blr"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="blr">Feb.</td> + <td class="br" align="center">29·962</td> + <td class="br" align="center">1·22</td> + <td class="br" align="center">44·7</td> + <td class="br" align="center">33·2</td> + <td class="br" align="center">38·4</td> + <td class="br" align="center">34·4</td> + <td class="br" align="center">85</td> + <td class="br" align="center">10</td> + <td class="br" align="center">1·6</td> + <td class="br" align="center">7·4</td> + <td class="br" align="center">S. to W.</td> + <td class="br" align="center">10</td> + <td class="br">10 frosty nights on the average.</td></tr> +<tr><td class="blr"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="blr">Mar.</td> + <td class="br" align="center">29·967</td> + <td class="br" align="center">1·23</td> + <td class="br" align="center">50·0</td> + <td class="br" align="center">35·3</td> + <td class="br" align="center">41·7</td> + <td class="br" align="center">36·4</td> + <td class="br" align="center">82</td> + <td class="br" align="center">10</td> + <td class="br" align="center">1·5</td> + <td class="br" align="center">6·6</td> + <td class="br" align="center">N. to E.</td> + <td class="br" align="center">12</td> + <td class="br">12 frosty nights on the average.<br />Strong winds.</td></tr> +<tr><td class="blr"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="blr">Apr.</td> + <td class="br" align="center">29·907</td> + <td class="br" align="center">1·06</td> + <td class="br" align="center">56·8</td> + <td class="br" align="center">38·6</td> + <td class="br" align="center">46·3</td> + <td class="br" align="center">39·9</td> + <td class="br" align="center">79</td> + <td class="br" align="center">11</td> + <td class="br" align="center">1·8</td> + <td class="br" align="center">6·1</td> + <td class="br" align="center">N. to E.</td> + <td class="br" align="center">14</td> + <td class="br">6 frosty nights on the average.</td></tr> +<tr><td class="blr"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="blr">May</td> + <td class="br" align="center">29·931</td> + <td class="br" align="center">1·02</td> + <td class="br" align="center">64·4</td> + <td class="br" align="center">44·2</td> + <td class="br" align="center">52·8</td> + <td class="br" align="center">45·5</td> + <td class="br" align="center">76</td> + <td class="br" align="center">11</td> + <td class="br" align="center">2·1</td> + <td class="br" align="center">6·1</td> + <td class="br" align="center">S. to W.</td> + <td class="br" align="center">15½</td> + <td class="br">Very rarely frost.</td></tr> +<tr><td class="blr"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="blr">June</td> + <td class="br" align="center">29·960</td> + <td class="br" align="center">0·89</td> + <td class="br" align="center">71·2</td> + <td class="br" align="center">50·2</td> + <td class="br" align="center">59·2</td> + <td class="br" align="center">50·8</td> + <td class="br" align="center">74</td> + <td class="br" align="center">11</td> + <td class="br" align="center">1·9</td> + <td class="br" align="center">6·1</td> + <td class="br" align="center">W. to N.</td> + <td class="br" align="center">16½</td> + <td class="br">Sun attains greatest North Declination, 21st.</td></tr> +<tr><td class="blr"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="blr">July</td> + <td class="br" align="center">29·970</td> + <td class="br" align="center">0·79</td> + <td class="br" align="center">73·8</td> + <td class="br" align="center">53·2</td> + <td class="br" align="center">61·9</td> + <td class="br" align="center">53·9</td> + <td class="br" align="center">76</td> + <td class="br" align="center">11</td> + <td class="br" align="center">2·7</td> + <td class="br" align="center">6·9</td> + <td class="br" align="center">W. to N.</td> + <td class="br" align="center">16</td> + <td class="br"> </td></tr> +<tr><td class="blr"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="blr">Aug.</td> + <td class="br" align="center">29·954</td> + <td class="br" align="center">0·97</td> + <td class="br" align="center">72·8</td> + <td class="br" align="center">53·4</td> + <td class="br" align="center">61·3</td> + <td class="br" align="center">54·1</td> + <td class="br" align="center">77</td> + <td class="br" align="center">11</td> + <td class="br" align="center">2·4</td> + <td class="br" align="center">6·5</td> + <td class="br" align="center">W. to N.</td> + <td class="br" align="center">14½</td> + <td class="br"> </td></tr> +<tr><td class="blr"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="blr">Sept.</td> + <td class="br" align="center">29·997</td> + <td class="br" align="center">0·95</td> + <td class="br" align="center">67·4</td> + <td class="br" align="center">48·9</td> + <td class="br" align="center">56·9</td> + <td class="br" align="center">51·1</td> + <td class="br" align="center">81</td> + <td class="br" align="center">12</td> + <td class="br" align="center">2·4</td> + <td class="br" align="center">5·9</td> + <td class="br" align="center">S. to W.</td> + <td class="br" align="center">12½</td> + <td class="br"> </td></tr> +<tr><td class="blr"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="blr">Oct.</td> + <td class="br" align="center">29·860</td> + <td class="br" align="center">1·33</td> + <td class="br" align="center">58·3</td> + <td class="br" align="center">43·7</td> + <td class="br" align="center">50·2</td> + <td class="br" align="center">46·0</td> + <td class="br" align="center">87</td> + <td class="br" align="center">13</td> + <td class="br" align="center">2·8</td> + <td class="br" align="center">6·9</td> + <td class="br" align="center">S. to W.</td> + <td class="br" align="center">10½</td> + <td class="br">A few frosty nights.<br />Heavy gales.</td></tr> +<tr><td class="blr"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="blr">Nov.</td> + <td class="br" align="center">29·929</td> + <td class="br" align="center">1·53</td> + <td class="br" align="center">49·3</td> + <td class="br" align="center">37·7</td> + <td class="br" align="center">43·4</td> + <td class="br" align="center">40·1</td> + <td class="br" align="center">89</td> + <td class="br" align="center">12</td> + <td class="br" align="center">2·4</td> + <td class="br" align="center">7·2</td> + <td class="br" align="center">S.W.</td> + <td class="br" align="center">9</td> + <td class="br">11 nights frosty.</td></tr> +<tr><td class="blr"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td> + <td class="br"> </td></tr> +<tr><td class="blr">Dec.</td> + <td class="br" align="center">29·979</td> + <td class="br" align="center">1·52</td> + <td class="br" align="center">45·0</td> + <td class="br" align="center">35·5</td> + <td class="br" align="center">40·1</td> + <td class="br" align="center">36·9</td> + <td class="br" align="center">89</td> + <td class="br" align="center">12</td> + <td class="br" align="center">1·9</td> + <td class="br" align="center">7·4</td> + <td class="br" align="center">W.</td> + <td class="br" align="center">8</td> + <td class="br">Sun attains greatest South Declination, 21st.</td></tr> +<tr><td class="btlr">Year</td> + <td class="btr" align="center">29·946</td> + <td class="btr" align="center">1·16</td> + <td class="btr" align="center">58·0</td> + <td class="btr" align="center">42·3</td> + <td class="btr" align="center">49·2</td> + <td class="btr" align="center">43·7</td> + <td class="btr" align="center">82</td> + <td class="btr" align="center">133</td> + <td class="btr" align="center">25·3</td> + <td class="btr" align="center">6·7</td> + <td class="btr" align="center">...</td> + <td class="btr" align="center">...</td> + <td class="btr"> </td></tr> +<tr><td class="bbtl"> </td> + <td class="bbt" align="center">1</td> + <td class="bbt" align="center">2</td> + <td class="bbt" align="center">3</td> + <td class="bbt" align="center">4</td> + <td class="bbt" align="center">5</td> + <td class="bbt" align="center">6</td> + <td class="bbt" align="center">7</td> + <td class="bbt" align="center">8</td> + <td class="bbt" align="center">9</td> + <td class="bbt" align="center">10</td> + <td class="bbt" align="center">11</td> + <td class="bbt" align="center">12</td> + <td class="bbtr" align="center">13</td></tr></table> + +<p><span class="pagenum"><a name="Page_150" id="Page_150">[Pg 150]</a></span>In the above Table, columns 1 to 10 are results obtained at the Royal +Observatory, Greenwich, by J. Glaisher, Esq., F.R.S. The data contained in +columns 2 and 10, are deduced from observations extending over the years +1841 to 1855 inclusive, and are copied from Edward Hughes’ <i>Third Reading +Book</i>; the other columns are results of observations made during the +twenty years ending 1861. The rest of the information is from Luke +Howard’s <i>Climate of London</i>.</p> + +<p>These valuable data indicate the characteristics of the weather in each +month in the suburbs of London, and will be found tolerably accurate as +indications of weather, and serviceable as standards for comparisons of +observed results, at most places in England.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_151" id="Page_151">[Pg 151]</a></span></p> +<p class="center"><span class="huge">STANDARD WORKS ON METEOROLOGY</span></p> +<p class="center">SUPPLIED BY NEGRETTI & ZAMBRA.</p> +<p> </p> + +<p class="center">THE WEATHER BOOK:<br /> +A MANUAL OF PRACTICAL METEOROLOGY.<br /> +By Vice-Admiral <span class="smcap">FitzRoy</span>, F.R.S., M.I.F., &c.<br /> +<i>Price</i>, £0 15 6</p> + +<p class="center">THE LAW OF STORMS,<br /> +By <span class="smcap">H. W. Dove</span>, F.R.S.<br /> +Translated by <span class="smcap">R. H. Scott</span>, M.A.<br /> +<i>Price</i>, £0 10 6</p> + +<p class="center">L. F. KÆMTZ’S “COMPLETE COURSE OF METEOROLOGY,”<br /> +Translated by <span class="smcap">C. V. Walker</span>, Esq.<br /> +<i>Price</i>, £0 12 6</p> + +<p class="center">PRACTICAL METEOROLOGY,<br /> +By <span class="smcap">John Drew</span>, Ph.D., F.R.A.S.<br /> +<i>Price</i>, £0 5 0</p> + +<p class="center">HYGROMETRICAL TABLES,<br /> +Adapted to the use of the Wet and Dry Bulb Thermometer,<br /> +By <span class="smcap">James Glaisher</span>, Esq., F.R.S.<br /> +<i>Price</i>, £0 2 6</p> + +<p class="center">TABLES OF THE CORRECTIONS FOR TEMPERATURES,<br /> +To reduce observations to the 32° Fahrenheit, for Barometers with brass scales<br /> +extending from the cistern to the top of the mercurial column,<br /> +By <span class="smcap">James Glaisher</span>, Esq., F.R.S.<br /> +<i>Price</i>, £0 1 0</p> + +<p class="center"><span class="pagenum"><a name="Page_152" id="Page_152">[Pg 152]</a></span>TABLE OF THE DIURNAL RANGE OF THE BAROMETER,<br /> +By <span class="smcap">James Glaisher</span>, Esq., F.R.S.<br /> +<i>Price</i>, £0 0 6</p> + +<p class="center">TABLES FOR CALCULATION OF HEIGHTS FROM OBSERVATIONS<br /> +ON THE BOILING-POINT OF WATER,<br /> +Adapted to the use of Negretti and Zambra’s Boiling-point Apparatus.<br /> +<i>Price</i>, £0 1 0</p> + +<p class="center">A THERMOMETRICAL TABLE,<br /> +ON THE SCALES OF FAHRENHEIT, REAUMUR, AND CENTIGRADE,<br /> +By <span class="smcap">Alfred S. Taylor</span>, Esq., M.D., &c.<br /> +<i>Price</i>, in Sheet, with explanatory Pamphlet, £0 1 6</p> + +<p class="center">METEOROLOGICAL TABLES,<br /> +For the reduction of Barometrical and Hygrometrical Observations, Determination<br /> +of Heights by the Barometer and Boiling-point Thermometer, &c.<br /> +By <span class="smcap">G. Harvey Simmonds</span>, M.B.M.S.<br /> +<i>Price</i>, £0 2 6</p> + +<p class="center">BAROMETER MANUAL,<br /> +Compiled by Vice-Admiral <span class="smcap">FitzRoy</span>, F.R.S.,<br /> +For the Board of Trade.<br /> +<i>Price</i>, £0 0 6</p> + +<p class="center">POCKET METEOROLOGICAL REGISTER AND NOTE-BOOK,<br /> +With Diagrams for exhibiting the Fluctuations of Barometer, &c.<br /> +Printed on metallic paper. <i>Price</i>, with Pencil, £0 3 0</p> + +<p class="center">LONDON:<br /> +PRINTED BY STRAHAN AND WILLIAMS,<br /> +7 LAWRENCE LAND, CHEAPSIDE, E.C.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_153" id="Page_153">[Pg 153]</a></span></p> +<p class="center"><span class="large">NEGRETTI & ZAMBRA’S</span><br /> +<span class="huge">PATENT RECORDING AND DEEP-SEA THERMOMETER.</span><small><a name="f20.1" id="f20.1" href="#f20">[20]</a></small></p> + + +<p>This Thermometer differs from all other Registering or Recording +Thermometers in the following important particulars:—</p> + +<p>I. The Thermometer contains only Mercury without any admixture of Alcohol +or other fluid.</p> + +<p>II. It has no indices or springs, and its indications are by the column of +Mercury only.</p> + +<p>III. It can be carried in any position, and cannot possibly be put out of +order except by actual breakage of the instrument.</p> + +<p>And lastly, it will indicate and record the exact temperature at any hour +of the day or night, or the exact temperature at any depth of the sea, +irrespective of either warm or cold currents, or stratum through which the +Thermometer may have to pass in its descent or ascent, this last very +special quality renders this Thermometer superior for deep-sea +temperatures to any others; for those now being used in the “Challenger” +sounding expedition are liable to give erroneous indications owing to +their indices slipping, and otherwise getting deranged—(This was proved +by Messrs. Negretti and Zambra at a Meeting of the British Meteorological +Society,) and <i>under certain conditions of temperature</i> it is not possible +by the old Thermometers to obtain true temperatures at certain depths +which might be required. <i>Annexed is a copy of a report to the Admiralty +from Captain G. S. Nares, of H.M.S. “Challenger,” dated Melbourne, March +25th, 1874, which we have taken from</i> <span class="smcap">Nature</span>, <i>July 30th, 1874, proving +the assertion.</i></p> + +<p>“In the report to the Admiralty of Capt. G. S. Nares, of H.M.S. +<i>Challenger</i> dated Melbourne, March 25, 1874, Capt. Nares, speaking of the +temperature of the ocean, especially near the pack edge of the ice, +says:—‘At a short distance from the pack, the surface water rose to 32°, +but at a depth of 40 fathoms we always found the temperature to be 29°; +this continued to 300 fathoms, the depth in which most of the icebergs +float, after which there is a stratum of slightly warmer water of 33° or +34°. As the thermometers had to pass through these two belts of water +before reaching the bottom, the indices registered those temperatures, and +it was impossible to obtain the exact temperature of the bottom whilst +near the ice, but the observations made in lower latitudes show that it is +about 31°. More exact results could not have been obtained even had Mr. +Siemens’s apparatus been on board.’ It seems to us that the difficulty +mentioned is one which would certainly have been surmounted by Messrs. +Negretti and Zambra’s new Recording Thermometers, a description of which +appeared in <span class="smcap">Nature</span>, vol. ix. p. 387; this being exactly one of the cases +to which this instrument is peculiarly adapted. We believe the inventors +and makers have greatly improved their Thermometer since our description +appeared, and no doubt means will be taken by the Admiralty to transmit +one to the <i>Challenger</i>.”</p> + +<div class="figright"><img src="images/ad_fig_1.jpg" alt="" /><br />Fig. 1.</div> + +<p class="center"><br /><span class="large">DESCRIPTION OF THE DEEP-SEA RECORDING THERMOMETER.</span></p> + +<p>In the first place, it must be observed that the bulb of the Thermometer +is protected so as to resist the pressure of the ocean, which varies +according to depth that of three thousand fathoms being something like +three tons pressure on the square inch. The manner of protecting the bulb +was invented by Messrs. Negretti and Zambra in 1857, and has been latterly +copied by other persons and brought out as a new invention. The manner of +protecting the bulb has been described by<span class="pagenum"><a name="Page_154" id="Page_154">[Pg 154]</a></span> the late Admiral R. FitzRoy, in +the first number of Meteorological Papers, page 55, published July 5th, +1857, as follows:</p> + +<p class="blockquot">“Referring to the erroneous readings of all thermometers, consequent +on their delicate bulbs being compressed by the great pressure of the +ocean, he says:—‘With a view to obviate this failing, Messrs. +Negretti and Zambra undertook to make a case for the weak bulbs, which +should transmit temperature, but resist pressure. Accordingly a tube +of thick glass is sealed outside the delicate bulb, between which and +the casing is a space all round, which is nearly filled with mercury. +The small space not so filled is a vacuum, into which the mercury can +be expanded, or forced by heat or mechanical compression, without +doing injury to or even compressing the inner or much more delicate +bulb.’”</p> + +<p>The construction of this instrument for deep-sea temperatures is as +follows:—</p> + +<div class="figleft"><img src="images/ad_fig_2.jpg" alt="" /><br />Fig. 2.</div> + +<p class="blockquot">In shape it is like a syphon with parallel legs, all in one piece and +having a continuous communication, as in the annexed figure. The scale +of the Thermometer is pivoted on a centre and being attached in a +perpendicular position to a simple apparatus (which will be presently +described), is lowered to any depth that may be desired. In its +descent the Thermometer acts as an ordinary instrument, the mercury +rising or falling according to the temperature of the stratum through +which it passes; but so soon as the descent ceases, and a reverse +motion is given to the line, so as to pull the Thermometer towards the +surface, the instrument turns once on its centre, first bulb +uppermost, and afterwards bulb downwards. This causes the mercury, +which was in the left-hand column, first to pass into the dilated +syphon bend at the top, and thence into the right-hand tube, where it +remains, indicating on a graduated scale the exact temperature at the +time it was turned over. The woodcut, Fig. 1, shows the position of +the mercury <i>after</i> the instrument has been thus turned on its centre. +A is the bulb; B the outer coating or protecting cylinder; C is the +space of rarefied air, which is reduced if the outer casing be +compressed; D is a small glass plug on the principle of Negretti and +Zambra’s Patent Maximum Thermometer, which cuts off, in the moment of +turning, the mercury in the tube from that of the bulb, thereby +ensuring that none but the mercury in the tube can be transferred into +the indicating column; E is an enlargement made in the bend so as to +enable the mercury to pass quickly from one tube to another in +revolving; and F is the indicating tube or Thermometer proper. In its +action, as soon as the Thermometer is put in motion, and immediately +the tube has acquired a slightly oblique position, the mercury breaks +off at the point D, runs into the curved and enlarged portion E, and +eventually falls into the tube F when this tube resumes its original +perpendicular position.</p> + +<div class="figright"><img src="images/ad_fig_3.jpg" alt="" /><br />Fig. 3.</div> + +<p><span class="pagenum"><a name="Page_155" id="Page_155">[Pg 155]</a></span>The contrivance for turning the Thermometer over may be described as a +frame with a vertical propeller; to this frame the instrument is pivoted. +On its descent through the water the propeller is lifted out of gear and +revolves freely on its axis; but so soon as the instrument is pulled +towards the surface the propeller falls into gear and revolves in the +contrary direction, turning the Thermometer over once, and then becoming +locked and immovable.</p> + +<div class="blockquot"> +<p><i>Directions for adjusting the Thermometer previous to its being lowered in +the Sea.</i></p> + +<p>I. The mercury must all be in the left-hand column.</p> + +<p>II. The short peg at the back of the thermometer must be in front of +the stop plate S +; in order to effect this, pull the knob which stops +the Thermometer, and slightly turn the propeller, to make the +Thermometer advance sufficiently to escape the stop plate.</p></div> + +<p>Negretti & Zambra’s Patent Atmospheric Recording Thermometer, Fig. 3, +differs from the Deep-sea Thermometer by its not having the double or +protected bulb, it not being required for resisting pressures. In this +case the instrument is turned over by a simple clock movement, which can +be set to any hour it may be desirable; the Thermometer is fixed on the +clock, and when the hand arrives at the hour determined upon, and to which +the clock is set as in setting an alarum clock, a spring is released and +the Thermometer turns over as before described.</p> + +<p>Messrs. Negretti and Zambra have arranged a Wet and Dry Bulb Hygrometer +upon the same plan.</p> + + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><span class="pagenum"><a name="Page_156" id="Page_156">[Pg 156]</a></span></p> + +<p class="center"><span class="huge">NEGRETTI & ZAMBRA’S</span></p> +<p class="center"><span class="large">PRICE LIST</span></p> +<p class="center">OF</p> +<p class="center"><span class="giant">STANDARD METEOROLOGICAL</span></p> +<p class="center">AND OTHER</p> +<p class="center"><span class="huge">PHILOSOPHICAL INSTRUMENTS.</span></p> + +<p><i>The marginal figures in this List and the numbers of the wood engravings +refer to paragraphs in “Negretti & Zambra’s Treatise on Meteorological +Instruments.”</i></p> + +<table border="0" cellpadding="0" cellspacing="5" summary="table"> +<tr><td> </td> + <td> </td> + <td colspan="4"> </td> + <td align="center">£</td> + <td align="center">s.</td> + <td align="center">d.</td></tr> +<tr><td align="right">4</td> + <td><b>Standard Barometers</b>, Fortin’s arrangement, as Fig. 3 with mahogany board</td> + <td colspan="4"> </td> + <td align="right">8</td> + <td align="right">8</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto ditto with Millemetre and English scales</td> + <td colspan="4"> </td> + <td align="right">9</td> + <td align="right">9</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto ditto with tube, 0·45 internal diameter and millimetre scale</td> + <td colspan="4"> </td> + <td align="right">10</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td><b>Observatory Standard Barometers</b>, extra large tubes and cisterns</td> + <td align="right">£25</td> + <td align="right">0</td> + <td align="right">0</td> + <td><span class="spacer2"> </span></td> + <td align="right">35</td> + <td align="right">0</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto ditto arranged for observations being taken by the Cathetometer</td> + <td colspan="4"> </td> + <td align="right">18</td> + <td align="right">18</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td><b>Cathetometer</b>, for use with above</td> + <td colspan="4"> </td> + <td align="right">21</td> + <td align="right">0</td> + <td align="right">0</td></tr> +<tr><td align="right">9</td> + <td><b>Self Compensating Standard Barometer</b>, Fig. 6</td> + <td colspan="4"> </td> + <td align="right">20</td> + <td align="right">0</td> + <td align="right">0</td></tr> +<tr><td align="right">10</td> + <td><b>Standard Barometer</b>, with electrical adjustment</td> + <td colspan="4"> </td> + <td align="right">15</td> + <td align="right">15</td> + <td align="right">0</td></tr> +<tr><td align="right">11</td> + <td><b>Pediment Barometers</b>, Fig 7</td> + <td align="right">£1</td> + <td align="right">1</td> + <td align="right">0</td> + <td> </td> + <td align="right">2</td> + <td align="right">2</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>Fig. 8</td> + <td align="right">£3</td> + <td align="right">3</td> + <td align="right">0</td> + <td> </td> + <td align="right">3</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>Fig. 9</td> + <td align="right">£4</td> + <td align="right">10</td> + <td align="right">0</td> + <td> </td> + <td align="right">5</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>Fig. 10</td> + <td colspan="4"> </td> + <td align="right">8</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto ditto ditto handsome carved mountings, in mahogany, oak, or walnut wood<span class="spacer"> </span> + <span class="spacer"> </span>£8 8 0</td> + <td align="right">£10</td> + <td align="right">10</td> + <td align="right">0</td> + <td> </td> + <td align="right">12</td> + <td align="right">12</td> + <td align="right">0</td></tr> +<tr><td align="right">14</td> + <td><b>FitzRoy’s Storm or Sea Coast Fishery Barometer</b>, Fig. 12</td> + <td colspan="4"> </td> + <td align="right">5</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto with two verniers</td> + <td colspan="4"> </td> + <td align="right">6</td> + <td align="right">6</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto mounted in ornamental carved frames, oak, walnut, or mahogany</td> + <td align="right">£6</td> + <td align="right">10</td> + <td align="right">0</td> + <td> </td> + <td align="right">8</td> + <td align="right">8</td> + <td align="right">0</td></tr> +<tr><td align="right">19</td> + <td><b>Marine Barometers</b>, ordinary forms, Figs. 13 and 14<span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span>£2 2s.</td> + <td align="right">£2</td> + <td colspan="2"><span style="margin-left: .2em;">10s.</span></td> + <td> </td> + <td align="right">3</td> + <td align="right">3</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>Best mounted</td> + <td align="right">£5</td> + <td colspan="2"><span style="margin-left: .7em;">5s.</span></td> + <td> </td> + <td align="right">6</td> + <td align="right">6</td> + <td align="right">0</td></tr> +<tr><td align="right">20</td> + <td><b>The Board of Trade or Kew Marine Barometer</b>, Fig. 15,<span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span>£4 4s.</td> + <td align="right">£5</td> + <td colspan="2"><span style="margin-left: .7em;">5s.</span></td> + <td> </td> + <td align="right">6</td> + <td align="right">6</td> + <td align="right">0</td></tr> +<tr><td valign="top" align="right">22</td> + <td><b>Negretti and Zambra’s FitzRoy Marine or Gun Barometer</b>, Fig. 16, with N. and Z.’s<br /> + Patent Porcelain Scales, as used in Her Majesty’s Navy</td> + <td colspan="4"> </td> + <td valign="bottom" align="right">5</td> + <td valign="bottom" align="right">10</td> + <td valign="bottom" align="right">0</td></tr> +<tr><td> </td> + <td>Extra Tube for ditto</td> + <td colspan="4"> </td> + <td align="right">1</td> + <td align="right">15</td> + <td align="right">0</td></tr> +<tr><td align="right"><span class="pagenum"><a name="Page_157" id="Page_157">[Pg 157]</a></span>25</td> + <td><b>Negretti and Zambra’s Farmer’s Barometer or Domestic Weather Glass</b>, Fig. 17</td> + <td colspan="4"> </td> + <td align="right">2</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td align="right">28</td> + <td><b>Negretti and Zambra’s Miner’s Barometers</b><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span>£1 1s.</td> + <td align="right">£2</td> + <td colspan="2"><span style="margin-left: .7em;">2s.</span></td> + <td> </td> + <td align="right">3</td> + <td align="right">3</td> + <td align="right">0</td></tr> +<tr><td align="right">31</td> + <td><b>Dial or Wheel Barometers</b>, Figs. 18, 19, 20, 21<span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span>£3 3s.</td> + <td align="right">£4</td> + <td colspan="2"><span style="margin-left: .7em;">4s.</span></td> + <td> </td> + <td align="right">5</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto ditto in carved ornamental mountings<span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span>£5 10s. + <span class="spacer2"> </span>£6 6s.</td> + <td align="right">£8</td> + <td colspan="2"><span style="margin-left: .7em;">8s.</span></td> + <td> </td> + <td align="right">10</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto ditto rosewood, inlaid with pearl or metal.<span class="spacer2"> </span>Made to order, Figs. 22 and 23.<br /> + <span style="margin-left: 1em;">Price varying with size, &c.</span></td></tr> +<tr><td align="right">37</td> + <td><b>Gay Lussac’s Syphon Tube Mountain Barometer</b></td> + <td align="right">£6</td> + <td align="right">6</td> + <td align="right">0</td> + <td> </td> + <td align="right">8</td> + <td align="right">8</td> + <td align="right">0</td></tr> +<tr><td align="right">32</td> + <td><b>Standard Syphon Barometer</b>, Gay Lussac’s arrangement, Fig. 24</td> + <td colspan="4"> </td> + <td align="right">5</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td valign="top" align="right">38</td> + <td><b>Negretti and Zambra’s Standard Mountain Barometer</b>, with Fortin’s cistern,<br />with tripod stand and travelling case, Fig. 30</td> + <td colspan="4"> </td> + <td align="right">10</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td valign="top" align="right">34</td> + <td><b>Barograph, or Self-registering Barometer</b>, with syphon mercurial tube.<br />Negretti and Zambra’s improved arrangement, Fig. 26</td> + <td align="right">18</td> + <td align="right">18</td> + <td align="right">0</td> + <td> </td> + <td align="right">25</td> + <td align="right">0</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td><b>Negretti and Zambra’s Self-recording Aneroid Barometer</b>, with <b>Clock</b></td> + <td colspan="4"> </td> + <td align="right">22</td> + <td align="right">0</td> + <td align="right">0</td></tr> +<tr><td> </td></tr> +<tr><td> </td><td colspan="5" align="center">48. <b>ANEROID BAROMETERS.</b></td></tr> +<tr><td> </td> + <td><b>Aneroid Barometers,</b> with card dials 4½ inches diameter, best quality.</td> + <td colspan="4"> </td> + <td align="right">2</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>with silvered metal dial</td> + <td colspan="4"> </td> + <td align="right">3</td> + <td align="right">0</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>with ditto and thermometer</td> + <td colspan="4"> </td> + <td align="right">3</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td colspan="3">Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>ditto with corrected scale, + as supplied by Negretti and Zambra to the Royal Navy</td> + <td colspan="2"> </td> + <td align="right">5</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td><b>Aneroid Barometers</b>, with elegantly-chased dials</td> + <td colspan="4"> </td> + <td align="right">4</td> + <td align="right">4</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>with raised ring on dial</td> + <td colspan="4"> </td> + <td align="right">5</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>with thermometer</td> + <td colspan="4"> </td> + <td align="right">6</td> + <td align="right">6</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td colspan="3"><b>Aneroid Barometer</b>, for altitude measurements with revolving ring, carrying index, range of scale<br /> + <span style="margin-left: 1em;">20,000 feet 4½ inches diameter, with magnifier</span></td> + <td colspan="2"> </td> + <td align="right">8</td> + <td align="right">8</td> + <td align="right">0</td></tr> +<tr><td> </td></tr> +<tr><td> </td><td colspan="5" align="center"><b>POCKET ANEROID BAROMETERS.</b> Fig. 34.</td></tr> +<tr><td align="right">49</td> + <td><b>Pocket Aneroid Barometer</b>, 2¾ inches diameter, with silvered metal scale</td> + <td colspan="4"> </td> + <td align="right">3</td> + <td align="right">3</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td colspan="3">Ditto<span class="spacer"> </span>ditto for measuring altitudes to 10,000 feet compensated for temperature, in leather case</td> + <td colspan="2"> </td> + <td align="right">5</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>ditto<span class="spacer"> </span> + <span class="spacer"> </span>to 20,000 feet, with magnifier</td> + <td colspan="4"> </td> + <td align="right">6</td> + <td align="right">6</td> + <td align="right">0</td></tr> +<tr><td> </td></tr> +<tr><td align="right">50</td> + <td><b>WATCH-SIZE ANEROID BAROMETERS</b> in gilt metal cases (see figure 35.)</td></tr> +<tr><td> </td> + <td><b>Watch-Size Aneroid Barometer</b>, weather range</td> + <td align="right">£3</td> + <td align="right">3</td> + <td align="right">0</td> + <td> </td> + <td align="right">4</td> + <td align="right">4</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td colspan="3">Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span> of best construction, extra thin, for meteorological observations<br /> + <span style="margin-left: 1em;">or altitude measurements to 10,000 feet</span></td> + <td colspan="2"> </td> + <td align="right">5</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td colspan="3">Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span> ditto to 20,000 feet, compensated for temperature</td> + <td colspan="2"> </td> + <td align="right">6</td> + <td align="right">6</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td colspan="5" align="center">Either of the above Watch-size Barometers may be had in Stout Silver Cases at a cost of £2 2s. extra</td></tr> +<tr><td> </td> + <td colspan="5" align="center"><i>Watch-size Aneroid Barometers in Solid Gold, highly-finished cases. £15 15s. to £21.</i></td></tr> +<tr><td> </td> + <td colspan="5" align="center">Table Stands for Aneroid Barometers of Carved Oak or other woods,<br />10s. 6d., 25s., 35s., to £5 5s.</td></tr> +<tr><td> </td> + <td colspan="5" align="center"><b>Ships’ Aneroid Barometers</b>, in suitable mountings £2 10s. + £3 3s. £5 5s. £6 6s.</td></tr> +<tr><td> <span class="pagenum"><a name="Page_158" id="Page_158">[Pg 158]</a></span></td></tr> +<tr><td align="right">47</td> + <td><b>Sympiesometer</b>, for Ship use</td> + <td align="right">£3</td> + <td align="right">3</td> + <td align="right">0</td> + <td> </td> + <td align="right">4</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>Pocket form, Fig. 32</td> + <td colspan="4"> </td> + <td align="right">4</td> + <td align="right">4</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td colspan="5" align="center">The Sympiesometer is now rarely used, the Aneroid Barometer being found<br />equally sensitive and less liable to derangement.</td></tr> +<tr><td> </td></tr> +<tr><td align="right">56</td> + <td><b>Independent Standard Thermometers</b>, Fig. 36</td> + <td colspan="4"> </td> + <td align="right">5</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td align="right">57</td> + <td><b>Standard Thermometers</b>, for Boiling Point Apparatus</td> + <td colspan="4"> </td> + <td align="right">1</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td><b>Chemists’ or Brewers’ Standard Reference Thermometers</b></td> + <td align="right">£1</td> + <td colspan="2"><span style="margin-left: .5em;">1s.</span></td> + <td> </td> + <td align="right">2</td> + <td align="right">2</td> + <td align="right">0</td></tr> +<tr><td align="right">47</td> + <td><b>Chemical Thermometers</b>, divided on the stem. Fig. 48.</td> + <td> </td> + <td>10s.</td> + <td>6d.</td> + <td> </td> + <td align="right">0</td> + <td align="right">15</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td><b>Chemical Thermometers</b>, Boxwood Scale<span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span>7s. 6d.</td> + <td> </td> + <td>10s.</td> + <td>6d.</td> + <td> </td> + <td align="right">0</td> + <td align="right">12</td> + <td align="right">6</td></tr> +<tr><td align="right">64</td> + <td><b>Thermometers on Boxwood Scales</b>, Fig. 37.<span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span>1s. 1s. 6d. 2s. 6d.</td> + <td> </td> + <td><span style="margin-left: .5em;">3s.</span></td> + <td>6d.</td> + <td> </td> + <td align="right">0</td> + <td align="right">4</td> + <td align="right">6</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>larger sizes</td> + <td> </td> + <td><span style="margin-left: .5em;">7s.</span></td> + <td>6d.</td> + <td> </td> + <td align="right">0</td> + <td align="right">12</td> + <td align="right">6</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>Engraved glass scales, Fig. 39<span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span>15s. £1 1s.</td> + <td align="right">£1</td> + <td colspan="2"><span style="margin-left: .5em;">5s.</span></td> + <td> </td> + <td align="right">1</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td></tr> +<tr><td> </td><td colspan="5" align="center"><b>POCKET THERMOMETERS, IN VARIOUS MOUNTINGS.</b></td></tr> +<tr><td> </td> + <td colspan="5" align="center">Fig. 38 10s. 6d.<span class="spacer"> </span>Fig. 40 10s. 6d. 15s.<span class="spacer"> </span> + Fig. 41 5s. 6d. 8s. 6d. 12s. 6d.</td></tr> +<tr><td align="right">63</td> + <td><b>Thermometers of extreme Sensitiveness</b>,<span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span>15s.</td> + <td align="right">£1</td> + <td colspan="2"><span style="margin-left: .3em;">10s.</span></td> + <td> </td> + <td align="right">2</td> + <td align="right">2</td> + <td align="right">0</td></tr> +<tr><td> </td></tr> +<tr><td> </td> + <td><b>Drawing Room or Mantel Thermometers</b>, various mountings, Figs. 42 and 43.<br /> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span>12s. 6d. 15s. £1 1s. £1 10s.</td> + <td valign="bottom" align="right">£2</td> + <td valign="bottom" colspan="2"><span style="margin-left: .8em;">2s.</span></td> + <td> </td> + <td valign="bottom" align="right">2</td> + <td valign="bottom" align="right">10</td> + <td valign="bottom" align="right">0</td></tr> +<tr><td> </td> + <td><b>Bracket Window Thermometers</b>, Fig. 46<span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span>12s. 6d. 15s.</td> + <td align="right">£1</td> + <td colspan="2"><span style="margin-left: .8em;">1s.</span></td> + <td> </td> + <td align="right">1</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td><b>Bath Thermometers</b>, Figs. 44</td> + <td> </td> + <td><span style="margin-left: 1em;">7s.</span></td> + <td colspan="2">6d.</td> + <td align="right">0</td> + <td align="right">15</td> + <td align="right">0</td></tr> +<tr><td align="right">66</td> + <td><b>Sugar Boiling Thermometers</b><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span>£1 12s.</td> + <td align="right">£2</td> + <td colspan="2"><span style="margin-left: .5em;">2s.</span></td> + <td> </td> + <td align="right">3</td> + <td align="right">3</td> + <td align="right">0</td></tr> +<tr><td align="right">67</td> + <td><b>Earth Thermometers</b>, Fig. 51</td> + <td align="right">£1</td> + <td align="right">10s.</td> + <td colspan="2"> </td> + <td align="right">2</td> + <td align="right">2</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td><span style="margin-left: 1em;">Hot Bed</span><span class="spacer"> </span>Ditto<span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + 12s. 6d.</td> + <td align="right">£1</td> + <td align="right">5s.</td> + <td colspan="2"> </td> + <td align="right">1</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td align="right">68</td> + <td><b>Marine Thermometer</b>, Fig. 52<span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span>7s. 6d.</td> + <td> </td> + <td align="right">8s.</td> + <td align="right">6d.</td> + <td> </td> + <td align="right">0</td> + <td align="right">10</td> + <td align="right">6</td></tr> +<tr><td align="right">65</td> + <td><b>Super Heated or Steam Pressure Thermometers</b>, Fig. 74, Figs. 49 and 50<span class="spacer"> </span><span class="spacer"> </span> + £1 5s. £1 10s.</td> + <td align="right">£2</td> + <td align="right">2s.</td> + <td colspan="2"> </td> + <td align="right">2</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td></tr> +<tr><td> </td><td colspan="5" align="center"><b>SELF-REGISTERING THERMOMETERS FOR HEAT.</b></td></tr> +<tr><td align="right">72</td> + <td><b>Negretti and Zambra’s Patent Standard Maximum Self-Registering Thermometer</b>,<small><a name="f21.1" id="f21.1" href="#f21">[21]</a></small> Fig. 54</td> + <td colspan="4"> </td> + <td align="right">1</td> + <td align="right">1</td> + <td align="right">0</td></tr> +<tr><td align="right">72</td> + <td><b>Negretti and Zambra’s Patent Maximum Thermometer</b>, on boxwood scale</td> + <td colspan="4"> </td> + <td align="right">0</td> + <td align="right">10</td> + <td align="right">6</td></tr> +<tr><td> </td> + <td>Ditto,<span class="spacer2"> </span>ditto,<span class="spacer2"> </span> + on Negretti and Zambra’s Patent Solid Porcelain or Metal Scales on oak mounting</td> + <td colspan="4"> </td> + <td align="right">0</td> + <td align="right">12</td> + <td align="right">6</td></tr> +<tr><td align="right">70</td> + <td><b>Rutherford’s Maximum Thermometer</b>, on boxwood or metal scale, with steel index<span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span>5s. 6d.</td> + <td> </td> + <td align="right">7s.</td> + <td align="right">6d.</td> + <td> </td> + <td align="right">0</td> + <td align="right">10</td> + <td align="right">6</td></tr> +<tr><td align="right">71</td> + <td><b>Phillip’s Maximum Thermometer</b>, on boxwood or metal scale, with air index<span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span>7s. 6d.</td> + <td> </td> + <td align="right">10</td> + <td align="right">6</td> + <td> </td> + <td align="right">0</td> + <td align="right">12</td> + <td align="right">6</td></tr> +<tr><td> </td></tr> +<tr><td> </td><td colspan="5" align="center"><b>SELF-REGISTERING THERMOMETERS FOR COLD.</b></td></tr> +<tr><td align="right">73</td> + <td><b>Negretti and Zambra’s Standard Minimum Self-Registering Thermometer</b>, Fig. 55</td> + <td colspan="4"> </td> + <td align="right">1</td> + <td align="right">1</td> + <td align="right">0</td></tr> +<tr><td align="right">73</td> + <td><b>Rutherford’s Minimum Thermometer</b>, on boxwood or metal scale<span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span>3s. 6d. 5s. 6d.</td> + <td> </td> + <td align="right">7s.</td> + <td align="right">6d.</td> + <td> </td> + <td align="right">0</td> + <td align="right">10</td> + <td align="right">6</td></tr> +<tr><td align="right"><span class="pagenum"><a name="Page_159" id="Page_159">[Pg 159]</a></span>73</td> + <td><b>Rutherford’s Minimum Thermometer</b>, on Negretti and Zambra’s Patent solid porcelain scale</td> + <td> </td> + <td align="right">10s.</td> + <td align="right">6d.</td> + <td> </td> + <td align="right">0</td> + <td align="right">12</td> + <td align="right">6</td></tr> +<tr><td> </td> + <td>Ditto, on Negretti and Zambra’s porcelain or metal scales and oak mounting</td> + <td colspan="4"> </td> + <td align="right">0</td> + <td align="right">12</td> + <td align="right">6</td></tr> +<tr><td valign="top" align="right">74</td> + <td><b>Negretti and Zambra’s Horticultural Self-Registering Thermometer.</b> The scale is made of<br /> + stout zinc, enclosing the tube; the figures and divisions are boldly marked for quickly and easily<br />reading the indications, Fig. 56</td> + <td colspan="4"> </td> + <td valign="bottom" align="right">0</td> + <td valign="bottom" align="right">3</td> + <td valign="bottom" align="right">6</td></tr> +<tr><td> </td></tr> +<tr><td align="right">83</td> + <td><b>Negretti and Zambra’s Patent Solar Radiation Thermometer</b>, Fig. 63</td> + <td colspan="4"> </td> + <td align="right">1</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td align="right">84</td> + <td>Ditto,<span class="spacer"> </span>ditto,<span class="spacer"> </span>ditto, in vacuo, Fig. 64</td> + <td colspan="4"> </td> + <td align="right">1</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto,<span class="spacer"> </span>ditto,<span class="spacer"> </span>ditto, improved form, with test gauge</td> + <td colspan="4"> </td> + <td align="right">2</td> + <td align="right">2</td> + <td align="right">0</td></tr> +<tr><td align="right">85</td> + <td><b>Negretti and Zambra’s Terrestrial Radiation Thermometer</b></td> + <td colspan="4"> </td> + <td align="right">1</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Brass Stands for above, Fig. 65</td> + <td colspan="4"> </td> + <td align="right">0</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td align="right">76 and 77</td> + <td><b>Negretti and Zambra’s Patent Mercurial Minimum Thermometers</b></td> + <td align="right">£2</td> + <td align="right">10s.</td> + <td colspan="2"> </td> + <td align="right">2</td> + <td align="right">2</td> + <td align="right">0</td></tr> +<tr><td valign="top" align="right">81</td> + <td><b>Maxima and Minima Thermometers</b>, on Sixe’s arrangement, Fig. 62, various forms of mounting<br /><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span>12s. 6d. 14s. 21s.</td> + <td> </td> + <td valign="bottom" align="right">30s.</td> + <td colspan="2"> </td> + <td valign="bottom" align="right">2</td> + <td valign="bottom" align="right">2</td> + <td valign="bottom" align="right">0</td></tr> +<tr><td> </td> + <td><b>Pocket Maxima and Minima Thermometers</b>, Negretti and Zambra’s Patent, in convenient cases</td> + <td align="right">£2</td> + <td align="right">2s.</td> + <td colspan="2"> </td> + <td align="right">2</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td valign="top" align="right">89</td> + <td colspan="4"><b>Deep Sea Registering Thermometer</b>, with Negretti and Zambra’s improved protected bulb,<br />in copper cylinder, Fig. 69.</td> + <td> </td> + <td valign="bottom" align="right">2</td> + <td valign="bottom" align="right">10</td> + <td valign="bottom" align="right">0</td></tr> +<tr><td valign="top" align="right">89<small><a href="#f21">[21]</a></small></td> + <td><b>Negretti and Zambra’s Improved Deep Sea Thermometer</b>, with vulcanite mountings,<br />in copper cylinder, with door, small size</td> + <td colspan="4"> </td> + <td valign="bottom" align="right">2</td> + <td valign="bottom" align="right">5</td> + <td valign="bottom" align="right">0</td></tr> +<tr><td align="right">90</td> + <td><b>Negretti and Zambra’s Patent Recording Deep Sea Thermometer</b></td> + <td colspan="4"> </td> + <td align="right">10</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td align="right">91</td> + <td>Ditto,<span class="spacer"> </span>ditto,<span class="spacer"> </span>ditto<span class="spacer"> </span><b>Recording Thermometer</b></td> + <td colspan="4"> </td> + <td align="right">4</td> + <td align="right">4</td> + <td align="right">0</td></tr> +<tr><td align="right">92</td> + <td>Ditto,<span class="spacer"> </span>ditto,<span class="spacer"> </span>ditto<span class="spacer"> </span><b>Hygrometer</b></td> + <td colspan="4"> </td> + <td align="right">6</td> + <td align="right">6</td> + <td align="right">0</td></tr> +<tr><td valign="top" align="right">93</td> + <td><b>Improved Boiling Point Mountain Thermometer</b>, or Hypsometric Apparatus, with Tables, Figs. 72 and 73,<br />in leather case with strap</td> + <td colspan="4"> </td> + <td valign="bottom" align="right">5</td> + <td valign="bottom" align="right">5</td> + <td valign="bottom" align="right">0</td></tr> +<tr><td> </td> + <td>Extra Thermometer for Ditto</td> + <td colspan="4"> </td> + <td align="right">1</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td align="right">106</td> + <td><b>Negretti and Zambra’s Standard Wet and Dry Bulb Hygrometer</b>, Fig. 79</td> + <td colspan="4"> </td> + <td align="right">2</td> + <td align="right">2</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Wet and Dry Bulb Hygrometers, various mountings<span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + <span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span><span class="spacer"> </span> + 30s. 25s. 21s.</td> + <td> </td> + <td align="right">14s.</td> + <td colspan="2"> </td> + <td align="right">0</td> + <td align="right">10</td> + <td align="right">6</td></tr> +<tr><td> </td> + <td>Pocket Hygrometers, in box</td> + <td align="right">£2</td> + <td align="right">2s.</td> + <td colspan="2"> </td> + <td align="right">2</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td align="right">103</td> + <td><b>Daniell’s Hygrometer</b>, Fig. 77</td> + <td colspan="4"> </td> + <td align="right">3</td> + <td align="right">3</td> + <td align="right">0</td></tr> +<tr><td align="right">104</td> + <td><b>Regnault’s Hygrometer</b>, Fig. 78</td> + <td align="right">£3</td> + <td align="right">10s.</td> + <td colspan="2"> </td> + <td align="right">5</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Aspirator for Ditto</td> + <td align="right">£1</td> + <td align="right">15s.</td> + <td colspan="2"> </td> + <td align="right">2</td> + <td align="right">15</td> + <td align="right">0</td></tr> +<tr><td> </td></tr> +<tr><td valign="top" align="right">110</td> + <td><b>Howard’s Rain Gauge</b>, has a 5-inch copper Funnel, with turned brass rim fitted to a stout stone-ware or<br /> + glass bottle, with a graduated glass measure, divided to 100ths of an inch</td> + <td colspan="4"> </td> + <td valign="bottom" align="right">0</td> + <td valign="bottom" align="right">10</td> + <td valign="bottom" align="right">6</td></tr> +<tr><td> </td> + <td><b>Symons’ Portable Rain Gauge</b>, (5-inch) with graduated glass measure, japanned tin</td> + <td colspan="4"> </td> + <td align="right">0</td> + <td align="right">10</td> + <td align="right">6</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto<span class="spacer"> </span>in stout copper</td> + <td colspan="4"> </td> + <td align="right">0</td> + <td align="right">15</td> + <td align="right">0</td></tr> +<tr><td valign="top" align="right">111</td> + <td><b>Glaisher’s Rain Gauge</b>, the receiving surface is 8-inches diameter, of stout japanned metal,<br />with graduated glass measure, Fig. 84</td> + <td colspan="4"> </td> + <td valign="bottom" align="right">1</td> + <td valign="bottom" align="right">1</td> + <td valign="bottom" align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto,<span class="spacer"> </span>of stout copper</td> + <td colspan="4"> </td> + <td align="right">1</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Receiving Pots for ditto, extra 2s. and 3s. 6d.</td></tr> +<tr><td valign="top" align="right"><span class="pagenum"><a name="Page_160" id="Page_160">[Pg 160]</a></span>113</td> + <td><b>Rain Gauge</b>, having a receiving surface of 12 inches diameter, and graduated glass gauge tube, divided to<br /> + hundredths of an inch, in japanned metal, with brass tap</td> + <td colspan="4"> </td> + <td valign="bottom" align="right">2</td> + <td valign="bottom" align="right">10</td> + <td valign="bottom" align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto, Fig. 85, in copper</td> + <td colspan="4"> </td> + <td align="right">3</td> + <td align="right">10</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto, with sliding rod instead of graduated tube, japanned tin</td> + <td colspan="4"> </td> + <td align="right">2</td> + <td align="right">2</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td><b>Rain Gauges</b>, of any form or area made to order, with suitable measuring glasses.</td></tr> +<tr><td> </td></tr> +<tr><td align="right">123</td> + <td><b>Lind’s Anemometer</b>, Fig. 86</td> + <td colspan="4"> </td> + <td align="right">2</td> + <td align="right">2</td> + <td align="right">0</td></tr> +<tr><td align="right">125</td> + <td><b>Robinson’s Anemometer</b>, Fig. 87</td> + <td colspan="4"> </td> + <td align="right">3</td> + <td align="right">3</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto,<span class="spacer"> </span>Improved arrangement</td> + <td align="right">£4</td> + <td align="right">10s.</td> + <td colspan="2"> </td> + <td align="right">5</td> + <td align="right">15</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto,<span class="spacer"> </span>with clutch movement, Fig. 88</td> + <td colspan="4"> </td> + <td align="right">6</td> + <td align="right">15</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td><b>Negretti and Zambra’s Improved Air Meter</b>, of extreme sensitiveness, very portable</td> + <td colspan="4"> </td> + <td align="right">4</td> + <td align="right">4</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Large Air Meters made to order.</td></tr> +<tr><td align="right">127</td> + <td><b>Osler’s Self-Registering Anemometer and Rain Gauge</b>, Fig. 89</td> + <td colspan="3">£84 to</td> + <td> </td> + <td align="right">150</td> + <td align="right">0</td> + <td align="right">0</td></tr> +<tr><td align="right">128</td> + <td><b>Berkley’s Anemometers</b> fitted up to order, <i>to suit the Observatory</i>.</td></tr> +<tr><td align="right">131</td> + <td><b>Gold Leaf Electrometer</b>, Fig. 90</td> + <td colspan="4"> </td> + <td align="right">1</td> + <td align="right">1</td> + <td align="right">0</td></tr> +<tr><td align="right">133</td> + <td><b>Peltier’s Electrometer</b></td> + <td colspan="4"> </td> + <td align="right">4</td> + <td align="right">4</td> + <td align="right">0</td></tr> +<tr><td align="right">134</td> + <td><b>Bohnenberger’s Electroscope</b>, Fig. 91</td> + <td colspan="4"> </td> + <td align="right">8</td> + <td align="right">8</td> + <td align="right">0</td></tr> +<tr><td align="right">135</td> + <td><b>Thompson’s Electrometer</b>, to order</td></tr> +<tr><td> </td> + <td><b>Lightning Conductors</b> fitted up to order.</td></tr> +<tr><td align="right">142</td> + <td><b>Ozone Cage</b>, Fig. 92</td> + <td colspan="4"> </td> + <td align="right">0</td> + <td align="right">18</td> + <td align="right">0</td></tr> +<tr><td> </td> + <td>Ditto<span class="spacer"> </span>ditto, copper</td> + <td colspan="4"> </td> + <td align="right">1</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td align="right">146</td> + <td><b>Leslie’s Differential Thermometer</b>, Fig. 93</td> + <td align="right">£1</td> + <td align="right">10s.</td> + <td colspan="2"> </td> + <td align="right">2</td> + <td align="right">2</td> + <td align="right">0</td></tr> +<tr><td align="right">148</td> + <td><b>Thermometer Stand (Glaisher’s)</b></td> + <td colspan="4"> </td> + <td align="right">3</td> + <td align="right">3</td> + <td align="right">0</td></tr> +<tr><td align="right">149</td> + <td><b>Thermometer Screen</b> for Sea use</td> + <td colspan="4"> </td> + <td align="right">3</td> + <td align="right">3</td> + <td align="right">0</td></tr> +<tr><td align="right">150</td> + <td><b>Anemoscope</b>, or Portable Vane, Fig. 94</td> + <td colspan="4"> </td> + <td align="right">2</td> + <td align="right">5</td> + <td align="right">0</td></tr> +<tr><td align="right">151</td> + <td><b>Evaporating Dish</b>, Fig. 95</td> + <td colspan="4"> </td> + <td align="right">1</td> + <td align="right">2</td> + <td align="right">6</td></tr> +<tr><td align="right">157</td> + <td><b>Sea Water Hydrometers</b>, Board of Trade Marine, Figs. 96 and 97</td> + <td colspan="4"> </td> + <td align="right">0</td> + <td align="right">5</td> + <td align="right">6</td></tr> +<tr><td align="right">158</td> + <td><b>Newman’s Self-Registering Tide Gauge</b>, Fig. 158, fitted to the Building to order</td> + <td colspan="2"> </td> + <td colspan="2" align="right">From</td> + <td align="right">50</td> + <td align="right">0</td> + <td align="right">0</td></tr></table> + + +<p> </p> +<p class="center"><i>Further Information as to Price, &c., will be found in</i><br /> +NEGRETTI & ZAMBRA’S<br /> +ENCYCLOPÆDIC CATALOGUE<br /> +OF<br /> +MATHEMATICAL, PHILOSOPHICAL, OPTICAL, PHOTOGRAPHIC,<br /> +AND<br /> +STANDARD<br /> +METEOROLOGICAL INSTRUMENTS,<br /> +<br /> +<i>Containing very numerous Comparative Tables of Reference,<br /> +and Illustrated by upwards of</i><br /> +<br /> +ELEVEN HUNDRED ENGRAVINGS.<br /> +<br /> +Royal 8vo. Cloth, Gilt Lettered—Price 5s. 6d.</p> + + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><strong>Footnotes:</strong></p> + +<p><a name="f1" id="f1" href="#f1.1">[1]</a> Second Number of “Meteorological Papers,” issued by the Board of +Trade.</p> + +<p><a name="f2" id="f2" href="#f2.1">[2]</a> With reference to these barometers, we have received the subjoined +testimonial, with permission to use it as we please.</p> + +<div class="blockquot"> +<p class="right">“<i>Meteorologic Office, 12th June, 1863.</i></p> + +<p>“<span class="smcap">Messrs. Negretti & Zambra</span>,</p> + +<p>“The barometers which you have lately supplied to Her Majesty’s ships +through this Office are much approved, being good for general service, +afloat or on land.</p> + +<p>“(Signed)<span class="spacer"> </span>R. FITZROY.”</p></div> + +<p><a name="f3" id="f3" href="#f3.1">[3]</a> <i>Vide</i> C. Daubeny, F.R.S., “On Climate.”</p> + +<p><a name="f4" id="f4" href="#f4.1">[4]</a> <i>Vide</i> Report of the British Association, 1862.</p> + +<p><a name="f5" id="f5" href="#f5.1">[5]</a> See <a href="#Page_42">page 42</a> for the Tables.</p> + +<p><a name="f6" id="f6" href="#f6.1">[6]</a> The quotations in this section are from Tyndall’s <i>Heat considered as +a Mode of Motion</i>.</p> + +<p><a name="f7" id="f7" href="#f7.1">[7]</a> Dr. Daubeny, F.R.S., <i>On Climate</i>.</p> + +<p><a name="f8" id="f8" href="#f8.1">[8]</a> Leslie <i>On the Relations of Air, Heat, and Moisture</i>.</p> + +<p><a name="f9" id="f9" href="#f9.1">[9]</a> Tyndall’s <i>Heat considered as a Mode of Motion</i>.</p> + +<p><a name="f10" id="f10" href="#f10.1">[10]</a> Vide <i>Horological Journal</i>, Vol. V.</p> + +<p><a name="f11" id="f11" href="#f11.1">[11]</a> <i>Hygrometrical Tables</i>, by J. Glaisher, Esq., F.R.S.</p> + +<p><a name="f12" id="f12" href="#f12.1">[12]</a> Vide <i>Report of the British Association</i>, 1862. It may be added, for +the information of those who are about to commence observing, that Mr. +Symons, of Camden Road Villas, London, is desirous of securing returns of +rain-fall from as many stations as possible, in order to render more +complete his annual reports to the British Association.</p> + +<p><a name="f13" id="f13" href="#f13.1">[13]</a> Luke Howard’s <i>Climate of London</i>.</p> + +<p><a name="f14" id="f14" href="#f14.1">[14]</a> Vide <i>Third Number of Meteorological Papers</i>, issued by the Board of +Trade.</p> + +<p><a name="f15" id="f15" href="#f15.1">[15]</a> <i>Elements of Physics</i>, by C. F. Peschel.</p> + +<p><a name="f16" id="f16" href="#f16.1">[16]</a> This description is modified from that in Report of the Jurors for +Class XIII. International Exhibition, 1862.</p> + +<p><a name="f17" id="f17" href="#f17.1">[17]</a> <i>All the Year Round</i>, No. 224.</p> + +<p><a name="f18" id="f18" href="#f18.1">[18]</a> <i>All the Year Round</i>, No. 224.</p> + +<p><a name="f19" id="f19" href="#f19.1">[19]</a> Vide <i>Jurors’ Reports</i>.</p> + +<p><a name="f20" id="f20" href="#f20.1">[20]</a> See also <a href="#Page_90">page 90</a> of this Treatise.</p> + +<p><a name="f21" id="f21" href="#f21.1">[21]</a> These Instruments are the only Maximum Thermometers that can be +recommended, as unless they be broken, they cannot be put out of +adjustment. Fully described under the head of Standard Maximum +Thermometers in our large Catalogue, and <a href="#Page_72">page 72</a> of our <i>Treatise on +Meteorological Instruments</i>.</p> + + +<p> </p><p> </p> +<hr style="width: 50%;" /> +<p><strong>Transcriber’s Note:</strong> In an effort to make the wide table on page 149 easier to read, the months were +abbreviated by the transcriber. In addition, “Temperature” was changed +to “Temp.” and “Temperatures” to “Temp’s.”</p> + + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of A Treatise on Meteorological +Instruments, by Henry Negretti and Joseph Zambra + +*** END OF THIS PROJECT GUTENBERG EBOOK TREATISE ON METEOROLOGICAL INSTRUMENTS *** + +***** This file should be named 36457-h.htm or 36457-h.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/3/6/4/5/36457/ + +Produced by The Online Distributed Proofreading Team at +https://www.pgdp.net (This file was produced from images +generously made available by The Internet Archive.) + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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