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+<title>The Project Gutenberg eBook of How Two Boys Made Their Own Electrical Apparatus, by Thomas M. (Thomas Matthew) St. John</title>
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+<h1>The Project Gutenberg eBook of How Two Boys Made Their Own Electrical
+Apparatus, by Thomas M. (Thomas Matthew) St. John</h1>
+<pre>
+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 <a href = "http://www.gutenberg.org">www.gutenberg.org</a></pre>
+<p>Title: How Two Boys Made Their Own Electrical Apparatus</p>
+<p>       Containing Complete Directions for Making All Kinds of Simple Apparatus for the Study of Elementary Electricity</p>
+<p>Author: Thomas M. (Thomas Matthew) St. John</p>
+<p>Release Date: March 15, 2009  [eBook #28335]</p>
+<p>Language: English</p>
+<p>Character set encoding: ISO-8859-1</p>
+<p>***START OF THE PROJECT GUTENBERG EBOOK HOW TWO BOYS MADE THEIR OWN ELECTRICAL APPARATUS***</p>
+<p>&nbsp;</p>
+<h3 class="pg">E-text prepared by Peter Vachuska, Chuck Greif, Greg Bergquist,<br />
+    and the Project Gutenberg Online Distributed Proofreading Team<br />
+    (http://www.pgdp.net)</h3>
+<p>&nbsp;</p>
+<div class="tn">
+<p class="center"><big><b>Transcriber&#8217;s Note</b></big></p>
+
+<p class="noin">The punctuation and spelling from the original text have been faithfully preserved. Only obvious
+typographical errors have been corrected. The front matter advertisements have been moved
+to the end with the other advertisements for the HTML version.</p>
+</div>
+<p>&nbsp;</p>
+<hr class="full" />
+<p>&nbsp;</p>
+<p>&nbsp;</p>
+<p>&nbsp;</p>
+
+<h1>
+How Two Boys Made<br />
+Their Own Electrical<br />
+Apparatus
+</h1>
+<p class="center">
+Containing Complete Directions for<br />
+Making All Kinds of Simple Apparatus<br />
+for the Study of Elementary Electricity<br />
+<br />
+BY<br />
+<br />
+<big>THOMAS M. ST. JOHN, Met. E.</big><br />
+<br />
+<small>Author of "Fun With Magnetism," "Fun With Electricity,"<br />
+"The Study of Elementary Electricity and Magnetism<br />
+by Experiment," "Things A Boy Should Know<br />
+About Electricity," etc.</small><br />
+</p>
+<hr style="width: 10%;" />
+<p class="center"><i>EIGHTH EDITION</i></p>
+<hr style="width: 10%;" />
+<p class="center"><big>THOMAS M. ST. JOHN</big><br />
+<br />
+<small>CASCADE RANCH</small></p>
+
+<div class='center'>
+<table border="0" width="25%" cellpadding="4" cellspacing="0" summary="publish locations">
+<tr>
+ <td align='left'><span class="smcap">East Windham</span></td>
+ <td align='right'><span class="smcap">New York</span></td>
+</tr>
+</table></div>
+<hr />
+
+
+
+
+<p class="center">
+<span class="smcap">COPYRIGHT, 1898</span>,
+<br />
+BY THOMAS M. ST. JOHN
+</p>
+
+
+
+<hr />
+<h2><a name="How_Two_Boys_Made_Their_Own_Electrical_Apparatus" id="How_Two_Boys_Made_Their_Own_Electrical_Apparatus"></a>How Two Boys Made Their Own Electrical Apparatus.</h2>
+
+
+<p class="center">TABLE OF CONTENTS.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="Contents">
+<tr>
+ <td align='right'><span class="smcap"><small>Chapter.</small></span></td>
+ <td align='left'>&nbsp;</td>
+ <td align='right'><span class="smcap"><small>Page.</small></span></td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_I">I.</a></td>
+ <td align='left'>Cells and Batteries,</td>
+ <td align='right'>5</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_II">II.</a></td>
+ <td align='left'>Battery Fluids and Solutions,</td>
+ <td align='right'>15</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_III">III.</a></td>
+ <td align='left'>Miscellaneous Apparatus and Methods of Construction,</td>
+ <td align='right'>20</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_IV">IV.</a></td>
+ <td align='left'>Switches and Cut-Outs,</td>
+ <td align='right'>28</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_V">V.</a></td>
+ <td align='left'>Binding-Posts and Connectors,</td>
+ <td align='right'>32</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_VI">VI.</a></td>
+ <td align='left'>Permanent Magnets,</td>
+ <td align='right'>37</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_VII">VII.</a></td>
+ <td align='left'>Magnetic Needles and Compasses,</td>
+ <td align='right'>40</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_VIII">VIII.</a></td>
+ <td align='left'>Yokes and Armatures,</td>
+ <td align='right'>45</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_IX">IX.</a></td>
+ <td align='left'>Electro-Magnets,</td>
+ <td align='right'>51</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_X">X.</a></td>
+ <td align='left'>Wire-Winding Apparatus,</td>
+ <td align='right'>60</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_XI">XI.</a></td>
+ <td align='left'>Induction Coils and Their Attachments,</td>
+ <td align='right'>64</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_XII">XII.</a></td>
+ <td align='left'>Contact Breakers and Current Interrupters,</td>
+ <td align='right'>75</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_XIII">XIII.</a></td>
+ <td align='left'>Current Detectors and Galvanometers,</td>
+ <td align='right'>78</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_XIV">XIV.</a></td>
+ <td align='left'>Telegraph Keys and Sounders,</td>
+ <td align='right'>92</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_XV">XV.</a></td>
+ <td align='left'>Electric Bells and Buzzers,</td>
+ <td align='right'>104</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_XVI">XVI.</a></td>
+ <td align='left'>Commutators and Current Reversers,</td>
+ <td align='right'>110</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_XVII">XVII.</a></td>
+ <td align='left'>Resistance Coils,</td>
+ <td align='right'>114</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_XVIII">XVIII.</a></td>
+ <td align='left'>Apparatus for Static Electricity,</td>
+ <td align='right'>117</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_XIX">XIX.</a></td>
+ <td align='left'>Electric Motors,</td>
+ <td align='right'>122</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_XX">XX.</a></td>
+ <td align='left'>Odds and Ends,</td>
+ <td align='right'>133</td>
+</tr>
+<tr>
+ <td align='right'><a href="#CHAPTER_XXI">XXI.</a></td>
+ <td align='left'>Tools and Materials,</td>
+ <td align='right'>137&ndash;141</td>
+</tr>
+</table></div>
+
+
+
+<hr />
+<h3>A WORD TO BOYS.</h3>
+
+
+<p>The author is well aware that the average boy has but few tools, and he
+has kept this fact constantly in mind. It is a very easy matter for a
+skilled mechanic to make, with proper tools, very fine-looking pieces of
+apparatus. It is <i>not</i> easy to make good apparatus with few tools and a
+limited amount of skill, <i>unless</i> you follow <i>simple methods</i>.</p>
+
+<p>By following the methods given, any boy of average ability can make the
+apparatus herein described.</p>
+
+<p>Most of the illustrations have been made directly from apparatus
+constructed by young boys.</p>
+
+<p>It is impossible to describe the different pieces of apparatus in any
+special or logical order. It is taken for granted that you have some
+book of simple experiments and explanations to serve as a guide for the
+order, and to give you an idea of just the apparatus needed for the
+special experiments.</p>
+
+<p>It would be foolish to start in and make all the apparatus described,
+without being able to intelligently use it in your experiments. <i>Take up
+a systematic course of simple experiments, and make your own apparatus,
+as needed.</i></p>
+
+<p>Before making any particular piece of apparatus, read what is said about
+the other pieces of the same general nature. This will often be a great
+help, and it may suggest improvements that you would like to have.</p>
+
+<p>In case your apparatus does not work as expected, read the directions
+again, and see if you have followed them. Wrong connections, poor
+connections, short circuits, broken wire, etc., will make trouble. With
+a little patience and care you will be able to locate and correct any
+troubles that may come up in such simple apparatus.</p>
+
+<p class="right">
+<span class="smcap">Thomas M. St. John.</span><br />
+</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_5" id="Page_5">[Pg 5]</a></span></p>
+<h2>How Two Boys Made Their Own Electrical Apparatus</h2>
+
+
+
+<hr style="width: 15%;" />
+<h3><a name="CHAPTER_I" id="CHAPTER_I"></a>CHAPTER I.</h3>
+
+<h4>CELLS AND BATTERIES.</h4>
+
+
+<p class="app"><a name="APPARATUS_1" id="APPARATUS_1"></a>APPARATUS 1.</p>
+
+<p><i><b>1. Carbon-Zinc Cell.</b></i> Fig. 1. If you have some rubber bands you can
+quickly make a cell out of rods of zinc and carbon. The rods are kept
+apart by putting a band, <i>B</i>, around each end of both rods. The bare
+wires are pinched under the upper bands. The whole is then bound
+together by means of the bands, <i>A</i>, and placed in a tumbler of fluid,
+as given in <a href="#APPARATUS_15">App. 15</a>. This method does not make first-class connections
+between the wire and rods. (<a href="#s3">See &sect; 3.</a>)</p>
+
+<div class="figcenter" style="width: 230px;"><a name="Fig_1" id="Fig_1"></a>
+<img src="images/figure1.jpg" width="230" height="475" alt="Fig. 1." title="" />
+<span class="caption">Fig. 1.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_2" id="APPARATUS_2"></a>APPARATUS 2.</p>
+
+<div class="figcenter" style="width: 300px;"><a name="Fig_2" id="Fig_2"></a>
+<img src="images/figure2.jpg" width="300" height="300" alt="Fig. 2." title="" />
+<span class="caption">Fig. 2.</span>
+</div>
+
+<p><i><b>2. Carbon-Zinc Cell.</b></i> Fig. 2. In case you want to make your cell out of
+carbon and zinc rods, and do not have any means of making holes for them
+in the wood, as in <a href="#APPARATUS_3">App. 3</a> and <a href="#APPARATUS_4">4</a>, you will find this method useful. Cut
+grooves, <i>G</i>, into one side of the wood, <i>A</i>, which should be about
+4&frac12; &times; 1 &times; &frac12; in. The grooves should be quite deep, and so placed that
+the rods will be about &frac14; in. apart. A strip of tin, <i>T</i>, &frac12; in. wide,
+should be bent around each<span class='pagenum'><a name="Page_6" id="Page_6">[Pg 6]</a></span> rod. The screw, <i>S</i>, put through the two
+thicknesses of tin will hold the rod in place. Another screw, <i>X</i>, acts
+as a binding-post. The zinc rod only is shown in Fig. 2. The carbon rod
+is arranged in the same way. Use the fluid of <a href="#APPARATUS_15">App. 15</a>.</p>
+
+<p><a name="s3" id="s3"></a>3. Note. When the bichromate solution of <a href="#APPARATUS_15">App. 15</a> is used for cells, the
+strong current is given, among other reasons, because the zinc is
+rapidly eaten up. This action goes on even when the circuit is broken,
+so always remove and wash the zinc as soon as you have finished.</p>
+
+
+<p class="app"><a name="APPARATUS_3" id="APPARATUS_3"></a>APPARATUS 3.</p>
+
+<p><i><b>4. Carbon-Zinc Cell.</b></i> Fig. 3. The wooden cross-piece, <i>A</i>, is 4&frac12; &times; 1
+&times; &frac12; in. The carbon and zinc rods, <i>C</i> and <i>Z</i>, are 4 in. long &times; &frac12;
+in. in diameter. The holes are bored, if you have a brace and bit, so
+that they are &frac34; in. apart, center to center. This makes the rods &frac14;
+in. apart. To make connections between the rods and outside wires, cut a
+shallow slot at the front side of each hole, so that you can put a
+narrow strip of tin or copper, <i>B</i>, in the hole by the side of each rod.
+Setscrews, <i>S</i>, screwed in the side of <i>A</i>, will hold the rods in place,
+and at the same time press the strips, <i>B</i>, against them. Connections
+can easily be made between wire and <i>B</i> by using a spring binding-post,
+<i>D</i>, or by fastening the wire direct to the strips, as shown in <a href="#APPARATUS_4">App. 4</a>.</p>
+
+<div class="figcenter" style="width: 300px;"><a name="Fig_3" id="Fig_3"></a>
+<img src="images/figure3.jpg" width="300" height="369" alt="Fig. 3." title="" />
+<span class="caption">Fig. 3.</span>
+</div>
+
+<p>Use the battery fluid given in <a href="#APPARATUS_15">App. 15</a>, and use a tumbler for the
+battery jar. This cell will run small, well-made motors, induction
+coils, etc. (<a href="#s3">See &sect; 3</a>.)</p>
+
+
+<p><span class='pagenum'><a name="Page_7" id="Page_7">[Pg 7]</a></span></p><p class="app"><a name="APPARATUS_4" id="APPARATUS_4"></a>APPARATUS 4.</p>
+
+<p><i><b>5. Carbon-Zinc Cell.</b></i> Fig. 4. The general construction of this cell is
+the same as that of <a href="#APPARATUS_3">App. 3</a>. There are 2 carbons, <i>C</i>, each 4 &times; &frac12; in.
+The holes for these are bored in <i>A</i> 1&frac14; in. apart, center to center.
+The zinc rod, <i>Z</i>, is a regular battery zinc, 6 &times; &#8540; in., and has a
+binding-post, <i>Y</i>, of its own. The rods, <i>C</i>, are held in <i>A</i>, and
+connections are made as explained in <a href="#APPARATUS_3">App. 3</a>.</p>
+
+<div class="figcenter" style="width: 300px;"><a name="Fig_4" id="Fig_4"></a>
+<img src="images/figure4.jpg" width="300" height="494" alt="Fig. 4." title="" />
+<span class="caption">Fig. 4.</span>
+</div>
+
+<p>The wire, <i>X</i>, is fastened direct to the strips, <i>B</i>, as shown. When
+ready to use this cell, be sure that the wire connecting the carbons
+does not touch <i>Z</i>. (Why?) The other wire is connected to <i>Y</i>. The
+wooden piece is 4&frac12; &times; 1 &times; &frac12; in. Use the battery fluid of <a href="#APPARATUS_15">App. 15</a> in
+a tumbler. This cell will run small motors, and is good for induction
+coils, etc. (<a href="#s3">See &sect; 3</a>.)</p>
+
+
+<p class="app"><a name="APPARATUS_5" id="APPARATUS_5"></a>APPARATUS 5.</p>
+
+<div class="figcenter" style="width: 300px;"><a name="Fig_5" id="Fig_5"></a>
+<img src="images/figure5.jpg" width="300" height="386" alt="Fig. 5." title="" />
+<span class="caption">Fig. 5.</span>
+</div>
+
+<p><i><b>6. Experimental Cell.</b></i> Fig. 5. Cut a strip each of copper, <i>C</i>, and
+zinc, <i>Z</i>. (See list of materials.) They should be about 2 in. wide and
+4 in. long. Punch a hole through each, one side of the center, for
+screws, <i>E</i>. The wooden cross-piece, <i>A</i>, should be 4&frac12; &times; 1 &times; &#8542; in.
+The battery-plates, or elements, should be screwed to this, taking care
+that the screws, <i>E</i>, do not touch each other. If the holes are<span class='pagenum'><a name="Page_8" id="Page_8">[Pg 8]</a></span> made in
+the position shown in Fig. 5, the screws can be arranged some distance
+apart.</p>
+
+<p>The wires leading from the cell may be fastened under the screws with
+copper burs, or spring binding-posts (<a href="#APPARATUS_42">App. 42</a>) can be slipped on the top
+of the plates.</p>
+
+<p>The solution to be used will depend upon what the cell is to do. For
+simple experiments use the dilute acid (<a href="#APPARATUS_14">App. 14</a>). If for small motors,
+use the formula given in <a href="#APPARATUS_15">App. 15</a>. The zinc should be well amalgamated.
+(<a href="#APPARATUS_20">App. 20</a>.)</p>
+
+
+<p class="app"><a name="APPARATUS_6" id="APPARATUS_6"></a>APPARATUS 6.</p>
+
+<div class="figcenter" style="width: 241px;"><a name="Fig_6" id="Fig_6"></a>
+<img src="images/figure6.jpg" width="241" height="342" alt="Fig. 6." title="" />
+<span class="caption">Fig. 6.</span>
+</div>
+
+<p><i><b>7. Experimental Cell.</b></i> Fig. 6. In some experiments a comparison is made
+between cells with large plates and cells with small ones. This form
+will be convenient to use where narrow plates are desired. Those shown
+are 4 &times; &frac12; in. They are screwed to the cross-piece, which is 4&frac12; &times; 1
+&times; &#8542; in. Do not let the screws touch each other. The wires are fastened
+under the screw-heads.</p>
+
+
+<p class="app"><a name="APPARATUS_7" id="APPARATUS_7"></a>APPARATUS 7.</p>
+
+<div class="figleft" style="width: 300px;"><a name="Fig_7" id="Fig_7"></a>
+<img src="images/figure7.jpg" width="300" height="408" alt="Fig. 7." title="" />
+<span class="caption">Fig. 7.</span>
+</div>
+
+<p><i><b>8. Experimental Two-fluid Cell.</b></i> Fig. 7. This cell has a zinc strip,
+<i>Z</i>, and copper cylinder, <i>C</i>, for the "elements." The porous cup, <i>P
+C</i>, is fully described in <a href="#APPARATUS_11">App. 11</a>. <i>Z</i> is 5 &times; 1 in., and should be well
+amalgamated<span class='pagenum'><a name="Page_9" id="Page_9">[Pg 9]</a></span> (<a href="#APPARATUS_20">App. 20</a>). (Study reasons for amalgamation.) A zinc rod,
+like that shown in Fig. 4, may be used instead of the strip. The copper
+cylinder, <i>C</i>, nearly surrounds <i>P C</i>, and is made from a piece of thin
+sheet-copper, 6 &times; 2 in. The narrow strip, or leader, <i>A</i>, is 5 &times; &frac12; in.
+To fasten it to <i>C</i>, punch two small holes in <i>C</i> and <i>A</i>, put short
+lengths of stout copper wire through the holes, and hammer them down so
+that they will act as rivets, <i>R</i>. <i>C</i> can be hung centrally in the
+tumbler by bending <i>A</i> as shown. <i>Y</i> and <i>X</i> are spring binding-posts
+(<a href="#APPARATUS_42">App. 42</a>). The battery wires can be fastened directly to <i>Z</i> and <i>A</i>, as
+suggested in Fig. 4.</p>
+
+<p><i>9. Setting up the Cell.</i> Arrange as in Fig. 7, but remove <i>Z</i> from <i>P
+C</i>. Pour some of the acid solution of <a href="#APPARATUS_14">App. 14</a> into <i>P C</i> until it stands
+about 2&frac12; in. deep, and at once pour the copper solution of <a href="#APPARATUS_16">App. 16</a> in
+the tumbler, on the outside of <i>P C</i>, until it stands at the same height
+as the liquid in <i>P C</i>. As soon as the liquids have soaked into <i>P C</i>,
+you can put <i>Z</i> in place, when the cell will be ready for use. Remove
+and wash <i>Z</i>, when you have finished, and if you wish to use this cell
+occasionally, remove the liquids and wash <i>P C</i> thoroughly in water.
+When dry it will be as good as new. The acid rapidly acts upon <i>Z</i>, so
+it is better to remove <i>Z</i> if you wish to leave the experimenting even
+for a few minutes only.</p>
+
+<p>Put a few crystals of copper sulphate (blue vitriol) in the tumbler
+under the copper, to keep the copper solution saturated. (See text-book
+for the chemical action in this two-fluid cell.)</p>
+
+
+<p class="app"><a name="APPARATUS_8" id="APPARATUS_8"></a>APPARATUS 8.</p>
+
+<div class="figright" style="width: 350px;"><a name="Fig_8" id="Fig_8"></a>
+<img src="images/figure8.jpg" width="350" height="359" alt="Fig. 8." title="" />
+<span class="caption">Fig. 8.</span>
+</div>
+
+<p><i><b>10. Two-fluid Battery.</b></i> Fig. 8. When two or more cells are joined
+together the combination is called a battery. Fig. 8 shows two
+experimental cells joined in series. (Study methods of joining cells.)
+For convenience,<span class='pagenum'><a name="Page_10" id="Page_10">[Pg 10]</a></span> and to keep them from being easily overturned, a frame
+has been made for them. The base, <i>B</i>, is 8 &times; 4 &times; &#8542; in. To the back of
+this is nailed the upright board, <i>A</i>, 8 &times; 4&frac12; &times; &frac12; in. On the top of
+<i>A</i> are 3 binding-posts, 1, 2, 3, which consist of metal strips 1&frac14; &times;
+&frac12; in. At the lower ends are screws which are connected with the cells,
+as shown. Spring binders can be easily slipped on and off the upper ends
+of the strips, so that one or two cells can be used at will. Bent
+strips, <i>C</i>, are nailed to <i>B</i>, to hold the tumblers firmly in place.
+This framework is not necessary, of course, to the proper working of the
+battery, but with it you are much less liable to upset the cells.</p>
+
+
+<p class="app"><a name="APPARATUS_9" id="APPARATUS_9"></a>APPARATUS 9.</p>
+
+<p><i><b>11. Gravity Cell.</b></i> Fig. 9. In the two-fluid cell of <a href="#APPARATUS_7">App. 7</a> the fluids
+were kept apart by the porous cup. The gravity cell is really a
+two-fluid cell in which the two liquids are kept separate by the joint
+action of the current and the force of gravity. This cell is used for
+telegraph lines and for other closed-circuit work.</p>
+
+<p><i>12. Construction.</i> The zinc and copper, <i>Z</i> and <i>C</i>, Fig. 9, can be
+purchased about as cheaply as you can make them. There are many forms of
+the zincs, the one shown being called the crow-foot shape. The copper
+may be star-shaped, or as shown. If you wish to make <i>C</i>, use thin
+sheet-copper. Brush copper, 1&frac34; in. wide, is excellent for the
+purpose. Use a piece 12 or 15 in. long, and fasten to one end of it a
+copper wire, <i>W</i>, which must be<span class='pagenum'><a name="Page_11" id="Page_11">[Pg 11]</a></span> covered with paraffined paper, or with
+rubber or glass tubing, where it passes up through the zinc sulphate
+solution and near <i>Z</i>. The glass jar, <i>J</i>, may be made from a large
+glass bottle. (See index for battery jars.)</p>
+
+<p><i>13. To Set Up the Cell.</i> (A) Place <i>C</i> upon the bottom of <i>J</i>, with <i>W</i>
+in the position shown. (B) Put in enough copper sulphate crystals to
+cover the bottom of <i>J</i>, but do not try to entirely cover <i>C</i>. At the
+start &frac12; lb. will be enough. (C) Pour in clean water until <i>J</i> is half
+full. (D) In another vessel dissolve 1 or 2 oz. of zinc sulphate in
+enough water to complete filling, <i>J</i>. (E) Hang <i>Z</i> in place (Fig. 9).
+<i>Z</i> must never touch <i>C</i>. They should be about 3 in. apart. A wire is
+attached to <i>Z</i> by the screw, <i>S</i>, and the hole, <i>H</i>. (F) Pour the zinc
+sulphate solution into <i>J</i> until it is within an inch of the top. It
+should cover <i>Z</i>.</p>
+
+<div class="figleft" style="width: 300px;"><a name="Fig_9" id="Fig_9"></a>
+<img src="images/figure9.jpg" width="300" height="394" alt="Fig. 9." title="" />
+<span class="caption">Fig. 9.</span>
+</div>
+
+<p>(G) Connect the wires leading from <i>Z</i> and <i>C</i> to your sounder and key.
+(See diagram.) The cell will be weak at first, and it may not be able to
+run your sounder. If this is the case, "short-circuit" it by allowing
+the current to run around and around through the sounder and key, the
+switch being closed. You may also "short-circuit" the cell by joining
+the two wires together. This will, in a few hours, make the dividing
+line between the blue and white quite distinct, when the cell will be
+stronger. If you have a short line only, the battery may be
+short-circuited through your sounder or other coils of wire for 5 or 6
+hours a day, without working it too much. It may be necessary to draw
+off some of the clear zinc sulphate,<span class='pagenum'><a name="Page_12" id="Page_12">[Pg 12]</a></span> replacing it with clear water, if
+the blue line gets too low. Add water occasionally to make up for
+evaporation.</p>
+
+<p><i>14. Regulating.</i> The two solutions are kept apart by gravity, as the
+copper sulphate is heavier than the zinc sulphate. The dividing line
+between the blue and white solutions is fairly clear when the battery
+works well, and it should be about half way between <i>C</i> and <i>Z</i>, or
+about at <i>J</i>, Fig. 9. Never allow the blue to get as high as <i>Z</i>, as
+this indicates that the cell is not worked enough. The dividing line can
+be lowered by allowing it to run a buzzer or bell for a few hours, or by
+simply short-circuiting it. If the blue gets much below <i>J</i> it indicates
+that you are working the cell too hard, or that you need more copper
+sulphate. The harder the cell works, the more zinc sulphate is formed,
+and the lower the dividing line becomes.</p>
+
+<p><i>15. Gravity Batteries</i> of two more cells are needed when used on
+telegraph lines. You will need 1 cell to each sounder; that is, for a
+short line in the house with two sounders, use 2 cells. If you use a few
+hundred feet of wire running to a friend's house, use 3 cells. They must
+be joined in series; that is, the copper of one to the zinc of the
+other. (See diagram of complete telegraph line.) Do not use ground
+connections for short lines and home-made sounders; use a return wire.
+Do not use different kinds of cells upon the same line.</p>
+
+
+<p class="app"><a name="APPARATUS_10" id="APPARATUS_10"></a>APPARATUS 10.</p>
+
+<p><i><b>16. Storage Battery.</b></i> To show the principle of storage batteries it is
+only necessary to use two plates of lead dipped in the battery fluid of
+<a href="#APPARATUS_14">App. 14</a>. The cell may be made as in <a href="#APPARATUS_5">App. 5</a>, Fig. 5, the only difference
+being that both plates are of sheet-lead. It will be an advantage to
+make the plates rough by hammering against<span class='pagenum'><a name="Page_13" id="Page_13">[Pg 13]</a></span> them a coarse file. (See
+explanations and experiments with this form of cell in text-book.)</p>
+
+
+<p class="app"><a name="APPARATUS_11" id="APPARATUS_11"></a>APPARATUS 11.</p>
+
+<div class="figright" style="width: 280px;"><a name="Fig_10" id="Fig_10"></a>
+<img src="images/figure10.jpg" width="280" height="498" alt="Fig. 10." title="" />
+<span class="caption">Fig. 10.</span>
+</div>
+
+<p><i><b>17. Porous Cups for Two-fluid Cells.</b></i> Fig. 10. Very good porous cups
+can be made from ordinary blotting-papers, the average ones measuring
+9&frac12; &times; 4 in. White ones should be used, so that you will not be
+bothered with the color coming out. Soak the edge along one end of the
+blotter in paraffine (Index) for about &frac14; in. When this is cold, roll
+the blotter into the form of a cylinder that is a little over 1 in.
+inside diameter, and have the paraffined end on the outside. This will
+make 2 thicknesses of paper all around, and a little to spare. Rub a hot
+nail over the paraffine to melt it, and stick the end to the cylinder.
+By putting on a little more paraffine along the edge where the end laps
+over, a good solid cylinder can be made. The cylinder should be
+strengthened still more by dipping each end into melted paraffine for
+about &#8539; in. The dark stripes around the ends and down the front of the
+cylinder (Fig. 10) are to represent the paraffine. Cut out a bottom
+about &frac14; in. larger all around than the cylinder. This may be
+paraffined to make it stiff. It should be fastened to the cylinder with
+paraffine. Paraffine is not acted upon or softened by water or acid, as
+is the case with glue.</p>
+
+
+<p class="app"><a name="APPARATUS_12" id="APPARATUS_12"></a>APPARATUS 12.</p>
+
+<p><i><b>18. Porous Cups for Two-fluid Cells.</b></i> Instead of the blotters of <a href="#APPARATUS_11">App.
+11</a>, you can use short lengths of mailing-tubes, which are used to
+protect pictures, etc., when sent by mail. If you find that the
+particular tube<span class='pagenum'><a name="Page_14" id="Page_14">[Pg 14]</a></span> tends to unwind when soaked, you can use a little
+paraffine along the edges of the spiral, as suggested in <a href="#APPARATUS_11">App. 11</a>.
+Bottoms can be made for the cups as before.</p>
+
+
+<p class="app"><a name="APPARATUS_13" id="APPARATUS_13"></a>APPARATUS 13.</p>
+
+<p><i><b>19. Porous Cups for Two-fluid Cells.</b></i> Ordinary unglazed earthen
+flower-pots make good cups. The hole in the bottom should be closed with
+a cork, or by fastening a piece of pasteboard over the hole with
+paraffine. The pasteboard may be fastened to the under side of the
+bottom more easily than to the upper side.</p>
+
+<p><i>20. Note.</i> It is a good idea to soak the top edge of porous cups for
+about &frac14; in. in paraffine to keep the solutions from crawling up by
+capillary attraction. If the solutions constantly evaporate from the
+soaked tops of the cups, they not only waste but they get the whole
+thing covered with crystals.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_15" id="Page_15">[Pg 15]</a></span></p>
+<h3><a name="CHAPTER_II" id="CHAPTER_II"></a>CHAPTER II.</h3>
+
+<h4>BATTERY FLUIDS AND SOLUTIONS.</h4>
+
+
+<p><i><b>21. Sulphuric Acid.</b></i> <span class="smcap">This acid must be handled with great care</span>, as it
+(the concentrated) is very strong, and will burn the hands, eat holes in
+clothing, carpets, etc.; it will even char wood. Do not let any of it
+drop anywhere accidentally. If you wish to pour concentrated acid into a
+bottle, place the bottle to be filled upon a plate, and wipe all drops
+of acid from the outside of it afterward. The concentrated acid should
+be kept in tightly-corked bottles, as it absorbs moisture from the air
+very rapidly. Ordinary corks should be paraffined if they are to be used
+in acid bottles, or they will be soon eaten up.</p>
+
+<p><i><a name="s22" id="s22"></a>22. Mixing.</i> When sulphuric acid and water are mixed, considerable heat
+is produced. <i>Never pour water into the acid</i>, as the heat would be
+produced so rapidly that the vessel containing the mixture might break.
+<i>Always</i> pour the acid into the water, and thoroughly stir the mixture
+at the same time. Earthen vessels do not break when heated as easily as
+glass ones. The mixing may be done in ordinary glass fruit-jars, if care
+be taken to pour the acid <i>slowly</i> into the water. The jars should be
+set in some larger dish, or in the sink, before adding the acid. If they
+get too hot, allow them to cool a little before proceeding with the
+mixing. As the acid is much heavier than water, it will immediately sink
+to the bottom of the jar, unless constantly stirred.</p>
+
+<p>23. There are different grades of acid upon the market. For battery
+purposes you do not need the chemically pure<span class='pagenum'><a name="Page_16" id="Page_16">[Pg 16]</a></span> (C P) acid. The ordinary
+"commercial acid" is all right, even though it is a little dark in
+color. You can get this at any drug-store. Get 5 or 10 cents' worth at a
+time.</p>
+
+
+<p class="app"><a name="APPARATUS_14" id="APPARATUS_14"></a>APPARATUS 14.</p>
+
+<p><i><b>24. Battery Fluid for Simple Cells.</b></i> For the simple cell (<a href="#APPARATUS_5">App. 5</a>), when
+it is to be used for experiments with detectors or in the study of
+polarization, etc., a very dilute acid is best. Mix 1 fluid ounce of
+commercial acid with 1 pint of water. This will make 17 fluid ounces
+(<a href="#APPARATUS_19">See App. 19</a>), and your mixture will be one-seventeenth acid. Make up a
+pint or quart bottle of this at a time, and label it with the date:</p>
+
+<p class="center">
+Dilute sulphuric acid.<br />
+1 part acid, 16 parts water.<br />
+Apparatus 14.<br />
+</p>
+
+<p><i>25. Note.</i> Do not fail to paste a label on all bottles as soon as you
+have put anything into them. Give the date, contents, and any other
+information that will help you to reproduce the mixture again. Do not
+write on them any abbreviations or other things that you will soon
+forget.</p>
+
+
+<p class="app"><a name="APPARATUS_15" id="APPARATUS_15"></a>APPARATUS 15.</p>
+
+<p><i><b>26. Battery Fluid; Bichromate Solution.</b></i> For running small motors,
+shocking coils, etc., this solution will be found good when used with
+the zinc and carbon elements given in <a href="#APPARATUS_3">App. 3</a> and <a href="#APPARATUS_4">4</a>. The bichromate
+destroys the hydrogen bubbles which help to polarize cells so rapidly
+when the plain dilute acid (<a href="#APPARATUS_14">App. 14</a>) is used. (Study polarization.) The
+zinc used in this fluid must be well amalgamated (<a href="#APPARATUS_20">App. 20</a>).</p>
+
+<p><i>Directions.</i> With 1 quart of cold water placed in a glass or earthen
+dish, slowly mix 4 fluid ounces of commercial<span class='pagenum'><a name="Page_17" id="Page_17">[Pg 17]</a></span> sulphuric acid. <i><a href="#s22">Read &sect;
+22</a> carefully.</i> When this gets about cold, add 4 ounces of bichromate of
+potash. Powdered bichromate will dissolve more quickly than the lump.
+Keep this fluid in corked bottles, labelled, with date:</p>
+
+<p class="center">
+Bichromate Battery Fluid.<br />
+Apparatus 15.<br />
+</p>
+
+<p>27. Always take the zinc from this fluid as soon as you have finished
+experimenting, or even if you have no use for the cell for a few
+minutes. The zinc and fluid are rapidly destroyed in bichromate cells
+even when the circuit is open. Always wash the carbon and zinc as soon
+as you take them from the fluid.</p>
+
+
+<p class="app"><a name="APPARATUS_16" id="APPARATUS_16"></a>APPARATUS 16.</p>
+
+<p><i><b>28. Battery Fluid.</b></i> For 2&ndash;fluid cells (<a href="#APPARATUS_7">App. 7</a>), a saturated solution of
+copper sulphate (blue vitriol) is needed. Place some of the crystals in
+a glass jar, with water, stir them around, and add the sulphate as long
+as it is dissolved. A few extra crystals should be left in the stock
+bottle so that the solution will always be saturated.</p>
+
+
+<p class="app"><a name="APPARATUS_17" id="APPARATUS_17"></a>APPARATUS 17.</p>
+
+<p><i><b>29. Vinegar Battery Fluid.</b></i> For a few of the experiments with
+detectors, etc., good strong vinegar does well as the exciting fluid.
+This may be used with the copper and zinc or carbon and zinc elements.
+The amount of current given with vinegar and <a href="#APPARATUS_4">App. 4</a> or <a href="#APPARATUS_5">5</a> is sufficient
+to show many of the simpler experiments.</p>
+
+
+<p class="app"><a name="APPARATUS_18" id="APPARATUS_18"></a>APPARATUS 18.</p>
+
+<p><i><b>30. Battery Fluid.</b></i> Strong brine, made by dissolving ordinary salt in
+water, will produce quite a little current with <a href="#APPARATUS_4">App. 4</a> or <a href="#APPARATUS_5">5</a>. The
+presence of the current is easily shown with the astatic detectors.</p>
+
+
+<p><span class='pagenum'><a name="Page_18" id="Page_18">[Pg 18]</a></span></p><p class="app"><a name="APPARATUS_19" id="APPARATUS_19"></a>APPARATUS 19.</p>
+
+<p><i><b>31. Measures for Water, Acids, etc.</b></i> If you do not own a graduated
+glass, such as druggists use for measuring liquids, the following plan
+will be found useful. In the mixing of battery fluids, etc., while it is
+not necessary to be absolutely exact, it is necessary to know
+approximately what you are doing.</p>
+
+<p>An ordinary glass pint fruit jar may be taken as the standard. This
+holds 16 fluid ounces, or 2 ordinary teacupfuls. A teacupful may then be
+taken as &frac12; pint, or 8 fluid ounces. You can probably find a small
+bottle that will hold 1 or 2 oz., and you can easily tell how much it
+holds by filling it and counting the number of times it is contained in
+the pint can.</p>
+
+<p>A slim bottle holding &frac12; pint can be made into a convenient measuring
+glass by scratching lines on it with the sharp edge of a hard file. The
+lines should be placed, of course, so that they will show how much
+liquid you must put into it to make 1 oz., 2 oz., etc. Instead of the
+file marks, a narrow strip of paper may be pasted upon the bottle, and
+the divisions shown by lines drawn upon the paper.</p>
+
+
+<p class="app"><a name="APPARATUS_20" id="APPARATUS_20"></a>APPARATUS 20.</p>
+
+<p><i><b>32. To Amalgamate Battery Plates.</b></i> To keep the <i>zinc</i> plates or rods in
+cells from being eaten or dissolved when the circuit is opened, they
+should be amalgamated; that is, they should have a coating of mercury.
+The local currents (see text-book) aid in rapidly destroying the zinc,
+unless it is amalgamated. Do not amalgamate copper plates&mdash;merely the
+zinc ones.</p>
+
+<p>33. Place a few drops of mercury in a butter dish. Dip the zinc into the
+solution of <a href="#APPARATUS_14">App. 14</a>, then lay it upon a flat board. This is necessary
+with <i>thin</i> sheet-zinc, as it becomes<span class='pagenum'><a name="Page_19" id="Page_19">[Pg 19]</a></span> very brittle when coated with
+mercury, and will not stand hard rubbing. If you also dip a very narrow
+piece of tin into the dilute sulphuric acid, you can use this as a spoon
+and lift one drop of mercury at a time from the butter dish to the zinc.
+By tapping the tin upon the zinc, the mercury will leave the tin. Put
+the mercury only where the zinc will be under the solutions in the cell,
+then rub the drops around with a small cloth that has been dipped in the
+acid. The zinc will become very bright and silvery, due to the mercury.
+Do not get too much mercury on it, just enough to give it a thin coat,
+as it will make the thin zinc so brittle that it will very easily break.
+Amalgamate both sides of the zinc.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_20" id="Page_20">[Pg 20]</a></span></p>
+<h3><a name="CHAPTER_III" id="CHAPTER_III"></a>CHAPTER III.</h3>
+
+<h4>MISCELLANEOUS APPARATUS AND METHODS OF CONSTRUCTION.</h4>
+
+
+<p class="app"><a name="APPARATUS_21" id="APPARATUS_21"></a>APPARATUS 21.</p>
+
+<p><i><b>34. For Annealing and Hardening Steel.</b></i> (See text-book for reasons why
+some parts of electrical apparatus should be made of hard steel, while
+other parts should be made of soft iron.)</p>
+
+<p><i>35. To anneal</i> or soften spring steel so that you can bend it without
+breaking it, heat it in a candle, gas, or alcohol flame until it is
+red-hot; allow the steel to cool in the air slowly.</p>
+
+<p><i>36. To harden</i> steel, heat as before, then suddenly plunge the red-hot
+piece into cold water. This will make the steel very hard and brittle.</p>
+
+<p>Small pieces may be held by pinching them between two pieces of wood.
+Needles and wires may be stuck in a cork, which will serve as a handle.
+(See text-book.)</p>
+
+
+<p class="app"><a name="APPARATUS_22" id="APPARATUS_22"></a>APPARATUS 22.</p>
+
+<div class="figleft" style="width: 212px;"><a name="Fig_11" id="Fig_11"></a>
+<img src="images/figure11.jpg" width="212" height="330" alt="Fig. 11." title="" />
+<span class="caption">Fig. 11.</span>
+</div>
+
+<p><i><b>37. Alcohol Lamp.</b></i> Fig. 11. An alcohol lamp is very useful in many
+experiments, and it is better than a candle for annealing or hardening
+steel needles when making small magnets (<a href="#APPARATUS_21">App. 21</a>). You can make a good
+lamp by using a small bottle with a wide opening. A vaseline bottle or
+even an ink bottle will do. Make a hole about &frac14; in. in diameter
+through the cork with a small round file, or burn it through with a hot
+nail. Make a cylinder of tin about 1&frac12; in. long and just large enough
+to push through the hole. The tin may be simply rolled up. If<span class='pagenum'><a name="Page_21" id="Page_21">[Pg 21]</a></span> you have
+glass tubing, use a short length of that instead of the tin. For the
+wick, roll up some flannel cloth. This should not fit the inside of the
+tin tube too tightly. The alcohol should be put into the lamp when you
+want to use it, and that left should be put back into the supply-bottle
+when you have finished, as alcohol evaporates very rapidly. The flame of
+this lamp is light-blue in color, and very hot.</p>
+
+<p><i>Caution.</i> Do not have your supply-bottle of alcohol near the lamp when
+you light the latter, or near any other flame. The vapor of alcohol is
+explosive.</p>
+
+
+<p class="app"><a name="APPARATUS_23" id="APPARATUS_23"></a>APPARATUS 23.</p>
+
+<p><i><b>38. Spool Holder for Wire.</b></i> Fig. 12. When winding magnets it is
+necessary to have the spool of wire so arranged that it will take care
+of itself and not interfere with the winding. If you have a brace and
+bit, bore a hole in a base &#8542; in. thick for a &frac14; in. dowel. The dowel
+should fit the hole tight. The spools of wire purchased can then be
+placed upon the dowel, where they will unwind evenly. The base may be
+nailed or clamped to a table.</p>
+
+<div class="figright" style="width: 291px;"><a name="Fig_12" id="Fig_12"></a>
+<img src="images/figure12.jpg" width="291" height="277" alt="Fig. 12." title="" />
+<span class="caption">Fig. 12.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_24" id="APPARATUS_24"></a>APPARATUS 24.</p>
+
+<p><i><b>39. Spool Holder for Wire.</b></i> If you have no brace and bit to make <a href="#APPARATUS_23">App.
+23</a>, nail a spool to a wooden base, place a short length of dowel in the
+spool, and use this combination as a spool holder. Make the dowel fit
+the spool by winding paper around it.</p>
+
+
+<p class="app"><a name="APPARATUS_25" id="APPARATUS_25"></a>APPARATUS 25.</p>
+
+<p><i><b>40. To Make Holes in Wood.</b></i> If you have a brace and a set of bits, or
+even a small hand-drill, it will be an easy matter to bore holes in
+wood. An awl should<span class='pagenum'><a name="Page_22" id="Page_22">[Pg 22]</a></span> be used to make holes for screws, such as those
+used in making binding-posts, etc., as the wood is very liable to split
+if a screw is forced into it without a previously-made hole.</p>
+
+<p>Red-hot nails, needles, etc., are easily made to burn holes of desired
+diameters. They may be heated in a gas flame or by means of the alcohol
+lamp (<a href="#APPARATUS_22">App. 22</a>). Flat pieces of hot steel will burn narrow slots, and
+small, square holes may be made with hot nails.</p>
+
+
+<p class="app"><a name="APPARATUS_26" id="APPARATUS_26"></a>APPARATUS 26.</p>
+
+<div class="figleft" style="width: 220px;"><a name="Fig_13" id="Fig_13"></a>
+<img src="images/figure13.jpg" width="220" height="467" alt="Fig. 13." title="" />
+<span class="caption">Fig. 13.</span>
+</div>
+
+<p><i><b>41. To Make Holes in Sheet-Metal.</b></i> Fig. 13. Holes may be punched in
+sheet-tin, copper, zinc, etc., in the following manner: Set a block of
+hard wood, <i>W</i>, on end; that is, place it so that you will pound
+directly against the <i>end</i> of the grain. Lay the metal, <i>T</i>, to be
+punched, upon this, and use a flat-ended punch. A sharp blow upon a good
+punch with a hammer will make a fairly clean hole; that is, it will cut
+out a piece of metal, and push it down into the wood. A sharp-pointed
+punch will merely push the metal aside, and leave a very ragged edge to
+the hole. A punch may be made of a nail by filing its end flat.</p>
+
+
+<p class="app"><a name="APPARATUS_27" id="APPARATUS_27"></a>APPARATUS 27.</p>
+
+<p><i><b>42. To Punch Holes through Thick Yokes, etc.</b></i> As soon as 5 or 6 layers
+are to be punched at one operation, the process becomes a little more
+difficult than that given in <a href="#APPARATUS_26">App. 26</a>. If you have an anvil, you can
+place the yoke over one of the round holes in it, and punch the tin
+right down into the hole, the ragged edges being afterward filed off.
+Hold the yoke as in <a href="#APPARATUS_79">App. 79</a> or <a href="#APPARATUS_80">80</a> for filing. As you will probably have
+no anvil, lay an<span class='pagenum'><a name="Page_23" id="Page_23">[Pg 23]</a></span> old nut from a bolt upon the end of the block of wood
+(<a href="#APPARATUS_26">App. 26</a>), place the metal to be punched over the hole, and imagine that
+you have an anvil. Very good results may be obtained by this method. The
+size of nut used will depend upon the size of hole wanted.</p>
+
+
+<p class="app"><a name="APPARATUS_28" id="APPARATUS_28"></a>APPARATUS 28.</p>
+
+<p><i><b>43. To Straighten Wires.</b></i> It is often necessary to have short lengths
+of wires straight, where they are to be made into bundles, etc. To
+straighten them, lay one or two at a time upon a perfectly flat surface,
+place a flat piece of board upon them, then roll them back and forth
+between the two. The upper board should be pressed down upon the wires
+while rolling them. If properly done, the wires can be quickly made as
+straight as needles.</p>
+
+<p><i><b>44. Push-Buttons.</b></i> Nearly every house has use for one or more
+push-buttons. The simple act of pressing your finger upon a movable
+button, or knob, may ring a bell a mile away, or do some other equally
+wonderful thing.</p>
+
+
+<p class="app"><a name="APPARATUS_29" id="APPARATUS_29"></a>APPARATUS 29.</p>
+
+<p><i><b>45. Push-Button.</b></i> Fig. 14. This is made quickly, and may be easily
+fastened to the window or door-casing. One wire is joined to <i>A</i> and the
+other to <i>C</i>. <i>B</i> is a strip of tin or other metal, about &#8541; in. wide
+and 2 in. long. It is bent so that it will not touch <i>A</i> unless it is
+pressed down. This may be placed anywhere, in an electric-bell circuit
+or other open circuit, where it is desired to let the current pass for a
+moment only at a time.</p>
+
+<div class="figcenter" style="width: 350px;"><a name="Fig_14" id="Fig_14"></a>
+<img src="images/figure14.jpg" width="350" height="159" alt="Fig. 14." title="" />
+<span class="caption">Fig. 14.</span>
+</div>
+
+
+<p><span class='pagenum'><a name="Page_24" id="Page_24">[Pg 24]</a></span></p><p class="app"><a name="APPARATUS_30" id="APPARATUS_30"></a>APPARATUS 30.</p>
+
+<p><i><b>46. Push-Button.</b></i> Fig. 15 and Fig. 16. By placing <a href="#APPARATUS_29">App. 29</a> in a box, we
+can make something that looks a little more like a real push-button.
+Fig. 15 shows a plan with the box-cover removed, and Fig. 16 shows a
+view of the inside of it, a part of the box being cut away. <i>C</i>, Fig.
+15, is a wooden pill-box 1 in. high and 1&frac34; in. in diameter. Make a
+&frac14; in. hole in the cover of <i>C</i> for the "button," <i>G</i>, which is a short
+piece of &frac14; in. dowel. This rests upon a single thickness of tin, <i>D</i>,
+which is cut into a strip &#8540; in. wide and about 1&frac14; in. long. In the
+bottom of <i>C</i> are two holes just large enough to allow the screws <i>E</i>
+and <i>F</i> to pass through. The wires, <i>A</i> and <i>B</i>, pass from the
+binding-posts, <i>X</i> and <i>Y</i>, through small holes burned through the sides
+of the box, and are fastened under the screw-heads. The whole box is
+screwed to the wooden base, which is 3 &times; 4 &times; &#8542; in., by the screws, <i>E</i>
+and <i>F</i>. <i>D</i> should have enough spring in it to raise itself and <i>G</i>
+when the pressure of the finger is removed. The circuit will be closed
+only when you press the button.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 15 and 16">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 224px;"><a name="Fig_15" id="Fig_15"></a>
+<img src="images/figure15.jpg" width="224" height="289" alt="Fig. 15." title="" />
+<span class="caption">Fig. 15.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_16" id="Fig_16"></a>
+<img src="images/figure16.jpg" width="300" height="227" alt="Fig. 16." title="" />
+<span class="caption">Fig. 16.</span>
+</div></td>
+</tr>
+</table></div>
+
+
+<p><span class='pagenum'><a name="Page_25" id="Page_25">[Pg 25]</a></span></p><p class="app"><a name="APPARATUS_31" id="APPARATUS_31"></a>APPARATUS 31.</p>
+
+<p><i><b>47. Push-Button.</b></i> Figs. 17, 18, 19. Fig. 17 shows a top view or plan of
+the apparatus. Fig. 18 is a sectional view; that is, we suppose that the
+button has been cut into two parts along its length and through the
+center line. Fig. 19 is an enlarged detail drawing of the underside of
+the spool, <i>C</i>. The same part is marked by the same letter in all of the
+figures.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 17, 18, and 19">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_17" id="Fig_17"></a>
+<img src="images/figure17.jpg" width="300" height="168" alt="Fig. 17." title="" />
+<span class="caption">Fig. 17.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_18" id="Fig_18"></a>
+<img src="images/figure18.jpg" width="300" height="224" alt="Fig. 18." title="" />
+<span class="caption">Fig. 18.</span>
+</div></td>
+</tr>
+<tr>
+<td align='center' colspan='2'><div class="figcenter" style="width: 234px;"><a name="Fig_19" id="Fig_19"></a>
+<img src="images/figure19.jpg" width="234" height="240" alt="Fig. 19." title="" />
+<span class="caption">Fig. 19.</span>
+</div></td>
+</tr>
+</table></div>
+
+<p>Saw an ordinary spool, <i>C</i>, into two parts. One-half of <i>C</i> will serve
+as the outside case for the button. The part to be pressed with the
+finger is a short length of &frac14; in. dowel. To keep this from falling out
+of the hole in <i>C</i>, a short piece of wire nail, <i>N</i>, has been put
+through a small hole in its lower end. A slot, <i>F</i>, has been burned or
+cut into the underside of <i>C</i>, so that <i>N</i> can pass up and down in it
+when <i>D</i> is raised and lowered. The rod, <i>D</i>, rests upon <i>A</i>, one of the
+contacts. This is a straight piece of tin, cut as shown in Fig. 17, the
+narrow part being &frac14; in. wide and 1&frac14; in. long. The wide part is &frac34;
+in. wide and 1 in. long. The other contact, <i>B</i>, is the same size as
+<i>A</i>. A deep groove, a little over &frac14; in. wide, is cut into the base so
+that the narrow part of <i>B</i> can be bent down below the end of <i>A</i>. The
+base shown is 4 &times; 2&frac12; &times; &#8542; in. The spool, <i>C</i>, is fastened to the
+base by 2 screws or wire<span class='pagenum'><a name="Page_26" id="Page_26">[Pg 26]</a></span> nails put up through the base, their positions
+being shown by the dots at <i>E</i>, Fig. 17. <i>X</i> and <i>Y</i>, Fig. 18, are 2
+screw binding-posts. It is evident that the current cannot pass from <i>X</i>
+to <i>Y</i>, unless the button, <i>D</i>, be pressed down so that the end of <i>A</i>
+will touch <i>B</i>.</p>
+
+
+<p class="app"><a name="APPARATUS_32" id="APPARATUS_32"></a>APPARATUS 32.</p>
+
+<p><i><b>48. Sifter for Iron Filings.</b></i> Fig. 20. In making magnetic figures with
+iron filings, it is an advantage to have the particles of iron fairly
+small and uniform in size. A simple sifter may be made by pricking holes
+in the bottom of a pasteboard pill-box with a pin. The sifter may be put
+away with the filings in it, provided you turn it upside down.</p>
+
+<div class="figcenter" style="width: 278px;"><a name="Fig_20" id="Fig_20"></a>
+<img src="images/figure20.jpg" width="278" height="217" alt="Fig. 20." title="" />
+<span class="caption">Fig. 20.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_33" id="APPARATUS_33"></a>APPARATUS 33.</p>
+
+<p><i><b>49. Sifter for Iron Filings.</b></i> Fig. 21. Punch small holes in the cover
+of a tin box with a small wire nail. If you have occasion to use sifters
+for other purposes, the different sizes can be made by using larger and
+smaller nails to punch the different tin covers. But one size of nail
+should be used for one sifter.</p>
+
+<div class="figleft" style="width: 300px;"><a name="Fig_21" id="Fig_21"></a>
+<img src="images/figure21.jpg" width="300" height="149" alt="Fig. 21." title="" />
+<span class="caption">Fig. 21.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_34" id="APPARATUS_34"></a>APPARATUS 34.</p>
+
+<p><i><b>50. Sifters</b></i> may be made by pricking holes in an envelope. A sifter
+with very small holes can be made of a piece of muslin cloth. This can
+be used in the form of a little bag, or a piece of it can be pasted over
+the open bottom of a pill-box.</p>
+
+
+<p><span class='pagenum'><a name="Page_27" id="Page_27">[Pg 27]</a></span></p><p class="app"><a name="APPARATUS_35" id="APPARATUS_35"></a>APPARATUS 35.</p>
+
+<p><i><b>51. To Cut Wires, Nails, etc.</b></i> If you have no wire-cutters, or large
+shears, you can cut large or small wires by hammering them against the
+sharp edge of another hammer, an anvil, or a piece of iron. Do not let
+the hammer itself hit upon the edge of the anvil. The above process will
+make a V-shaped dent on one side of even large wires, or nails, when
+they may be broken by bending back and forth.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_28" id="Page_28">[Pg 28]</a></span></p>
+<h3><a name="CHAPTER_IV" id="CHAPTER_IV"></a>CHAPTER IV.</h3>
+
+<h4>SWITCHES AND CUT-OUTS.</h4>
+
+
+<p><i><b>52. Switches, Cut-Outs.</b></i> Where apparatus is to be used frequently, such
+as for telephone and telegraph lines, it pays to make your switches,
+etc., carefully. The use of these switches, etc., will be shown in the
+proper place. Their construction only will be given here.</p>
+
+
+<p class="app"><a name="APPARATUS_36" id="APPARATUS_36"></a>APPARATUS 36.</p>
+
+<div class="figright" style="width: 300px;"><a name="Fig_22" id="Fig_22"></a>
+<img src="images/figure22.jpg" width="300" height="324" alt="Fig. 22." title="" />
+<span class="caption">Fig. 22.</span>
+</div>
+
+<p><i><b>53. Cut-Out.</b></i> Fig. 22. Details. <i>X</i>, <i>Y</i>, and <i>Z</i> represent 3
+binding-posts like <a href="#APPARATUS_42">App. 42</a>. These are fastened to a wooden base that is
+about 3 &times; 5 &times; &frac34;. The ends of the wires shown come from and go to the
+other pieces of apparatus. <i>Q</i> shows a stout wire or strip of 2 or 3
+thicknesses of tin. Suppose we have an apparatus, as, for example, an
+electric bell, which we want to have ring when someone at a distance
+desires to call us. If we use a telephone or telegraph instrument we
+shall want to cut the bell out of the circuit as soon as we hear the
+call and are ready to talk. Suppose the current comes to us through the
+wire, <i>A</i>, Fig. 22. It can pass by the wire, <i>C</i>, through the bell and
+back to <i>X</i>. If we wanted simply to have the bell ring, the current
+could pass directly from <i>X</i> into the earth, or over a return wire back
+to the push-button at our friend's house. If, however, we are to use
+some other instrument, by lifting the end of <i>Q</i> out of <i>X</i> and pushing
+it into <i>Y</i>, the bell will be cut out, and the current can pass on
+wherever we need it.</p>
+
+
+<p><span class='pagenum'><a name="Page_29" id="Page_29">[Pg 29]</a></span></p><p class="app"><a name="APPARATUS_37" id="APPARATUS_37"></a>APPARATUS 37.</p>
+
+<p><i><b>54. Cut-Out.</b></i> Fig. 23. The main features of this are like those of <a href="#APPARATUS_36">App.
+36</a>. The three binding-posts are like <a href="#APPARATUS_46">App. 46</a>. Instead of a band of metal
+to change connections, as <i>Q</i> in <a href="#APPARATUS_36">App. 36</a>, a stout copper wire is used.
+This can be easily changed from one of the upper binding-posts to the
+other, thereby throwing in or cutting out any piece of apparatus joined
+with the upper connectors.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 23 and 24">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_23" id="Fig_23"></a>
+<img src="images/figure23.jpg" width="300" height="357" alt="Fig. 23." title="" />
+<span class="caption">Fig. 23.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_24" id="Fig_24"></a>
+<img src="images/figure24.jpg" width="300" height="463" alt="Fig. 24." title="" />
+<span class="caption">Fig. 24.</span>
+</div></td>
+</tr>
+</table></div>
+
+
+<p class="app"><a name="APPARATUS_38" id="APPARATUS_38"></a>APPARATUS 38.</p>
+
+<p><i><b>55. Switch.</b></i> Fig. 24. This simple switch has but one contact point,
+<i>D</i>, which is a screw-head. This switch may be used anywhere in the
+circuit by simply cutting the wire carrying the current, and joining the
+ends of the wire to the binding-posts <i>X</i> and <i>Y</i>. The metal strip, <i>E</i>,
+is made of 2 or 3 thicknesses of tin. It is &#8541; in. wide and about 5 in.
+long, and presses down upon <i>D</i>, when swung to the left, thus closing
+the circuit. The short metal strips shown are &#8541; &times; 1&frac14; in. The upper
+strip is joined to the end of <i>E</i> by a coiled copper wire, <i>C W</i>. (See
+<a href="#APPARATUS_50">App. 50</a>.) If the current enters by the wire, <i>A</i>, it will pass through
+<i>C W</i>, <i>E</i>, <i>D</i> and out at <i>B</i>. The strip <i>E</i><span class='pagenum'><a name="Page_30" id="Page_30">[Pg 30]</a></span> is pivoted at <i>F</i> by a
+small screw. The base may be 3 or 4 &times; 5 &times; &#8542; in.</p>
+
+
+<p class="app"><a name="APPARATUS_39" id="APPARATUS_39"></a>APPARATUS 39.</p>
+
+<p><i><b>56. Switch.</b></i> Fig. 25. By increasing the number of contact points and
+the wires leading from them, a switch may be made to throw in one or
+more pieces of apparatus. This variety of switch is useful in connection
+with resistance coils (Index). By joining the ends of the coils with the
+points 1, 2, 3, etc., more or less resistance can be easily thrown in by
+simply swinging the lever, <i>E</i>, around to the left or right. The uses of
+this will be again referred to.</p>
+
+<div class="figcenter" style="width: 350px;">
+<img src="images/figure25.jpg" width="350" height="391" alt="Fig. 25." title="" />
+<span class="caption"><a name="Fig_25" id="Fig_25"></a>Fig. 25.</span>
+</div>
+
+<p><i>Details.</i> The base of the one shown in Fig. 25 is 4 &times; 5 &times; &#8542; in.
+thick. The switch, <i>E</i>, is a band of 2 thicknesses of tin &#8541; in. wide.
+It is pivoted at <i>F</i> with a screw. To the end of <i>E</i> is fastened a
+copper wire, which leads to the upper binding-post, <i>X</i> (<a href="#APPARATUS_46">App. 46</a>). The
+apparatus has 5 contact points, marked 1, 2, 3, etc. These consist of
+brass screws and copper washers. With <i>F</i> as a center draw the arc of a
+circle that has a radius of 4 in. Place<span class='pagenum'><a name="Page_31" id="Page_31">[Pg 31]</a></span> the screws 1, 2, etc., along
+this arc, and about &#8541; in. apart, center to center; that is, the screws
+are all 4 in. from <i>F</i>, and are, therefore, in the form of a curve.</p>
+
+<p>The last screw forms a part of the binding-post, <i>Y</i>. Suppose 4 pieces
+of apparatus, marked <i>A</i>, <i>B</i>, <i>C</i>, and <i>D</i>, be connected with 1, 2,
+etc., as shown. These may be, for example, coils of wire to be used as
+resistance coils. If the current enters at <i>X</i>, it will pass along at
+<i>E</i> and be ready to leave at <i>Y</i>, as soon as <i>E</i> touches one of the
+contact points. If <i>E</i> be placed upon 1, the current will be obliged to
+pass through all of the coils, <i>A</i>, <i>B</i>, etc., before it can get to <i>Y</i>.
+In this case the resistance will be greatest. If <i>E</i> be now moved on to
+2, only <i>A</i> will be cut out, and the total resistance reduced. By
+placing <i>E</i> upon 4, but one coil, <i>D</i>, will be in the circuit. When <i>E</i>
+is upon 5 the current will pass through the switch with practically no
+resistance. This is the principle upon which current regulators work.
+(Study resistance in text-book.) When <i>E</i> is in the position shown in
+Fig. 25 no current can pass.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_32" id="Page_32">[Pg 32]</a></span></p>
+<h3><a name="CHAPTER_V" id="CHAPTER_V"></a>CHAPTER V.</h3>
+
+<h4>BINDING-POSTS AND CONNECTORS.</h4>
+
+
+<p><i><b>57. Binding-Posts</b></i> are used to make connections between two pieces of
+apparatus, between two or more wires, between a wire and any apparatus,
+etc., etc. They are used simply for convenience, so that the wires can
+be quickly fastened or unfastened to the apparatus. There are many ways
+of making them at home. The following forms will be found useful and
+practical. Although some that are given are really connectors instead of
+binding-posts, we shall give them the general name of binding-posts.</p>
+
+
+<p class="app"><a name="APPARATUS_40" id="APPARATUS_40"></a>APPARATUS 40.</p>
+
+<p><i><b>58. Binding-Post.</b></i> About the simplest form is a screw, or a nail with a
+flat head. The bare wire may be placed under the head of the screw or
+nail before forcing it entirely into the wood. This will keep the end of
+the wire in place, and another wire may be joined electrically to the
+first by merely touching it to the screw-head, or by placing it under
+the screw-head.</p>
+
+
+<p class="app"><a name="APPARATUS_41" id="APPARATUS_41"></a>APPARATUS 41.</p>
+
+<div class="figleft" style="width: 194px;">
+<img src="images/figure26.jpg" width="194" height="128" alt="Fig. 26." title="" />
+<span class="caption"><a name="Fig_26" id="Fig_26"></a>Fig. 26.</span>
+</div>
+
+<p><i><b>59. Binding-Post.</b></i> Fig. 26. This consists of a screw and a copper
+washer or "bur." The screw is a "round-headed brass" one, &#8541; in. long,
+number 5 or 7. The copper burs are No. 8, and fit nicely around the
+screws. By using 2 burs instead of 1, several wires may be easily joined
+together at one point. Scrape the covering from the ends of the wires,
+and place them between the burs.</p>
+
+
+<p><span class='pagenum'><a name="Page_33" id="Page_33">[Pg 33]</a></span></p><p class="app"><a name="APPARATUS_42" id="APPARATUS_42"></a>APPARATUS 42.</p>
+
+<p><i><b>60. Binding-Post.</b></i> Fig. 27. A coiled spring serves very well as a
+connector. One end should be fastened to the apparatus, as shown, by
+clamping it under a screw-head. The other end of the coil should be
+pulled out a little, away from the other turns, so that you can stretch
+the spring in order to put the bare ends of wires between the turns. Any
+number of wires placed between these turns will be pinched and
+electrically connected. The coil should be about &frac12; in. long and less
+than &frac12; in. in diameter. You can make a coil by tightly wrapping stiff
+iron wire around a pencil. The steel wire springs taken from old
+window-shades are excellent for this purpose. They may be cut into
+lengths with tinner's shears.</p>
+
+
+<p class="app"><a name="APPARATUS_43" id="APPARATUS_43"></a>APPARATUS 43.</p>
+
+<p><i><b>61. Binding-Post.</b></i> Fig. 28. Two copper or tin strips fastened at one
+end by a screw, the upper strip being bent a little at one end, make a
+connector that is useful for some purposes, where you want to make and
+break the connection frequently. The bare end of the wire which belongs
+to the apparatus is fastened under the screw-head. The outside wire, or
+wires, to be connected are pushed between the strips of metal. Another
+way is to fasten the outside wire to a strip of metal about &frac12; in.
+wide, and then push this between the strips shown in the figure. The
+strips shown should be about &frac34; in. wide and 1&frac14; in. long.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 27, 28, and 29">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 194px;"><a name="Fig_27" id="Fig_27"></a>
+<img src="images/figure27.jpg" width="194" height="128" alt="Fig. 27." title="" />
+<span class="caption">Fig. 27.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 194px;"><a name="Fig_28" id="Fig_28"></a>
+<img src="images/figure28.jpg" width="194" height="128" alt="Fig. 28." title="" />
+<span class="caption">Fig. 28.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 194px;"><a name="Fig_29" id="Fig_29"></a>
+<img src="images/figure29.jpg" width="194" height="151" alt="Fig. 29." title="" />
+<span class="caption">Fig. 29.</span>
+</div></td>
+</tr>
+</table></div>
+
+
+<p class="app"><a name="APPARATUS_44" id="APPARATUS_44"></a>APPARATUS 44.</p>
+
+<p><i><b>62. Binding-Post.</b></i> Fig. 29. A combination made between <a href="#APPARATUS_42">App. 42</a> and <a href="#APPARATUS_43">43</a>
+does well. Fasten a metal strip,<span class='pagenum'><a name="Page_34" id="Page_34">[Pg 34]</a></span> &frac34; in. &times; 1&frac14; in., to the apparatus
+by means of a screw. The apparatus wire should be fastened under the
+screw-head. A short length of spring may be pushed upon the upright part
+of the strip, as shown. Into this you can quickly fasten the outside
+wires.</p>
+
+
+<p class="app"><a name="APPARATUS_45" id="APPARATUS_45"></a>APPARATUS 45.</p>
+
+<p><i><b>63. Binding-Post.</b></i> Fig. 30. This makes a very simple and practical
+binding-post for home-made apparatus. It consists of a screw-eye,
+preferably of brass. The circle or eye should be about &#8540; or &frac12; in. in
+diameter. The thread on such a screw-eye will be about &frac12; in. long. Two
+copper burs are used to pinch the wires.</p>
+
+
+<p class="app"><a name="APPARATUS_46" id="APPARATUS_46"></a>APPARATUS 46.</p>
+
+<p><i><b>64. Binding-Post.</b></i> Fig. 31. This consists of a screw, screw-eye, bur
+and a metal strip, &frac34; &times; 1&frac14; in. The apparatus wire should be fastened
+under the screw-head. Any outside wires which are to be joined to the
+apparatus should be clamped under the bur by turning the screw-eye. A
+small hole should be made in the wood before putting in the screw-eye.
+(See <a href="#APPARATUS_25">App. 25</a>.) Do not turn the screw-eye too hard, or you will spoil the
+thread made in the wood.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 30, 31, and 32">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 194px;"><a name="Fig_30" id="Fig_30"></a>
+<img src="images/figure30.jpg" width="194" height="191" alt="Fig. 30." title="" />
+<span class="caption">Fig. 30.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 194px;"><a name="Fig_31" id="Fig_31"></a>
+<img src="images/figure31.jpg" width="194" height="148" alt="Fig. 31." title="" />
+<span class="caption">Fig. 31.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 194px;"><a name="Fig_32" id="Fig_32"></a>
+<img src="images/figure32.jpg" width="194" height="133" alt="Fig. 32." title="" />
+<span class="caption">Fig. 32.</span>
+</div></td>
+</tr>
+</table></div>
+
+
+<p class="app"><a name="APPARATUS_47" id="APPARATUS_47"></a>APPARATUS 47.</p>
+
+<p><i><b>65. Binding-Post.</b></i> Fig. 32. The size of the bolt used in this form of
+binding-post will depend somewhat upon the thickness of the base of the
+apparatus. In general, a &frac34; or &#8542; in. base should be used where screws
+or<span class='pagenum'><a name="Page_35" id="Page_35">[Pg 35]</a></span> screw-eyes are necessary. With this kind (Fig. 32) a thin base can
+be used. The head is shown counter-sunk into the bottom of the base.
+This is not necessary, provided at least 3 heads are placed far enough
+apart to form legs for the apparatus to stand on. Strips of wood may be
+nailed upon the underside of the base to make room for the heads in case
+they are not used as legs. The wires should be pinched between the nut
+and the copper bur shown. If the bolt is too large for a bur, an iron
+washer may be used. A washer may be made of tin, or two nuts may be
+used.</p>
+
+
+<p class="app"><a name="APPARATUS_48" id="APPARATUS_48"></a>APPARATUS 48.</p>
+
+<div class="figleft" style="width: 194px;"><a name="Fig_33" id="Fig_33"></a>
+<img src="images/figure33.jpg" width="194" height="133" alt="Fig. 33." title="" />
+<span class="caption">Fig. 33.</span>
+</div>
+
+<p><i><b>66. Binding-Post.</b></i> Fig. 33. This is a suggestion for a combination of
+<a href="#APPARATUS_44">App. 44</a> and <a href="#APPARATUS_47">47</a>. It is useful in school apparatus. Wires may be
+permanently fastened on the right, under the nut, and a spring, as in
+<a href="#APPARATUS_44">App. 44</a>, may be slipped on the metal strip at the left, which is held
+under the head of the bolt.</p>
+
+
+<p class="app"><a name="APPARATUS_49" id="APPARATUS_49"></a>APPARATUS 49.</p>
+
+<p><i><b>67. Mercury Connector.</b></i> A cup of mercury may be used as a connector.
+Make a small hole about &frac14; in. in diameter and depth, in a piece of
+wood, and place 2 or 3 drops of mercury in this. The ends of wires
+dipped in this will be electrically connected.</p>
+
+
+<p class="app"><a name="APPARATUS_50" id="APPARATUS_50"></a>APPARATUS 50.</p>
+
+<div class="figright" style="width: 218px;"><a name="Fig_34" id="Fig_34"></a>
+<img src="images/figure34.jpg" width="218" height="133" alt="Fig. 34." title="" />
+<span class="caption">Fig. 34.</span>
+</div>
+
+<p><i><b>68. Connector.</b></i> Fig. 34. This shows how a wire may be fastened to one
+end of a short strip of tin. At the other end of the strip a slot is
+cut. This may straddle the body of a screw, or when left plain may be
+used to slip between the two metal strips shown in <a href="#APPARATUS_43">App. 43</a>.</p>
+
+
+<p><span class='pagenum'><a name="Page_36" id="Page_36">[Pg 36]</a></span></p><p class="app"><a name="APPARATUS_51" id="APPARATUS_51"></a>APPARATUS 51.</p>
+
+<p><i><b>69. Binding-Post.</b></i> Fig. 35. The ends of two or more wires may be
+quickly joined electrically by placing them between the nuts of a short
+bolt. By using 3 nuts the bolt will more easily connect a large number
+of wires.</p>
+
+<div class="figcenter" style="width: 200px;"><a name="Fig_35" id="Fig_35"></a>
+<img src="images/figure35.jpg" width="200" height="104" alt="Fig. 35." title="" />
+<span class="caption">Fig. 35.</span>
+</div>
+
+<p class="center"><i><b>Make Additional Notes and Sketches Here.</b></i></p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_37" id="Page_37">[Pg 37]</a></span></p>
+<h3><a name="CHAPTER_VI" id="CHAPTER_VI"></a>CHAPTER VI.</h3>
+
+<h4>PERMANENT MAGNETS.</h4>
+
+
+<p><i><b>70. Permanent Magnets</b></i> may be made in many ways and from many different
+kinds of steel. The steel used for needles, watch and clock springs,
+files, cutting tools, etc., is generally of good quality, and it is
+already hard enough to retain magnetism. (See Retentivity in text-book.)</p>
+
+
+<p class="app"><a name="APPARATUS_52" id="APPARATUS_52"></a>APPARATUS 52.</p>
+
+<p><i><b>71. Bar Magnet.</b></i> A straight magnet is called a bar magnet. Magnetize a
+sewing-needle. For some experiments a needle-magnet, as we may call it,
+is better than a large magnet.</p>
+
+
+<p class="app"><a name="APPARATUS_53" id="APPARATUS_53"></a>APPARATUS 53.</p>
+
+<p><i><b>72. Bar Magnet.</b></i> A harness-needle, which is thicker and stronger than a
+sewing-needle, makes an excellent bar magnet.</p>
+
+
+<p class="app"><a name="APPARATUS_54" id="APPARATUS_54"></a>APPARATUS 54.</p>
+
+<p><i><b>73. Bar Magnet.</b></i> For long slim magnets use a knitting-needle. Some
+knitting-pins, as they are sometimes called, break off short when bent,
+but most of them will bend considerably before breaking. These slim
+magnets are excellent for the study of Consequent Poles. (See
+text-book.)</p>
+
+
+<p class="app"><a name="APPARATUS_55" id="APPARATUS_55"></a>APPARATUS 55.</p>
+
+<p><i><b>74. Flexible Bar Magnets.</b></i> It is often necessary to have flexible
+magnets so that they may be bent into different shapes. These may be
+made from watch or clock springs, as such steel, called spring steel,
+will straighten out again as soon as the pressure is removed from it.
+Corset<span class='pagenum'><a name="Page_38" id="Page_38">[Pg 38]</a></span> steels, dress steels, hack-saw blades, etc., make good thin
+flexible bar magnets.</p>
+
+
+<p class="app"><a name="APPARATUS_56" id="APPARATUS_56"></a>APPARATUS 56.</p>
+
+<p><i><b>75. Strong Bar Magnets</b></i> may be made from flat files. The handle end may
+be broken off so that the two ends of the file shall be nearly alike in
+size. These should be magnetized upon an electro-magnet.</p>
+
+
+<p class="app"><a name="APPARATUS_57" id="APPARATUS_57"></a>APPARATUS 57.</p>
+
+<p><i><b>76. Compound Bar Magnets</b></i> are made by first magnetizing several thin
+pieces of steel, and then riveting them together so that their like
+poles shall be together, and pull together. To make a small compound bar
+magnet, magnetize several harness-needles, or even sewing-needles, and
+then bind them into a little bundle with all the <i>N</i> poles at the same
+end. Melted paraffine dropped in between them will hold them together.
+Rubber bands may be used also, or, if but one end is to be experimented
+with, the points may be stuck into a cork, and the heads used to do the
+lifting.</p>
+
+
+<p class="app"><a name="APPARATUS_58" id="APPARATUS_58"></a>APPARATUS 58.</p>
+
+<p><i><b>77. Small Horseshoe Magnets</b></i> may be made from needles or from other
+pieces of steel used for bar magnets. They should be annealed (<a href="#APPARATUS_21">App. 21</a>)
+at their centers at least, so that you can bend them into the desired
+shape. In the case of bright needles, like harness-needles, the part
+annealed will become blackened. If you heat the center only, and the
+ends remain bright for about &frac12; inch, you will not need to harden the
+needle again. It is an advantage to have the center of the magnet a
+little soft, as it is not then liable to break. The ends alone may be
+hardened by holding the bent portion away from the candle or gas flame,
+while heating the ends. The bent steel should be magnetized by drawing
+its ends across the poles of a horseshoe magnet.</p>
+
+
+<p><span class='pagenum'><a name="Page_39" id="Page_39">[Pg 39]</a></span></p><p class="app"><a name="APPARATUS_59" id="APPARATUS_59"></a>APPARATUS 59.</p>
+
+<p><i><b>78. Flexible Horseshoe Magnets</b></i> may be made of thin spring steel. The
+distance between the poles can be regulated at will by bending the steel
+more or less. The poles may be held at any desired distance apart by
+thread or wire, which should be wound around the legs of the magnet a
+little above the poles. This will keep the steel from straightening out.</p>
+
+
+<p class="app"><a name="APPARATUS_60" id="APPARATUS_60"></a>APPARATUS 60.</p>
+
+<p><i><b>79. Horseshoe Magnet.</b></i> Fig. 36 and 37. Magnetize two harness-needles,
+and stick them into a cork so that the poles shall be arranged as shown.
+The distance between the poles can be regulated to suit. This forms a
+very simple and efficient magnet, with the advantages of a real
+horseshoe magnet.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 36 and 37">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 179px;"><a name="Fig_36" id="Fig_36"></a>
+<img src="images/figure36.jpg" width="179" height="282" alt="Fig. 36." title="" />
+<span class="caption">Fig. 36.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 179px;"><a name="Fig_37" id="Fig_37"></a>
+<img src="images/figure37.jpg" width="179" height="282" alt="Fig. 37." title="" />
+<span class="caption">Fig. 37.</span>
+</div></td>
+</tr>
+</table></div>
+
+
+<p class="app"><a name="APPARATUS_61" id="APPARATUS_61"></a>APPARATUS 61.</p>
+
+<p><i><b>80. Armatures.</b></i> All home-made magnets should be provided with
+armatures, or keepers. These are made of soft iron on the regular
+magnets, and tend to keep the magnet strong. (See text-book.) For the
+bar magnets described, a piece of sheet-tin, upon which to lay them, is
+all that is needed for an armature. The lines of force will pass through
+this. For the horseshoe magnets described, strips of tin, soft iron
+wires, or even a wire nail placed across the poles will greatly aid in
+keeping in the strength. The little magnets should not be dropped or
+jarred. (Study the theory of magnetism in text-book.)</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_40" id="Page_40">[Pg 40]</a></span></p>
+<h3><a name="CHAPTER_VII" id="CHAPTER_VII"></a>CHAPTER VII.</h3>
+
+<h4>MAGNETIC NEEDLES AND COMPASSES.</h4>
+
+
+<p><i><b>81. Magnetic Needles and Compasses</b></i> consist chiefly of a short
+bar-magnet. When used to tell the directions, north, east, etc., the
+apparatus is generally called a compass. When we speak of the "needle,"
+we really mean the compass-needle. The little magnet may be almost any
+piece of magnetized steel, provided it is arranged so that it can easily
+swing around. There are several ways of supporting the compass-needle.
+It may rest upon a pivot, it may be hung from a fine thread, or it may
+be floated upon water with the aid of a cork, etc.</p>
+
+<p><i>82. Uses.</i> We all know that compasses are used to point to the north
+and south, and we speak of the "points of the compass." This, of course,
+is the most important use of the compass, and it has been known for
+centuries. In the laboratory it is used to <i>show or detect the presence
+of currents of electricity</i>, and, in connection with coils of wire, it
+may show the relative strengths of two currents, etc. When used for such
+purposes it generally has special forms and sizes. (<a href="#CHAPTER_XIII">See Galvanometers
+and Detectors.</a>)</p>
+
+
+<p class="app"><a name="APPARATUS_62" id="APPARATUS_62"></a>APPARATUS 62.</p>
+
+<p><i><b>83. Compass.</b></i> An oily sewing-needle will float upon the surface of
+water, when it is carefully let down to the water. A little butter may
+be rubbed upon the previously-magnetized needle to make it float better.</p>
+
+<div class="figleft" style="width: 350px;"><a name="Fig_38" id="Fig_38"></a>
+<img src="images/figure38.jpg" width="350" height="141" alt="Fig. 38." title="" />
+<span class="caption">Fig. 38.</span>
+</div>
+
+
+<p><span class='pagenum'><a name="Page_41" id="Page_41">[Pg 41]</a></span></p><p class="app"><a name="APPARATUS_63" id="APPARATUS_63"></a>APPARATUS 63.</p>
+
+<p><i><b>84. Compass.</b></i> Fig. 38 shows a magnetized sewing-needle floated upon a
+cork. The needle may be permanently fastened to the cork with a few
+drops of melted paraffine.</p>
+
+
+<p class="app"><a name="APPARATUS_64" id="APPARATUS_64"></a>APPARATUS 64.</p>
+
+<p><i><b>85. Compass.</b></i> Fig. 39. With a sharp knife make a cut part way through a
+flat cork. Into the cut push a short length of magnetized watch-spring.
+In the illustration the spring is shown partly removed from the cut.
+Float the cork.</p>
+
+
+<p class="app"><a name="APPARATUS_65" id="APPARATUS_65"></a>APPARATUS 65.</p>
+
+<p><i><b>86. Compass.</b></i> Fig. 40. Stick a pin, <i>P</i>, into a pasteboard, cork, or
+wooden base, <i>B</i>. Bend a piece of stiff paper double, as shown, and then
+stick through it, on each side, a magnetized sewing-needle, <i>S N</i>. The
+north poles of the needles should be at the same end of the paper. Why?
+Balance the paper upon the pin-pivot, and see it fly around to the north
+and south.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 39, 40, and 41">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 200px;"><a name="Fig_39" id="Fig_39"></a>
+<img src="images/figure39.jpg" width="200" height="91" alt="Fig. 39." title="" />
+<span class="caption">Fig. 39.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 200px;"><a name="Fig_40" id="Fig_40"></a>
+<img src="images/figure40.jpg" width="200" height="115" alt="Fig. 40." title="" />
+<span class="caption">Fig. 40.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 200px;"><a name="Fig_41" id="Fig_41"></a>
+<img src="images/figure41.jpg" width="200" height="99" alt="Fig. 41." title="" />
+<span class="caption">Fig. 41.</span>
+</div></td>
+</tr>
+</table></div>
+
+
+<p class="app"><a name="APPARATUS_66" id="APPARATUS_66"></a>APPARATUS 66.</p>
+
+<p><i><b>87. Compass.</b></i> Fig. 41. It is an advantage to have a magnetic needle
+that is always ready for use. <i>The support</i> is made by driving a pin
+through the <i>top</i> of a wooden pill-box, which should be about 1&frac34; in.
+in diameter. This gives plenty of room under and around the needle. If
+the pin be left too long, it will not be possible to put the bottom and
+top of the box together when you want to put<span class='pagenum'><a name="Page_42" id="Page_42">[Pg 42]</a></span> the compass away. Cut the
+pin off (<a href="#APPARATUS_35">App. 35</a>) at the right length, so that the magnetic needle can
+be safely put away in the closed pill-box.</p>
+
+<p><i>88. The "Needle,"</i> that is the short bar magnet, may be made of
+watch-spring. As the spring is already quite hard and brittle, it may be
+easily broken into desired lengths. It is always better to make 3 or 4
+needles at a time, as some will swing more easily than others, and time
+will be saved in making them. Break off 3 or 4 pieces of thin spring,
+each about 1&frac12; in. long. Bend them as in Fig. 42. A good dent, not a
+hole, should be made at the center of each to keep them upon the support
+or pin-point. A "center punch," not too sharp, is the best tool to use,
+but a slight dent may be made with a sharp wire nail, provided the
+watch-spring is first annealed or softened. (<a href="#APPARATUS_21">See App. 21</a>.) Do not place
+the spring directly upon iron or steel when making the dent, as these
+might injure the point of the punch, and the dent would not be deep
+enough. Fig. 42 shows a good way to make dents in steel springs. Place 2
+or 3 layers of copper or lead between the anvil and the spring. A hammer
+or hatchet will do for the anvil. As the copper will give easily, a good
+dent may be made by striking the punch or nail with a hammer. If the
+spring has been annealed before denting it, it should be hardened again
+(<a href="#APPARATUS_21">App. 21</a>) before magnetizing it, so that it will retain magnetism well.
+(See Residual Magnetism in text-book.)</p>
+
+<div class="figleft" style="width: 300px;"><a name="Fig_42" id="Fig_42"></a>
+<img src="images/figure42.jpg" width="300" height="216" alt="Fig. 42." title="" />
+<span class="caption">Fig. 42.</span>
+</div>
+
+<p><i>89. Balancing.</i> After a dent has been made, place the spring upon its
+support so that the pin-point shall be in the dent. It will, no doubt,
+need balancing. If one end is<span class='pagenum'><a name="Page_43" id="Page_43">[Pg 43]</a></span> but <i>slightly</i> heavier than the other,
+the spring may be balanced by magnetizing it so that the lighter end
+shall become a north pole. This will then tend to "dip" and make the
+needle swing horizontally. If one end is <i>much</i> heavier than the other,
+it should first be magnetized and then balanced by cutting little pieces
+from the heavier end with tinners' shears, or by weighting the lighter
+end with thread, which may be wound around it. The finished
+compass-needle should swing very freely, and should finally come to rest
+in an <i>N</i> and <i>S</i> line after vibrating back and forth several times.</p>
+
+
+<p class="app"><a name="APPARATUS_67" id="APPARATUS_67"></a>APPARATUS 67.</p>
+
+<p><i><b>90. Glass-Covered Compass.</b></i> A perspective view of this apparatus is
+shown in the tangent galvanometer. (See Index.) The outside band, <i>E</i>,
+is made of thick paper, 1 in. wide, and with such a diameter that it
+just fits around the glass. In this model, the glass from an old
+alarm-clock was used, it being 4 in. in diameter. Four pasteboard strips
+were sewed to the inside of the paper band <i>E</i>. They were made &#8542; in.
+long, so that the glass, when resting upon them, would be near the top
+of <i>E</i>.</p>
+
+<p>The needle should be not over 1 in. long, if it is to be used in the
+galvanometer. A long slender paper pointer should be stuck to the top of
+the needle. Be careful to have the combined needle and pointer well
+balanced, so that it will swing freely. A circle graduated into 5&ndash;degree
+spaces should be fastened under the needle.</p>
+
+<p><i><b>91. Astatic Needles.</b></i> In the magnetic needles so far described, the
+pointing-power has been quite strong. By pointing-power we mean the
+tendency to swing around to the <i>N</i> and <i>S</i>. In <a href="#APPARATUS_65">App. 65</a> the 2 needle
+magnets had considerable pointing-power, because they helped each other.
+For some experiments in electricity a magnetic needle is<span class='pagenum'><a name="Page_44" id="Page_44">[Pg 44]</a></span> required which
+has but <i>little</i> pointing-power; in fact, to detect the presence of very
+feeble currents by means of the needle, the less the pointing-power the
+better. Can you think of any way to arrange <a href="#APPARATUS_65">App. 65</a> so that it shall
+have very little pointing-power?</p>
+
+
+<p class="app"><a name="APPARATUS_68" id="APPARATUS_68"></a>APPARATUS 68.</p>
+
+<p><i><b>92. Astatic Needle.</b></i> Fig. 43. Turn one of the needle magnets of <a href="#APPARATUS_65">App. 65</a>
+end for end, so that the <i>N</i> pole of one shall be at the same end of the
+paper as the <i>S</i> pole of the other. You can see that by this arrangement
+one needle pulls against the other. The magnetic field still remains
+about the little magnets, otherwise this combination would be of no
+value in the construction of galvanometers. The more nearly equal the
+magnets are in strength, the less the pointing-power of the combination.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 43 and 44">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_43" id="Fig_43"></a>
+<img src="images/figure43.jpg" width="300" height="169" alt="Fig. 43." title="" />
+<span class="caption">Fig. 43.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_44" id="Fig_44"></a>
+<img src="images/figure44.jpg" width="300" height="179" alt="Fig. 44." title="" />
+<span class="caption">Fig. 44.</span>
+</div></td>
+</tr>
+</table></div>
+
+
+<p class="app"><a name="APPARATUS_69" id="APPARATUS_69"></a>APPARATUS 69.</p>
+
+<p><i><b>93. Astatic Needle.</b></i> Fig. 44. Magnetize two sewing-needles as equally
+as possible, by rubbing them over the pole of a magnet an equal number
+of times. Remove the covering from a piece of fine copper wire, say No.
+30, and use the bare wire to wind about the needles, as shown. Be sure
+to place the poles of the little magnets as in the Fig. This combination
+may be supported by a fine thread. It is used for Astatic Detectors.
+(See Index.)</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_45" id="Page_45">[Pg 45]</a></span></p>
+<h3><a name="CHAPTER_VIII" id="CHAPTER_VIII"></a>CHAPTER VIII.</h3>
+
+<h4>YOKES AND ARMATURES.</h4>
+
+
+<p><i><b>94. Yokes</b></i> are used to fasten two straight electro-magnets together to
+form a horseshoe electro-magnet. The reasons for using them should be
+understood. Soft iron should be used for yokes and armatures, as this is
+the best conductor of lines of magnetic force. Sheet-tin is made of thin
+iron, which is coated with tin. (Try a magnet upon a tin can.) This soft
+iron is very easily handled, bent, and punched, and is very useful for
+many purposes. The tin from old tomato cans, cracker boxes, etc., is
+just as good as any. The method of making your yokes will depend
+entirely upon the tools at your command. Several ways are given. <i>Y</i>,
+Fig. 47, shows the position of the yoke.</p>
+
+
+<p class="app"><a name="APPARATUS_70" id="APPARATUS_70"></a>APPARATUS 70.</p>
+
+<p><i><b>95. Yoke.</b></i> For the experimental magnets (<a href="#APPARATUS_89">App. 89</a>) a fairly large yoke
+is required in order to have the magnets far enough apart. If you have
+only a nail punch (<a href="#APPARATUS_26">App. 26</a>) with which to make holes in tin, you will be
+obliged to punch but one thickness at a time. (See method of punching
+sheet-metal, <a href="#APPARATUS_26">App. 26</a>.) Cut 5 or 6 pieces of the tin, 3&frac14; &times; 1 in. With
+a center punch (tools) or sharp-pointed nail make small dents (2 in.
+apart) in each piece to mark the places where the holes are to be
+punched. Punch <span class="above">5</span>&#8260;<span class="below">16</span> in. holes in each piece. If you do this carefully,
+the holes in the different pieces will match, and the bolts can be
+pushed or screwed into these. When screwing in the bolt magnets turn
+them by their heads; do not pinch the coils, as this loosens the wire.</p>
+
+<p><span class='pagenum'><a name="Page_46" id="Page_46">[Pg 46]</a></span></p><p>If you have a good punch, it is better to make the yoke as in <a href="#APPARATUS_27">App. 27</a>,
+instead of using separate pieces of tin.</p>
+
+
+<p class="app"><a name="APPARATUS_71" id="APPARATUS_71"></a>APPARATUS 71.</p>
+
+<p><i><b>96. Yoke.</b></i> Fig. 45 and 46. Cut a strip of tin 6 in. long by 3&frac14; in.
+wide. Bend one end of it so that it will lap over &frac34; in. (Fig. 46);
+hammer it down gently, then bend this over and over until the whole tin
+is used. The final result will be a flat roll, 3&frac14; by about 1 in. This
+should be hammered flat.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 45 and 46">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_45" id="Fig_45"></a>
+<img src="images/figure45.jpg" width="300" height="88" alt="Fig. 45." title="" />
+<span class="caption">Fig. 45.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_46" id="Fig_46"></a>
+<img src="images/figure46.jpg" width="300" height="144" alt="Fig. 46." title="" />
+<span class="caption">Fig. 46.</span>
+</div></td>
+</tr>
+</table></div>
+
+<p>If you have the tools it is easy to drill two <span class="above">5</span>&#8260;<span class="below">16</span> holes in this strip.
+They should be 2 in. apart; that is, 2 in. from the center of one to
+that of the other. Start the holes with a center punch.</p>
+
+<p><i><b>97.</b></i> If you have no way of drilling the holes, they must be punched.
+(See <a href="#APPARATUS_27">App. 27</a>.) This will make the strip bulge out on the underside
+around the holes. This bur, or most of it, should be filed off. (See
+<a href="#APPARATUS_79">App. 79</a> for method of filing thin pieces of metal.) The resulting yoke
+may be held firmly to the magnets by the use of 2 extra nuts, as in Fig.
+67. Remember that the magnets must be held <i>firmly</i> in the yoke.</p>
+
+
+<p class="app"><a name="APPARATUS_72" id="APPARATUS_72"></a>APPARATUS 72.</p>
+
+<p><i><b>98. Yoke.</b></i> The best way of making this, of course, is to cut a piece of
+bar-iron the right size. For <span class="above">5</span>&#8260;<span class="below">16</span> bolts the strip of wrought iron should
+be about &frac34; in. wide and <span class="above">3</span>&#8260;<span class="below">16</span> or &frac14; in. thick. Any blacksmith can make
+this and punch or drill the holes. If taps and dies (tools) are at<span class='pagenum'><a name="Page_47" id="Page_47">[Pg 47]</a></span>
+hand, the hole may be drilled and tapped to fit the thread on the bolt.
+It is very easy to make good looking apparatus if you have, and can use,
+a whole machine shop full of tools. The lengths of yokes will depend
+upon the special uses to be made of them.</p>
+
+
+<p class="app"><a name="APPARATUS_73" id="APPARATUS_73"></a>APPARATUS 73.</p>
+
+<p><i><b>99. Yoke.</b></i> Fig. 47. The yoke, <i>Y</i>, is a part of a carriage. This can be
+bought at a blacksmith's. The holes are already in, but it may require
+some filing before the nuts of the bolt magnets will fit down firmly.</p>
+
+<div class="figright" style="width: 240px;"><a name="Fig_47" id="Fig_47"></a>
+<img src="images/figure47.jpg" width="240" height="220" alt="Fig. 47." title="" />
+<span class="caption">Fig. 47.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_74" id="APPARATUS_74"></a>APPARATUS 74.</p>
+
+<p><i><b>100. Tin Armatures</b></i> may be made by bending together 5 or 6 thicknesses
+of tin. Different forms of tin armatures are shown under telegraph
+sounders; these should have a hole punched at the center; through this
+is put a screw. The length of the armature will depend upon the distance
+the magnets are placed apart; they should be about &frac34; in. wide.</p>
+
+
+<p class="app"><a name="APPARATUS_75" id="APPARATUS_75"></a>APPARATUS 75.</p>
+
+<p><i><b>101. Nail Armatures.</b></i> Fig. 48. A nail, <i>N</i>, placed through a piece of
+wood, <i>A</i>, will serve as a very simple armature. To make it a little
+heavier, if necessary, a piece of annealed iron wire, <i>W</i>, may be wound
+around <i>N</i>. Care should be taken to have the two parts fairly alike in
+size and weight.</p>
+
+<div class="figleft" style="width: 350px;"><a name="Fig_48" id="Fig_48"></a>
+<img src="images/figure48.jpg" width="350" height="172" alt="Fig. 48." title="" />
+<span class="caption">Fig. 48.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_76" id="APPARATUS_76"></a>APPARATUS 76.</p>
+
+<p><i><b>102. Wire Armatures.</b></i> Fig. 49. Annealed iron wires make good armatures.
+The short lengths of wire should be straightened (<a href="#APPARATUS_28">See App. 28</a>) before
+binding them<span class='pagenum'><a name="Page_48" id="Page_48">[Pg 48]</a></span> into a bundle. They may be held together with thread or
+paraffine, until they are in place, as, for example, in a wooden piece,
+<i>A</i>, Fig. 49. The bundle of wires should fit snugly into the hole made
+through <i>A</i>, and the wires should be bound together at each end with
+wire.</p>
+
+<div class="figright" style="width: 300px;"><a name="Fig_49" id="Fig_49"></a>
+<img src="images/figure49.jpg" width="300" height="106" alt="Fig. 49." title="" />
+<span class="caption">Fig. 49.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_77" id="APPARATUS_77"></a>APPARATUS 77.</p>
+
+<p><i><b>103. Trembling Armature.</b></i> Fig. 50. Armatures to be used upon electric
+bells, automatic current interrupters, buzzers, etc., may be called
+trembling armatures. They may be made entirely of sheet-tin. The part,
+<i>F</i>, which gives it the spring, should be about &#8541; in. wide. Its length
+will depend upon the particular apparatus to be made. It is made of 2
+thicknesses of thin tin. See Fig. 50 for dimensions. The part <i>N</i>
+projects beyond <i>L</i>. This may be used to tap against a regulating screw,
+or to fasten a hammer on for an electric bell. The part, <i>L</i>, should
+have about 4 layers of tin on each side of <i>F</i>, and it should pinch <i>F</i>
+tightly.</p>
+
+<div class="figleft" style="width: 350px;"><a name="Fig_50" id="Fig_50"></a>
+<img src="images/figure50.jpg" width="350" height="152" alt="Fig. 50." title="" />
+<span class="caption">Fig. 50.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_78" id="APPARATUS_78"></a>APPARATUS 78.</p>
+
+<p><i><b>104. Trembling Armature.</b></i> Fig. 51. When very rapid motions are desired
+in a trembling armature, <a href="#APPARATUS_77">App. 77</a> will be a little heavy. A light and
+quick-acting armature can be made of sheet-tin. The exact dimensions
+will depend upon the use to be made of it, but you will find the
+following a guide. Cut the part, <i>B</i>, <i>E</i>, out of<span class='pagenum'><a name="Page_49" id="Page_49">[Pg 49]</a></span> <i>thin</i> tin. The
+covers and bottoms of tin cans are thinner than their bodies. The narrow
+part, <i>B</i>, should be about &frac14; in. wide and 2 in. long for a small
+apparatus, while <i>E</i> may be &frac34; in. square. Through <i>E</i> is a screw,
+which holds it firmly to a wooden piece, <i>D</i>, about &frac34; in. square. The
+part, <i>E</i>, can be made longer than its width, so that two screws can be
+used; this will keep <i>A</i> from jarring up or down.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_51" id="Fig_51"></a>
+<img src="images/figure51.jpg" width="400" height="287" alt="Fig. 51." title="" />
+<span class="caption">Fig. 51.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_79" id="APPARATUS_79"></a>APPARATUS 79.</p>
+
+<div class="figcenter" style="width: 350px;"><a name="Fig_52" id="Fig_52"></a>
+<img src="images/figure52.jpg" width="350" height="479" alt="Fig. 52." title="" />
+<span class="caption">Fig. 52.</span>
+</div>
+
+<p><i><b>105. To File Thin Metal Strips.</b></i> Fig. 52. When sheet-metal is punched
+by the methods usually employed by boys, a bulge or bur is made on the
+underside around the hole. If this bur be hammered to flatten it, the
+hole is distorted and made smaller. It is better to file the bur<span class='pagenum'><a name="Page_50" id="Page_50">[Pg 50]</a></span> down,
+at least part way. It is not convenient to file a piece of thin metal
+when it is held in a vise. It is better to use either a metal or a
+wooden clamp, as shown in Fig. 52; then the filing can be quickly and
+easily done. <i>Y</i> is the yoke to be filed. It is well to place a piece of
+metal, <i>I</i>, between the table and the end of the screw.</p>
+
+
+<p class="app"><a name="APPARATUS_80" id="APPARATUS_80"></a>APPARATUS 80.</p>
+
+<p><i><b>106. Clamp.</b></i> Fig. 53. If you have no clamp to hold metal strips while
+filing them, you can put a screw, <i>S</i>, through one hole to hold the
+strip down fairly tight. Drive a nail, <i>N</i>, behind the strip. This will
+keep it from turning while you file the free end.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_53" id="Fig_53"></a>
+<img src="images/figure53.jpg" width="400" height="205" alt="Fig. 53." title="" />
+<span class="caption">Fig. 53.</span>
+</div>
+
+<hr style='width: 20%;' />
+
+<p><i><b>Electro-Magnetic Armatures.</b></i> A description of this form of armature is
+given in the chapter on electric motors. (See Index.)</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_51" id="Page_51">[Pg 51]</a></span></p>
+<h3><a name="CHAPTER_IX" id="CHAPTER_IX"></a>CHAPTER IX.</h3>
+
+<h4>ELECTRO-MAGNETS.</h4>
+
+
+<p><i><b>107. Electro-Magnets</b></i> are absolutely necessary in the construction of
+most pieces of electrical apparatus. There are several ways of making
+them at home. To quickly make a good-looking one, a winder (<a href="#APPARATUS_93">App. 93</a>) is
+required. We shall divide our electro-magnets into four parts: <i>Core,
+washers, insulation, and coil.</i></p>
+
+<p>Of course, you know that when a current of electricity passes through a
+wire, a magnetic field is produced around the wire. A coil of wire, or
+helix, has a stronger field than a straight wire carrying the same
+current, because each turn or convolution adds its field to that of the
+other turns. By having the center of the helix made of iron, instead of
+air, wood, or other non-magnetic bodies, the strength of the magnet is
+greatly increased. This central core may be fixed permanently in the
+coil, or be removable. For our purposes fixed cores are just as good as
+movable ones, and the coils are easily wound upon them.</p>
+
+<p>When wire is wound by hand from a spool into a coil, or around a core,
+it soon becomes twisted and tangled. Make a winder. This will keep the
+wire straight and save much time.</p>
+
+
+<p class="app"><a name="APPARATUS_81" id="APPARATUS_81"></a>APPARATUS 81.</p>
+
+<div class="figright" style="width: 300px;"><a name="Fig_54" id="Fig_54"></a>
+<img src="images/figure54.jpg" width="300" height="248" alt="Fig. 54." title="" />
+<span class="caption">Fig. 54.</span>
+</div>
+
+<p><i><b>108. Electro-Magnet.</b></i> Fig. 54. Drive a nail into a board so that it
+will project about &frac34; of an inch. A soft, or wrought-iron, nail is
+best, but a short, thick wire-nail will do. If you do not have a thick
+nail, use an iron screw. Wind 3 or 4 layers of insulated copper wire
+around it, and fasten the bare ends of the wire down with bent pins.
+Number 24 wire will be found a good size for<span class='pagenum'><a name="Page_52" id="Page_52">[Pg 52]</a></span> experimental purposes.
+Touch the wires leading from the battery to the ends of the coil, and
+see if the nail will lift pieces of iron.</p>
+
+<p><i><a name="s109" id="s109"></a>109. Note.</i> Always leave at least 6 in. of wire at the ends of all
+coils and windings. This is needed for connections and repairs, as the
+wire is liable to get broken at any time around the binding-posts.</p>
+
+<p><i><a name="s110" id="s110"></a>110. Note.</i> After you have wound wire upon a core or spool, keep it
+from untwisting by taking a loop or hitch around it with the wire. Fig.
+55 shows how this is done. Pull the end of the wire enough to make the
+loop stay in place.</p>
+
+
+<p class="app"><br /><a name="APPARATUS_82" id="APPARATUS_82"></a>APPARATUS 82.</p>
+
+<p><i><b>111. Electro-Magnet.</b></i> Fig. 56. Cut annealed iron wire into pieces, 3
+inches long, straighten them (<a href="#APPARATUS_28">App. 28</a>), and tie them with thread into a
+bundle about <span class="above">5</span>&#8260;<span class="below">16</span> in. in diameter. Melted paraffine run in between the
+wires will hold them in together, but stout thread will do. Wind 3 or 5
+layers of No. 24 insulated copper wire upon the soft iron core. This is
+useful for simple experiments, and this idea may be applied to magnets
+to be used in pieces of apparatus. Hold the bundle of wires in a vise,
+and file the ends smooth, before winding on the wire. Paraffine should
+be used to hold the turns of insulated wire together.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 55, 56, and 57">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 200px;"><a name="Fig_55" id="Fig_55"></a>
+<img src="images/figure55.jpg" width="200" height="206" alt="Fig. 55." title="" />
+<span class="caption">Fig. 55.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 200px;">
+<img src="images/figure56.jpg" width="200" height="119" alt="Fig. 56." title="" />
+<span class="caption"><a name="Fig_56" id="Fig_56"></a>Fig. 56.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 200px;">
+<img src="images/figure57.jpg" width="200" height="119" alt="Fig. 57." title="" />
+<span class="caption">Fig. 57.</span>
+</div></td>
+</tr>
+</table></div>
+
+
+<p class="app"><a name="APPARATUS_83" id="APPARATUS_83"></a>APPARATUS 83.</p>
+
+<p><i><b>112. Electro-Magnet.</b></i> Fig. 57. An electro-magnet with a <i>removable
+core</i> may be made by winding the wire<span class='pagenum'><a name="Page_53" id="Page_53">[Pg 53]</a></span> on a spool. The core is made, as
+in <a href="#APPARATUS_82">App. 82</a>, of soft iron wires, bound together with stout thread. A bolt
+may be used instead of the wire, but the wire loses its magnetism much
+quicker than a soft steel bolt would. (Study residual magnetism.) This
+magnet is strong enough for many purposes, but the wire is too far from
+the core, on account of the thickness of the wood, to make it efficient.
+The wire may be wound on by hand, but a winder (<a href="#APPARATUS_93">App. 93</a>) will do much
+better and quicker work.</p>
+
+
+<p class="app"><a name="APPARATUS_84" id="APPARATUS_84"></a>APPARATUS 84.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 58 and 59">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_58" id="Fig_58"></a>
+<img src="images/figure58.jpg" width="300" height="311" alt="Fig. 58." title="" />
+<span class="caption">Fig. 58.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_59" id="Fig_59"></a>
+<img src="images/figure59.jpg" width="300" height="307" alt="Fig. 59." title="" />
+<span class="caption">Fig. 59.</span>
+</div></td>
+</tr>
+</table></div>
+
+<p><i><b>113. Horseshoe Electro-Magnet.</b></i> Fig. 58. Bend soft iron wires, and make
+a bundle of them. If you wish to wind the wire around spools, the bundle
+cannot be very large. It will be found best to make the bundle about &#8540;
+in. in diameter, and not to use the spools. Strong paper should be
+wrapped once or twice around the legs of the horseshoe, and the
+insulated wire, say 4 layers, can then be wound directly upon this. (<a href="#s115">See
+&sect; 115</a> for method of making connection between the coils.) It is a little
+troublesome to wind wire upon a horseshoe like this, and for <a href="#APPARATUS_85">App. 85</a>.
+Spools are handier, because each can be wound separately, and then be
+slipped in place. The ends of the horseshoe should be filed smooth.</p>
+
+
+<p><span class='pagenum'><a name="Page_54" id="Page_54">[Pg 54]</a></span></p><p class="app"><a name="APPARATUS_85" id="APPARATUS_85"></a>APPARATUS 85.</p>
+
+<p><i><b>114. Electro-Magnet.</b></i> Fig. 59. An ordinary iron staple is useful as the
+core of a small magnet. One like this is shown also in Fig. 94, used as
+a telegraph sounder. It takes some time to wind 4 layers of wire on to
+each leg of the staple, so be sure to <a href="#s115">see &sect; 115</a> about the method of
+winding. In Fig. 59 the half-hitches (<a href="#s110">&sect; 110</a>) are not shown. Coat the
+finished coils with paraffine.</p>
+
+<div class="figleft" style="width: 250px;"><a name="Fig_60" id="Fig_60"></a>
+<img src="images/figure60.jpg" width="250" height="129" alt="Fig. 60." title="" />
+<span class="caption">Fig. 60.</span>
+</div>
+
+<p><i><a name="s115" id="s115"></a>115. Method of Joining Coils.</i> Fig. 60. If <i>A</i> and <i>B</i> represent the
+two cores of a horseshoe electro-magnet, the coils must be joined in
+such a manner that the current will pass around them in opposite
+directions, in order to make them unlike poles. The current is supposed
+to pass around <i>B</i>, Fig. 60, in the direction taken by clock hands,
+while it passes around <i>A</i> in an anti-clockwise direction. The inside
+ends, <a href="#s123">&sect; 123</a>, of the coils may be twisted together, or fastened under a
+screw-head. In Fig. 60 one coil is shown to be a continuation of the
+other.</p>
+
+
+<p class="app"><br /><br /><a name="APPARATUS_86" id="APPARATUS_86"></a>APPARATUS 86.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 61 and 62">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_61" id="Fig_61"></a>
+<img src="images/figure61.jpg" width="300" height="198" alt="Fig. 61." title="" />
+<span class="caption">Fig. 61.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_62" id="Fig_62"></a>
+<img src="images/figure62.jpg" width="300" height="186" alt="Fig. 62." title="" />
+<span class="caption">Fig. 62.</span>
+</div></td>
+</tr>
+</table></div>
+
+<p><i><b>116. Electro-Magnet.</b></i> Fig. 61. Wind 6 layers of No. 24 or 25 insulated
+copper wire around a <span class="above">5</span>&#8260;<span class="below">16</span> machine-bolt that is 2&frac12; in. long. Fig. 61
+shows one method of holding the bolt solidly in an upright position, so
+that magnetic figures can be easily made and the magnet studied. Two
+nuts are used, the lower one being counter-sunk, so<span class='pagenum'><a name="Page_55" id="Page_55">[Pg 55]</a></span> that the base will
+stand flat upon the table. This bolt is shown without washers (<a href="#s119">&sect; 119</a>),
+and will do fairly well to show the action of electro-magnets. The ends
+of the wire should always be left 5 or 6 in. long, and be led out to
+binding-posts. The coil may be held in place, and its turns kept from
+untwisting by coating it with paraffine. The base may be of any desired
+size.</p>
+
+
+<p class="app"><a name="APPARATUS_87" id="APPARATUS_87"></a>APPARATUS 87.</p>
+
+<p><i><b>117. Electro-Magnet Core.</b></i> Fig. 62. This shows another method of
+fastening a bolt-core in an upright position. This is done without the
+use of two nuts. A strip of tin, <i>T</i>, 1 in. wide, is punched and slipped
+onto the <span class="above">5</span>&#8260;<span class="below">16</span> bolt before the nut is screwed on and the coil wound. This
+is fastened to the base by screws, <i>S</i>. Washers, <i>W</i>, are here shown.
+(<a href="#s119">See &sect; 119</a> for washers.)</p>
+
+
+<p class="app"><a name="APPARATUS_88" id="APPARATUS_88"></a>APPARATUS 88.</p>
+
+<div class="figleft" style="width: 175px;"><a name="Fig_63" id="Fig_63"></a>
+<img src="images/figure63.jpg" width="175" height="492" alt="Fig. 63." title="" />
+<span class="caption">Fig. 63.</span>
+</div>
+
+<p><i><b>118. Bolt Electro-Magnets</b></i> are easy to make, according to the
+directions given, and they are, when finished, more like the regular
+purchased magnets than any of the other forms described. With proper
+batteries (<a href="#APPARATUS_3">App. 3</a>, <a href="#APPARATUS_4">4</a>, etc.,) they can be used for a great variety of
+purposes, as will be seen. There are many forms of bolts in the market,
+but the ordinary "machine bolt," <span class="above">5</span>&#8260;<span class="below">16</span> in. in diameter, is best for our
+purposes. The ones 2 and 2&frac12; in. long are used.</p>
+
+<p><i><a name="s119" id="s119"></a>119. Washers</i> or coil ends are used on the bolt magnets so that
+considerable wire can be wound on closely and evenly. These are made out
+of thick pasteboard, which cuts smoother if it has been soaked in melted
+paraffine. Unless you know how, you will find it a hard job to make the
+hole in the exact center of the washer. The method of easily making
+washers is illustrated in Fig. 63.</p>
+
+<p>First place a spool (the end of which is &#8542; or 1 in. in<span class='pagenum'><a name="Page_56" id="Page_56">[Pg 56]</a></span> diameter) upon
+the table, and lay the pasteboard upon this. Push a large round nail
+through the pasteboard into the hole in the spool. The nail should be
+nearly as large as the hole. Use the large nail as a handle, and with
+the shears cut around the edge of the spool end. Cut the washer as round
+as possible, and be careful not to cut into the spool.</p>
+
+<p>The holes in the washers will be a little smaller than the <span class="above">5</span>&#8260;<span class="below">16</span> bolt.
+This will make the washers hold tightly to the bolt when you force them
+on. Fig. 64 shows the bolt-core, with the washers in place. If you
+cannot get a large nail, a lead-pencil, or sharpened dowel, will do to
+force through the pasteboard.</p>
+
+<p><i>120. Insulation of Cores.</i> While the covering on the wire would
+probably be all that is necessary to thoroughly insulate the coil from
+the core, it is better to wind a layer or two of paraffine paper around
+the bolt (Fig. 65) before winding.</p>
+
+<p><i>121. The Coils</i> of wire to be used upon the bolt-cores should be put on
+with the winder (<a href="#APPARATUS_93">App. 93</a>). For all ordinary purposes No. 24 or 25 single
+or double cotton covered copper wire will do. It is better to put on an
+even number of layers. The winding (See Fig. 70) begins at the nut-end
+of the bolt, and by using 6 or 8 layers of wire,<span class='pagenum'><a name="Page_57" id="Page_57">[Pg 57]</a></span> instead of 5 or 7,
+both coil ends will be at the same end of the bolt.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 64, 65 and 65.5">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 129px;"><a name="Fig_64" id="Fig_64"></a>
+<img src="images/figure64.jpg" width="129" height="230" alt="Fig. 64." title="" />
+<span class="caption">Fig. 64.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 156px;"><a name="Fig_65" id="Fig_65"></a>
+<img src="images/figure65.jpg" width="156" height="230" alt="Fig. 65." title="" />
+<span class="caption">Fig. 65.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 156px;"><a name="Fig_65.5" id="Fig_65.5"></a>
+<img src="images/figure65a.jpg" width="156" height="230" alt="Fig. 65.5." title="" />
+<span class="caption">Fig. 65&frac12;.</span>
+</div></td>
+</tr>
+</table></div>
+
+<p><i>122. Method of Winding the Coils.</i> The winders used for bolt magnets
+are described in <a href="#APPARATUS_91">App. 91</a>, etc. We shall suppose that the washer, <i>W</i>,
+Fig. 70, and the insulation, <i>I</i>, are upon the bolt before screwing it
+into the winder-nut, <i>W N</i>. Make a pinhole, <i>P H</i>, in the right-hand
+washer, as near the bolt-nut, <i>B N</i>, as possible. Stick about 6 in. of
+the wire through <i>P H</i>, and wind this end around <i>W N</i>, as shown, to
+hold the wire. The supply of wire should be upon a spool slipped onto
+some stationary rod (<a href="#APPARATUS_23">App. 23</a>), so that you can give your entire
+attention to winding. Begin to turn the winder slowly at first. Turn the
+handle towards you when it is at the bottom, as in Fig. 70; that is, if
+you look at it from the side, turn the handle clockwise. Let the wire
+slip through your left hand as the turns are made, and guide it so that
+the turns will be close together. If they go on crooked, unwind at once,
+then rewind properly. You can guide the wire best by holding your left
+hand about 8 or 10 inches from the bolt. As soon as you reach the left
+side or head end of the bolt, feed the wire towards the right. If at any
+time the layers become rough on account of one turn slipping down
+between turns of the previous layer, fasten a piece of paraffine paper
+around the coil as soon as the imperfect layer is completed. Wind on 8
+layers, and count the number of turns in one or two of them, so that you
+can tell about how many turns in all you have around the core. Make a
+"half-hitch" (<a href="#s110">see &sect; 110</a>) with the wire when the last layer is finished,
+to keep it from unwinding, and leave a 6 in. end.</p>
+
+<p>The coil should be protected by fastening around it a piece of
+dark-colored stiff paper. Paraffine paper is good for this purpose. With
+a little practice you will be able<span class='pagenum'><a name="Page_58" id="Page_58">[Pg 58]</a></span> to rapidly and neatly wind on the
+wire. The winder-nut, <i>W N</i>, must hold the bolt solidly to keep it from
+wobbling.</p>
+
+<p><a name="s123" id="s123"></a>123. We shall call the starting end of the wire which passes through <i>P
+H</i>, the <i>inside end</i>, and the end of the last layer the <i>outside end</i>.
+This can pass out between the washer and the paper covering.</p>
+
+
+<p class="app"><a name="APPARATUS_89" id="APPARATUS_89"></a>APPARATUS 89.</p>
+
+<p><i><b>124. Experimental Horseshoe Electro-Magnet.</b></i> Fig. 66. Among the most
+useful pieces of apparatus for home use, is a good horseshoe
+electro-magnet. Fig. 66 shows a very convenient and practical form. With
+this, alone, can be shown all the principles of telegraph sounders,
+electric bells, etc. They are excellent for making magnetic figures (See
+text-book). You are supposed to be looking down on the App. in Fig. 66.
+The bolts are 2 in. apart center to center.</p>
+
+<div class="figcenter" style="width: 375px;"><a name="Fig_66" id="Fig_66"></a>
+<img src="images/figure66.jpg" width="375" height="334" alt="Fig. 66." title="" />
+<span class="caption">Fig. 66.</span>
+</div>
+
+<p><i>The bolt magnets</i> are fully described in <a href="#APPARATUS_88">App. 88</a>; <i>the binding-posts</i>,
+as <a href="#APPARATUS_46">App. 46</a>; <i>the yoke</i>, as <a href="#APPARATUS_71">App. 71</a>; the method of <i>fastening to the
+base</i>, as <a href="#APPARATUS_90">App. 90</a>; the <i>base</i> is 5 &times; 4 &times; &#8542; in.; the magnets are made
+of <span class="above">5</span>&#8260;<span class="below">16</span> bolts, 2&frac12; in. long.</p>
+
+<p><i><a name="s125" id="s125"></a>125. To Join the Coils</i>, fasten the two <i>inside</i> ends (<a href="#s123">&sect;123</a>) of the
+wire to a middle binding-post, and carry the <i>outside</i> ends to the two
+outside binding-posts. In this way<span class='pagenum'><a name="Page_59" id="Page_59">[Pg 59]</a></span> you can use either magnet alone, if
+desired (See experiments in text-book), or change the polarity at will
+by changing the connections. (<a href="#s115">See &sect; 115</a> and <a href="#s123">123</a>.)</p>
+
+
+<p class="app"><a name="APPARATUS_90" id="APPARATUS_90"></a>APPARATUS 90.</p>
+
+<p><i><b>126. Fastenings for Electro-Magnet.</b></i> Fig. 67. When both electro-magnets
+are to be permanently fastened to a base, especially if tin yokes are to
+be used, as in <a href="#APPARATUS_89">App. 89</a>, it is best to use a nut on each side of the
+yoke. It is important to have a perfectly tight connection between bolt
+and yoke. Several ways of fastening the bolts and yokes are shown; but
+it will be found best to cut holes in the base for the lower nuts, and
+to screw the yoke directly to the base. This makes a solid and pleasing
+arrangement. For the experimental magnets (<a href="#APPARATUS_89">App. 89</a>) make the yoke 3&frac14;
+in. long, and place the magnets 2 in. apart center to center.</p>
+
+<div class="figcenter" style="width: 375px;"><a name="Fig_67" id="Fig_67"></a>
+<img src="images/figure67.jpg" width="375" height="162" alt="Fig. 67." title="" />
+<span class="caption">Fig. 67.</span>
+</div>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_60" id="Page_60">[Pg 60]</a></span></p>
+<h3><a name="CHAPTER_X" id="CHAPTER_X"></a>CHAPTER X.</h3>
+
+<h4>WIRE WINDING APPARATUS.</h4>
+
+
+<p class="app"><a name="APPARATUS_91" id="APPARATUS_91"></a>APPARATUS 91.</p>
+
+<p><i><b>127. Winder.</b></i> Fig. 68. In case you do not have any means of making a
+smooth hole for the "bearings" of the winders of <a href="#APPARATUS_93">App. 93</a> and <a href="#APPARATUS_94">94</a>, you can
+use a spool for the purpose. <i>B</i> is the end of a piece of board about 1
+in. thick, 3 in. wide, and 6 in. long. The spool, <i>A</i>, is laid upon
+this, a band of tin, <i>T</i>, being used to hold it down firmly upon the end
+of <i>B</i>. Screws, <i>S</i>, hold <i>T</i> down. A stove-bolt axle (<a href="#APPARATUS_93">See App. 93</a>) is
+shown, and by using a nut, as explained, bolt magnets may be wound. By
+using the handle of <a href="#APPARATUS_92">App. 92</a>, this arrangement can be used to wind almost
+anything, when used together with the attachment of <a href="#APPARATUS_95">App. 95</a>.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 68 and 69">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 282px;"><a name="Fig_68" id="Fig_68"></a>
+<img src="images/figure68.jpg" width="282" height="308" alt="Fig. 68." title="" />
+<span class="caption">Fig. 68.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 307px;"><a name="Fig_69" id="Fig_69"></a>
+<img src="images/figure69.jpg" width="307" height="294" alt="Fig. 69." title="" />
+<span class="caption">Fig. 69.</span>
+</div></td>
+</tr>
+</table></div>
+
+
+<p class="app"><a name="APPARATUS_92" id="APPARATUS_92"></a>APPARATUS 92.</p>
+
+<p><i><b>128. Crank for Winders, etc.</b></i> Fig. 69. This form of crank or handle
+will be found easier to make than the one in which a wire is expanded in
+the slot of a stove bolt, and it can be used for many purposes,
+especially where dowels serve as axles. Wrap a little paper around the
+end of the &frac14; in. dowel, <i>D</i>, and push it part way into<span class='pagenum'><a name="Page_61" id="Page_61">[Pg 61]</a></span> the spool,
+<i>A</i>, then put in a set-screw, <i>S</i>, to keep <i>A</i> from twisting upon <i>D</i>.
+The straight end of the wire, <i>H</i>, should be put into a hole, <i>B</i>, and
+another set-screw used to fasten it into the spool.</p>
+
+
+<p class="app"><a name="APPARATUS_93" id="APPARATUS_93"></a>APPARATUS 93.</p>
+
+<p><i><b>129. Winder.</b></i> Fig. 70. For winding bolt magnets, this form of winder is
+very useful. It consists of a "stove bolt," <i>S B</i>, 2 in. long (total
+length) and <span class="above">5</span>&#8260;<span class="below">16</span> in. in diameter.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_70" id="Fig_70"></a>
+<img src="images/figure70.jpg" width="400" height="475" alt="Fig. 70." title="" />
+<span class="caption">Fig. 70.</span>
+</div>
+
+<p><i>130. Handle or Crank</i>, <i>H</i>, is made of a stout wire, 4 in. long, bent
+at the lower end as shown. <i>H</i> is fastened into the slot of <i>S B</i>. To do
+this the end of <i>H</i> is hammered flat until it will just slip into the
+slot. It may be soldered there, or be made to fit by expanding it so
+that it will press out against the sides of the slot. To do this, place
+<i>S B</i> into a hole in an anvil, or hold it in a vise, being careful not
+to injure the thread. Place the flattened end of <i>H</i> in the slot, and
+strike it on top so that it will expand and be pinched in the slot; but
+do not pound it so hard that you<span class='pagenum'><a name="Page_62" id="Page_62">[Pg 62]</a></span> split the bolt head. Three or four
+good center-punch dents upon the wire over the slot will help to expand
+it.</p>
+
+<p><i>131. The Framework</i> is made of wood, the dimensions being shown in Fig.
+70. A <span class="above">5</span>&#8260;<span class="below">16</span> hole should be made for <i>S B</i>, the thread of which will stick
+through about &frac14; in. so that the winder-nut, <i>W N</i>, can be turned onto
+it. <i>W N</i> should be on but 2 or 3 threads of <i>S B</i>. This will leave part
+of it for the thread of the bolt magnet, and when this and <i>S B</i> meet in
+center of <i>W N</i> they will bind against each other and hold the bolt
+tight. The winder can be nailed or screwed at S to the edge of a table
+or held in a vise.</p>
+
+
+<p class="app"><a name="APPARATUS_94" id="APPARATUS_94"></a>APPARATUS 94.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_71" id="Fig_71"></a>
+<img src="images/figure71.jpg" width="400" height="377" alt="Fig. 71." title="" />
+<span class="caption">Fig. 71.</span>
+</div>
+
+<p><i><b>132. Winder.</b></i> Fig. 71. This shows a winder that can be used for several
+purposes by arranging different attachments. It will be first described
+as shown in Fig. 71, where it is being used to wind a bolt magnet. The
+principal dimensions are shown in the figure. It is made of &frac34; in. wood
+about 3 in. wide, the two outer parts <i>X</i> and <i>Z</i> being nailed to the
+center one, <i>Y</i>, which is to be held in a vise, or fastened to the edge
+of a table. A <span class="above">5</span>&#8260;<span class="below">16</span> in. hole should be made through the upper part <i>X</i>
+and <i>Z</i> at one side of the center, so that a long <span class="above">5</span>&#8260;<span class="below">16</span> bolt can be put
+through and used as described in <a href="#APPARATUS_93">App. 93</a>, if desired. A smaller<span class='pagenum'><a name="Page_63" id="Page_63">[Pg 63]</a></span> hole,
+&frac14; in., should be made on the other side of the center for a &frac14; in.
+dowel. The dowel, <i>D</i>, is shown, and this size is a little smaller than
+the hole in ordinary spools, shown at <i>A</i> and <i>B</i>. One-quarter in.
+dowels can be made to fit fairly tight into the holes by wrapping paper
+around them. Five-sixteenth bolts can be screwed into the spool holes,
+shown by the bolt magnet in Fig. 71. To firmly hold a spool from
+twisting around upon the dowel-axle, a set-screw, <i>S S</i>, is needed.
+These are small screws, say &#8541; in. long, No. 5. A small hole should be
+made into the spool before forcing in the screw. (<a href="#APPARATUS_25">App. 25</a>.)</p>
+
+<p>The spools <i>A</i> and <i>B</i> are fastened in this way, by set-screws, to <i>D</i>.
+The handle, <i>H</i>, is made as in <a href="#APPARATUS_93">App. 93</a>, in this case a <i>short</i> stove
+bolt, <i>S B</i>, being used and screwed into <i>B</i>. Fig. 69 shows a very
+simple form of handle for all such purposes, which may be used instead
+of the one here shown. The details of winding on the wire are given
+under <a href="#APPARATUS_88">App. 88</a>.</p>
+
+
+<p class="app"><a name="APPARATUS_95" id="APPARATUS_95"></a>APPARATUS 95.</p>
+
+<p><i><b>133. Attachment for Winder.</b></i> Fig. 72. By using this addition to <a href="#APPARATUS_93">App. 93</a>
+or 94, almost any ordinary kind of windings can be made. The wooden
+block, <i>A</i>, may be about 2 in. square and &#8542; in. thick. A set-screw,
+<i>S</i>, binds it to the dowel-axle, <i>D</i>, which is made to turn by one of
+the forms of cranks given, and which is held in one of the frameworks.
+Windings like that shown in <a href="#APPARATUS_112">App. 112</a>, Fig. 85, can easily be done with
+this, the upright part, with the two spools, being screwed right to <i>A</i>
+of Fig. 72.</p>
+
+<div class="figcenter" style="width: 351px;"><a name="Fig_72" id="Fig_72"></a>
+<img src="images/figure72.jpg" width="351" height="274" alt="Fig. 72." title="" />
+<span class="caption">Fig. 72.</span>
+</div>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_64" id="Page_64">[Pg 64]</a></span></p>
+<h3><a name="CHAPTER_XI" id="CHAPTER_XI"></a>CHAPTER XI.</h3>
+
+<h4>INDUCTION COILS AND THEIR ATTACHMENTS.</h4>
+
+
+<p><i><b>134. Induction Coils</b></i>, or shocking coils, are rather expensive to buy,
+and altogether too complicated for boys to make by the methods usually
+given in books. The method here given is simple, the materials are
+cheap, and if you make them according to directions, you will have an
+apparatus that will, be able to make your friends dance to a rather
+lively tune. The amount of shock can be regulated perfectly (<a href="#APPARATUS_103">App. 103</a>).</p>
+
+<p><i>Winding.</i> Full instructions have been given for making bolt magnets
+(<a href="#APPARATUS_88">App. 88</a>). The winding of our induction coils is done in the same way by
+the same winder as the bolt magnets (<a href="#APPARATUS_93">App. 93</a>), or by hand. You will find
+it a very tiresome and troublesome job, however, to wind on 12 or 15
+hundred turns of fine wire by hand. Make a winder.</p>
+
+<p>Several different forms of induction coils are shown. The <i>coil</i> is the
+most important feature, however, and we shall consider that separately.
+When you understand the construction of one coil, you can readily apply
+this to the different forms. Some form of <i>contact breaker</i>, or <i>current
+interrupter</i>, is needed also. These will be treated by themselves. The
+<i>connections</i> will be discussed under each form of apparatus.</p>
+
+
+<p class="app"><a name="APPARATUS_96" id="APPARATUS_96"></a>APPARATUS 96.</p>
+
+<p><i><b>135. Induction Coil; Construction of Coil Proper.</b></i> Figs. 73, 74. An
+induction coil is a peculiar and wonderful apparatus. There are at least
+two coils<span class='pagenum'><a name="Page_65" id="Page_65">[Pg 65]</a></span> to each one. These are both wound upon the same core. They
+are made of different sizes of wire, are wound separately, and the
+strangest thing of all is, that these two coils are not connected with
+each other in any way. If they were not thoroughly insulated from each
+other, the coil would be of no value. (Study induction.) The winding of
+the two coils is done as explained in <a href="#APPARATUS_88">App. 88</a>.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 73 and 74">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 196px;"><a name="Fig_73" id="Fig_73"></a>
+<img src="images/figure73.jpg" width="196" height="371" alt="Fig. 73." title="" />
+<span class="caption">Fig. 73.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 196px;"><a name="Fig_74" id="Fig_74"></a>
+<img src="images/figure74.jpg" width="196" height="391" alt="Fig. 74." title="" />
+<span class="caption">Fig. 74.</span>
+</div></td>
+</tr>
+</table></div>
+
+<p><i>136. The Core</i> is made of a <span class="above">5</span>&#8260;<span class="below">16</span> machine bolt, 2&frac12; in. long. Leave
+but 2 or 3 threads at the end, just enough to fasten it solidly to the
+winder (<a href="#APPARATUS_93">App. 93</a>). The washers should be about 1&#8541; in. apart inside,
+and they should be made around a spool (<a href="#s119">&sect; 119</a>) that is fully 1 in. in
+diameter.</p>
+
+<p><i><a name="s137" id="s137"></a>137. The Inside or Primary Coil</i> could be wound directly upon the bolt;
+but it is much better to cover the bolt with one or two thicknesses of
+paraffined paper, <i>I</i> (Index), as shown. A pinhole, <i>H</i>, in the washer
+is for the inside end (<a href="#s123">see &sect; 123</a>) of the primary coil, and the hole,
+<i>J</i>, is for the outside end of it.</p>
+
+<p>The primary coil should be made of 3 layers of wire, which should be
+coarser than that used for the secondary coil. For our purposes it is
+best not to use a wire coarser than No. 20, and not finer than No. 24.</p>
+
+<p>Use No. 24 insulated copper wire if you are going to connect ordinary
+batteries with it. A bichromate cell (<a href="#APPARATUS_4">App. 4</a>) is best. Put about 6 in.
+(<a href="#s109">see &sect; 109</a>) of wire through <i>H</i>, and with <a href="#APPARATUS_93">App. 93</a> wind on 3 layers of
+say No. 24 wire. There being an odd number of layers, the winding will
+stop at the head end of the bolt, where a half<span class='pagenum'><a name="Page_66" id="Page_66">[Pg 66]</a></span> hitch (<a href="#s110">see &sect; 110</a>) should
+be taken before passing the wire through the hole, <i>J</i>. Cut the wire 6
+in. from the hole. Write down the number of turns of wire to each layer
+and the total number of turns. You now have a 3&ndash;layer coil, and a
+current passed through this will magnetize the bolt; you have&mdash;so
+far&mdash;merely an electro-magnet. Cover the primary coil with 2 layers of
+paraffined paper, <i>K</i> (Fig. 74), and put some paraffine between the
+edges of <i>K</i> and the washers, so that the wire of the secondary coil
+cannot possibly come in contact with that already wound on.</p>
+
+<p><i><a name="s138" id="s138"></a>138. The Secondary Coil</i> should be made of a large number of turns of
+fine wire. Do not use anything coarser than No. 30. This is a good size,
+as finer wire is very easily broken by unskilled hands. For the size of
+bolt mentioned put on 13 layers. There will be about 100 turns to each
+layer, making a total of about 1,300 turns of No. 30 wire. Write down
+the total number of turns in <i>your</i> coil. To start the secondary coil,
+make a pinhole, <i>L</i>, just outside of the insulation, <i>K</i>, of the primary
+coil. Put 6 in. of wire through this, wind the end around the nut (<a href="#APPARATUS_93">App.
+93</a>, Fig. 70), and wind on as evenly as possible 13 layers. If the layers
+become rough, it is well to put a band of paper around after each 3 or
+4. When you have finished take a half hitch (<a href="#s110">&sect; 110</a>), and leave a 6-in.
+length free. Cover the secondary coil with strong paper. This coil may
+be used on any of the forms of shockers given.</p>
+
+
+<p class="app"><a name="APPARATUS_97" id="APPARATUS_97"></a>APPARATUS 97.</p>
+
+<div class="figleft" style="width: 350px;"><a name="Fig_75" id="Fig_75"></a>
+<img src="images/figure75.jpg" width="350" height="480" alt="Fig. 75." title="" />
+<span class="caption">Fig. 75.</span>
+</div>
+
+<p><i>139. Induction Coil.</i> Fig. 75. <i>The base</i> is made of a piece of board,
+7 &times; 5 &times; &#8542; in. The locations of the different parts are shown in the
+figure. <i>The coil</i> is explained in detail in <a href="#APPARATUS_96">App. 96</a>. It is fastened to
+the base by a thin copper strip, 4, which is bent over the coil and held
+down<span class='pagenum'><a name="Page_67" id="Page_67">[Pg 67]</a></span> by screws, 3. If you haven't any copper you can use a <i>narrow</i>
+strip of tin. Do not use a wide piece of tin or iron. The coil may be
+held down firmly by strong twine placed around each end of it. The twine
+should pass through holes in the base, and be tied on the underside of
+the base. <i>The binding-posts</i> are like <a href="#APPARATUS_46">App. 46</a>.</p>
+
+<p><i>140. The Current Interrupter</i> consists of a tin or copper strip, <i>R</i>, 6
+in. long and &frac12; or &frac34; in. wide. At one end of <i>R</i> is a screw, <i>S</i>,
+which is used as a binding-post for the outside end, <i>B</i>, of the primary
+coil. (<a href="#s137">See &sect; 137</a>.) Along the center line of the strip, <i>R</i>, are driven
+1-in. wire nails, <i>Q</i>. These are placed &frac14; in. apart, and they should
+go into the wood enough only to make them solid. (See Fig. 81.) Do not
+drive them in so far that they will split the base. A stout wire, <i>P</i>,
+fastened at one end only completes the interrupter.</p>
+
+<p><i>141. The Connections.</i> The binding-posts, <i>W</i> and <i>X</i>, should be
+connected with the wires leading from a battery. Use the bichromate
+batteries of <a href="#APPARATUS_3">App. 3</a> or <a href="#APPARATUS_4">4</a>. A dry battery will do. If the current enters
+at <i>X</i>, it will pass around the primary coil (<a href="#s137">&sect; 137</a>) and out through <i>B</i>
+into <i>R</i>. It can go no farther until the free end of <i>P</i> is made to
+touch <i>R</i>, or one of the nails, <i>Q</i>, when the circuit will be closed.
+The current will fly around and around through the battery, primary
+coil, and interrupter as long as the end of <i>P</i> touches a nail. The
+battery current does<span class='pagenum'><a name="Page_68" id="Page_68">[Pg 68]</a></span> not get into the secondary coil at all. You can
+see, then, that the <i>primary circuit</i>, that is, the one passing through
+the coarse wire, will be rapidly opened and closed by bumping the free
+end of <i>P</i> along upon the row of nails.</p>
+
+<p>The wires, <i>C</i> and <i>D</i>, coming from the secondary coil (<a href="#s138">&sect; 138</a>) are in
+connection with <i>Y</i> and <i>Z</i>, to which are connected the wires leading
+from the handles (<a href="#APPARATUS_101">App. 101</a>) held by the person receiving the shock.</p>
+
+<p><i>142. To use the coil</i>, arrange as explained. Let your friend hold the
+handles (<a href="#APPARATUS_101">App. 101</a>) while you scrape the end of <i>P</i> back and forth along
+the row of nails. For those who cannot stand much of a shock, use a
+regulator (<a href="#APPARATUS_103">App. 103</a>).</p>
+
+
+<p class="app"><a name="APPARATUS_98" id="APPARATUS_98"></a>APPARATUS 98.</p>
+
+<p><i><b>143. Induction Coil.</b></i> Fig. 76. In case you wish to make the interrupter
+as a separate piece of apparatus, as <a href="#APPARATUS_104">App. 104</a>, this arrangement will be
+found good. The <i>base</i> is 5 &times; 4 &times; &#8542; in. The <i>coil</i> is explained in
+<a href="#APPARATUS_96">App. 96</a>, and the methods of holding it to the base are given in <a href="#APPARATUS_97">App. 97</a>.
+The <i>binding-posts</i> are like <a href="#APPARATUS_46">App. 46</a>.</p>
+
+<div class="figcenter" style="width: 350px;"><a name="Fig_76" id="Fig_76"></a>
+<img src="images/figure76.jpg" width="350" height="450" alt="Fig. 76." title="" />
+<span class="caption">Fig. 76.</span>
+</div>
+
+<p><i>The Connections.</i> We shall suppose that you have the interrupter of
+<a href="#APPARATUS_104">App. 104</a>, Fig. 81. The ends of the primary coil (<a href="#s137">&sect; 137</a>) are fastened
+under the screws of <i>X</i> and <i>W</i>, and those of the secondary coil to <i>Y</i>
+and <i>Z</i>. Connect one battery wire with <i>X</i> and the other battery wire to
+the interrupter at <i>S</i>, Fig. 81. Fasten the end of a stout wire to <i>W</i>,
+and leave the other end free to scrape along on the nails, <i>Q</i>, of the
+interrupter. This will then open and<span class='pagenum'><a name="Page_69" id="Page_69">[Pg 69]</a></span> close the primary circuit. The
+handles (<a href="#APPARATUS_101">App. 101</a>) are connected with <i>Y</i> and <i>Z</i>, as explained in <a href="#APPARATUS_97">App.
+97</a>. Use the battery of <a href="#APPARATUS_3">App. 3</a> or <a href="#APPARATUS_4">4</a>.</p>
+
+
+<p class="app"><a name="APPARATUS_99" id="APPARATUS_99"></a>APPARATUS 99.</p>
+
+<p><i><b>144. Induction Coil.</b></i> Fig. 77. If you wish to fasten your coil in an
+upright position the apparatus will look like Fig. 77. The <i>base</i> may be
+5 &times; 4 &times; &#8542; in. The <i>binding-posts</i> are like <a href="#APPARATUS_46">App. 46</a>. The <i>coil</i> is made
+as explained in <a href="#APPARATUS_96">App. 96</a>; but to have all the ends of the coils come out
+at the bottom, as shown, an even number of layers of wire will be
+necessary. It will be just as well to have an odd number of layers as
+before, and to bring the wire ends down the side of the coil. The coil
+is fastened to the base with screws, <i>S</i>, passing through a tin strip,
+<i>T</i>, which has a hole punched for the bolt. <i>T</i> is squeezed between the
+regular nut on the bolt and an extra one on the underside of it. See
+Fig. 61 for suggestion of another method of holding bolts upright. <i>The
+connections</i> should be made with an outside interrupter, battery, and
+handles, as explained in <a href="#APPARATUS_98">App. 98</a>.</p>
+
+<div class="figcenter" style="width: 350px;"><a name="Fig_77" id="Fig_77"></a>
+<img src="images/figure77.jpg" width="350" height="240" alt="Fig. 77." title="" />
+<span class="caption">Fig. 77.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_100" id="APPARATUS_100"></a>APPARATUS 100.</p>
+
+<p><i><b>145. Induction Coil.</b></i> Fig. 78, 78&ndash;A, 78&ndash;B. In case you wish to make a
+larger coil than those already described, the following will be found
+practical. It is made<span class='pagenum'><a name="Page_70" id="Page_70">[Pg 70]</a></span> in the same general way as before, an automatic
+interrupter, however, being added.</p>
+
+<p><i>The Core</i> is a machine-bolt, 4&frac12; in. long and <span class="above">5</span>&#8260;<span class="below">16</span> in. in diameter.
+You may use a carriage-bolt of the same dimensions, if you file away the
+square shoulder at the head end, so that it will be the same size as the
+body of the bolt. Paste a piece of thick paper upon the head, so that
+<i>A</i> will strike the paper instead of the iron. <i>The Washers</i> should be
+made around a spool that is fully 1 in. in diameter. (<a href="#s119">See &sect; 119</a>.) The
+core should be insulated with paraffine paper before winding on the
+primary coil. (<a href="#APPARATUS_88">See App. 88</a>.) The washers are 3&#8542; in. apart, inside.
+<i>The winding of the coils</i> should be done with <a href="#APPARATUS_93">App. 93</a>, or some other
+winder. The winder-nut, <i>W N</i>, Fig. 70, must hold the long core
+perfectly tight, to avoid wobbling. <i>The base</i> is 8 &times; 5 &times; &#8542; in. The
+different parts are placed as shown. The coil is fastened to the base as
+in <a href="#APPARATUS_97">App. 97</a>. <i>For binding-posts</i> see <a href="#APPARATUS_46">App. 46</a>.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_78" id="Fig_78"></a>
+<img src="images/figure78.jpg" width="400" height="251" alt="Fig. 78." title="" />
+<span class="caption">Fig. 78.</span>
+</div>
+
+<p><i>146. The Primary Coil</i> (<a href="#s137">&sect; 137</a>) is made by winding 3 layers of No. 24
+insulated copper wire upon the insulated<span class='pagenum'><a name="Page_71" id="Page_71">[Pg 71]</a></span> core. One end, 6, is fastened
+to <i>W</i> (<a href="#s109">See &sect; 109</a>), and the other end, 5, is held under the screw-head,
+<i>R</i>. Wind at least two layers of paraffined paper around this coil
+before winding on the secondary coil.</p>
+
+<p><i>147. The Secondary Coil</i> (<a href="#s138">&sect; 138</a>) is made of No. 30 insulated copper
+wire, there being 11 or 13 layers, each having about 200 turns. This
+makes, in all, about 2,500 turns of fine wire. If your winder works
+properly and the long core is strongly held by the winder-nut, you will
+have no trouble, although it takes a little time to wind on so many
+turns. The ends of this coil, 7 and 8, are fastened to <i>Y</i> and <i>Z</i>,
+which are made like <a href="#APPARATUS_46">App. 46</a>. It will be found best to wrap a piece of
+thin paper around the coil after every 3 or 4 layers are wound on. This
+makes better insulation, and makes the winding easier. Protect the coil
+by covering it with thick paper. The whole coil, when completed, is
+about 1 in. in diameter.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 78a and 78b">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_78-A" id="Fig_78-A"></a>
+<img src="images/figure78a.jpg" width="300" height="221" alt="Fig. 78-A." title="" />
+<span class="caption">Fig. 78-A.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_78-B" id="Fig_78-B"></a>
+<img src="images/figure78b.jpg" width="300" height="136" alt="Fig. 78-B." title="" />
+<span class="caption">Fig. 78-B.</span>
+</div></td>
+</tr>
+</table></div>
+
+<p><i><a name="s148" id="s148"></a>148. The Automatic Interrupter</i> (Figs. 78, 78-A, 78-B) consists of
+several parts. <i>B, E, C</i> is a piece of <i>thin</i> tin, all in one piece. The
+part, <i>B</i>, is &frac14; in. wide and 1&frac34; in. long. Its exact height above
+the base will depend upon the diameter of your coil. For the coil here
+described, 1 in. in diameter, the top edge of <i>B</i> is &#8541; in. above the
+base. See Fig. 78-B for shape of <i>B, E, C</i> before bending it, and for
+its dimensions. Around the end of <i>B</i> are tightly wound<span class='pagenum'><a name="Page_72" id="Page_72">[Pg 72]</a></span> several turns
+of tin, making the armature or hammer, <i>A</i>, which should not be allowed
+to strike against the head of the bolt on account of residual magnetism.
+(See text-book.) A piece of thick paper pasted on the head for <i>A</i> to
+strike upon is best. <i>A</i> will probably not get near enough to the bolt
+to strike it, but this will depend upon how you arrange the parts.</p>
+
+<p><i>D</i> is a wooden piece, 1 in. high, 1 in. wide, and &#8540; or &frac12; in. thick;
+it is nailed to the base. Through its center is a hole for the
+screw-eye, <i>S I</i>, which is the regulating-screw. <i>F</i> is a piece of
+copper, brass, or tin, &#8541; &times; 1&frac34; in. It is held to the base by the
+screw, <i>S</i>, and is bent so that it presses tightly against <i>S I</i>.
+Through <i>F</i> is a screw, <i>R</i>, to hold one end of the primary coil.</p>
+
+<p><i>149. Adjustment and Use.</i> The battery wires should be joined to <i>W</i> and
+<i>X</i>, and the handles to the secondary coil at <i>Y</i> and <i>Z</i>, unless a
+regulator (<a href="#APPARATUS_103">App. 103</a>) is used. Let us consider the primary circuit. If
+the current enters at <i>W</i> it will pass through the primary coil and out
+at <i>X</i>, after going through 5, <i>R</i>, <i>F</i>, <i>S I</i>, <i>B</i>, <i>E</i>, and <i>C</i>. The
+instant that the current passes, the bolt becomes magnetized; this
+attracts <i>A</i>, which pulls <i>B</i> away from the end of <i>S I</i>, thus
+automatically opening the circuit. <i>B</i> at once springs back to its
+former position against <i>S I</i>, as <i>A</i> is no longer attracted; the
+circuit is closed and the operation is rapidly repeated. <i>B</i> should
+press gently against <i>S I</i>, which must be screwed back and forth, until
+the best results are obtained. While not in use <i>A</i> should be about &#8539;
+or <span class="above">3</span>&#8260;<span class="below">16</span> in. from the bolt-head. The armature, <i>A</i>, should vibrate back
+and forth very rapidly. If this coil gives too much shock with one cell
+of <a href="#APPARATUS_3">App. 3</a> or <a href="#APPARATUS_4">4</a>, put a regulator (<a href="#APPARATUS_103">App. 103</a>) between <i>Y</i> and one of the
+handles (<a href="#APPARATUS_101">App. 101</a>).</p>
+
+
+<p><span class='pagenum'><a name="Page_73" id="Page_73">[Pg 73]</a></span></p><p class="app"><a name="APPARATUS_101" id="APPARATUS_101"></a>APPARATUS 101.</p>
+
+<div class="figright" style="width: 150px;"><a name="Fig_79" id="Fig_79"></a>
+<img src="images/figure79.jpg" width="150" height="430" alt="Fig. 79." title="" />
+<span class="caption">Fig. 79.</span>
+</div>
+
+<p><i><b>150. Handles for Shocking Coils.</b></i> Fig. 79. Ordinary sheet-tin makes
+good handles. Cut 2 pieces, each 6 &times; 4&frac12; in., and connect a stout
+copper wire to each. This may be done as suggested in Fig. 79, where the
+tin laps tightly over the bare end of the wire, or by punching 4 or 5
+holes through the tin, and weaving the wire back and forth through the
+holes. Be sure that a tight and permanent connection is made. The wires
+joined to the handles should be about No. 20, and be 4 or 5 feet long.
+Roll the tin into a cylinder, so that the connection will be on the
+inside.</p>
+
+
+<p class="app"><a name="APPARATUS_102" id="APPARATUS_102"></a>APPARATUS 102.</p>
+
+<p><i><b>151. Handles for Shocking Coils.</b></i> Very neat handles may be made from
+4-in. lengths of brass tubing that is about &frac34; in. in diameter. The
+wires leading to the coil may be soldered to the handles.</p>
+
+
+<p class="app"><a name="APPARATUS_103" id="APPARATUS_103"></a>APPARATUS 103.</p>
+
+<p><i><b>152. Current Regulator for Induction Coils.</b></i> Fig. 80. If your coil
+gives too much of a shock with one cell of <a href="#APPARATUS_3">App. 3</a> or <a href="#APPARATUS_4">4</a>, you can pull the
+carbon and zinc partly out of the solution to weaken the shock, or you
+can use a water regulator. <i>T</i> is an ordinary tin tomato can nearly
+filled with water, <i>L</i> is a lamp chimney. One wire, <i>A</i>, is fastened to
+<i>T</i> directly, or by a spring binding-post. The other wire, <i>B</i>, is
+fastened to a piece of copper, <i>C</i>, which may be raised or lowered
+inside of <i>L</i>. <i>D</i> is a piece of pasteboard with a small hole in its
+center.</p>
+
+<p><i>153. Use.</i> If this apparatus be put anywhere in the primary circuit,
+the amount of shock can be regulated by<span class='pagenum'><a name="Page_74" id="Page_74">[Pg 74]</a></span> raising or lowering <i>C</i>. When
+<i>C</i> is raised, the current has to pass through a longer column of water
+than it does when <i>C</i> is near the bottom of <i>L</i>. When <i>C</i> touches <i>T</i>,
+the current passes easily. If it were not for the chimney, the current
+would pass to the sides of <i>T</i>.</p>
+
+<div class="figcenter" style="width: 246px;"><a name="Fig_80" id="Fig_80"></a>
+<img src="images/figure80.jpg" width="246" height="468" alt="Fig. 80." title="" />
+<span class="caption">Fig. 80.</span>
+</div>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_75" id="Page_75">[Pg 75]</a></span></p>
+<h3><a name="CHAPTER_XII" id="CHAPTER_XII"></a>CHAPTER XII.</h3>
+
+<h4>CONTACT BREAKERS AND CURRENT INTERRUPTERS.</h4>
+
+
+<p><i><b>154. Contact Breakers; Current Interrupters.</b></i> It is often necessary to
+make and break the electric current at frequent intervals. This can be
+done by an ordinary key (<a href="#APPARATUS_118">App. 118</a>) by rapidly raising and lowering it.
+It is more convenient, however, to use some other form of apparatus. The
+current may be interrupted automatically; that is, it may be made to do
+the work itself (<a href="#APPARATUS_100">App. 100</a>), or each make and break in it may be governed
+by the student.</p>
+
+
+<p class="app"><a name="APPARATUS_104" id="APPARATUS_104"></a>APPARATUS 104.</p>
+
+<div class="figcenter" style="width: 350px;"><a name="Fig_81" id="Fig_81"></a>
+<img src="images/figure81.jpg" width="350" height="116" alt="Fig. 81." title="" />
+<span class="caption">Fig. 81.</span>
+</div>
+
+<p><i><b>155. Interrupter.</b></i> Fig. 81. The body of this consists of a strip of
+wood, 6 or 7 in. long, 1&frac12; in. wide, and &#8542; in. thick. Cut a strip of
+tin 1 in. wide and long enough to bend down over the ends of the wood.
+Fasten the tin to the wood with small wire nails, driving the nails into
+the ends as well as into the top of the strip. Make a "center line"
+along the tin as a guide, and then drive 1-in. wire nails through the
+tin into the wood, so that they will make a row the length of the wood,
+and stand about &frac14; in. apart. On one end make a hole through the tin,
+and put in a screw-eye binding-post (<a href="#APPARATUS_45">App. 45</a>). It is evident that if a
+wire from one pole of<span class='pagenum'><a name="Page_76" id="Page_76">[Pg 76]</a></span> a battery be connected with the binding-post, it
+will also be electrically connected with the tin strip and nails. By
+touching the wire from the other battery-pole to the tin or to any nail,
+the circuit will be closed. If this last-mentioned wire be drawn along
+entirely above the tin, so that its end can bump along from one nail to
+another, you can see that the current will be closed every time a nail
+is touched, and be opened every time it jumps through the air. This
+apparatus can be connected with shocking coils, induction apparatus,
+etc., etc. Its use will be more clearly shown in connection with such
+apparatus.</p>
+
+
+<p class="app"><a name="APPARATUS_105" id="APPARATUS_105"></a>APPARATUS 105.</p>
+
+<div class="figcenter" style="width: 350px;"><a name="Fig_82" id="Fig_82"></a>
+<img src="images/figure82.jpg" width="350" height="116" alt="Fig. 82." title="" />
+<span class="caption">Fig. 82.</span>
+</div>
+
+<p><i><b>156. Interrupter.</b></i> Fig. 82. The nails in this apparatus are placed in a
+circle about 4 in. in diameter. They are electrically connected to each
+other by a bare copper wire, which is wound around each nail several
+times, and then led out to one of the binding-posts. In the center of
+the circle is a nail, or screw, which is connected by a wire to the
+other binding-post, care being taken not to allow the two wires to touch
+each other. Around the central screw is wound one end of a stout wire,
+the other end of which reaches out from the screw far enough to touch
+the nails. When this stout wire touches any nail, a current entering one
+binding-post can pass through nails, screw, etc., and out at the other
+binding-post. When the end of the stout wire is between two nails, the
+current cannot flow. By placing the finger against this stout wire and
+turning it around rapidly, the<span class='pagenum'><a name="Page_77" id="Page_77">[Pg 77]</a></span> current can be interrupted as desired.
+The base should be about 5 &times; 6 &times; &#8542; in.</p>
+
+
+<p class="app"><a name="APPARATUS_106" id="APPARATUS_106"></a>APPARATUS 106.</p>
+
+<p><i><b>157. Interrupter.</b></i> Wind the end of the wire from one pole of the
+battery around the handle of the file. Scrape the other wire along the
+rough file. As it jumps from one ridge to another the current will be
+rapidly interrupted.</p>
+
+
+<p class="app"><a name="APPARATUS_107" id="APPARATUS_107"></a>APPARATUS 107.</p>
+
+<p><i><b>158. Interrupter.</b></i> Hold the end of the wire from one pole of a battery
+upon a saw-blade. Draw the other wire along over the teeth of the saw.
+As the wire jumps from one tooth to the next the current will be broken.</p>
+
+
+<p class="app"><a name="APPARATUS_108" id="APPARATUS_108"></a>APPARATUS 108.</p>
+
+<p><i><b>159. Automatic Interrupter.</b></i> An ordinary electric bell, or buzzer, may
+be used as an interrupter. Every time the vibrating armature swings, the
+circuit is opened. The combination of a battery, induction coil, and
+electric bell makes a very good outfit for medical purposes. The
+automatic interrupter used on <a href="#APPARATUS_100">App. 100</a> should be studied.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_78" id="Page_78">[Pg 78]</a></span></p>
+<h3><a name="CHAPTER_XIII" id="CHAPTER_XIII"></a>CHAPTER XIII.</h3>
+
+<h4>CURRENT DETECTORS AND GALVANOMETERS.</h4>
+
+
+<p><i><b>160. Current Detectors; Galvanometers.</b></i> When a wire carrying a current
+of sufficient strength is properly brought near a magnetic needle, the
+latter will be deflected from its <i>N</i> and <i>S</i> line. The conducting wire
+has a magnetic field while the current passes through it, and this gives
+the wire the power to act upon a magnetic needle just as another magnet
+would.</p>
+
+<p>The action of detectors, etc., depends upon this fact; and, strange to
+say, the magnetic field about the wire disappears the instant the
+current ceases to pass. The combination, thus, of a coil of wire and a
+magnetic needle, properly arranged, makes an instrument with which the
+presence of electricity can be detected. When the strength of a current
+is to be measured, or the strengths of two currents are to be compared,
+the apparatus is called a galvanometer. The method of making these
+pieces of apparatus will depend upon the strength of current to be
+tested or measured.</p>
+
+
+<p class="app"><a name="APPARATUS_109" id="APPARATUS_109"></a>APPARATUS 109.</p>
+
+<p><i><b>161. Current Detector.</b></i> Figs. 38 and 40 show magnetic needles. These
+may be used to detect a current by holding the conducting wire near them
+and parallel to the needle. This form is not sensitive to weak currents.
+The delicacy of the apparatus is increased by allowing the wire to pass
+above and below the needle several times as in the next apparatus.</p>
+
+
+<p><span class='pagenum'><a name="Page_79" id="Page_79">[Pg 79]</a></span></p><p class="app"><a name="APPARATUS_110" id="APPARATUS_110"></a>APPARATUS 110.</p>
+
+<p><i><b>162. Current Detector.</b></i> Fig. 83 consists, like all detectors, of a coil
+and a magnetic needle. The other parts are merely for convenience. Each
+turn of the coil helps to move the needle when the current passes.</p>
+
+<div class="figright" style="width: 350px;"><a name="Fig_83" id="Fig_83"></a>
+<img src="images/figure83.jpg" width="350" height="126" alt="Fig. 83." title="" />
+<span class="caption">Fig. 83.</span>
+</div>
+
+<p><i><a name="s163" id="s163"></a>163. The Coil</i> is made by winding 10 feet of No. 30 insulated copper
+wire around the end of a broom-handle or other cylinder that is about 1
+inch in diameter. This length of wire makes about 32 turns around such a
+cylinder. The exact length of wire for this makes no difference. After
+winding it, the coil should be slipped from the handle, being careful to
+hold it in such a way that it cannot uncoil and spring away from you.
+Tie the coil together with thread, in 3 or 4 places, to keep it in
+shape, and leave 5 or 6 in. of wire free at each end, so that
+connections can be made with other pieces of apparatus. After this is
+done press the coil into the shape shown, Fig. 83. This brings the wire
+near the needle and allows a longer needle to be used. The coil may be
+fastened to a pasteboard base. To do this, prick 4 holes in the base
+near the ends of the oval coil, and pass a strong thread through these
+with the aid of a sewing-needle. Tie the thread on the underside of the
+base at each end. If this is well done, the coil will be held firmly in
+an upright position. Paraffine may be used instead of the thread.</p>
+
+<p>The ends of the wire should be made bare, and these may be sewed to the
+base to keep them in place.</p>
+
+<p><i>164. The Needle</i> may be supported upon a pin or needle-point. The piece
+of needle should be stuck through a cork which has a slot cut into its
+underside, so that it will straddle the lower part of the coil. The
+height of the<span class='pagenum'><a name="Page_80" id="Page_80">[Pg 80]</a></span> needle-point should be fixed so that the horizontal ends
+of the magnetic needle will be near the axis of the coil, that is, along
+its central line.</p>
+
+<p><i>165. To Use the Detector</i>, turn its base around until the coil is in
+the <i>N</i> and <i>S</i> line&mdash;that is, until the magnetic needle is parallel to
+the length of the coil and wholly inside of it. Touch the ends of the
+coil with the two ends of the wire, which is supposed to carry a
+current. The needle will fly around until it is nearly perpendicular to
+its former position, if the current is strong enough.</p>
+
+
+<p class="app"><a name="APPARATUS_111" id="APPARATUS_111"></a>APPARATUS 111.</p>
+
+<div class="figleft" style="width: 350px;"><a name="Fig_84" id="Fig_84"></a>
+<img src="images/figure84.jpg" width="350" height="227" alt="Fig. 84." title="" />
+<span class="caption">Fig. 84.</span>
+</div>
+
+<p><i><b>166. Current Detector.</b></i> Fig. 84. To make a more substantial detector
+than <a href="#APPARATUS_110">App. 110</a>, the coil should be fastened to a wooden base. The coil
+may be made of 10 ft. No. 30 wire, as explained. (<a href="#s163">&sect; 163</a>.) A hole should
+be made in the base with a small awl or with a hot wire, and into this
+should be set a pin, head down. The hole need not be larger than the
+pin-head, and when you find out how high the pin-point should be above
+the base, the pin may be fastened in place with a little paraffine,
+which should be pressed into the hole around the pin. The coil may be
+fastened in place with paraffine. The ends of the coil may be connected
+with binding-posts, described in <a href="#APPARATUS_46">App. 46</a>, as shown, or with any other
+desired form.</p>
+
+<p><i>The base</i> should be 4 &times; 5 &times; &#8542; inches. The coil looks well when placed
+about 1 in. from the edge of the base. The binding-posts may be about 1
+in. from the edges.</p>
+
+
+<p><span class='pagenum'><a name="Page_81" id="Page_81">[Pg 81]</a></span></p><p class="app"><br /><a name="APPARATUS_112" id="APPARATUS_112"></a>APPARATUS 112.</p>
+
+<p><i><b>167. Current Detector.</b></i> Fig. 85. This is more troublesome to make than
+<a href="#APPARATUS_111">App. 111</a>, but perhaps it looks more scientific.</p>
+
+<div class="figright" style="width: 350px;"><a name="Fig_85" id="Fig_85"></a>
+<img src="images/figure85.jpg" width="350" height="264" alt="Fig. 85." title="" />
+<span class="caption">Fig. 85.</span>
+</div>
+
+<p><i>168. The Coil</i> is wound around 2 ordinary spools which are glued to a
+vertical piece, which, in turn, is screwed to a base. You should not use
+<i>iron</i> nails or screws in the construction of electrical apparatus, when
+a magnetic needle is to be used in connection with it, as these would
+attract the needle. The spools may be pushed onto dowels which are
+fastened into the vertical piece. Small brass screws are good for the
+purpose also, if you haven't good glue or the dowels. This coil, etc.,
+may be used in connection with an astatic needle. The coil may be wound
+with <a href="#APPARATUS_93">App. 93</a> or <a href="#APPARATUS_94">94</a>, if you make the attachment of <a href="#APPARATUS_95">App. 95</a>, and screw the
+upright carrying the spools to the attachment.</p>
+
+<p>The <i>binding-posts</i>, shown in Fig. 85, are not to be advised. It will be
+better to use those of <a href="#APPARATUS_45">App. 45</a>. The <i>magnetic needle</i> is supported by a
+sewing-needle stuck through a cork. This may be fastened to the base
+with paraffine.</p>
+
+<p><i><b>169.</b></i> It is often troublesome to turn the apparatus around until the
+needle becomes parallel to the length of the coil. To avoid this, a
+small bar magnet, shown in the Fig. 85, may be laid on top of the coil.
+A magnetized sewing-needle will do, and this will keep the magnetic
+needle quiet and parallel to it when the current is not passing through
+the coil. Of course, it takes a little more current to move the magnetic
+needle when the bar magnet is in place, than it does without the magnet.</p>
+
+<p><i><b>170.</b></i> By allowing the current to enter the right-hand<span class='pagenum'><a name="Page_82" id="Page_82">[Pg 82]</a></span> binding-post, as
+you look at it from the front (Fig. 85), it will go around the coil in
+the direction of the hands of a clock, that is, from left to right on
+top. This, of course, is not necessary to merely detect the presence of
+a current. In order, however, to determine the direction of currents by
+means of a magnetic needle, study the effect with a single turn of wire
+at first. (See text-book.)</p>
+
+<p><i>171. Dimensions.</i> The base is 5 &times; 4 &times; &#8541; in. The upright piece is 5 &times;
+3&frac12; &times; &#8541; in. The spools are 2&frac12; in. apart center to center.</p>
+
+
+<p class="app"><a name="APPARATUS_113" id="APPARATUS_113"></a>APPARATUS 113.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_86" id="Fig_86"></a>
+<img src="images/figure86.jpg" width="400" height="538" alt="Fig. 86." title="" />
+<span class="caption">Fig. 86.</span>
+</div>
+
+<p><i><b>172. Astatic Current Detector.</b></i> Fig. 86. The ordinary magnetic needle
+points to the north quite strongly. It is evident, then, that this
+pointing-power must be overcome by the magnetic field around the coil of
+wire, before the needle can be forced from the <i>N</i> and <i>S</i> line. <i>Very</i>
+weak currents will not visibly move the magnetic<span class='pagenum'><a name="Page_83" id="Page_83">[Pg 83]</a></span> needle in the
+detectors so far described. You should remember that no action will take
+place unless the magnetic field around the magnetic needle is acted upon
+by that around the coil. In order to make an instrument that will be
+very sensitive, we must have strong fields about the needle and coil,
+and we must, at the same time, decrease the pointing-power of the
+needle. We can increase the strength of the field about the needle, and
+at the same time decrease its pointing-power by using an astatic needle.
+(<a href="#APPARATUS_69">See App. 69</a>.) The arrangement shown in Fig. 86 is a very simple one,
+and it is quite sensitive.</p>
+
+<p><i>173. Details of Construction.</i> The base is 4 &times; 5 &times; &#8542; in. The <i>coil</i>
+is made from 10 ft. of No. 30 insulated copper wire. (<a href="#s163">See &sect; 163</a> for
+details about coil making.) The <i>binding-posts</i> are like <a href="#APPARATUS_41">App. 41</a>. The
+<i>Astatic Needle</i> is described for <a href="#APPARATUS_69">App. 69</a>. The needles may be broken
+off, if too long for the coil. They are supported by a fine thread hung
+from a screw-eye, which may be turned to adjust the position of the
+needles. This is not necessary, as the thread may be hung from a plain
+wire arm that reaches out from the upright rod. This rod is a 6-in.
+piece of dowel, &frac14; or <span class="above">5</span>&#8260;<span class="below">16</span> in. in diameter. It stands in an ordinary
+spool which should be glued to the base. Do not nail it to the base. The
+wire arm may be of iron, as it is some distance above the needle; but it
+is better to use a stiff brass or copper one. In the figure one end of
+the wire is twisted around the screw-eye, making a nut for the screw-eye
+to turn in.</p>
+
+<p>Hang the astatic needle so that the wire between the two parts will not
+quite touch the coil. The needles should be parallel to the coil before
+testing for currents. They will fly around very decidedly with even
+fairly weak currents.</p>
+
+
+<p><span class='pagenum'><a name="Page_84" id="Page_84">[Pg 84]</a></span></p><p class="app"><a name="APPARATUS_114" id="APPARATUS_114"></a>APPARATUS 114.</p>
+
+<div class="figleft" style="width: 175px;"><a name="Fig_87" id="Fig_87"></a>
+<img src="images/figure87.jpg" width="175" height="381" alt="Fig. 87." title="" />
+<span class="caption">Fig. 87.</span>
+</div>
+
+<p><i><b>174. Astatic Current Detector.</b></i> Fig. 87. For a description of the
+wood-work, coil, etc., see <a href="#APPARATUS_112">App. 112</a>; for the astatic needle see <a href="#APPARATUS_69">App. 69</a>;
+for the method of supporting the needle see <a href="#APPARATUS_113">App. 113</a>, Fig. 86. The top
+part of the coil is spread apart a little to allow the lower needle to
+be dropped through the opening thus made, and to allow the wire joining
+the two needles to be free to turn. The needles may be broken off a
+little, if necessary, or an opening may be cut into the vertical part of
+the frame, so that they can swing more freely. This detector will
+indicate quite feeble currents.</p>
+
+
+<p class="app"><a name="APPARATUS_115" id="APPARATUS_115"></a>APPARATUS 115.</p>
+
+<p><i><b>175. Astatic Detector.</b></i> Fig. 88. As previously Stated, the
+sensitiveness of a detector can be made greater by increasing the
+strength of the coil-field for a given current. This may be done by
+increasing the number of turns of wire in the coil. The most convenient
+way will be to use two coils, one on each side of the astatic needle.</p>
+
+<p><i>176. The Support</i>, or framework, is a lamp chimney. By this the astatic
+needle is suspended and protected from air currents. The chimney should
+be at least 3 in. in diameter at the bottom, about 10 in. high, with a
+plain round top. Upon the top of the chimney is placed the cover of a
+wooden pill-box, 2 in. in diameter.</p>
+
+<p><i>177. The Coils</i> should be made separately, for convenience. Each should
+be of 10 ft. No. 30 wire. (<a href="#s163">See details &sect; 163</a>.) Cut out a round piece of
+stiff pasteboard, just large enough to go inside of the bottom of the
+chimney. Fasten the coils to this by sewing (<a href="#s163">&sect; 163</a>), or with<span class='pagenum'><a name="Page_85" id="Page_85">[Pg 85]</a></span> paraffine,
+so that they shall be symmetrically located and &#8540; in. apart. The
+pasteboard circle may be fastened to the base with small brass screws.
+Do not use any iron nails or tacks. In this, all four ends of wire are
+brought out under the edge of the chimney (Fig. 88). Cut little grooves
+in the base for the wire to sink into, so that the chimney will rest
+firmly upon the base all around. The ends of the wires are fastened to
+three binding-posts.</p>
+
+<div class="figcenter" style="width: 375px;"><a name="Fig_88" id="Fig_88"></a>
+<img src="images/figure88.jpg" width="375" height="647" alt="Fig. 88." title="" />
+<span class="caption">Fig. 88.</span>
+</div>
+
+<p><i>178. Joining the Coils.</i> The end of one coil must be joined to the
+beginning of the other properly, or the action of one will destroy that
+of the other. Fig. 89 shows the two coils, <i>A</i> and <i>B</i>. If the current
+enters at the binding-post, <i>X</i>, it will pass through the turns of coil
+<i>A</i>, in the direction of clock-hands, then out to <i>Y</i>, where <i>B</i> begins,
+around <i>B</i> in the same way, and then to <i>Z</i>. <i>Y</i> may be<span class='pagenum'><a name="Page_86" id="Page_86">[Pg 86]</a></span> simply a
+screw-eye binding-post (<a href="#APPARATUS_41">App. 41</a>). By this arrangement one or both coils
+can be used at a time. If the current is very weak, use both coils; that
+is, connect the ends of wires to be tested with the two outside
+binding-posts. If they are joined to the middle and one outside post,
+one coil only will be in the circuit.</p>
+
+<p><i>179. The Base</i> should be about 7 &times; 5 &times; &#8542; in. Fasten three bent brass
+or copper strips to the base with brass screws to hold the chimney
+steady. By bending them in more or less you can make a snug fit around
+the chimney.</p>
+
+<div class="figleft" style="width: 250px;"><a name="Fig_89" id="Fig_89"></a>
+<img src="images/figure89.jpg" width="250" height="187" alt="Fig. 89." title="" />
+<span class="caption">Fig. 89.</span>
+</div>
+
+<p><i>180. Adjusting the Needle.</i> In the center of the box-cover is a small
+hole. The thread from the needle passes through this. The upper end of
+the thread is wound around a screw-eye, which is screwed into the cover
+near one edge. By turning the cover around, the needle can be made to
+hang parallel to the coils, and by turning the screw-eye, the needle can
+be raised or lowered. A small hole should be made in the cover before
+putting in the screw-eye, or you will be liable to split the wood.</p>
+
+<p><i>181. Use.</i> This apparatus will indicate very slight currents; in fact,
+as feeble ones as the student will have occasion to experiment with,
+such as induced currents, currents of thermo-electricity, and currents
+produced by exceedingly weak batteries. (See text-book.)</p>
+
+
+<p class="app"><br /><br /><a name="APPARATUS_116" id="APPARATUS_116"></a>APPARATUS 116.</p>
+
+<p><i><b>182. Tangent Galvanometer.</b></i> Fig. 90. For the uses of this form of
+galvanometer see text-book. Do not use any iron in making this
+apparatus. <i>The base</i> is 5 &times; 4 &times; &#8542; in. At its front end are three
+binding-posts.<span class='pagenum'><a name="Page_87" id="Page_87">[Pg 87]</a></span> <i>The pasteboard band</i>, G, is 1&frac14; in. wide and 6 in. in
+diameter. Cut the pasteboard 21 in. long and 1&frac14; in. wide, then bend
+it into the form of a circle. There will be a lap of about 3 in., and
+you can make it solid by sewing the two ends together at the lap.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_90" id="Fig_90"></a>
+<img src="images/figure90.jpg" width="400" height="597" alt="Fig. 90." title="" />
+<span class="caption">Fig. 90.</span>
+</div>
+
+<p><i>183. The Coils</i> maybe made of No. 24 insulated copper wire, which
+should be wound on before fastening <i>G</i> to the base. There are two
+separate coils, one having five turns and the other ten turns. Leaving a
+6-in. length, <i>A</i>, for connections, wind five turns of wire on to <i>G</i>,
+putting them on clockwise; that is, pass them over the top of <i>G</i> from
+left to right. Tie thread around <i>G</i> and the wire to hold them together
+after you have five turns on, and cut a 6-in. end, <i>B</i>. Now begin with
+<i>C</i>, and wind on ten turns, bringing the end of them out at <i>D</i>. Punch
+holes, <i>F</i>, through <i>G</i> on each side of the coils, run twine, <i>T</i>,<span class='pagenum'><a name="Page_88" id="Page_88">[Pg 88]</a></span>
+through them, and tie <i>T</i> on the outside of <i>G</i>. Do this in three or
+four places, to firmly hold the coils.</p>
+
+<p><i>184. Fastening Coils to Base.</i> The band and coils will not rest
+squarely upon the base, so cut two pieces of wood, <i>E</i>, about 2 &times; &frac14; &times;
+&frac14; in., to be put under <i>G</i>, one being on each side of the coil. Make
+holes through the base, pass strong cord, <i>H</i>, through them, and over
+the inside of <i>G</i>, then tie under the base. This should tightly squeeze
+<i>E</i>, and hold <i>G</i> upright and firm.</p>
+
+<p><i>185. The Connections.</i> <i>A</i> and <i>B</i> are the ends of the five-turn coil;
+<i>C</i> and <i>D</i> are the ends of the ten-turn coil. If the battery-wires are
+connected with <i>X</i> and <i>Y</i>, the current will pass through five turns of
+wire; if connected with <i>Y</i> and <i>Z</i>, it will pass through ten turns; if
+with <i>X</i> and <i>Z</i>, the current will pass through the entire fifteen
+turns. In this way the strength of the magnetic field about the coil can
+be regulated, and its effect upon the magnetic needle, <i>M</i>, changed.</p>
+
+<p><i>186. To Support the Needle</i>, glue or sew two strips, <i>I</i>, to <i>G</i>. They
+must be in such a position that the poles of <i>M</i> will be as nearly as
+possible in a horizontal line drawn through the center of the circle,
+<i>G</i>. After you have made <i>M</i> (<a href="#APPARATUS_66">App. 66</a>), and have found where the pieces,
+<i>I</i>, should be, fasten them to <i>G</i>, and then to <i>I</i> glue a pasteboard
+strip, <i>J</i>, about 1&frac14; in. wide. Run a pin, <i>P</i>, up through the center
+of <i>J</i> to support <i>M</i>.</p>
+
+<p><i>187. The Magnetic Needle</i>, <i>M</i>, should not be over 1 in. long for this
+kind of an instrument. (<a href="#APPARATUS_66">See App. 66</a> for full directions for making it.)
+On the top of <i>M</i> should be fastened a light paper pointer or index,
+<i>L</i>. The short end should be made large, so that the long slim end will
+not over-turn <i>M</i>; that is, the pointer should balance itself. It may be
+fastened to <i>M</i> with paraffine or a drop of sealing-wax. If carefully
+balanced, the pointer can be made quite long.</p>
+
+<p><span class='pagenum'><a name="Page_89" id="Page_89">[Pg 89]</a></span></p><p><i>188. The Graduated Circle</i>, <i>K</i>, is described. (Index.) With this you
+can tell through how many degrees the needle is deflected, when the
+current passes. The strength of different currents can be compared, and
+many interesting experiments performed with the tangent galvanometer.
+For clearness, the circle, <i>K</i>, is shown small. In order to have the
+divisions on it far enough apart, <i>K</i> should be about 4 in. in diameter.
+The zero points should be at the front and back of the instrument, when
+a pointer is used on the needle.</p>
+
+<p><i>189. How to Use It.</i> For full explanations, and for the study of
+experimental cells, etc., by means of the tangent galvanometer, see
+text-book. It will be impossible for you to get <i>M</i> exactly in the
+center of <i>G</i>; you cannot get the pointer exactly at right angles with
+<i>M</i>; hence, if you pass a certain current through the coils, and the
+pointer reads 20 degrees, you will find, if you reverse the current,
+making it go through the coil in an opposite direction, that the pointer
+may read 24 degrees on the opposite side of the zero. To get the <i>true</i>
+reading, then, take the average of the two, which in the case mentioned
+would be 22 degrees. (See current reversers.)</p>
+
+
+<p class="app"><a name="APPARATUS_117" id="APPARATUS_117"></a>APPARATUS 117.</p>
+
+<p><i><b>190. Tangent Galvanometer.</b></i> Fig. 91. <i>The base</i> consists of 2 parts,
+<i>A</i> and <i>B</i>. It is not necessary to use two pieces if you have wood that
+is at least &#8542; in. thick. This is given as a suggestion in case you
+have nothing but thin boards. By screwing <i>B</i> to <i>A</i> the base is made
+thick enough to take the screws for binding-posts. The base proper, <i>A</i>,
+is 8&frac12; &times; 5 &times; &frac12; in. If you make this of &#8542; in. stuff, you will not
+need <i>B</i>.</p>
+
+<p><i>The Back</i>, <i>C</i>, is 10 &times; 8&frac12; &times; &frac12; in. It is screwed to the base. Do
+not use nails, as these affect the magnetic<span class='pagenum'><a name="Page_90" id="Page_90">[Pg 90]</a></span> needle. Find the center of
+<i>C</i>, and with this as a center, draw two circles, (that is, the
+circumferences of two circles,) one 5 in. in diameter to show where to
+cut out a hole, <i>H</i>, and the other 7 in. in diameter to serve as a guide
+for fastening on the spools, <i>F</i>.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_91" id="Fig_91"></a>
+<img src="images/figure91.jpg" width="400" height="479" alt="Fig. 91." title="" />
+<span class="caption">Fig. 91.</span>
+</div>
+
+<p><i>The Spools</i>, <i>F</i>, are glued to <i>C</i>. If you have brass screws, these may
+be used instead of the spools; they should be left sticking out from <i>C</i>
+about 1 in. Around the spools or screws, fasten a pasteboard band, <i>G</i>,
+on which to wind the wire. <i>G</i> may be about 1 in. wide; it should be
+kept in the circular form by sewing the ends together where they lap.
+(Read directions in <a href="#APPARATUS_116">App. 116</a>.)</p>
+
+<p><i>191. The Coils</i> on this model are 4 in number. (<a href="#APPARATUS_116">See App. 116</a> for the
+method of winding.) The first coil is made of coarse wire, No. 18, its
+ends being joined to the binding-posts, <i>V</i> and <i>W</i>. The second coil has
+5 turns of No. 24 insulated copper wire, its ends being joined to <i>W</i>
+and <i>X</i>. The third coil has 10 turns of the same size wire, No. 24, and
+is joined to <i>X</i> and <i>Y</i>. The fourth coil has 20 turns of the same
+joined to <i>Y</i> and <i>Z</i>. If you want to use<span class='pagenum'><a name="Page_91" id="Page_91">[Pg 91]</a></span> the galvanometer for quite
+weak currents, it would be well to make a fifth coil of 20 turns of No.
+30 wire, and join it with <i>Z</i> and a new binding-post. The ends of the
+coils are run through small screw-eyes before passing to <i>X</i>, <i>Y</i>, etc.
+This is not necessary, it merely keeps them in place.</p>
+
+<p><i>The Binding-Posts</i> are like <a href="#APPARATUS_43">App. 43</a>. Any other desired style may be
+used, those of <a href="#APPARATUS_46">App. 46</a> being preferred.</p>
+
+<p><i>The Hole</i>, <i>H</i>, is 5 in. in diameter. It should be cut out about &frac12;
+in. below the center of the circles to allow for <i>D</i>, and for the
+pin-point which supports the magnetic needle, the poles of which should
+be in the line passing through the center of the coils. The method of
+cutting the hole, <i>H</i>, through <i>C</i>, will depend upon the tools at your
+service.</p>
+
+<p><i>D</i> is the front edge of an adjustable table, like that explained.
+(Index.) It is 4&frac14; in. wide. It supports the magnetic needle which is
+inside of <i>E</i>.</p>
+
+<p><i>E</i> is the outside of a glass-covered compass. (<a href="#APPARATUS_67">See App. 67</a> for
+details.) The needle should not be over 1 in. long.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_92" id="Page_92">[Pg 92]</a></span></p>
+<h3><a name="CHAPTER_XIV" id="CHAPTER_XIV"></a>CHAPTER XIV.</h3>
+
+<h4>TELEGRAPH KEYS AND SOUNDERS.</h4>
+
+
+<p class="app"><a name="APPARATUS_118" id="APPARATUS_118"></a>APPARATUS 118.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_92" id="Fig_92"></a>
+<img src="images/figure92.jpg" width="400" height="122" alt="Fig. 92." title="" />
+<span class="caption">Fig. 92.</span>
+</div>
+
+<p><i><b>192. Telegraph Keys.</b></i> Fig. 92. Telegraph keys are merely pieces of
+apparatus by which the circuit can be conveniently and rapidly opened or
+closed at the will of the operator. An ordinary push-button may be used
+to turn off and on the current, but it is not so convenient as a "key."
+Fig. 92 shows a side view of a simple key. <i>C</i> is a metal strip about
+&frac34; in. wide and 4 or 5 in. long. At the left end it is fastened to the
+base with a screw, <i>A</i>. Another screw, <i>X</i>, serves as one binding-post.
+Y is another screw binding-post. <i>W</i> is a short wire, used to regulate
+the amount of spring to the key. This is done by moving <i>W</i> to the right
+or left. If the current enters at <i>X</i>, it will pass along <i>C</i> and out at
+<i>Y</i>, when <i>C</i> is pressed down. By moving <i>C</i> up and down according to a
+previously arranged set of signals, messages can be sent by means of the
+electric current. (See telegraph alphabet.) This apparatus is not a good
+one where the line is to be run with a "closed circuit battery," or
+where it is to be used very often. It will do, however, for places where
+a push-button would be too tiresome to use. The right end of <i>C</i> is
+curved. This curve serves as a handle. <i>D</i> and <i>E</i> are wires leading
+from <i>X</i> and <i>Y</i>.</p>
+
+
+<p><span class='pagenum'><a name="Page_93" id="Page_93">[Pg 93]</a></span></p><p class="app"><a name="APPARATUS_119" id="APPARATUS_119"></a>APPARATUS 119.</p>
+
+<p><i><b>193. Telegraph Key.</b></i> Fig. 93. <i>The base</i> is 5 &times; 4 &times; &#8542; in. <i>The key</i>,
+<i>C</i>, is made of two thicknesses of tin. It is made into a strip 5&frac12; &times;
+&frac34; in., then the front end is bent up for a handle, as suggested in
+Fig. 92, the front end being above the base so that it will not touch
+the strap, <i>D</i>, unless it is pressed down. <i>C</i> is fastened to the base
+by a screw, <i>H</i>, which also binds one end of the copper wire, <i>C W</i>.
+About &frac34; in. from <i>H</i> is placed <i>X</i>, which is a screw-eye binding-post.
+Under <i>C</i> is the wire, <i>W</i>, which is used to regulate the amount of
+spring in <i>C</i>, by moving it forward or backward. <i>S I</i> shows the
+position of a screw-eye, or of an ordinary screw put into the base
+through <i>C</i>. The hole in <i>C</i> should be made so that <i>C</i> can move up and
+down easily around the screw. This is used to make a click when the key
+is allowed to spring up. The downward click is made when <i>C</i> strikes <i>D</i>
+at each depression.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_93" id="Fig_93"></a>
+<img src="images/figure93.jpg" width="400" height="427" alt="Fig. 93." title="" />
+<span class="caption">Fig. 93.</span>
+</div>
+
+<p><i>The Strap</i>, <i>D</i>, is made of tin. It is 4 &times; &frac12; in. before bending up
+the right end a little. It is fastened to the base by the screw, <i>F</i>,
+and by the other binding-post, <i>Y</i>.<span class='pagenum'><a name="Page_94" id="Page_94">[Pg 94]</a></span> Its right end is raised enough to
+allow the arm, <i>E</i>, to pass under it, but it must press down well upon
+<i>E</i> when <i>E</i> is forced toward <i>F</i>.</p>
+
+<p><i>The Swinging Arm or Switch</i>, <i>E</i>, is also made of tin, and measures,
+finished, 4&frac12; &times; &frac12; in. Its front end should be bent up a little for
+convenience in handling it. (See Fig. 92.) <i>E</i> is pivoted at <i>G</i> by a
+screw, which also binds the wire, <i>C W</i>. Fig. 24 shows another way to
+make the pivot and connection.</p>
+
+<p><i><a name="s194" id="s194"></a>194. Operation.</i> See Fig. 99 for the details of the connections of a
+home-made telegraph line. When you are using the line and telegraphing
+to your friend, the switch, <i>E</i>, of your instrument must be open, as in
+Fig. 93, and the corresponding switch on his instrument must be closed;
+that is, the circuit must be opened and closed at but one place at a
+time. As soon as you have finished, your switch must be closed. He will
+open his and proceed. When you have both finished, both switches must be
+closed. If your friend left his switch open, you could not call him over
+the line, as no current could pass into his sounder.</p>
+
+<p><i><a name="s195" id="s195"></a>195. Batteries.</i> As the circuit has to be left closed for hours and
+perhaps days at a time, so that either operator can call the other, a
+closed-circuit battery is necessary. (<a href="#APPARATUS_9">See App. 9</a>.) A dry cell,
+Leclanch&eacute;, or other open-circuit cell would not be at all suitable for a
+telegraph line, as it would soon polarize. Large Daniel cells, which are
+2&ndash;fluid cells like <a href="#APPARATUS_7">App. 7</a>, or gravity cells (<a href="#APPARATUS_9">App. 9</a>) are the best for
+your line.</p>
+
+
+<p class="app"><a name="APPARATUS_120" id="APPARATUS_120"></a>APPARATUS 120.</p>
+
+<p><i><b>196. Telegraph Sounder.</b></i> Fig. 94. The wood-work consists of 2 parts;
+the base, <i>B</i>, is 6 &times; 4 &times; &frac34; in., and the back, <i>A</i>, is 6 &times; 5 &times; &frac12; in.
+<i>A</i> is nailed or screwed to <i>B</i>.</p>
+
+<div class="figright" style="width: 350px;"><a name="Fig_94" id="Fig_94"></a>
+<img src="images/figure94.jpg" width="350" height="302" alt="Fig. 94." title="" />
+<span class="caption">Fig. 94.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_95" id="Page_95">[Pg 95]</a></span></p><p><i>The Magnet</i>, <i>M</i>, is fully described in <a href="#APPARATUS_85">App. 85</a>. <i>M</i> is held firmly to
+<i>A</i> by cord or wire, which should pass around it near the poles and at
+the curved part. The wire should pass through small holes in <i>A</i>, and be
+tied at the back. Wire nails driven into <i>A</i> at the sides of <i>M</i> will
+keep it from moving about. The wires from the magnet coils are led to
+two spring binding-posts, <i>X</i> and <i>Y</i>.</p>
+
+<p><i>197. The Armature</i>, <i>C</i>, is made of a narrow piece of thin <i>iron</i>,
+about 5&frac12; &times; &frac14; &times; &#8539; in. It may be made by bending up 3 or 4
+thicknesses of tin into that shape. This is the part which will be
+attracted by <i>M</i>, when the current passes, and which will make the
+clicks by which the message can be read. (See telegraph alphabet.) There
+are many ways by which <i>C</i> can be held near <i>M</i>. The figure shows how it
+can be done entirely with 1-in. wire nails. At the right end of <i>C</i> two
+nails are driven into <i>A</i> above and below <i>C</i>. They are just far enough
+apart to allow the left end of <i>C</i> to be raised and lowered without
+binding; in other words, these nails make a pivot for <i>C</i> to swing upon,
+and they help to support it at the same time. The left end of <i>C</i> must
+not quite touch the poles of <i>M</i> when the current passes, because the
+residual magnetism would keep <i>C</i> from dropping back into place. To
+adjust the armature, pass the current through <i>M</i>, hold <i>C</i> so that it
+will not <i>quite</i> touch the poles, then drive in the upper nail, 2. Put
+another nail, 1, below <i>C</i>, so that <i>M</i> will not have to lift <i>C</i> more
+than &#8539; or <span class="above">3</span>&#8260;<span class="below">16</span> in. Try the nails in different positions until <i>C</i>
+quickly rises and falls when the circuit is closed and opened. A nail,
+3,<span class='pagenum'><a name="Page_96" id="Page_96">[Pg 96]</a></span> driven in front of <i>C</i>, will keep its right end in place. No springs
+are needed, as gravity acts upon <i>C</i> instantly, bringing it to the
+lowest position as soon as the current ceases to flow.</p>
+
+<p><i>198. The Battery</i> will depend upon how much you want to use the
+sounder. If just to show the principle of it, almost any cell of medium
+strength will do, like that of <a href="#APPARATUS_3">App. 3</a>, <a href="#APPARATUS_4">4</a> or <a href="#APPARATUS_5">5</a>. A dry battery will do,
+but if you use the sounder much, an open-circuit battery will soon use
+itself up. Where much work is needed of the battery use <a href="#APPARATUS_9">App. 9</a>.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_95" id="Fig_95"></a>
+<img src="images/figure95.jpg" width="400" height="318" alt="Fig. 95." title="" />
+<span class="caption">Fig. 95.</span>
+</div>
+
+<p><i>The Key</i> like <a href="#APPARATUS_119">App. 119</a> is best. Push-buttons are handy where used only
+for experiments, and not for the actual sending of messages.</p>
+
+
+<p class="app"><a name="APPARATUS_121" id="APPARATUS_121"></a>APPARATUS 121.</p>
+
+<p><i><b>199. Telegraph Sounder.</b></i> Fig. 95. This makes a simple and efficient
+sounder for short lines. The <i>base</i>, <i>B</i>, is 7 &times; 4&frac12; &times; &#8542; in. The
+<i>back</i>, <i>A</i>, is 7 &times; 4&frac12; &times; &frac12; in.; it is nailed to <i>B</i>. The piece <i>D</i>
+is 4 &times; &frac34; &times; &frac34; in.; it is nailed to <i>A</i>. <i>C</i> is a wooden piece 1&frac12; &times;
+&frac34; &times; &frac34; in.; it is nailed to <i>A</i>, and in its top is a screw, <i>E</i>,
+which is used as a regulating-screw to keep the armature, <i>L</i>, from
+touching the poles.</p>
+
+<p><span class='pagenum'><a name="Page_97" id="Page_97">[Pg 97]</a></span></p><p><i>200. The Armature</i>, <i>L</i>, is explained as <a href="#APPARATUS_77">App. 77</a>. The two thicknesses
+of tin at <i>F</i> must not be too thick, or it will take too much battery
+power to work the sounder. If you find that it is too stiff to bend
+down, when the current is on, try the arrangement of <a href="#APPARATUS_122">App. 122</a>, which is
+easier to make and regulate. The whole point depends upon the tin you
+have. The end of <i>L</i> must tap against <i>E</i>. A hole is punched in the part
+<i>F</i>, and a screw, <i>G</i>, holds it to <i>D</i>. <i>L</i> should rest about &#8539; in.
+above the poles and gently press against a screw or nail, <i>V</i>.</p>
+
+<p><i>201. The Magnets</i> are like <a href="#APPARATUS_89">App. 89</a>. They are made as in <a href="#APPARATUS_88">App. 88</a>, and
+held down like <a href="#APPARATUS_90">App. 90</a>. These should be placed very near the back, <i>A</i>,
+so that the armature will be over them. If your yoke is not too wide the
+coils may rest against <i>A</i>. <i>Y</i> and <i>Z</i> are binding-posts like <a href="#APPARATUS_46">App. 46</a>.</p>
+
+<p><i>202. Connections.</i> Join the coils as explained in <a href="#s125">&sect; 125</a> and <a href="#s115">see &sect; 115</a>.
+Instead of a third or middle binding-post, as in Fig. 66, hold the two
+inside ends between a screw-head and a copper bur. The method of joining
+the wires for a line with two outfits, is shown in <a href="#APPARATUS_124">App. 124</a>. If you have
+but one key, sounder, and battery, simply join the line wire to the
+return wire there shown. A gravity cell is best. (<a href="#APPARATUS_9">See App. 9</a>.)</p>
+
+<p><i><a name="s203" id="s203"></a>203. Hints About Adjusting.</i> If you have the right spring to the part
+<i>F</i>, of the armature, you will have no trouble. It must not be so weak
+that it allows <i>L</i> to strike upon the poles, as the residual magnetism
+(Text-book) will hold <i>L</i> down after the current has ceased to pass. No
+springs are necessary, if your tin is right. Do not have <i>L</i> too far
+away from the poles. The distance is regulated by the position of <i>V</i>.
+If you have trouble in getting it to work see <a href="#APPARATUS_122">App. 122</a>. The poles must
+be opposite in nature.</p>
+
+
+<p><span class='pagenum'><a name="Page_98" id="Page_98">[Pg 98]</a></span></p><p class="app"><a name="APPARATUS_122" id="APPARATUS_122"></a>APPARATUS 122.</p>
+
+<div class="figcenter" style="width: 350px;"><a name="Fig_96" id="Fig_96"></a>
+<img src="images/figure96.jpg" width="350" height="265" alt="Fig. 96." title="" />
+<span class="caption">Fig. 96.</span>
+</div>
+
+<p><i><b>204. Telegraph Sounder.</b></i> Fig. 96. The magnets, connections, etc., are
+like those of <a href="#APPARATUS_121">App. 121</a>, no binding-posts, etc., being here shown. The
+armature is straight, however, the part <i>F</i> resting upon <i>D</i>. A hole is
+made in the end of <i>F</i>, and through this is a screw or nail, <i>S</i>. The
+hole must be large enough to allow <i>S</i> to pass through easily. This acts
+as a bearing or pivot. <i>L</i> is kept up against <i>V</i> by the rubber-band,
+<i>J</i>, one end of which passes around the end of <i>L</i>; to the other end of
+<i>J</i> is a thread, which is tied around a screw-eye, <i>K</i>. By turning the
+screw-eye, the band may be made to pull more or less upon <i>L</i>. In this
+way the apparatus may be regulated according to your battery. The
+general dimensions and explanations are given in <a href="#APPARATUS_121">App. 121</a>. <i>D</i> is made
+of such a height that it will bring <i>L</i> about &#8539; or <span class="above">3</span>&#8260;<span class="below">16</span> in. above the
+poles.</p>
+
+
+<p class="app"><a name="APPARATUS_123" id="APPARATUS_123"></a>APPARATUS 123.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_97" id="Fig_97"></a>
+<img src="images/figure97.jpg" width="400" height="260" alt="Fig. 97." title="" />
+<span class="caption">Fig. 97.</span>
+</div>
+
+<p><i><b>205. Telegraph Sounder.</b></i> Figs. 97 and 98. This apparatus looks a little
+more like a regular sounder than <a href="#APPARATUS_121">App. 121</a> and <a href="#APPARATUS_122">122</a>, but it is much harder
+to make and adjust. In this the lower nuts of the bolts are not sunk
+into the base, and the magnets are made of 2-in. bolts. If you change
+this and fasten them like <a href="#APPARATUS_89">App. 89</a> and <a href="#APPARATUS_90">90</a>, it will simply<span class='pagenum'><a name="Page_99" id="Page_99">[Pg 99]</a></span> change the
+dimensions of the small parts. The sizes given are for this particular
+instrument.</p>
+
+<p>Fig. 97 shows a perspective view, and Fig. 98 is a plan or top-view of
+it, with dimensions.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_98" id="Fig_98"></a>
+<img src="images/figure98.jpg" width="400" height="267" alt="Fig. 98." title="" />
+<span class="caption">Fig. 98.</span>
+</div>
+
+<p><i>206. The Base</i>, <i>B</i>, is 6 &times; 4 &times; &#8542; in. <i>The magnet</i>, <i>M</i>, is explained
+in <a href="#APPARATUS_89">App. 89</a>. Its wires are attached to the binding-posts like <a href="#APPARATUS_46">App. 46</a>.
+<i>The armature</i>, <i>A</i>, is 2&frac12; &times; &frac34; &times; &#8539; in., and made as described in
+<a href="#APPARATUS_71">App. 71</a>. <i>The piece</i>, <i>D</i>, is 2&frac12; &times; 1&#8540; &times; &frac12; in., and is screwed to
+<i>B</i> from below, after the two uprights, <i>C</i>, are nailed to it. <i>The
+uprights</i>, <i>C</i>, are 2&frac34; &times; &#8542; &times; &frac12; in. They are nailed to <i>D</i>. <i>The
+nail</i>, <i>N</i>, runs through both uprights, and acts as the bearing for <i>F</i>
+to rock up and down upon. The hole for <i>N</i> is 2 in. above <i>B</i>. It must
+not be too loose in the holes, or <i>F</i> will rock sidewise, and allow <i>A</i>
+to touch one of the magnets. <i>The upright</i>, <i>E</i>, is 2&frac34; &times; &frac34; &times; &frac34;
+in., and is screwed or nailed to <i>B</i> from below. A screw, <i>G</i>, is put
+into the side of <i>E</i> near the top. This screw has the underside of the
+head filed flat, and against this the screw, <i>L</i>, taps when the armature
+is attracted. <i>The arm</i>, <i>F</i>, which carries the armature, <i>A</i>, is 4&frac12;
+&times; &frac12; &times; &frac12; in., and is pivoted by means of <i>N</i>, which passes through it
+and the uprights <i>C</i>. <i>F</i> must swing up and down freely. The hole for
+<i>N</i>, in this model, is 1&frac34; in. from the armature end.</p>
+
+<p><span class='pagenum'><a name="Page_100" id="Page_100">[Pg 100]</a></span></p><p><i>207. The armature</i> is fastened to <i>F</i> by a screw, <i>S</i>. A copper bur is
+put under the head of <i>S</i> to aid in keeping <i>A</i> from rocking sidewise.
+Through <i>F</i>, and about half way between <i>C</i> and <i>L</i>, is put a screw,
+<i>I</i>, the lower end of which taps against the head of a screw, <i>H</i>, which
+is put into <i>D</i>. By unscrewing <i>H</i> a little, <i>F</i> will be raised, and <i>A</i>
+will be brought nearer the poles of <i>M</i>. <i>The rubber-band</i>, <i>J</i>, is
+placed over the head of <i>I</i>, and has tied to it a thread, <i>O</i>, which in
+turn is tied to a screw-eye, <i>K</i>. <i>K</i> screws into the end of <i>B</i>, and by
+turning it one way or the other, the tension, or pull, on <i>J</i> may be
+increased or diminished. There must be enough spring in <i>J</i> to pull <i>A</i>
+up after the current ceases; it must not pull so much that the magnet
+cannot draw <i>A</i> down hard enough to make a good click between <i>L</i> and
+<i>G</i>.</p>
+
+<p><i>The Magnet</i>, <i>M</i>, is explained in <a href="#APPARATUS_89">App. 89</a>, and the construction of one
+bolt magnet is given in detail in <a href="#APPARATUS_88">App. 88</a>. In this particular sounder
+the bolts are 2 in. long under the heads, thus bringing the tops of the
+bolt-heads about 2&frac14; in. above <i>B</i>. <i>M</i> is held to the base by a band
+of tin, <i>T</i>. The yoke may be screwed to <i>B</i>, as suggested in <a href="#APPARATUS_90">App. 90</a>.
+This is the better plan.</p>
+
+<p><i>208. Adjustment.</i> You will find, although you make all of the parts
+with the dimensions given, that you will have to try, and change, and
+adjust before everything will work perfectly. <i>A</i> must not be allowed to
+touch the poles of <i>M</i> when it is pulled down, on account of the
+residual magnetism, which would keep it pulled down. Adjust this with
+<i>F</i>. The armature must not be pulled too far up from the poles of <i>M</i> by
+the tension in <i>J</i>; adjust this with <i>I</i> and <i>H</i>. If your battery is
+weak, the pull of <i>J</i> must be small, just enough to raise <i>A</i>.</p>
+
+<p><i>The Battery.</i> It is supposed, if you make an instrument like this, that
+you expect to use it for a line. In<span class='pagenum'><a name="Page_101" id="Page_101">[Pg 101]</a></span> that case make a regular gravity
+battery like the cell of <a href="#APPARATUS_9">App. 9</a>. See Fig. 99 for line connections, and
+Fig. 98 for plan view of this sounder.</p>
+
+
+<p class="app"><a name="APPARATUS_124" id="APPARATUS_124"></a>APPARATUS 124.</p>
+
+<p><i><b>209. Telegraph Line; Connections.</b></i> Fig. 99 shows the complete
+connections for our telegraph line, with two complete outfits. The
+capital letters are used on the right side, <i>R</i>, and small letters are
+on the left side, <i>L</i>. <i>The batteries</i>, <i>B</i>, <i>b</i>, are like <a href="#APPARATUS_9">App. 9</a>. <i>The
+keys</i>, <i>K</i>, <i>k</i>, are like <a href="#APPARATUS_119">App. 119</a>. The sounders, <i>S</i>, <i>s</i>, are like
+<a href="#APPARATUS_121">App. 121</a> or <a href="#APPARATUS_122">122</a>.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_99" id="Fig_99"></a>
+<img src="images/figure99.jpg" width="400" height="243" alt="Fig. 99." title="" />
+<span class="caption">Fig. 99.</span>
+</div>
+
+<p>210. The two stations, <i>R</i> and <i>L</i>, may be near each other, or in
+different houses. The <i>return wire</i>, <i>R W</i>, passes from the copper of
+<i>b</i> to the zinc of <i>B</i>. This is <i>important</i>. If the cells are not joined
+properly, they will not work. It is better to have the cells together,
+on a short line, joined in series. The <i>line wire</i>, <i>L W</i>, and the
+return wire, <i>R W</i>, may be made of insulated copper wire for short lines
+in the house. Ordinary annunciator wire, No. 20, is good and cheap. The
+kind that is double cotton wrapped, waxed, and paraffined, has about 235
+ft. to the pound. You should get at least 5 ft. for 1 cent. If your line
+stretches from one house to another you will find it better to use iron
+wire. Galvanized iron or steel wire No. 14 is good. This size<span class='pagenum'><a name="Page_102" id="Page_102">[Pg 102]</a></span> weighs
+about 100 lbs. to the mile. The return and line wires must not touch
+each other at any point; they must not touch any pipe or other piece of
+metal that will short circuit your batteries. It is best to use
+porcelain or glass insulators to support your wires if the line is long;
+but for short lines, where you use a return wire, you may support the
+wires upon poles or trees by means of loops made of strong cord or wire.</p>
+
+<p><i>211. Operation.</i> Suppose <i>R</i> (right) and <i>L</i> (left) have a line. By
+studying Fig. 99 you will see that <i>R's</i> switch, <i>E</i>, is open while <i>e</i>
+is closed. The whole system, then, has but one place where the circuit
+is open. As soon as <i>R</i> presses his key, <i>K</i>, the circuit is closed, the
+current from both cells rushes around through <i>K</i>, <i>S</i>, <i>L W</i>, <i>s</i>, <i>k</i>,
+<i>b</i>, <i>R W</i>, and <i>B</i>. This magnetizes the bolts of both <i>S</i> and <i>s</i>, and
+their armatures come down with a click upon the regulating-screws, where
+they remain as long as the current passes. As soon as <i>R</i> raises his key
+the armatures rise, making the up-click. <i>R</i> can, in this way, regulate
+the time between the two clicks. If he presses <i>K</i> down and lets it up
+quickly, the two clicks that his friend <i>L</i> hears from <i>s</i> are close
+together; this makes what is called a <i>dot</i>. If <i>R</i> holds <i>K</i> down
+longer, it makes a longer time between the clicks for <i>L</i> to hear, and
+this makes a <i>dash</i>. <i>R</i>, of course, hears his own sounder, which is
+making the dots and dashes also.</p>
+
+<p>As soon as <i>R</i> has finished, he closes his switch, <i>E</i>. <i>L</i> then opens
+his switch and proceeds to answer. Both <i>E</i> and <i>e</i> should be left
+closed when you are through talking.</p>
+
+<p>(Read <a href="#s194">&sect; 194</a>, <a href="#s195">195</a>, and study what is said in <a href="#APPARATUS_9">App. 9</a> about the gravity
+cell to be used on such a line.)</p>
+
+<p><i><b>212. Telegraph Alphabet.</b></i> The letters are represented by combinations
+of <i>dots</i>, <i>dashes</i> and <i>spaces</i>. A <i>dot</i> is made by pressing the key
+down, and raising it at once;<span class='pagenum'><a name="Page_103" id="Page_103">[Pg 103]</a></span> that is, the key is raised as soon as it
+strikes. This makes the letter <i>E</i>. The <i>dash</i> is made by pressing down
+the key, and allowing the current to pass about as long as it takes to
+make 3 dots; this makes the letter <i>T</i>. A long dash for <i>L</i> should take
+about as long as for 5 dots. <i>Spaces</i> occur in a letter and between
+words. To make a dash you hesitate while the lever of the key is down,
+to make a space, you hesitate while the key is up. <i>H</i> is made with 4
+dots without hesitation or space. By putting a space between the dots
+the letter &amp;, <i>Y</i> or <i>Z</i> is made according to the position of the space.
+Notice that letters containing dashes do not contain spaces. A space is
+really the opposite of a dash. The letters <i>C</i>, <i>E</i>, <i>H</i>, <i>I</i>, <i>O</i>, <i>P</i>,
+<i>R</i>, <i>S</i>, <i>Y</i>, <i>Z</i>, and &amp; are made entirely of dots or of dots and
+spaces.</p>
+
+<p>You should notice that several letters are the reverse of others; <i>A</i> is
+the reverse of <i>N</i>, <i>B</i> of <i>V</i>, <i>D</i> of <i>U</i>, <i>C</i> of <i>R</i>, <i>Q</i> of <i>X</i>, and
+<i>Z</i> of <i>&amp;</i>. The student should study some book upon telegraphy, if he
+desires to become expert. Punctuation marks are left out of the alphabet
+here given, as boys will find very little use for them.</p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/amorse.jpg" width="500" height="324" alt="Morse Code Table" title="" />
+</div>
+
+<hr /><p><span class='pagenum'><a name="Page_104" id="Page_104">[Pg 104]</a></span></p>
+<h3><a name="CHAPTER_XV" id="CHAPTER_XV"></a>CHAPTER XV.</h3>
+
+<h4>ELECTRIC BELLS AND BUZZERS.</h4>
+
+
+<p class="app"><a name="APPARATUS_125" id="APPARATUS_125"></a>APPARATUS 125.</p>
+
+<p><i><b>213. Electric Buzzer.</b></i> Fig. 100. A buzzer is, in construction, very
+similar to an electric bell; in fact, you will have a buzzer by removing
+the bell from any ordinary electric bell. They are used in places where
+the loud sound of a bell would be objectionable. As the buzzer is easier
+to make than a bell, we shall discuss it first.</p>
+
+<p>214. The arrangement of the parts, (Fig. 100), is very much like that of
+the sounder of <a href="#APPARATUS_121">App. 121</a>, Fig. 95. The armature is, in this case, a
+vibrating one and acts on the same principle as the automatic
+interrupter on <a href="#APPARATUS_100">App. 100</a>, which you should study. (<a href="#s148">See &sect; 148</a>.) The
+general dimensions may be taken from <a href="#APPARATUS_121">App. 121</a>. The base, <i>B</i>, in this
+case is about 1 in. wide. <i>D</i> also is made 1 in. wide. <i>H</i> is 1 &times; 1 &times;
+&frac12; in., and is nailed to <i>A</i>. Through its center is a hole for the
+regulating screw-eye, <i>I</i>. The end of <i>I</i> presses against <i>F</i>. The exact
+position of <i>H</i> will have to be determined after the magnets are in
+place. The armature, <i>L</i>, should be about &#8539; or <span class="above">3</span>&#8260;<span class="below">16</span> in. above the
+poles. They are not allowed to strike the poles, as a screw, <i>E</i>,
+regulates that. (<a href="#s203">See &sect; 203</a>). <i>Y</i> and <i>Z</i> are two binding-posts, like
+<a href="#APPARATUS_46">App. 46</a>. To these are connected the battery wires. The strip of tin or
+copper, which forms <i>Y</i>, is cut like a letter <span class="bigt">T</span> there being
+three holes in it, one near the end of each arm. The screw-eye, 2, and
+the screw, 3, are put through the horizontal part of the <span class="bigt">T</span>, and
+the regulating-screw, <i>I</i>, passes through the hole in the vertical part<span class='pagenum'><a name="Page_105" id="Page_105">[Pg 105]</a></span>
+which springs up against <i>I</i>, thus forming an electrical connection
+between <i>Y</i> and <i>I</i>. The magnets are made and fastened as in <a href="#APPARATUS_89">App. 89</a>.</p>
+
+<p><i>215. Connections.</i> The inside ends of the magnet coils, (<a href="#s123">&sect; 123</a>), are
+fastened between a screw-head and a copper bur, <i>S</i>. One outside end
+goes to <i>Z</i>, and the other under the screw, <i>G</i>, which holds <i>F</i> to <i>D</i>.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_100" id="Fig_100"></a>
+<img src="images/figure100.jpg" width="400" height="264" alt="Fig. 100." title="" />
+<span class="caption">Fig. 100.</span>
+</div>
+
+<p><i>216. Adjustment.</i> The part, <i>F</i>, and the screw, <i>E</i>, must be just high
+enough to keep <i>L</i> from striking the poles of <i>M</i>. If <i>F</i> is too weak,
+it will bend down to <i>M</i>. If <i>F</i> is too strong, it will take too much
+battery power to run it. In case there is not strength enough in <i>F</i> to
+quickly raise <i>L</i> when the current ceases to pass, arrange a screw-eye
+and rubber band as shown in Fig. 96. <i>I</i> should be <i>slowly</i> turned one
+way or the other, until it touches <i>F</i> just right to allow <i>L</i> to
+vibrate back and forth rapidly.</p>
+
+<p><i>217. Operation.</i> We shall suppose that you have all parts adjusted and
+the battery wires joined to <i>Y</i> and <i>Z</i>. If the current enters at <i>Z</i>,
+it will fly around through the coils, through <i>G</i>, <i>F</i>, up <i>I</i>, through
+the T-shaped tin and out at <i>Y</i>. The current was in <i>L</i>, but it could
+not get out at any other place than at <i>Y</i>. As soon as the bolts were
+magnetized, <i>L</i> was forcibly drawn down, pulling <i>F</i> away from <i>I</i>,<span class='pagenum'><a name="Page_106" id="Page_106">[Pg 106]</a></span>
+thus opening the circuit. As the bolts were no longer magnets, <i>F</i>
+sprang right back to <i>I</i>, the current passed long enough to re-magnetize
+the bolts. This operation was rapidly repeated.</p>
+
+<p><i>218. Use.</i> If you wish to use the buzzer simply to call some one
+occasionally, a dry battery or Leclanch&eacute; cell is best. This apparatus is
+good to work a gravity cell when it needs regulating.</p>
+
+
+<p class="app"><a name="APPARATUS_126" id="APPARATUS_126"></a>APPARATUS 126.</p>
+
+<div class="figcenter" style="width: 350px;"><a name="Fig_101" id="Fig_101"></a>
+<img src="images/figure101.jpg" width="350" height="577" alt="Fig. 101." title="" />
+<span class="caption">Fig. 101.</span>
+</div>
+
+<p><i><b>219. Electric Bell.</b></i> Fig. 101. Before making this bell, carefully read
+the directions and explanations given for the electric buzzer, <a href="#APPARATUS_125">App. 125</a>.
+The parts are very much alike in the two instruments, and most of the
+lettering of them has been made the same in the illustrations. If you
+look at Fig. 101 from the side, with the letters <i>M</i> and <i>Q</i> at the
+bottom, you will see that this bell is merely a modified form of <a href="#APPARATUS_125">App.
+125</a>.</p>
+
+<p><i>The Base</i> is 7 &times; 5 &times; &frac12; in. To the upper end of this<span class='pagenum'><a name="Page_107" id="Page_107">[Pg 107]</a></span> is nailed the
+cross piece, <i>D</i>. To <i>D</i> are fastened the binding-posts.</p>
+
+<p><i>The Parts</i>, <i>F</i>, <i>G</i>, <i>H</i>, <i>I</i>, <i>J</i>, <i>K</i>, <i>L</i>, <i>M</i>, <i>N</i>, <i>P</i>, <i>Q</i>, are
+the same as explained in <a href="#APPARATUS_121">App. 121</a> and <a href="#APPARATUS_125">125</a>.</p>
+
+<p><i>The Magnet</i> is fastened to the base by a tin strip, <i>C</i>, which is
+screwed down at both ends. By nailing a strip, like <i>D</i>, along the left
+side of the base, the magnet may be fastened to this. This strip would
+take the place of the base of <a href="#APPARATUS_125">App. 125</a>.</p>
+
+<p>The piece, <i>F</i>, of two thicknesses of tin, is made longer than it was in
+<a href="#APPARATUS_125">App. 125</a>; in fact, it projects through <i>L</i> and forms the part <i>N</i>. To
+the lower end of <i>N</i> is fastened a large bullet. Hold the cutting-edge
+of a strong knife-blade upon the bullet, and with a few taps of a hammer
+drive the blade into it to make a gash.</p>
+
+<p>Put the end of <i>N</i> into the cut, then hammer the bullet so that <i>N</i> will
+be pinched. If you have no bullet, cut a long strip of tin, about &#8540;
+in. wide, and wind this about the end of <i>N</i> to serve as a ball.</p>
+
+<p><i>The Bell</i>, <i>E</i>, may be taken from an old alarm-clock. This is not
+screwed directly to the base, as it would not ring well. After you have
+the ball, <i>O</i>, properly fixed, hold <i>E</i>, so that <i>O</i> will strike it near
+its rim; then cut a piece of wood about &#8541; &times; &#8541;, and long enough to
+put under <i>E</i>, to raise its rim to the right place. This piece must be
+screwed to the base from the underside, and on to its top is placed the
+screw which passes through the bell. In other words, <i>E</i> is mounted upon
+a rod which is fastened to the base.</p>
+
+<p><i>The Adjustments</i> are made as in <a href="#APPARATUS_125">App. 125</a>. By bending <i>N</i> a little, <i>O</i>
+can be made to tap <i>E</i> properly.</p>
+
+<p><i>The Battery</i> for a bell that is to be used much should be an open
+circuit one, such as the Leclanch&eacute;, or the ordinary dry batteries. It is
+cheaper to buy a dry battery than it<span class='pagenum'><a name="Page_108" id="Page_108">[Pg 108]</a></span> is to make one suitable for bells.
+<i>A</i> and <i>B</i> show wires that lead to the bell from the battery. One of
+the wires should be passed through a push-button.</p>
+
+
+<p class="app"><a name="APPARATUS_127" id="APPARATUS_127"></a>APPARATUS 127.</p>
+
+<p><i><b>220. Electric Bell.</b></i> By arranging the buzzer of <a href="#APPARATUS_125">App. 125</a> with a bell,
+you can use the same for an electric bell. The part, <i>F</i>, should be made
+long enough to extend entirely through <i>L</i>, and project beyond <i>L</i> for
+about 2 in. To the end of this is fastened a large bullet, or a band of
+tin. (<a href="#APPARATUS_126">See App. 126</a>.)</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_102" id="Fig_102"></a>
+<img src="images/figure102.jpg" width="400" height="312" alt="Fig. 102." title="" />
+<span class="caption">Fig. 102.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_128" id="APPARATUS_128"></a>APPARATUS 128.</p>
+
+<p><i><b>221. Combination Buzzer and Telegraph Sounder.</b></i> Fig. 102. This
+apparatus is good for experimental purposes, where you do not wish to go
+to the trouble to make two separate pieces. For the dimensions and
+explanations see <a href="#APPARATUS_121">App. 121</a> and <a href="#APPARATUS_125">125</a>. There is but a slight change in <a href="#APPARATUS_125">App.
+125</a> to make this.</p>
+
+<p><i>222. Connections.</i> The inside ends (<a href="#s123">&sect; 123</a>) of the magnet wires are
+fastened together at <i>S</i>. The outside ends<span class='pagenum'><a name="Page_109" id="Page_109">[Pg 109]</a></span> are joined to the two
+binding-posts, <i>Y</i> and <i>Z</i>, made like <a href="#APPARATUS_46">App. 46</a>. A wire, <i>P</i>, joins <i>Y</i>
+with the screw in <i>T</i>, which is a piece of stiff tin or copper, which
+presses down upon the top of <i>I</i>. In this way a connection may always be
+had between <i>I</i> and <i>T</i>. A wire, <i>R</i>, joins <i>F</i> electrically with <i>X</i>;
+it is held under the head of the screw, <i>G</i>. (<a href="#APPARATUS_125">See App. 125</a> about
+adjustments.)</p>
+
+<p><i>223. Operation.</i> When you wish to use the apparatus as a <i>buzzer</i>, join
+your battery wires to <i>X</i> and <i>Z</i>. If the current enters <i>Z</i>, it will
+pass through the magnet coils out to <i>Y</i>, through <i>P</i>, <i>T</i>, <i>I</i>, <i>F</i>,
+and <i>R</i> to <i>X</i>. If you use it as a <i>telegraph sounder</i>, join the battery
+wires to <i>Y</i> and <i>Z</i>. The current will then pass simply through the
+coils; it will not bother to go into <i>P</i>, <i>F</i>, etc., as it has no place
+it can escape. If used simply for experimental purposes almost any cell
+of sufficient strength will do. If for telegraph, use <a href="#APPARATUS_9">App. 9</a>; if for
+buzzer, use an open circuit cell, as, for example, a dry cell.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_110" id="Page_110">[Pg 110]</a></span></p>
+<h3><a name="CHAPTER_XVI" id="CHAPTER_XVI"></a>CHAPTER XVI.</h3>
+
+<h4>COMMUTATORS AND CURRENT REVERSERS.</h4>
+
+
+<p><i><b>224. Commutators and Current Reversers</b></i> are useful in some experiments,
+as, for example, those with tangent galvanometers (<a href="#APPARATUS_116">App. 116</a>, <a href="#APPARATUS_117">117</a>), in
+which readings are made with the current passing around the coil in one
+direction, and again made at once with the current reversed. The use of
+commutators on motors and dynamos should be understood. The reversers
+herein shown are, of course, not at all like those used on motors.
+Current reversers are used in connection with the needle-telegraph and
+many other instruments.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_103" id="Fig_103"></a>
+<img src="images/figure103.jpg" width="400" height="492" alt="Fig. 103." title="" />
+<span class="caption">Fig. 103.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_129" id="APPARATUS_129"></a>APPARATUS 129.</p>
+
+<p><i><b>225. Current Reverser.</b></i> Fig. 103. The <i>base</i> is 5 &times; 4 &times; &#8542; in. To this
+are fastened four <i>metal straps</i>, <i>A</i>, <i>B</i>, <i>C</i>, and <i>D</i>. These may be
+made of brass, aluminum,<span class='pagenum'><a name="Page_111" id="Page_111">[Pg 111]</a></span> or even of tin. If made of tin, use one
+thickness of metal for <i>C</i> and <i>D</i>, and two thicknesses for <i>A</i> and <i>B</i>.
+Each strap has two &#8539; in. holes punched in it, their positions being
+shown by the screw-heads and screw-eye binding-posts.</p>
+
+<p><i>Construction.</i> <i>C</i> is 3&frac34; &times; &frac12; in. Fasten this to the base first. At
+the left end is a small screw, while the right end is held down by the
+binding-post, <i>W</i>. The keys, <i>A</i> and <i>B</i>, should have quite a little
+spring to them. These are cut 5 &times; &frac34; in. The front end of each is bent
+over a little (see the key <a href="#APPARATUS_118">App. 118</a>, Fig. 92) so that they may be more
+easily grasped. The length after bending will be less than 5 in. The
+front ends should be raised from the base (Fig. 92) so that they will
+not touch <i>C</i>, unless pressed down. The &#8539; in. holes in the end of <i>A</i>
+are about &frac34; in. apart, one being used for a screw to hold it to the
+base, and the other for the binding-post, <i>Y</i>. The strap, <i>D</i>, is 3&frac34;
+&times; &frac12; in. It is fastened at one end by a screw, and at the other end by
+<i>X</i>. <i>D</i> is bent about &frac34; in. from each end, so that its middle part
+stands above the base about &frac14; in. The straps, <i>A</i> and <i>B</i>, press up
+against <i>D</i>, unless they are held down with the hand.</p>
+
+<p><i>226. Connections.</i> <i>W</i> and <i>X</i> are joined to the poles of the battery
+to be used. <i>Y</i> and <i>Z</i> are joined to the apparatus in which the current
+must be passed in one direction, and then in the opposite direction. A
+tangent galvanometer, or a needle-telegraph instrument, for example, may
+be connected with <i>Y</i> and <i>Z</i>.</p>
+
+<p><i>227. Operation.</i> Suppose that the battery current enters at <i>W</i>. As
+long as both keys are raised, the current can go no farther. Now,
+imagine that we press <i>A</i> down solidly upon <i>C</i>, the current will pass
+along <i>A</i>, which does not now touch <i>D</i>, out through <i>Y</i> into the
+galvanometer, back to <i>Z</i>, into <i>D</i>, and to the battery again; that is,
+the<span class='pagenum'><a name="Page_112" id="Page_112">[Pg 112]</a></span> current will enter the galvanometer from <i>Y</i>. Now, suppose that we
+let <i>A</i> spring up against <i>D</i> again, and press <i>B</i> down, the current
+still coming into <i>W</i> from the battery; the current will pass along <i>B</i>,
+out through <i>Z</i>, into the galvanometer, back to <i>Y</i>, through <i>D</i>, and
+back to the battery. It is evident, then, that the current can be made
+to pass out of <i>Y</i> or <i>Z</i> to the galvanometer at will by pressing down
+<i>A</i> or <i>B</i>.</p>
+
+
+<p class="app"><a name="APPARATUS_130" id="APPARATUS_130"></a>APPARATUS 130.</p>
+
+<div class="figcenter" style="width: 368px;"><a name="Fig_104" id="Fig_104"></a>
+<img src="images/figure104.jpg" width="368" height="460" alt="Fig. 104." title="" />
+<span class="caption">Fig. 104.</span>
+</div>
+
+<p><i><b>228. Current Reverser.</b></i> Fig. 104. The wooden base is 7 &times; 5 &times; &#8542; in. To
+this are fastened two brass or tin straps, <i>C</i> and <i>D</i>, 5 &times; &frac12; in. They
+are fastened at the front ends by screws, <i>S</i>, while the binding-posts,
+<i>Y</i> and <i>Z</i>, hold the other ends solid. <i>X</i> and <i>W</i> are two screw-eye
+binding-posts (<a href="#APPARATUS_45">App. 45</a>). The small square piece of wood, <i>T</i>, is 3 &times; 3 &times;
+&frac12; in. Through the corners of <i>T</i>, and in positions so that they will
+be directly over <i>C</i> and <i>D</i>, are put four screw binding-posts, 1, 2, 3,
+4 (<a href="#APPARATUS_41">App. 41</a>). The screws, however, pass entirely through <i>T</i>, and stick
+out about &frac14; in. on the underside of it. The wire, <i>A</i>, connects <i>W</i>, 1
+and 4, while the wire, <i>B</i>, connects <i>X</i>, 2 and 3. <i>A</i> and <i>B</i> must not
+touch each other where they cross on the top of <i>T</i>. <i>N</i> is a wire nail
+that serves as a handle.<span class='pagenum'><a name="Page_113" id="Page_113">[Pg 113]</a></span> If we were to place <i>T</i>, holding the four
+corner screws, upon the straps, <i>C</i> and <i>D</i>, it is evident that all the
+screws would touch the straps, if they were properly adjusted. We must
+fix things so that two only can touch the straps at a time. Put a screw,
+<i>Q</i>, through the center of <i>T</i>, from the bottom, so that it will stick
+out of the bottom more than the screws, 1, 2, etc. The screws, 2 and 4,
+will be lifted from <i>C</i> and <i>D</i> when the handle, <i>N</i>, is pressed down.
+By raising <i>N</i>, the top, <i>T</i>, can be made to rock up and down upon <i>Q</i>
+as a pivot. By lifting <i>N</i> far enough, 2 and 4 will be pressed against
+<i>C</i> and <i>D</i>, while 1 and 3 will be raised. A spring, <i>R</i>, is shown
+joined to <i>T</i> and to the base. This will hold the screws, 2 and 4, down
+upon <i>C</i> and <i>D</i>, unless <i>N</i> is pressed down.</p>
+
+<p><i>229. Operation.</i> We shall first suppose that the spring, <i>R</i>, is
+holding 2 and 4 in contact with <i>C</i> and <i>D</i>; 1 and 3 will, of course, be
+held up in the air. Imagine that we have a galvanometer connected with
+<i>Y</i> and <i>Z</i>. If the battery current enters at <i>W</i>, it will pass along
+<i>A</i> to 4, before it can find a chance to escape. It will pass through 4
+into <i>D</i>, and into the galvanometer by way of <i>Z</i>, then back by way of
+<i>Y</i>, up 2, and out to the battery from <i>X</i>. If we now press the handle,
+<i>N</i>, down, the current will pass from <i>W</i> to 1, down 1 through <i>C</i> and
+<i>Y</i> to the galvanometer. It will return to the battery by way of <i>Z</i>,
+<i>D</i>, 3, <i>B</i>, and <i>X</i>. The current can then be rapidly reversed by
+raising and lowering <i>N</i>.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_114" id="Page_114">[Pg 114]</a></span></p>
+<h3><a name="CHAPTER_XVII" id="CHAPTER_XVII"></a>CHAPTER XVII.</h3>
+
+<h4>RESISTANCE COILS.</h4>
+
+
+<p class="app"><a name="APPARATUS_131" id="APPARATUS_131"></a>APPARATUS 131.</p>
+
+<p><i><b>230. Resistance Coils.</b></i> Fig. 105. For experiments in resistance (See
+text-book), a set of <i>standard</i> resistances is necessary. There are many
+ways in which the resistances may be made; you can arrange them upon a
+long board, upon a rack, or wind the wires around spools. We generally
+speak of resistance <i>coils</i>. The Ohm is taken as the standard. If you
+use <i>copper</i> wire, you may take 9 ft. 9 in. of No. 30 insulated wire as
+<i>your</i> standard Ohm. You could, of course, take any other length of any
+size as <i>your</i> standard, but it will be best to make your coils with a
+certain number of Ohms resistance. If you have no No. 30 wire, you may
+use 39 ft. 1 in. of No. 24 insulated copper wire for 1 Ohm. (See wire
+tables in text-book.)</p>
+
+<div class="figcenter" style="width: 265px;"><a name="Fig_105" id="Fig_105"></a>
+<img src="images/figure105.jpg" width="265" height="353" alt="Fig. 105." title="" />
+<span class="caption">Fig. 105.</span>
+</div>
+
+<p>231. To avoid the magnetic effect (See resistance coils, in text-book),
+the wire should be measured off, then doubled, before winding it upon
+the spools. The wire may be held to the spool with paraffine. Fig. 105
+shows how the<span class='pagenum'><a name="Page_115" id="Page_115">[Pg 115]</a></span> doubled wire looks on the spool, a few turns only being
+shown. Do not use any nails or other iron in connection with the coils
+proper.</p>
+
+<p>232. By making 4 coils having, respectively, 1, 2, 2, and 5 Ohms
+resistance, you will be able to use any number of Ohms from 1 to 10.
+These will be very handy in connection with a "Wheatstone's bridge" for
+comparing resistances. (See text-book for experiments). The coils should
+be mounted upon a base with proper binding-posts, so that one or more
+coils can be used at a time. (<a href="#APPARATUS_132">See App. 132</a>.) For the 2&ndash;Ohm coil use, of
+course, twice as much of the same kind of wire as for the 1&ndash;Ohm coil.</p>
+
+
+<p class="app"><a name="APPARATUS_132" id="APPARATUS_132"></a>APPARATUS 132.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_106" id="Fig_106"></a>
+<img src="images/figure106.jpg" width="400" height="194" alt="Fig. 106." title="" />
+<span class="caption">Fig. 106.</span>
+</div>
+
+<p><i><b>233. Resistance Coils.</b></i> Fig. 106. The construction of one coil is given
+in <a href="#APPARATUS_131">App. 131</a>. To have the set of coils so that they can be easily used,
+place the spools upon a base which, in the model, is 8&frac12; &times; 4 &times; &#8542; in.
+The spools are 1&frac34; in. apart, center to center, and should be glued to
+the base. Fig. 106 is a plan of the apparatus. <i>U</i>, <i>V</i>, etc., are
+binding-posts like <a href="#APPARATUS_46">App. 46</a>. The figures between them show how many Ohms
+resistance there are in the coil above. The coils <i>A</i>, <i>B</i>, <i>C</i>, <i>D</i>,
+and <i>E</i> are wound respectively for 1, 2, 2, 5 and 10 Ohms.</p>
+
+<p><i>234. Connections.</i> If you join a Wheatstone's bridge,<span class='pagenum'><a name="Page_116" id="Page_116">[Pg 116]</a></span> for example,
+with <i>U</i> and <i>V</i> (Fig. 106), the resistance added will be but 1 Ohm; if
+you join with <i>U</i> and <i>W</i>, the coils <i>A</i> and <i>B</i> will be in the circuit
+and make 3 Ohms resistance; if <i>V</i> and <i>X</i>, 4 Ohms; if <i>V</i> and <i>Y</i>, 9
+Ohms; if <i>U</i> and <i>Z</i>, the whole, or 20 Ohms.</p>
+
+
+<p class="app"><a name="APPARATUS_133" id="APPARATUS_133"></a>APPARATUS 133.</p>
+
+<p><i><b>235. Resistance Coils.</b></i> For use in some experiments in comparing the
+resistance, diameter, lengths, etc., of wires (See text-book), it is
+very handy to have coils made a certain number of meters long. (The
+meter is a French unit of measure and represents 39&middot;3705 of our inches).
+German-silver wire has a much greater resistance than copper wire of the
+same size and length.</p>
+
+<p>(<i>a</i>) Make a coil (<a href="#APPARATUS_131">See App. 131</a> for method) containing 1 meter of No. 30
+German-silver wire.</p>
+
+<p>(<i>b</i>) Make a coil with 2 meters No. 30 German-silver wire.</p>
+
+<p>(<i>c</i>) Make one with 2 meters of No. 28 German-silver wire.</p>
+
+<p>(<i>d</i>) Make one with 20 meters of No. 30 copper wire.</p>
+
+<p>The above wire must be insulated if it is to be wound upon spools. Bare
+wire may be arranged on boards or racks so that the current may not be
+short circuited.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_117" id="Page_117">[Pg 117]</a></span></p>
+<h3><a name="CHAPTER_XVIII" id="CHAPTER_XVIII"></a>CHAPTER XVIII.</h3>
+
+<h4>APPARATUS FOR STATIC ELECTRICITY.</h4>
+
+
+<p><i><b>236. Static or Frictional Electricity.</b></i> There are many interesting and
+instructive experiments in this branch of electricity. All that can be
+done here is to explain a few pieces of simple apparatus to show the
+presence of static electricity, it being taken for granted that you know
+how to produce it, and that you have some book of simple experiments.</p>
+
+<p><i><b>237. Electroscopes</b></i> are instruments for showing the presence of static
+electricity.</p>
+
+
+<p class="app"><a name="APPARATUS_134" id="APPARATUS_134"></a>APPARATUS 134.</p>
+
+<p><i><b>238. Thread Electroscope.</b></i> A piece of ordinary thread may be used for
+this purpose. Tie one end of it to the back of a chair or other support.</p>
+
+
+<p class="app"><a name="APPARATUS_135" id="APPARATUS_135"></a>APPARATUS 135.</p>
+
+<div class="figright" style="width: 200px;"><a name="Fig_107" id="Fig_107"></a>
+<img src="images/figure107.jpg" width="200" height="202" alt="Fig. 107." title="" />
+<span class="caption">Fig. 107.</span>
+</div>
+
+<p><i><b>239. Pith-Ball Electroscope.</b></i> Fig. 107. The pith from elder,
+corn-stalk, milk-weed, etc., is very light and porous. When this is tied
+to the end of a silk thread, we get the pith-ball electroscope, so much
+talked about in nearly every text-book on physics. The upper end of the
+thread may be tied to any suitable support. Fig. 117 shows a book, lead
+pencil, and a small weight to hold the pencil steady. The thread is tied
+to one end of the pencil.</p>
+
+
+<p class="app"><a name="APPARATUS_136" id="APPARATUS_136"></a>APPARATUS 136.</p>
+
+<p><i><b>240. Support for Electroscopes, etc.</b></i> Fig. 108. Glue or nail a spool,
+<i>S</i>, to a wooden base, <i>B</i>, measuring<span class='pagenum'><a name="Page_118" id="Page_118">[Pg 118]</a></span> about 4 &times; 5 in. Wrap some paper
+around a 7 in. length of &frac14; in. dowel, <i>D</i>, to make it fit the hole in
+<i>S</i>. Wind one end of a wire, <i>W</i>, around the top end of <i>D</i>. To the
+outer end of <i>W</i> tie a <i>silk</i> thread, <i>S T</i>, on the lower end of which
+may be tied a piece of pith or material to serve as an electroscope.</p>
+
+<div class="figcenter" style="width: 300px;"><a name="Fig_108" id="Fig_108"></a>
+<img src="images/figure108.jpg" width="300" height="421" alt="Fig. 108." title="" />
+<span class="caption">Fig. 108.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_137" id="APPARATUS_137"></a>APPARATUS 137.</p>
+
+<p><i><b>241. Carbon Electroscope.</b></i> Carbon will be found to make a most
+excellent electroscope, as it is light and a good conductor of
+electricity. Light an ordinary match and let it burn until it is charred
+through and through. The black substance remaining is carbon. Tie a
+small piece of the carbon, about &frac14; in. long, to one end of a silk
+thread, and support the thread as in Fig. 107 or 108.</p>
+
+
+<p class="app"><a name="APPARATUS_138" id="APPARATUS_138"></a>APPARATUS 138.</p>
+
+<p><i><b>242. Pivoted Electroscope.</b></i> Fig. 109 and 110. Fold a piece of stiff
+paper double, then cut it into the shape shown. It should be about 3 in.
+long and 1 in. wide when opened out. A hole, <i>B</i>, about &frac12; in. in
+diameter should be cut in it while folded. A piece of paper, <i>C</i>, should
+be pasted to <i>A</i>, so that its top, where it is creased,<span class='pagenum'><a name="Page_119" id="Page_119">[Pg 119]</a></span> will be about
+&#8539; in. above the top of <i>A</i>. The support consists of a pin, <i>E</i>, stuck
+through a cork, <i>D</i>. Balance the paper on the pin, which passes up
+through the hole, <i>B</i>. An electrified body brought near this apparatus
+will make it whirl around very decidedly.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 109 and 110">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_109" id="Fig_109"></a>
+<img src="images/figure109.jpg" width="300" height="113" alt="Fig. 109." title="" />
+<span class="caption">Fig. 109.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_110" id="Fig_110"></a>
+<img src="images/figure110.jpg" width="300" height="124" alt="Fig. 110." title="" />
+<span class="caption">Fig. 110.</span>
+</div></td>
+</tr>
+</table></div>
+
+
+<p class="app"><a name="APPARATUS_139" id="APPARATUS_139"></a>APPARATUS 139.</p>
+
+<p><i><b>243. Fancy Electroscope.</b></i> Fig. 111. Fold a piece of stiff paper double,
+then cut out some fancy-shaped figure, as suggested, and draw the face,
+clothes, etc., to suit. This being folded through the center for
+cutting, it can be balanced upon a pin-point as explained in <a href="#APPARATUS_138">App. 138</a>.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 111 and 112">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 201px;"><a name="Fig_111" id="Fig_111"></a>
+<img src="images/figure111.jpg" width="201" height="320" alt="Fig. 111." title="" />
+<span class="caption">Fig. 111.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 316px;"><a name="Fig_112" id="Fig_112"></a>
+<img src="images/figure112.jpg" width="316" height="274" alt="Fig. 112." title="" />
+<span class="caption">Fig. 112.</span>
+</div></td>
+</tr>
+</table></div>
+
+
+<p class="app"><a name="APPARATUS_140" id="APPARATUS_140"></a>APPARATUS 140.</p>
+
+<p><i><b>244. Box-Cover Electroscope.</b></i> Fig. 112. A pasteboard box-cover,
+balanced upon a pin, makes a fairly good electroscope, although it is
+not nearly so sensitive as <a href="#APPARATUS_138">App. 138</a>. The pin may be stuck in the upper
+end of the dowel, <i>D</i>, shown in Fig. 108.</p>
+
+
+<p><span class='pagenum'><a name="Page_120" id="Page_120">[Pg 120]</a></span></p><p class="app"><a name="APPARATUS_141" id="APPARATUS_141"></a>APPARATUS 141.</p>
+
+<p><i><b>245. Leaf Electroscope.</b></i> Fig. 113. This is a very sensitive instrument,
+and can be used to tell the <i>kind</i> of static electricity on a body, as
+well as the mere presence of it. (See experiments in text-book.) The
+lamp chimney acts as a support for the leaves, <i>L</i>, and it protects them
+from currents of air. A tin box-cover, <i>C</i>, has a small hole punched
+through its center. Through this is pushed one end of a wire, <i>W</i>. This
+may be a hairpin, straightened. The upper end is bent over at right
+angles, after passing it through the hole. The lower end is bent as
+shown. On this horizontal part is fastened the leaf. These should be
+made of aluminum leaf, or of Dutch metal. The former will stand more
+rough handling than the latter. Goldleaf is used for very sensitive
+instruments. It is a little too delicate for unskilled hands.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 113 and 114">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 300px;"><a name="Fig_113" id="Fig_113"></a>
+<img src="images/figure113.jpg" width="300" height="479" alt="Fig. 113." title="" />
+<span class="caption">Fig. 113.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 273px;"><a name="Fig_114" id="Fig_114"></a>
+<img src="images/figure114.jpg" width="273" height="404" alt="Fig. 114." title="" />
+<span class="caption">Fig. 114.</span>
+</div></td>
+</tr>
+</table></div>
+
+<p>246. To cut the aluminum leaf, place it between two pieces of paper,
+then cut paper and all into the desired shape. The piece should be about
+3 in. long and 1 in. wide. Fold this across the middle, and stick it to
+the underside of the wire (Fig. 113). Saliva will make it adhere to the
+wire, if you have nothing better.</p>
+
+
+<p><span class='pagenum'><a name="Page_121" id="Page_121">[Pg 121]</a></span></p><p class="app"><a name="APPARATUS_142" id="APPARATUS_142"></a>APPARATUS 142.</p>
+
+<p><i><b>247. To Show Where a Charge of Static Electricity Resides.</b></i> Fig. 114.
+This shows a tin baking-powder box placed upon a hot tumbler. A moist
+cotton thread is hung over the edge of the box. (See experiments in
+text-book.) The box will become charged by touching it with a charged
+body. The thread will show whether the charge resides upon the inside or
+upon the outside of the box.</p>
+
+
+<p class="app"><a name="APPARATUS_143" id="APPARATUS_143"></a>APPARATUS 143.</p>
+
+<div class="figcenter" style="width: 279px;"><a name="Fig_115" id="Fig_115"></a>
+<img src="images/figure115.jpg" width="279" height="249" alt="Fig. 115." title="" />
+<span class="caption">Fig. 115.</span>
+</div>
+
+<p><i><b>248. Support for Electrified Combs.</b></i> Fig. 115. In the study of static
+electricity, ordinary ebonite combs can be used to great advantage. A
+bent hairpin will serve as a cradle to support them. A silk thread may
+be tied to the wire, but a narrow silk ribbon is better than thread, as
+it will hold the comb steady.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_122" id="Page_122">[Pg 122]</a></span></p>
+<h3><a name="CHAPTER_XIX" id="CHAPTER_XIX"></a>CHAPTER XIX.</h3>
+
+<h4>ELECTRIC MOTORS.</h4>
+
+
+<p><i><b>249. An Electric Motor</b></i> is really a machine. If it be supplied with a
+proper current of electricity, its armature will revolve; and, if a
+pulley or wheel be fastened to the revolving shaft, a belt can be
+attached, and the motor made to do work. There are many kinds of motors,
+and many simple experiments which aid in understanding them. All that
+can be done here, however, is to show how to make simple motors. (See
+text-book for experiments.)</p>
+
+
+<p class="app"><a name="APPARATUS_144" id="APPARATUS_144"></a>APPARATUS 144.</p>
+
+<p><i><b>250. Electric Motor.</b></i> Fig. 116, 117. Fig. 116 shows a plan or top view,
+and Fig. 117 shows a side view, with a part of the apparatus removed,
+for clearness.</p>
+
+<p>The <i>base</i>, <i>B</i>, is 5 &times; 4 &times; &#8542; in. The <i>upright</i>, <i>U</i>, is 3&frac12; &times; 1&frac12;
+&times; &frac12; in., and is nailed or screwed to <i>B</i>. The <i>binding-posts</i>, <i>X</i> and
+<i>Y</i> are like <a href="#APPARATUS_46">App. 46</a>. 4 is a screw binding-post.</p>
+
+<p><i>251. The Field-Magnets</i>, as the large electro-magnets on a motor are
+called, are made of <span class="above">5</span>&#8260;<span class="below">16</span> machine-bolts, 2&frac12; in. long. The washers are
+1&frac12; in. apart inside. (<a href="#APPARATUS_88">See App. 88</a> for full directions.) The bolt
+cores are 2 in. apart, center to center. (<a href="#APPARATUS_89">See App. 89</a>.) The tin yoke,
+<i>D</i>, is made like <a href="#APPARATUS_71">App. 71</a>, and it is fastened to the base, like <a href="#APPARATUS_90">App. 90</a>.
+The hole for the screw, however, is made a little to one side of the
+center, so that a dent can be made at the center for the bottom of the
+shaft, 8, to turn in. Make the dent with a center punch. The yoke is<span class='pagenum'><a name="Page_123" id="Page_123">[Pg 123]</a></span>
+fastened to <i>B</i>, so that one edge of it is 1&frac12; in. from the back edge
+of <i>B</i>. (Fig. 116).</p>
+
+<p><i><a name="s252" id="s252"></a>252. The Armature</i>, <i>A</i>, is made of 6 or 8 thicknesses of tin, 2&frac12;
+in. long and &frac34; wide. (<a href="#APPARATUS_71">See App. 71</a>.) In its center is punched or
+drilled a &frac14; in. hole, so that it can be slipped onto the &frac14; in.
+"sink-bolt," 8. If you have taps you can make the hole a little smaller
+than &frac14; in., and thread it so that it will screw onto 8. <i>A</i> must be
+heavy enough to revolve a few times when once started. It is pinched
+between two nuts, 9 and 11, so that it just clears the poles when it
+turns. (<a href="#APPARATUS_145">See App. 145</a> for another form of armature.)</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_116" id="Fig_116"></a>
+<img src="images/figure116.jpg" width="400" height="540" alt="Fig. 116." title="" />
+<span class="caption">Fig. 116.</span>
+</div>
+
+<p><i><a name="s253" id="s253"></a>253. The shaft or axle</i>, 8, is made of a "sink-bolt" that is 3 in. long
+and &frac14; in. in diameter. These sink-bolts are threaded over their entire
+length, and are furnished with two nuts, 9 and 11, Fig. 117. File or
+grind<span class='pagenum'><a name="Page_124" id="Page_124">[Pg 124]</a></span> the end of 8 to a point, so that it will turn easily in a dent
+made for it in the yoke, <i>D</i>, or in a dent made in another piece of tin
+fastened over the yoke. The shaft is held in a vertical position by the
+arm, <i>C</i>.</p>
+
+<p><i><a name="s254" id="s254"></a>254. The Arm</i>, <i>C</i>, is made of 2 or 3 thicknesses of tin. It is 3 &times; &frac34;
+in.; it has in one end a hole for the shaft to revolve in easily, and in
+its other end a slot is cut. A screw-eye and bur are used to hold <i>C</i> to
+the upright, <i>U</i>. By this means the shaft can be moved and regulated as
+to position.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_117" id="Fig_117"></a>
+<img src="images/figure117.jpg" width="400" height="300" alt="Fig. 117." title="" />
+<span class="caption">Fig. 117.</span>
+</div>
+
+<p><i><a name="s255" id="s255"></a>255. The Commutator</i>, 9, (Fig. 117), is made of one of the nuts
+furnished with the shaft. Two of its corners are filed or ground off, so
+that it has the shape shown at the right, in Fig. 117. The copper wire,
+10, rubs against 9, as the pointed part of it comes around. 10 is really
+a "brush," and carries the current into 9 at the right time.</p>
+
+<p><i>256. Connections.</i> Join the two inside ends (<a href="#s123">&sect; 123</a>) of the coils to 4.
+The outside end of 2 is joined to <i>X</i>; the outside end, 7, of the other
+coil, 6, is carried up under or<span class='pagenum'><a name="Page_125" id="Page_125">[Pg 125]</a></span> around the screw-eye, <i>S I</i>, and then
+its bare end reaches out and gently scrapes against the top of the
+shaft, 8. The wire, 10, leads from <i>Y</i> to the back of the base, where it
+is carried up to a screw, 12, which holds it to <i>U</i>. Its bare end
+reaches out to gently scrape against the commutator, 9, when it swings
+around. This wire, 10, should not press against 9 during the <i>entire</i>
+revolution.</p>
+
+<p><i><a name="s257" id="s257"></a>257. Adjustment.</i> Suppose the current enters at <i>X</i>. When the "brush,"
+10, presses against the commutator, 9, the current passes through <i>X</i>,
+1, 2, 3, 4, 5, 6, 7, down 8 to 9, and out through 10 to <i>Y</i>. (The
+current, of course, goes down into <i>D</i> and into the bolt-cores also; but
+it can go no farther, if the coils are properly insulated, and <i>A</i> is
+not allowed to touch the cores. It is better to have the end of the
+shaft rest upon a piece of glass, having a slight depression made with a
+file, or in a dent made in tin which rests upon wood, the tin having no
+connection with <i>D</i>.) If 10 should continue to press against 9, the
+current would continue to pass, and <i>A</i> would be held firmly in place,
+directly over 2 and 6, and, of course, the shaft could not revolve. If,
+however, the brush leaves 9 (See plan of 9 at side of Fig. 117), just as
+<i>A</i> gets over the coils, or an instant before it gets there, the weight
+of <i>A</i> will carry it beyond the coils. No current should pass again,
+until <i>A</i> is at least at right angles to a line drawn through the center
+of the coils. If the current again passes, the ends of <i>A</i> will be
+attracted by the bolt-cores.</p>
+
+<p>In other words, the current should pass a little less than one-half of
+the time, and this is divided into two parts. Suppose you start <i>A</i> with
+your finger; the current should be shut off automatically just before
+the center of <i>A</i> gets over the center of the bolt-cores. <i>A</i> makes &frac14;
+of a revolution without current, and just after it gets beyond this, the
+current passes for nearly &frac14; of a revolution,<span class='pagenum'><a name="Page_126" id="Page_126">[Pg 126]</a></span> which brings the ends
+over the poles again. The next &frac14; of a turn it has no current, because
+the flat side of 9 is opposite the brush, 10, as during the first &frac14;.
+The last &frac14; the current passes again. The exact position of the
+commutator will depend upon the way you arrange the brush. The positions
+of 9 and 10 can be found by trial, so that the circuit will be promptly
+opened and closed at the proper moment. Start the motor by turning the
+armature.</p>
+
+<p><i>258. Batteries.</i> The amount of power needed will depend upon how well
+you make the motor. One cell of <a href="#APPARATUS_3">App. 3</a> or <a href="#APPARATUS_4">4</a> will run a well made one,
+but it is better to use 2 cells. Join the wires to <i>X</i> and <i>Y</i>.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_118" id="Fig_118"></a>
+<img src="images/figure118.jpg" width="400" height="456" alt="Fig. 118." title="" />
+<span class="caption">Fig. 118.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_145" id="APPARATUS_145"></a>APPARATUS 145.</p>
+
+<p><i><b>259. Armature for Motors.</b></i> Fig. 118 shows another form of armature that
+may be used for small motors like <a href="#APPARATUS_144">App. 144</a>; in fact, you may find that
+this form is easier to make than that of <a href="#APPARATUS_144">App. 144</a>. <i>M</i> is a <span class="above">5</span>&#8260;<span class="below">16</span> machine
+screw, 1&frac12; in. long, 9 being the nut furnished with it. 9 is filed as
+explained in <a href="#s255">&sect; 255</a>, and forms the commutator. <i>C</i> is the arm (<a href="#s254">&sect; 254</a>).
+<i>A</i> is the armature<span class='pagenum'><a name="Page_127" id="Page_127">[Pg 127]</a></span> (<a href="#s252">&sect; 252</a>). <i>A</i> is held firmly in place between the
+spool, <i>E</i>, and 9. <i>S</i> is a set-screw which passes through <i>E</i>, and
+holds the piece of &frac14; in. dowel, <i>F</i>, in place. <i>N</i> is a needle-point
+fastened in the end of <i>F</i>. <i>N</i> revolves in a dent made in a piece of
+tin, <i>H</i>, which rests upon a wooden strip, <i>G</i>. <i>G</i> is cut away on its
+underside, so that it will straddle the yoke, <i>D</i>, Fig. 117; it is
+nailed to the base. This is given as a suggestion. By making <i>F</i> a
+little longer, <i>N</i> can turn in a dent made in the yoke, below <i>G</i>.</p>
+
+<p><i>260. Adjustments.</i> <i>M</i>, being <span class="above">5</span>&#8260;<span class="below">16</span> in. in diameter, will screw solidly
+into the hole in <i>E</i>. Place 9 upon it first, then <i>A</i>, and screw it
+about &frac12; way into <i>E</i>. 9 will serve as a lock-nut by turning it so that
+it will pinch <i>A</i> and hold it firmly against the top of <i>E</i>. <i>F</i> should
+reach half way into <i>E</i>. Put <i>N</i> in place after you have <i>H</i> and <i>G</i>
+arranged. You can then cut the upper end of <i>F</i> at such a place that it
+will bring <i>A</i> about &#8539; in. from the top of the magnet-cores. Paper
+wrapped around <i>F</i> will make a good fit in <i>E</i>. The current should enter
+<i>M</i> and leave 9, as fully explained in <a href="#APPARATUS_144">App. 144</a>. (<a href="#s257">See &sect; 257</a>).</p>
+
+
+<p class="app"><a name="APPARATUS_146" id="APPARATUS_146"></a>APPARATUS 146.</p>
+
+<p><i><b>261. Electric Motor.</b></i> Fig. 119, 120, 121, 122. Fig. 119 shows a front
+view, and Fig. 120 a side view of the whole motor. Fig. 121 shows the
+part that revolves, and includes the <i>shaft</i>, <i>armature</i> and
+<i>commutator</i>. Fig. 122 shows a section of the commutator. All the
+dimensions are taken from a model. You can modify the size to suit.</p>
+
+<p><i>262. Wood-work.</i> The <i>base</i> is 7 &times; 5 &times; &#8542; in. The <i>uprights</i>, <i>U</i>, are
+3&frac12; &times; 1 &times; &frac34; in. They are screwed or nailed to the base from below,
+their 1-in. sides being towards you in Fig. 119. They are 4&frac14; in.
+apart, inside, in this model. The piece, <i>A</i>, is 2&frac12; &times; &#8542; &times; &#8541; in.,
+and is cut<span class='pagenum'><a name="Page_128" id="Page_128">[Pg 128]</a></span> away on the underside to straddle the yoke. Fig. 118 is a
+suggestion as to its shape. <i>A</i> is screwed or nailed to <i>B</i>.</p>
+
+<p><i>263. Tin-work.</i> The horizontal arm, <i>T</i>, is made of 3 thicknesses, and
+holds the shaft in a vertical position. <i>T</i> is 6&frac14; &times; &frac34;. In its ends
+are slots, and in its center is a hole so that the &frac14; in. shaft can
+revolve easily, but not too loosely. The slots allow an adjustment, the
+screws, <i>S</i>, holding <i>T</i> to <i>U</i>. The shaft rests in a dent made in a
+piece of tin which is tacked to <i>A</i>. The yokes are elsewhere described.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_119" id="Fig_119"></a>
+<img src="images/figure119.jpg" width="400" height="305" alt="Fig. 119." title="" />
+<span class="caption">Fig. 119.</span>
+</div>
+
+<p><i>264. Field-Magnets.</i> In this model they were made of <span class="above">5</span>&#8260;<span class="below">16</span> bolts, 2 in.
+long, placed 2 in. apart center to center. The washers are 1&#8539; in.
+apart inside. (<a href="#APPARATUS_88">See App. 88</a> for full directions.) <a href="#APPARATUS_89">App. 89</a> and <a href="#APPARATUS_71">71</a> should
+be studied. Except in size, they are made as in <a href="#APPARATUS_144">App. 144</a>. They have 8
+layers of No. 24 or 25 wire.</p>
+
+<p><i>265. The Armature</i>, Fig. 121, on this style of motor consists of a
+regular horseshoe electro-magnet, made in the same general way as the
+field-magnets. The electro-magnets, 12 and 16, are smaller, however,
+than the field-magnets.<span class='pagenum'><a name="Page_129" id="Page_129">[Pg 129]</a></span> The <i>cores</i> are &frac14; in. stove-bolts, 1&frac14; in.
+long under the head. They are placed 2 in. apart, center to center. They
+are insulated and wound as fully explained in <a href="#APPARATUS_88">App. 88</a>. These &frac14; in.
+bolts require a change in your winder. (<a href="#APPARATUS_147">See App. 147</a> for this.) If you
+wish to use <span class="above">5</span>&#8260;<span class="below">16</span> bolts, you may use the same axle for your winder as
+before. The washers are &#8541; in. apart, inside. The cores are wound with
+4 or 6 layers of No. 24 or 25 wire. This makes them about &frac34; in. in
+diameter. They are held in a tin yoke, 14, made of 5 or 6 thicknesses of
+tin. 14 is 3 &times; &frac34; in., and has 3 holes punched in it. The two outside
+holes are 2 in. apart. Through these pass the bolts, which are held
+firmly by the 2 nuts. The shaft, <i>S B</i>, is a sink-bolt, 3 in. long, and
+&frac14; in. in diameter. (<a href="#s253">See &sect; 253</a>.) The inside ends (<a href="#s123">&sect; 123</a>) of the coils
+should be firmly twisted together or held under the top nuts to make a
+good connection between them.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_120" id="Fig_120"></a>
+<img src="images/figure120.jpg" width="400" height="351" alt="Fig. 120." title="" />
+<span class="caption">Fig. 120.</span>
+</div>
+
+<p><i>266. The Commutator</i> is in two parts, which must be insulated from each
+other. The 2 sections are made out of thin tin or copper in the shape of
+an inverted <span class="bigt">T</span>, as shown at 10, Fig. 121. The arms of the
+<span class="bigt">T</span> are about &#8540;<span class='pagenum'><a name="Page_130" id="Page_130">[Pg 130]</a></span> in. wide, the horizontal ones reaching about
+half around the spool, <i>E</i>. The vertical arm reaches over the top of
+<i>E</i>, and is held down by a small screw, <i>J</i>. The sections, 10, must not
+touch the shaft. The outside wires (<a href="#s123">&sect; 123</a>) of 12 and 16 are fastened
+under these screws, <i>J</i>, and they must not touch the shaft. Bend the tin
+sections so that they will be as nearly round as possible. The spool,
+<i>E</i>, has been sawed off so that it will go between the field-magnets.
+Wind paper around the shaft to make it fit solidly into <i>E</i>. <i>S</i> is a
+small screw that holds <i>E</i> in place, if the paper does not hold it tight
+enough.</p>
+
+<div class='center'>
+<table border="0" cellpadding="6" cellspacing="0" summary="Figs. 121 and 122">
+<tr class='tr1'>
+<td align='center'><div class="figcenter" style="width: 350px;"><a name="Fig_121" id="Fig_121"></a>
+<img src="images/figure121.jpg" width="350" height="314" alt="Fig. 121." title="" />
+<span class="caption">Fig. 121.</span>
+</div></td>
+
+<td align='center'><div class="figcenter" style="width: 250px;"><a name="Fig_122" id="Fig_122"></a>
+<img src="images/figure122.jpg" width="250" height="254" alt="Fig. 122." title="" />
+<span class="caption">Fig. 122.</span>
+</div></td>
+</tr>
+</table></div>
+
+<p>Fig. 122 shows a section of the spool and tin sections with the brushes
+pressing against them. The sections do not touch each other, and the
+brushes touch opposite sections. It is evident, then, that the current
+must pass through the coils 12 and 16 in order to get from one section
+of the commutator to the other, provided you have no short circuits
+through the shaft or elsewhere. The slots in the commutator must be
+directly under the center line of the yoke, 14, as seen in Fig. 121.</p>
+
+<p><i>267. The brushes</i>, 9 and 19, Fig. 120, are made of very thin tin or
+copper. They are cut to the shape shown, the narrow part being about &#8539;
+in. wide, and long enough to<span class='pagenum'><a name="Page_131" id="Page_131">[Pg 131]</a></span> reach at least to the center-line of the
+apparatus. The foot, or bottom part of the brushes, should be about
+1&frac14; &times; &frac34; in. These are used to fasten them to the base and to make
+connections. If you have no <i>thin</i> metal for brushes, use copper wires,
+and arrange them so that they will press gently against the commutator.</p>
+
+<p><i>268. Connections.</i> The inside ends (<a href="#s123">&sect; 123</a>) of the field-magnets are
+held at 4. The outside end of coil 2 is joined to <i>X</i>, and that of coil
+6 to 8, the foot of the brush which presses against 10. The section, 10,
+of the commutator is joined to 11, the outside end of coil 12, its
+inside end being fastened to the inside end of coil, 16, either by
+twisting them together, or by fastening them under the top nuts of the
+armature yoke, 14. The outside end of coil 16 is joined to the other
+commutator section, 18. The brush, 19, completes the circuit. In the
+foot of 19 is the binding-post, <i>Y</i>.</p>
+
+<p>If the current enters at <i>X</i>, it will pass through 1, 2, 3, 4, 5, 6, 7,
+8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and out at <i>Y</i>, provided
+10 and 18 are in contact with 9 and 19. Be careful not to have any short
+circuits. If, for example, the wire 7 touches 4, or if 3 touches 8, or
+if the wires 11 and 17 touch the shaft, your current will not pass where
+you expect, and you will have trouble.</p>
+
+<p><i>269. Adjustment.</i> The armature cores should just clear the poles of the
+field-magnets as they turn. This must be regulated by the thickness of
+<i>A</i> and the position of the nuts on the shaft, <i>S B</i>. The slots in the
+commutator must be under the center of the yoke, 14. The brushes, 9 and
+19, must touch 10 and 18, but not so hard that they will stop the motor.
+Wire brushes are more easily adjusted than tin or sheet-copper ones. The
+tin arm, <i>T</i>, must hold the shaft properly. The point of the shaft must
+allow it to turn easily. The motor will turn<span class='pagenum'><a name="Page_132" id="Page_132">[Pg 132]</a></span> clockwise if the
+attachments are made as shown. Use 1 or 2 good bichromate cells, like
+<a href="#APPARATUS_3">App. 3</a> or <a href="#APPARATUS_4">4</a>.</p>
+
+<p><i>270. Operation.</i> The current will pass through the field-coils in the
+same direction, as long as the battery wires are not changed. The
+current is reversed in the armature-coils every time the brushes change
+from one section to the other of the commutator; that is, it flows in
+one direction during one-half of a revolution, and in the opposite
+direction during the other half. This reverses the poles of the
+armature-magnets every &frac12; revolution. (See text-book for full
+explanations and for simple experiments with electric motors.)</p>
+
+
+<p class="app"><a name="APPARATUS_147" id="APPARATUS_147"></a>APPARATUS 147.</p>
+
+<p><i><b>271. Attachment for Winder.</b></i> In winding small electro-magnets for
+armature, etc., in which cores are used that are not <span class="above">5</span>&#8260;<span class="below">16</span> in. in
+diameter, your winder will have to be slightly changed. Its <span class="above">5</span>&#8260;<span class="below">16</span>
+stove-bolt will have to be removed, and a &frac14; in. one put in instead.
+This may be done by making a handle for the &frac14; in. bolt. To keep this
+from wobbling in the <span class="above">5</span>&#8260;<span class="below">16</span> hole, wind stiff paper around the bolt until
+it fits quite tightly. The whole winder is explained as <a href="#APPARATUS_93">App. 93</a>.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_133" id="Page_133">[Pg 133]</a></span></p>
+<h3><a name="CHAPTER_XX" id="CHAPTER_XX"></a>CHAPTER XX.</h3>
+
+<h4>ODDS AND ENDS.</h4>
+
+
+<p class="app"><a name="APPARATUS_148" id="APPARATUS_148"></a>APPARATUS 148.</p>
+
+<p><i><b>272. Graduated Circles.</b></i> Fig. 123. For compasses (<a href="#APPARATUS_67">App. 67</a>), and for use
+in connection with tangent galvanometers (<a href="#APPARATUS_116">App. 116</a>), a graduated circle
+is necessary. Fig. 123 is a reduced drawing from an original that is 4
+in. in diameter. The long lines are 10 degrees apart, the smallest
+divisions shown being 5 degrees apart. Single degrees can be determined
+with considerable accuracy with the eye.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_123" id="Fig_123"></a>
+<img src="images/figure123.jpg" width="400" height="391" alt="Fig. 123." title="" />
+<span class="caption">Fig. 123.</span>
+</div>
+
+<p><i>To divide the circle.</i> Divide the circumference into 4 equal parts;
+these will be 90 degrees from each other, there being 360 degrees in
+every circle. Divide each quarter into nine equal parts with a pair of
+dividers; these will be for the long lines, 10 degrees apart. Divide
+each of these into two equal parts. If you are used to drawing, you can
+divide the circle still more, but 5&ndash;degree divisions will do.</p>
+
+
+<p><span class='pagenum'><a name="Page_134" id="Page_134">[Pg 134]</a></span></p><p class="app"><a name="APPARATUS_149" id="APPARATUS_149"></a>APPARATUS 149.</p>
+
+<p><i><b>273. Adjustable Table.</b></i> Fig. 124. A table that can be raised or lowered
+is useful. The one shown at <i>D</i>, Fig. 124, is used for the galvanometer
+of A<a href="#APPARATUS_117">pp. 117</a>. The dimensions are given in the figure. The upright piece,
+<i>U</i>, is fastened to <i>D</i> with brass screws, <i>not</i> with nails, as these
+would affect the needle. It is placed at one side of <i>D</i> so that the
+compass needle placed in the center of <i>D</i> will also be in the center of
+the wire coils when used in <a href="#APPARATUS_117">App. 117</a>. The table is fastened in any
+position by a screw-eye, <i>S I</i>, which presses a copper washer, <i>W</i>,
+against <i>U</i>. <i>S I</i> works through a narrow slot, <i>S</i>, and screws into the
+back of the galvanometer. By making <i>S</i> longer, the table may be used
+for other laboratory purposes, if it is joined with some other form of
+standard.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_124" id="Fig_124"></a>
+<img src="images/figure124.jpg" width="400" height="357" alt="Fig. 124." title="" />
+<span class="caption">Fig. 124.</span>
+</div>
+
+
+<p class="app"><a name="APPARATUS_150" id="APPARATUS_150"></a>APPARATUS 150.</p>
+
+<p><i><b>274. Glue Pot.</b></i> If you have occasion to use glue, you can make a good
+glue pot out of 2 tin cans, one being placed inside the other. Put &frac14;
+teacupful of glue in the inside can. If you have time, cover it with
+cold water, and let it soften. If you are in a hurry, cover it with hot
+water. Set this inside can into the other, in which you have boiling
+water. Do not let the water boil<span class='pagenum'><a name="Page_135" id="Page_135">[Pg 135]</a></span> over. The solder will not melt from
+ordinary tomato cans, if you keep water in them. Thin the glue with a
+little hot water until it drips from the brush in drops. Have the glue
+hot and fairly thin, and apply quickly. Hold the pieces of wood together
+by pressure until the glue hardens.</p>
+
+
+<p class="app"><a name="APPARATUS_151" id="APPARATUS_151"></a>APPARATUS 151.</p>
+
+<p><i><b>275. Paraffine Paper and Cardboard</b></i> are extremely useful for insulating
+purposes. The paraffine used in candles will do, if you cannot get it in
+block form. While ordinary paper will do for simple apparatus to wind
+about coils, etc., you will find that paraffine paper can be handled
+very rapidly. To melt the paraffine you should use a double boiler, or
+one made of a shallow basin set in a pan of water. The water should be
+boiled. This will melt the paraffine in the basin. Strips of paper just
+passed through the melted paraffine will become soaked, and the
+paraffine will quickly harden in the air. Allow thick cardboard to soak
+for a minute or two, to drive out all the air. This makes excellent
+washers for electro-magnets. (<a href="#s119">See &sect; 119</a>.) To make one piece of this
+paper stick to another, merely pass a clean hot nail over the two where
+they lap. To hold coils of wire together, or to wooden bases, use a few
+drops of paraffine applied with a large hot nail.</p>
+
+<p><i>276. Caution.</i> Do not heat paraffine directly upon the fire or over a
+burner, unless you watch it constantly. It will burn if its temperature
+is raised too much. It is better to heat it with steam, as you do glue.</p>
+
+
+<p class="app"><a name="APPARATUS_152" id="APPARATUS_152"></a>APPARATUS 152.</p>
+
+<p><i><b>277. Battery Jars.</b></i> For small cells, use glass tumblers. Ordinary glass
+fruit jars are good. Even earthen bowls may be used, and for large
+cells&mdash;if you<span class='pagenum'><a name="Page_136" id="Page_136">[Pg 136]</a></span> have nothing better&mdash;you can use small earthen crocks or
+jars.</p>
+
+<p><i>278. Glass Bottles</i> can be cut off so that they will make excellent
+jars. If you have thin bottles, you can cut them with strong cord. Tie
+one end of the cord, which should be 5 or 6 feet long, to a door knob or
+to a solid post. Tie the other end around your body. Make one complete
+turn of the cord around the bottle where you wish to cut it; draw the
+cord tight by stepping back, and with both hands draw the bottle back
+and forth vigorously many times, so that the cord will rub it hard and
+make it very hot. Do not let the cord move lengthwise upon the bottle.
+This will make a circle around the bottle that is very hot. Immediately
+plunge the bottle into cold water, the colder the better. Use ice-water,
+if you have it. If you produce heat enough, the bottle should crack all
+the way around very neatly. File off any sharp corners and edges with a
+wet file.</p>
+
+<p><i>279. A hot iron</i> can be used with success to cut off a bottle. File a
+deep groove first, hold the red-hot iron first on one side of file mark
+and then on the other to start the crack. You can lead the crack
+wherever you wish by keeping the iron about &#8539; in. ahead of it.</p>
+
+<p><i>280. A small gas-flame</i> will be much better than a hot iron, and you
+may easily use it, if you have glass tubing, rubber tubing, etc., in
+your shop. Draw out the glass so that the gas will burn in a fine
+needle-like flame about 1 in. long. Keep the point of the flame about
+&frac14; in. ahead of the crack. The glass tube should be held in a rubber
+tube connected with the gas pipe.</p>
+
+
+
+<hr /><p><span class='pagenum'><a name="Page_137" id="Page_137">[Pg 137]</a></span></p>
+<h3><a name="CHAPTER_XXI" id="CHAPTER_XXI"></a>CHAPTER XXI.</h3>
+
+<h4>TOOLS AND MATERIALS.</h4>
+
+
+<p><i><b>281. Your Workshop.</b></i> If possible, keep all your work, tools and
+apparatus in one room, and lock the door when you leave.</p>
+
+<p>The <i>work-bench</i> may be made of an old kitchen table, or of a strong,
+large box. The <i>tool chest</i> may be made of any clean box about the size
+of a soap box. <i>Shelves</i> can be made by setting soap or starch boxes on
+their sides, one above the other.</p>
+
+<p><i><b>282. The tools</b></i> needed are generally mentioned in the proper places,
+under the directions for construction. It is better to buy your tools as
+required, than to buy too many at once, some of which you may not need.
+If you have absolutely no tools, not even a saw or hammer, you will be
+obliged to buy or borrow, although a great deal can be done with a good
+knife. Do not be satisfied with rough-looking pieces of apparatus.</p>
+
+<p>There are a few important tools needed for this work. While substitutes
+can be found for most of them, the boy who has access to a wood-working
+bench and tools will be able to do better and more rapid work than the
+boy who has no such tools.</p>
+
+<p><i>283. List of tools.</i> The following tools are needed, if rapid, accurate
+work is desired:</p>
+
+<p>(1.) Lead pencil. (2.) A rule, divided into sixteenths for measuring. A
+straight foot rule will do,&mdash;cost one cent. (3.) Steel point for
+scratching lines on tin and copper. A stout needle-point is just the
+thing. (4.) An awl for making holes in wood; one that is a little less<span class='pagenum'><a name="Page_138" id="Page_138">[Pg 138]</a></span>
+than &#8539; in. in diameter is best. (<a href="#APPARATUS_25">See App. 25</a>.) (5.) A try-square with
+a 6 in. blade, so that you can mark out your apparatus with square
+corners. You can use a square-cornered box or piece of pasteboard, if
+you have no try-square. (6.) Chisels are very useful, but you can do
+wonders with a good sharp knife. (7.) Screw-driver. Do not use a good
+knife-blade for a screw-driver. (8.) A saw, one with teeth that are not
+too coarse is to be preferred. (9.) A plane is extremely useful to make
+your wood-work smooth and neat; but a great deal can be done with the
+sharp edges of broken glass, followed by a good rubbing with fine
+sand-paper. (10.) A brace and a set of bits may be needed in 2 or 3
+cases, but nearly all of the holes can be made as in <a href="#APPARATUS_25">App. 25</a>. (11.)
+Punches for sheet-tin, etc., will save much time. (<a href="#APPARATUS_26">See App. 26</a>, <a href="#APPARATUS_27">27</a>.) For
+small holes in binding-posts, etc., use a flat-ended punch, &#8539; in. in
+diameter. You should have one &frac14; or <span class="above">5</span>&#8260;<span class="below">16</span> in. in diameter, if you make
+your yokes, armatures, etc., as in Chapter VIII. A blacksmith will help
+you out with this. (12.) A center-punch or sharp-pointed punch for
+making dents in metal. A sharp-pointed wire nail will do for tin and
+copper. (13.) Files for metal. (14.) Some sort of a vice or clamp. (See
+<a href="#APPARATUS_79">App. 79</a>, <a href="#APPARATUS_80">80</a>.) (15.) Shears for cutting sheet-tin, etc. A pair of old
+shears will do. (16.) An anvil or piece of old iron that may be used to
+hammer on to flatten tin, etc. An old flat-iron makes a good anvil.
+(17.) Hammer.</p>
+
+<p>The small hollow handle tool sets are very handy, and they contain small
+chisels, awls, screw-driver, etc. These sets cost from 50 cents up.</p>
+
+<p><i><b>284. Materials.</b></i> For <i>wood</i> you will find the sides and ends of clean
+soap or starch boxes about the right thickness; they are fairly smooth
+to begin with. For thin wood use cigar boxes. The pieces from old boxes<span class='pagenum'><a name="Page_139" id="Page_139">[Pg 139]</a></span>
+should be removed with care, and saved in one place, which may be called
+your lumber yard. All nails should be removed with a claw-hammer. Look
+out for nails when using a saw, plane or other edged tool. (<a href="#s297">See &sect; 297</a>.)
+The edges of bases, etc., may be bevelled as shown in Fig. 95. This is
+not necessary, but it adds greatly to the appearance.</p>
+
+<p><i>285. Screw-Eyes.</i> Brass screw-eyes, with copper burs, make excellent
+binding-posts. (<a href="#APPARATUS_45">App. 45</a>, <a href="#APPARATUS_46">46</a>.) Those that are &#8540; in. in diameter inside
+the circle are about right. These are about 1&frac14; in. long in all, with
+a &frac12; in. thread.</p>
+
+<p><i>286. Copper Burs</i>, such as are used with rivets, are very handy. The
+size that is &frac12; in. in diameter, with a &#8539; in. hole, is good.</p>
+
+<div class="figcenter" style="width: 400px;"><a name="Fig_125" id="Fig_125"></a>
+<img src="images/figure125.jpg" width="400" height="103" alt="Fig. 125." title="" />
+<span class="caption">Fig. 125.</span>
+</div>
+
+<p><i>287. Copper Wire.</i> This can be bought at an electrician's. The only
+trouble, however, in buying small quantities is that you may have to pay
+a large price in proportion. If you get it on &frac12; lb. spools you can
+handle it much better (<a href="#APPARATUS_23">see App. 23</a>) than you can if you have it in a
+tangle. It is well to have &frac12; lb. of No. 24 or 25 for electro-magnets,
+current-detectors, etc., etc. &frac12; lb. of No. 30 will not be too much, if
+you make induction coils. If you handle your wire carefully, single
+cotton-covered will do. Double cotton-covered is better than single, but
+it costs more. Be careful not to injure the covering. (See below for
+splicing wire.) Look out for broken wire.</p>
+
+<p><i>288. Splicing Wire.</i> Fig. 125. Do not simply touch<span class='pagenum'><a name="Page_140" id="Page_140">[Pg 140]</a></span> two wires together
+and imagine that you have a good connection; a mere twist is not
+sufficient. Clean the ends of old wire thoroughly with a file or
+knife-blade, and join them as shown in Fig. 125.</p>
+
+<p><i>289. Copper.</i> Sheet-copper can be purchased at a tinsmith's or at a
+hardware store. Electricians usually have a thin variety of copper
+called brush copper, which makes good battery-plates, binding-posts,
+etc. You can cut this thin copper with an ordinary pair of shears.</p>
+
+<p>290. <i>Iron.</i> For thin sheet-iron, nothing is better than sheet-tin. (See
+tin.) Hoop iron is thicker than tin, and makes good yokes, etc. In many
+cases, ordinary nails may be used where a magnetic substance is needed.
+Annealed iron wire is extremely soft. (See text-book for experiments
+with steel and iron.)</p>
+
+<p><i>291. Steel.</i> Old files, watch-springs, clock-springs, corset-steels,
+knitting-needles, harness-needles, hack-saw blades, sewing-needles, etc.,
+are generally made of a good quality of steel.</p>
+
+<p><i>292. Zinc</i>, in the sheet form, can be bought at a hardware store. For a
+few cents you can get quite a large piece. Get the thick pieces for
+heavy battery-plates of an electrician. You do not need anything that is
+thicker than &#8539; in. The zinc rods are usually amalgamated.</p>
+
+<p><i>293. Lead</i> can be bought at a plumber's, tinsmith's, or hardware store.
+You may want some for a storage cell.</p>
+
+<p><i>294. Nails.</i> Wire nails are best for light work. Get an assortment from
+&frac12; in. long up to 1&frac12; in.</p>
+
+<p><i>295. Screws</i>. It is better to use brass screws around electrical
+apparatus. For the small work, for binding-posts, etc., use &#8541; No. 5.
+Another handy size is No. 7,<span class='pagenum'><a name="Page_141" id="Page_141">[Pg 141]</a></span> from &frac34; to 1&frac14; in. long. The
+round-headed screws are best, unless you want to countersink them.</p>
+
+<p><i>296. Tin.</i> This is really thin sheet-iron, covered with tin. Save up
+tomato-cans, cracker-boxes, condensed-milk cans, etc. The cracker-boxes
+are just as good as sheet-tin, as the pieces are large and clean. You
+can remove the solder from cans by heating them in the kitchen fire.
+Knock out the bottoms with a poker when the solder gets soft. Clean the
+tin with sand-paper.</p>
+
+<p><i><a name="s297" id="s297"></a>297. Carbons.</i> You can get carbon rods or plates at an electrician's.
+If you have arc electric lights in your city, you will be able to pick
+up carbons; these, however, generally have a coating of copper, which
+must be eaten off with dilute nitric acid. This is a bother. You will
+find it cheaper to buy the &frac12; in. rods that are 12 in. long, and
+uncoated.</p>
+
+<p><i>298. Shellac.</i> Your wood-work will be much improved by using shellac
+upon it after you have thoroughly sand-papered it. You can get it, all
+prepared, at a paint store. Wood-alcohol is used to thin it if it gets
+too thick. Keep it in a wide-mouth bottle. Paint it on quickly and
+evenly with a brush, and do not go over it again when it is partly dry.
+Wait until it is thoroughly hard before putting on a second coat. It
+should be fairly thin to spread well. Clean your brush in wood-alcohol
+before putting it away, and keep the shellac bottle tightly corked. A
+small tin can or a teacup is best to hold the shellac when using it.</p>
+<hr />
+
+<p class="t1"><big>HOW TWO BOYS MADE THEIR OWN ELECTRICAL APPARATUS</big></p>
+
+<p class="center"><b>By THOMAS M. ST. JOHN, Met. E.</b></p>
+
+
+<div class='center'>
+<table border="0" width="35%" cellpadding="4" cellspacing="0" summary="eigth edition">
+<tr>
+ <td align='left'>EIGHTH EDITION</td>
+ <td align='right'><b>Price, postpaid, $1.00</b></td>
+</tr>
+</table></div>
+
+<p>This book contains 141 pages, 125 illustrations, and directions for
+making 152 pieces of apparatus. Size, 5&times;7&frac12;; red cloth.</p>
+
+<p><b>CONTENTS:</b> <i>Chapter</i> I. Cells and Batteries.&mdash;II. Battery Fluids and
+Solutions.&mdash;III. Miscellaneous Apparatus and Methods of
+Construction.&mdash;IV. Switches and Cut-Outs.&mdash;V. Binding-Posts and
+Connectors.&mdash;VI. Permanent Magnets.&mdash;VII. Magnetic Needles and
+Compasses.&mdash;VIII. Yokes and Armatures.&mdash;IX. Electro-Magnets.&mdash;X.
+Wire-Winding Apparatus.&mdash;XI. Induction Coils and Their
+Attachments.&mdash;XII. Contact Breakers and Current Interrupters.&mdash;XIII.
+Current Detectors and Galvanometers.&mdash;XIV. Telegraph Keys and
+Sounders.&mdash;XV. Electric Bells and Buzzers.&mdash;XVI. Commutators and Current
+Reversers.&mdash;XVII. Resistance Coils.&mdash;XVIII. Apparatus for Static
+Electricity.&mdash;XIX. Electric Motors.&mdash;XX. Odds and Ends.&mdash;XXI. Tools and
+Materials.</p>
+
+<div class="blockquot"><p>"The author of this book is a teacher and writer of great
+ingenuity, and we imagine that the effect of such a book as this
+falling into juvenile hands must be highly stimulating and
+beneficial. It is full of explicit details and instructions in
+regard to a great variety of apparatus, and the materials required
+are all within the compass of very modest pocket-money. Moreover,
+it is systematic and entirely without rhetorical frills, so that
+the student can go right along without being diverted from good
+helpful work that will lead him to build useful apparatus and make
+him understand what he is about. The drawings are plain and
+excellent. We heartily commend the book."&mdash;<i>Electrical Engineer.</i></p>
+
+<p>"Those who visited the electrical exhibition last May cannot have
+failed to notice on the south gallery a very interesting exhibit,
+consisting, as it did, of electrical apparatus made by boys. The
+various devices there shown, comprising electro-magnets, telegraph
+keys and sounders, resistance coils, etc., were turned out by boys
+following the instructions given in the book with the above title,
+which is unquestionably one of the most practical little works yet
+written that treat of similar subjects, for, with but a limited
+amount of mechanical knowledge, and by closely following the
+instructions given, almost any electrical device may be made at
+very small expense. That such a book fills a long-felt want may be
+inferred from the number of inquiries we are constantly receiving
+from persons desiring to make their own induction coils and other
+apparatus."&mdash;<i>Electricity.</i></p>
+
+<p>"At the electrical show in New York last May one of the most
+interesting exhibits was that of simple electrical apparatus made
+by the boys in one of the private schools in the city. This
+apparatus, made by boys of thirteen to fifteen years of age, was
+from designs by the author of this clever little book, and it was
+remarkable to see what an ingenious use had been made of old tin
+tomato-cans, cracker-boxes, bolts, screws, wire, and wood. With
+these simple materials telegraph instruments, coils, buzzers,
+current detectors, motors, switches, armatures, and an almost
+endless variety of apparatus were made. In his book Mr. St. John
+has given directions in simple language for making and using these
+devices, and has illustrated these directions with admirable
+diagrams and cuts. The little volume is unique, and will prove
+exceedingly helpful to those of our young readers who are fortunate
+enough to possess themselves of a copy. For schools where a course
+of elementary science is taught, no better text-book in the first
+steps in electricity is obtainable."&mdash;<i>The Great Round World.</i> </p></div>
+<hr />
+
+<p class="t1">Exhibit of Experimental Electrical Apparatus</p>
+
+<p class="center">AT THE ELECTRICAL SHOW, MADISON SQUARE GARDEN, NEW YORK.</p>
+
+<p><small>While only 40 pieces of simple apparatus were shown in this exhibit, it
+gave visitors something of an idea of what young boys can do if given
+proper designs.</small></p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/ad1.jpg" width="500" height="185" alt="Exhibit" title="" />
+</div>
+
+<p class="center"><b>"HOW TWO BOYS MADE THEIR OWN ELECTRICAL APPARATUS"<br />
+Gives Proper Designs&mdash;Designs for over 150 Things.</b></p>
+
+<hr />
+<p class="t1"><big>BY THE SAME AUTHOR&mdash;(LIST R)</big></p>
+
+
+<div class='table1'>
+<table border="0" cellpadding="4" cellspacing="0" summary="By the same author">
+<tr class='tr1'>
+ <td align='left'><span class="smcap">List No.</span></td>
+ <td align='right'><span class="smcap">List Price</span></td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R1&mdash;FUN WITH MAGNETISM.</b> A book and complete outfit of apparatus for
+sixty-one experiments. Weight 4 ounces.</td>
+ <td align='right'>$0.35**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R2&mdash;FUN WITH ELECTRICITY.</b> A book and complete outfit of apparatus for
+sixty experiments. Weight 1 pound.</td>
+ <td align='right'>$0.65**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R3&mdash;FUN WITH PUZZLES.</b> A book and complete outfit for four hundred
+puzzles with key to them. One pound.</td>
+ <td align='right'>$0.35**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R4&mdash;FUN WITH SOAP-BUBBLES.</b> A book and complete outfit of apparatus for
+fancy bubbles and films. One pound.</td>
+ <td align='right'>$0.35**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R5&mdash;FUN WITH SHADOWS.</b> A book and complete outfit of apparatus for shadow
+pictures, pantomimes, etc. One pound.</td>
+ <td align='right'>$0.35**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R6&mdash;FUN WITH PHOTOGRAPHY.</b> A book and complete outfit of apparatus for
+amateur work. One pound.</td>
+ <td align='right'>$0.65**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R7&mdash;FUN WITH CHEMISTRY.</b> A book and complete outfit of apparatus for
+forty-one experiments. One pound.</td>
+ <td align='right'>$0.65**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R41&mdash;ELECTRIC SHOOTING GAME.</b> Absolutely harmless; fascinating. Paper
+bullets shot by electricity. One pound.</td>
+ <td align='right'>$0.35**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R42&mdash;ELECTRIC AIR-SHIPS AND OTHER GAMES.</b> Great fun. Get into the game;
+be an aviator at home; for two players. One pound.</td>
+ <td align='right'>$0.35**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R43&mdash;ELECTRIC FORTUNE-TELLER</b> tells a lot. Mysteriously electric. Comic
+and otherwise. In preparation. One pound.</td>
+ <td align='right'>$0.35**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R51&mdash;HOW TWO BOYS MADE THEIR OWN ELECTRICAL APPARATUS.</b> A book containing
+complete directions for making many kinds of electrical apparatus.
+Seventh edition; 141 pages; cloth.</td>
+ <td align='right'>$1.00**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R52&mdash;THE STUDY OF ELEMENTARY ELECTRICITY AND MAGNETISM BY EXPERIMENT.</b> A
+text-book for students and others. Systematic course for home or school.
+220 pages; 200 experiments; cloth; fourth edition.<br />
+This book with 105 pieces of apparatus complete, by express $6.25</td>
+ <td align='right'>$1.25**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R53&mdash;THINGS A BOY SHOULD KNOW ABOUT ELECTRICITY</b> explains in simple
+language things a boy wants to know, things he should know. Seventh
+edition. 180 pages; cloth.</td>
+ <td align='right'>$1.00**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R54&mdash;REAL ELECTRIC TOY-MAKING FOR BOYS</b> contains complete directions for
+making and using many electrical toys. Over 100 original drawings,
+diagrams and plates. Second edition; 140 pages, cloth.</td>
+ <td align='right'>$1.00**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R55&mdash;WIRELESS TELEGRAPHY FOR AMATEURS AND STUDENTS</b> contains theoretical
+and practical information, together with directions for performing
+numerous experiments on wireless with simple home-made apparatus. Third
+and enlarged edition in preparation.</td>
+ <td align='right'>$1.00**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R56&mdash;ELECTRICAL HANDICRAFT</b> contains complete directions for making and
+using nearly 150 pieces of electrical apparatus, including various
+devices and outfits for experimental purposes. New ideas and inexpensive
+supplies. Cloth; 252 pages; 250 drawings. Second edition.</td>
+ <td align='right'>$1.00**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R57C&mdash;THE STUDY OF ELECTRIC MOTORS BY EXPERIMENT</b> contains sixty
+experiments that bear directly upon the construction, operation and
+explanation of electric motors, together with much helpful information
+upon the apparatus required. Over 100 pages; paper cover.</td>
+ <td align='right'>$0.35**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'><b>R58&mdash;THINGS A BOY SHOULD KNOW ABOUT WIRELESS</b> contains much practical and
+some theoretical information on the operation and explanation of
+wireless outfits, together with numerous wiring-diagrams. Third edition;
+126 pages; cloth.</td>
+ <td align='right'>$1.00**</td>
+</tr>
+</table></div>
+
+<p class="center"><b>Ask your Bookseller, Toy-dealer or Electrical Store for our Books,
+Games, Toys and Electrical Apparatus.</b></p>
+
+<p class="center"><b>Write for Catalogue.</b></p>
+
+<p class="center"><b><big>THOMAS M. ST. JOHN, Cascade Ranch, East Windham, N.Y.</big></b></p>
+<hr />
+
+<p class="t1">THINGS A BOY SHOULD KNOW ABOUT ELECTRICITY.</p>
+
+<p class="center">By THOMAS M. ST. JOHN, Met. E.</p>
+
+<p class="center">
+The book contains 180 pages, and 260 illustrations; it measures<br />
+5 &times; 7&frac12; in., and is bound in cloth.</p>
+
+
+<div class='center'>
+<table border="0" width="35%" cellpadding="4" cellspacing="0" summary="Seventh Edition">
+<tr>
+ <td align='left'>Seventh Edition</td>
+ <td align='right'><b>Price, postpaid, $1.00</b></td>
+</tr>
+</table></div>
+
+<div class="blockquot"><p><b>CONTENTS</b>: <i>Chapter</i> I. About Frictional Electricity.&mdash;II. About
+Magnets and Magnetism.&mdash;III. How Electricity is Generated by the
+Voltaic Cell.&mdash;IV. Various Voltaic Cells.&mdash;V. About Push-Buttons,
+Switches and Binding-Posts.&mdash;VI. Units and Apparatus for Electrical
+Measurements.&mdash;VII. Chemical Effects of the Electric
+Current.&mdash;VIII. How Electroplating and Electrotyping are Done.&mdash;IX.
+The Storage Battery and How it Works.&mdash;X. How Electricity is
+Generated by Heat.&mdash;XI. Magnetic Effects of the Electric
+Current.&mdash;XII. How Electricity is Generated by Induction.&mdash;XIII.
+How the Induction Coil Works.&mdash;XIV. The Electric Telegraph, and How
+it Sends Messages.&mdash;XV. The Electric Bell and Some of its
+Uses.&mdash;XVI. The Telephone, and How it Transmits Speech.&mdash;XVII. How
+Electricity is Generated by Dynamos.&mdash;XVIII. How the Electric
+Current is Transformed.&mdash;XIX. How Electric Currents are Distributed
+for Use.&mdash;XX. How Heat is Produced by the Electric Current.&mdash;XXI.
+How Light is Produced by the Incandescent Lamp.&mdash;XXII. How Light is
+Produced by the Arc Lamp.&mdash;XXIII. X-Rays, and How the Bones of the
+Human Body are Photographed.&mdash;XXIV. The Electric Motor and How it
+Does Work.&mdash;XXV. Electric Cars, Boats and Automobiles.&mdash;XXVI. A
+Word About Central Stations.&mdash;XXVII. Miscellaneous Uses of
+Electricity. </p></div>
+
+<p>This book explains, in simple, straightforward language, many things
+about electricity; things in which the American boy is intensely
+interested; things he wants to know; things he should know.</p>
+
+<p>It is free from technical language and rhetorical frills, but it tells
+how things work, and why they work.</p>
+
+<p>It is brimful of illustrations&mdash;the best that can be had&mdash;illustrations
+that are taken directly from apparatus and machinery, and that show what
+they are intended to show.</p>
+
+<p>This book does not contain experiments, or tell how to make apparatus;
+our other books do that. After explaining the simple principles of
+electricity, it shows how these principles are used and combined to make
+electricity do every-day work.</p>
+
+<hr style='width: 20%;' />
+
+<p class="center"><i><b><big>Everyone Should Know About Electricity.</big></b></i></p>
+
+<hr style='width: 20%;' />
+
+<p class="center"><b><big>A VERY APPROPRIATE PRESENT</big></b></p>
+<hr />
+
+<p class="t1"><big>Things a Boy Should<br /> Know About Wireless</big></p>
+
+<p class="center">
+<i>By</i><br />
+<big>THOMAS M. ST. JOHN, Met. E.</big><br />
+<br />
+<small><i>Author of "Things a Boy Should Know about Electricity," "Fun with<br />
+Electricity," "The Study of Elementary Electricity and Magnetism by<br />
+Experiment," "The Study of Electric Motors by Experiment," "Electrical<br />
+Handicraft," Etc., Etc.</i></small><br />
+<br />
+<b>126 Pages&mdash;109 Illustrations and Diagrams<br />
+Bound in Cloth&mdash;Net $1.00</b><br />
+</p>
+
+<p>This book contains much practical and some theoretical information
+regarding the operation and explanation of wireless outfits. It
+discusses enough of the theoretical side to make the student sure of
+himself and to give a well-rounded knowledge of this most practical
+subject.</p>
+
+<p>The author has explained the various pieces of apparatus needed in a
+wireless station in such a clear manner that the student can not fail to
+understand how they work and why they work. The numerous drawings and
+diagrams simplify the discussions to such an extent that the reader will
+not want to skip a single paragraph.</p>
+
+<p>"Things a Boy Should Know About Wireless" will be welcomed by thousands
+of enthusiasts and it should find its way into every library.</p>
+
+<p class="center">
+From<br />
+<br />
+<big>THOMAS M. ST. JOHN<br />
+<br />
+Cascade Ranch.<br />
+East Windham,&mdash;N.Y.</big><br />
+</p>
+<hr />
+
+<p class="t1">The Study of Elementary<br /> Electricity and Magnetism<br /> by Experiment</p>
+
+<p class="center">
+<b>By THOMAS M. ST. JOHN, Met. E.</b></p>
+
+<div class='center'>
+<table border="0" width="35%" cellpadding="4" cellspacing="0" summary="Fourth Edition">
+<tr>
+ <td align='left'><i>FOURTH EDITION</i></td>
+ <td align='right'><i>Price, postpaid, $1.25.</i></td>
+</tr>
+</table></div>
+
+<p class="center">
+<b>The book contains 220 pages and 168 illustrations. It measures<br />
+5 &times; 7&frac12; in., and it is bound in green cloth.</b>
+</p>
+
+<div class="blockquot"><p><b>CONTENTS</b>: <b>Part I. Magnetism.</b>&mdash;<i>Chapter</i> I. Iron and Steel.&mdash;II.
+Magnets.&mdash;III. Induced Magnetism.&mdash;IV. The Magnetic Field.&mdash;V.
+Terrestrial Magnetism. <b>Part II. Static Electricity.</b>&mdash;VI.
+Electrification.&mdash;VII. Insulators and Conductors&mdash;VIII. Charging
+and Discharging Conductors.&mdash;IX. Induced Electrification.&mdash;X.
+Condensation of Electrification.&mdash;XI. Electroscopes.&mdash;XII.
+Miscellaneous Experiments.&mdash;XIII. Atmospheric Electricity. <b>Part
+III. Current Electricity.</b>&mdash;XIV. Construction and Use of
+Apparatus.&mdash;XV. Galvanic Cells and Batteries.&mdash;XVI. The Electric
+Circuit.&mdash;XVII. Electromotive Force.&mdash;XVIII. Electrical
+Resistance.&mdash;XIX. Measurement of Resistance.&mdash;XX. Current
+Strength.&mdash;XXI. Chemical Effects of the Electric Current.&mdash;XXII.
+Electromagnetism.&mdash;XXIII. Electromagnets.&mdash;XXIV. Thermo
+electricity.&mdash;XXV. Induced Currents.&mdash;XXVI. The Production of
+Motion by Currents.&mdash;XXVII. Applications of Electricity.&mdash;XXVIII.
+Wire Tables.&mdash;Apparatus List.&mdash;Index.</p></div>
+
+<p>This is a text-book for amateurs, students, and others who want to take
+up a systematic course of electrical experiments at home or in school.
+It will give a practical and experimental knowledge of elementary
+electricity, and thoroughly prepare students for advanced work. Full
+directions are given for</p>
+
+<p class="t1">
+<b>TWO HUNDRED EXPERIMENTS.</b><br />
+</p>
+
+<p>The experiments and discussions are so planned that the student is
+always prepared for what follows. Although the experiments may be
+performed with the apparatus that is usually found in school
+laboratories, the author has designed a complete set of apparatus for
+those who want to have their own outfit.</p>
+
+<hr style='width: 20%;' />
+
+<p><i><b>If you want to take up a systematic course of experiments&mdash;experiments
+that will build a lasting foundation for your electrical knowledge&mdash;this
+book will serve as a valuable guide.</b></i></p>
+<hr />
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/ad2.jpg" width="600" height="157" alt="Student's Discount" title="" />
+</div>
+
+<hr />
+<p><small>Fun With Magnetism and Fun With Electricity have started more young men
+upon electrical careers than any other scientific outfits ever placed
+before the public. The thousands upon thousands that have been sold in
+all parts of the world have furnished fun and science for people of all
+ages, and the mere fact that they are listed by the New York Board of
+Education, and recommend to the pupils and teachers of the New York
+public and private schools is a guarantee of their value. Were it not
+for the fact that these are made in such large quantities and sold by
+stores, agents and mail-order houses, the price would be much higher.
+Don't fail to get these. They have a national reputation.</small></p>
+
+<p class="t1"><b>FUN WITH MAGNETISM</b></p>
+
+<p><small>This outfit contains a 32-page book of instructions, with 45
+illustrations, together with a complete set of apparatus for performing
+61 fascinating experiments. It will give you some new ideas about
+magnetism and start you at the right place in your study of electricity.
+Think what that means&mdash;to start right!</small></p>
+
+<p><small>The book contains experiments with the horseshoe magnet, with bar
+magnets, with floating magnets, etc., etc., thus giving a practical
+knowledge of the subject; and it is all done in such an interesting way
+that one can't help remembering it. Every experiment clinches some fact
+and every fact is important.</small></p>
+
+<p><small>Amusing Experiments.&mdash;Something for Nervous People to Try.&mdash;The Jersey
+Mosquito.&mdash;The Stampede.&mdash;The Runaway.&mdash;The Dog-fight.&mdash;The
+Whirligig.&mdash;The Naval Battle.&mdash;A String of Fish.&mdash;A Magnetic Gun.&mdash;A Top
+Upside down.&mdash;A Magnetic Windmill.&mdash;A Compass Upside down.&mdash;The Magnetic
+Acrobat.&mdash;The Busy Ant-hill.&mdash;The Magnetic Bridge.&mdash;The
+Merry-go-Round.&mdash;The Tight-rope Walker.&mdash;A Magnetic Motor Using
+Attractions and Repulsions.&mdash;And 43 Others.</small></p>
+
+<p><small>No. R1&mdash;"Fun with Magnetism," Complete Outfit, postpaid $0.35**</small></p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/ad3.jpg" width="600" height="185" alt="Fun With" title="" />
+</div>
+
+<p class="t1"><b>FUN WITH ELECTRICITY</b></p>
+
+<p><small>The author of this Fun with Science series has spent a great deal of
+time and money in experimenting to devise apparatus that will do the
+proper work and be, at the same time, simple and cheap, and in no outfit
+has he succeeded better than in Fun with Electricity. When you think of
+an outfit retailing for 50c. and covering the whole subject of "Static
+Electricity," giving 60 scientific experiments upon its production,
+conduction and induction, with a 55&ndash;page book of instructions with 38
+drawings, and a complete set of apparatus of 20 articles for performing
+these 60 experiments, you will understand why the sales of this outfit
+have been enormous. As the subject is presented in a fascinating
+way&mdash;and not as mere dry science&mdash;every one likes to do the experiments.
+No wonder these sets are highly praised by parents and educators in
+every part of the country!</small></p>
+
+<p><small>There is Fun in these Experiments: Chain Lightning.&mdash;An Electric
+Whirligig.&mdash;The Baby Thunderstorm.&mdash;A Race with Electricity.&mdash;An
+Electric Frog Pond.&mdash;An Electric Ding-Dong.&mdash;The Magic Finger.&mdash;Daddy
+Long-Legs.&mdash;Jumping Sally.&mdash;An Electric Kite.&mdash;Very Shocking.&mdash;Condensed
+Lightning.&mdash;An Electric Fly-Trap.&mdash;The Merry Pendulum.&mdash;An Electric
+Ferry-Boat.&mdash;A Funny Piece of Paper.&mdash;A Joke on the Family
+Cat.&mdash;Electricity Plays Leap-Frog.&mdash;Lightning Goes Over a
+Bridge.&mdash;Electricity Carries a Lantern.&mdash;And 40 Others.</small></p>
+
+<p><small>There isn't an outfit anywhere at any price that gives better value for
+the money. An ideal present for a boy.</small></p>
+
+<p><small>No. R2&mdash;"Fun with Electricity," Complete Outfit, postpaid $0.65**</small></p>
+<hr />
+
+<p class="t1"><b>FUN WITH PUZZLES</b></p>
+
+<p><small>Here is an outfit that every boy and girl should have, for it is
+amusing, instructive and educational. It is real fun to do puzzles and
+to puzzle your friends, and this book contains some real brain-teasers
+that will make you think. The book contains 15 chapters, 80 pages, and
+128 illustrations, and measures 5&times;7&frac12; inches. If you can't do any
+particular puzzle you will find its solution in the "key," which is
+bound with the book. If you want to win prizes by doing the puzzles in
+the magazines, you will find this book of four hundred puzzles a regular
+school of puzzles that will give you a thorough training for this kind
+of work. The book alone is well worth the price, to say nothing of the
+outfit of numbers, counters, pictures, etc.</small></p>
+
+<p><small>Contents of Book: <i>Chapter</i> (1) Secret Writing. (2) Magic Triangles,
+Squares, Rectangles, Hexagons, Crosses, Circles, etc. (3) Dropped Letter
+and Dropped Word Puzzles. (4) Mixed Proverbs, Prose and Rhyme. (5) Word
+Diamonds, Squares, Triangles, and Rhomboids. (6) Numerical Enigmas. (7)
+Jumbled Writing and Magic Proverbs. (8) Dissected Puzzles. (9) Hidden
+and Concealed Words. (10) Divided Cakes, Pies, Gardens, Farms, etc. (11)
+Bicycle and Boat Puzzles. (12) Various Word and Letter Puzzles. (13)
+Puzzles with Counters. (14) Combination Puzzles. (15) Mazes and
+Labyrinths.</small></p>
+
+<p><small>Secret Writing is explained in this book, and it shows how you can write
+letters to your friends and be sure that no one can read them unless
+they are also in the secret. This one thing alone will give you a great
+deal of enjoyment. Get this outfit and have some fun.</small></p>
+
+<p><small>No. R3&mdash;"Fun with Puzzles," Complete Outfit, postpaid $0.35**</small></p>
+
+<hr />
+
+<p class="t1"><b>FUN WITH SOAP-BUBBLES</b></p>
+
+<p><small>Fancy Bubbles and Films are not easily blown without special apparatus,
+and even with the proper outfit one must "know how." That's why we
+furnish a 16&ndash;page book with every set to show just how to do it. With
+the aid of the 21 illustrations and the directions you can produce
+remarkable results that will surprise and entertain your friends. A
+child can do it as well as a grown person.</small></p>
+
+<div class="figright" style="width: 348px;">
+<img src="images/ad4.jpg" width="348" height="270" alt="Soap Bubbles" title="" />
+</div>
+
+<p><small>Soap-Bubble Parties using these outfits create real sensations. Why not
+be the first in your town to give a "Fun with Soap-Bubbles Party?" Just
+write and ask about the price for any special number of them&mdash;say six or
+a dozen.</small></p>
+
+<p><small>Contents of Book: Twenty-one Illustrations.&mdash;Introduction.&mdash;The Colors
+of Soap-Bubbles.&mdash;The Outfit.&mdash;Soap Mixture.&mdash;Useful Hints.&mdash;Bubbles
+Blown with Pipes.&mdash;Bubbles Blown with Straws.&mdash;Bubbles Blown with the
+Horn.&mdash;Floating Bubbles.&mdash;Baby Bubbles.&mdash;Smoke Bubbles.&mdash;Bombshell
+Bubbles.&mdash;Dancing Bubbles.&mdash;Bubble Games.&mdash;Supported Bubbles.&mdash;Bubble
+Cluster.&mdash;Suspended Bubbles.&mdash;Bubble Lamp Chimney.&mdash;Bubble
+Lenses.&mdash;Bubble Basket.&mdash;Bubble Bellows.&mdash;To Draw a Bubble Through a
+Ring.&mdash;Bubble Acorn.&mdash;Bubble Bottle.&mdash;A Bubble Within a Bubble.&mdash;Another
+Way.&mdash;Bubble Shade.&mdash;Bubble Hammock.&mdash;Wrestling Bubbles.&mdash;A Smoking
+Bubble.&mdash;Soap Films.&mdash;The Tennis Racket Film.&mdash;Fish-net
+Film.&mdash;Pan-shaped Film.&mdash;Bow and Arrow Film.&mdash;Bubble Dome.&mdash;Double
+Bubble Dome.&mdash;Pyramid Bubbles.&mdash;Turtle-back Bubbles.&mdash;Soap-Bubbles and
+Frictional Electricity.</small></p>
+
+<p><small>"There is nothing more beautiful than the airy-fairy soap-bubble with
+its everchanging colors." This outfit gives the best possible amusement
+for old and young.</small></p>
+
+<p><small>No. R4&mdash;"Fun with Soap-Bubbles," Complete Outfit, postpaid $0.35**</small></p>
+
+<p><small>Three extra packages of prepared soap, postpaid .10</small></p>
+<hr />
+
+<p class="t1"><b>FUN WITH SHADOWS</b></p>
+
+<p><small>No wonder shadow-making has been popular for several centuries! What
+could give keener delight than comical shadow-pictures, pantomimes,
+entertainments, etc.? Professional shadowists use wires, forms, and
+various devices to aid them, and that is why they get such wonderful
+results on the stage. Do you want to do the same thing right in your own
+home and entertain your friends with all kinds of fancy shadows? You can
+do it with this outfit, for the book contains 100 illustrations and
+diagrams with directions for using the numerous articles included in the
+box. You will be surprised to see how easily you can make these funny
+shadows with the aid of the outfit. Better get one now and make shadows
+like a professional.</small></p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/ad5.jpg" width="500" height="164" alt="Shadows" title="" />
+</div>
+
+<p><small>The Outfit contains everything necessary for all ordinary shadow
+pictures, shadow entertainments, shadow plays, etc. The following
+articles are included: One book of Instructions called "Fun with
+Shadows"; 1 Shadow Screen; 2 Sheets of Tracing Paper; 1 Coil of Wire for
+Movable Figures; 1 Cardboard Frame for Circular Screen; 1 Cardboard
+House for Stage Scenery; 1 Jointed Wire Fish-pole and Line; 2 Bent Wire
+Scenery Holders; 4 Clamps for Screen; 1 Wire Figure Support; 1 Wire for
+Oar; 2 Spring Wire Table Clamps; 1 Wire Candlestick Holder; 5 Cardboard
+Plates containing the following printed figures that should be cut out
+with shears; 12 Character Hats; 1 Boat; 1 Oar-blade; 1 Fish; 1
+Candlestick; 1 Cardboard Plate containing printed parts for making
+movable figures.</small></p>
+
+<p><small>No. R5&mdash;"Fun with Shadows," Complete Outfit, postpaid $0.35**</small></p>
+
+<hr />
+
+<p class="t1"><b>FUN WITH PHOTOGRAPHY</b></p>
+
+<p><small>Popular Pastimes are numerous, but to many there is nothing more
+fascinating than photography. The magic of sunshine, the wonders of
+nature, and the beauties of art are tools in the hands of the amateur
+photographer. If you want to get a start in this up-to-date hobby, this
+outfit will help you. You will enjoy the work and be delighted with the
+beautiful pictures you can make.</small></p>
+
+<p><small>The Outfit contains everything necessary for making prints&mdash;together
+with other articles to be used in various ways. The following things are
+included: One Illustrated Book of Instructions, called "Fun With
+Photography"; 1 Package of Sensitized Paper; 1 Printing Frame, including
+Glass, Back, and Spring; 1 Set of Masks for Printing Frame; 1 Set of
+Patterns for Fancy Shapes; 1 Book of Negatives (Patented) Ready for Use;
+6 Sheets of Blank Negative Paper; 1 Alphabet Sheet; 1 Package of Card
+Mounts; 1 Package of Folding Mounts; 1 Package of "Fixo."</small></p>
+
+<p><small>Contents of Book: Chapter I. Introduction.&mdash;Photography.&mdash;Magic
+Sunshine.&mdash;The Outfit.&mdash;II. General Instructions.&mdash;The Sensitized
+Paper.&mdash;How the Effects are Produced.&mdash;Negatives.&mdash;Prints.&mdash;Printing
+Frames.&mdash;Our Printing Frame.&mdash;Putting Negatives in Printing
+Frame.&mdash;Printing.&mdash;Developing.&mdash;Fixing.&mdash;Drying&mdash;- Trimming.&mdash;Fancy
+Shapes.&mdash;Mounting.&mdash;III. Negatives and How to Make Them.&mdash;The
+Paper.&mdash;Making Transparent Paper.&mdash;Making the Negatives.&mdash;Printed
+Negatives.&mdash;Perforated Negatives.&mdash;Negatives Made from Magazine
+Pictures.&mdash;Ground Glass Negatives.&mdash;IV. Nature Photography.&mdash;Aids to
+Nature Study.&mdash;Ferns and Leaves.&mdash;Photographing Leaves.&mdash;Perforating
+Leaves.&mdash;Drying Leaves, Ferns, etc., for Negatives.&mdash;Flowers.&mdash;V.
+Miscellaneous Photographs.&mdash;Magnetic Photographs.&mdash;Combination
+Pictures.&mdash;Initial Pictures.&mdash;Name Plates.&mdash;Christmas, Easter and
+Birthday Cards.</small></p>
+
+<p><small>No. R6&mdash;"Fun with Photography," Complete Outfit, Postpaid $0.65**</small></p>
+<hr />
+
+<p class="t1"><b>FUN WITH CHEMISTRY</b></p>
+
+<div class="figleft" style="width: 430px;">
+<img src="images/ad6.jpg" width="430" height="296" alt="Fun With Chemistry" title="" />
+</div>
+
+<p><small>Chemistry is universally considered to be an interesting subject, even
+in school, and it is certainly an important one in these days of
+scientific progress. This outfit starts you at the right place and
+presents the elements of the subject in a most interesting fashion. The
+experiments are so enjoyable that you will take pleasure in doing them
+over and over again, and you will want to do them for your friends. You
+can have a lot of fun with this set, and even if you have taken advanced
+courses in the subject you will find something new in these experiments.
+The more you know about chemistry the more you will enjoy it, for then
+you can more easily appreciate what a splendid outfit this is for the
+money.</small></p>
+
+<p><small>The Outfit contains over 20 different articles, including chemicals,
+test-tubes, adjustable ring-stand, litmus paper, filter paper, glass
+tubing, etc.; in fact, everything needed for the forty-one experiments.
+The Book of Instructions is fully illustrated, and measures 5&times;7&frac12;
+inches.</small></p>
+
+<p><small>Fun Found Here: From White to Black, or the Phantom Ship.&mdash;Yellow
+Tears.&mdash;Smoke Pearls.&mdash;An Ocean of Smoke.&mdash;A Tiny Whirlwind.&mdash;A Smoke
+Cascade.&mdash;An Explosion in a Teacup.&mdash;A Gas Factory in a
+Test-Tube.&mdash;Making Charcoal.&mdash;Flame Goes Over a Bridge.&mdash;A Smoke
+Toboggan-Slide.&mdash;Fountains of Flame.&mdash;Making an Acid.&mdash;Making an
+Alkali.&mdash;A Chemical Fight.&mdash;Through Walls of Flame.&mdash;An Artificial Gas
+Well.&mdash;A Lampblack Factory.&mdash;Steam from a Flame.&mdash;The Flame that
+Committed Suicide.&mdash;Chemical Soup.&mdash;A Baby Skating-Rink.&mdash;A Magic
+Milk-Shake.&mdash;The Wizard's Breath.&mdash;A Chemical Curtain.&mdash;Scrambled
+Chemicals.&mdash;And Many Other Experiments.</small></p>
+
+<p><small>No. R7&mdash;"Fun with Chemistry," Complete Outfit, postpaid $0.65**</small></p>
+
+<hr />
+
+<p class="t1"><b>ELECTRIC SHOOTING GAME</b></p>
+
+<div class="figleft" style="width: 428px;">
+<img src="images/ad7.jpg" width="428" height="262" alt="Electric Shooting" title="" />
+</div>
+
+<p><small>Shooting Animals by electricity is certainly a most original game, and
+it will furnish a vast amount of amusement to all. The game is patented
+and copyrighted&mdash;because it is really a brand-new idea in games&mdash;and it
+brings into use that most mysterious something called electricity. While
+the electricity is perfectly harmless, there being no batteries, acids
+or liquids, it is very active and you will have plenty to laugh at. It
+is so simple that the smallest child can play it and so fascinating that
+grandpa will want to try it.</small></p>
+
+<p><small>The "game-preserve" is neatly printed in colors, and the birds and wild
+animals are well worth hunting. Each has a fixed value&mdash;and some of them
+must not be shot at all&mdash;so there is ample chance for skill.
+Tissue-paper bullets are actually shot from the "electric gun" by
+electricity, and it is truly a weird sight to see them shoot through the
+air impelled by this unseen force.</small></p>
+
+<p><small>The Outfit contains the "Game-Preserve," the "Electric Gun," the
+"Shooting-Box," and the "Electric Bullets," together with complete
+illustrated directions, all placed in a neat box.</small></p>
+
+<p><small>No. R41&mdash;"Electric Shooting Game," complete, postpaid $0.35**</small></p>
+
+<hr />
+
+<p class="t1"><b>NEW IDEA TIT-TAT-TOE</b></p>
+
+<p><small>Splendid game for two, three, or four players; great improvement upon
+the good old game; fascinating game instantly learned; nothing better
+for children's parties and progressive birthday parties; box with
+game-board, 12 men, directions; discount for party orders.</small></p>
+
+<p><small>No. R21&mdash;New Idea Tit-Tat-Toe, sample, postpaid $0.15</small></p>
+<hr />
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/ad8.jpg" width="600" height="995" alt="Electric Air Ships" title="" />
+</div>
+<hr />
+
+<p class="t1"><b>REAL ELECTRIC TOY-MAKING FOR BOYS</b></p>
+
+<p class="center">
+<b><i>By</i> THOMAS M. ST. JOHN. Met. E.</b><br />
+<br />
+This book contains 140 pages and over one hundred<br />
+original drawings, diagrams, and full-page plates.<br />
+<br />
+It measures 5&times;7&frac12; in., and is bound in cloth.<br />
+<br />
+<b>SECOND EDITION</b> Price, postpaid, $1.00<br />
+</p>
+
+<p><b>CONTENTS</b>: <small><i>Chapter</i> I. Toys Operated by Permanent Magnets.&mdash;II. Toys
+Operated by Static Electricity.&mdash;III. Making Electromagnets for
+Toys.&mdash;IV. Electric Batteries.&mdash;V. Circuits and Connections.&mdash;VI. Toys
+Operated by Electromagnets. VII. Making Solenoids for Toys.&mdash;VIII. Toys
+Operated by Solenoids.&mdash;IX. Electric Motors.&mdash;X. Power, Speed, and
+Gearing.&mdash;XI. Shafting and Bearings.&mdash;XII. Pulleys and
+Winding-Drums.&mdash;XIII. Belts and Cables.&mdash;XIV. Toys Operated by Electric
+Motors.&mdash;XV. Miscellaneous Electric Toys.&mdash;XVI. Tools.&mdash;XVII.
+Materials.&mdash;XVIII. Various Aids to Construction.</small></p>
+
+<p><small>While planning this book, Mr. St. John definitely decided that he would
+not fill it with descriptions of complicated, machine-made instruments
+and apparatus, under the name of "Toy-Making," for it is just as
+impossible for most boys to get the parts for such things as it is for
+them to do the required machine work even after they have the raw
+materials.</small></p>
+
+<p><small>Great care has been taken in designing the toys which are described in
+this book, in order to make them so simple that any boy of average
+ability can construct them out of ordinary materials. The author can
+personally guarantee the designs, for there is no guesswork about them.
+Every toy was made, changed, and experimented with until it was as
+simple as possible; the drawings were then made from the perfected
+models.</small></p>
+
+<p><small>As the result of the enormous amount of work and experimenting which
+were required to originate and perfect so many new models, the author
+feels that this book may be truly called "Real Electric Toy-Making for
+Boys."</small></p>
+
+<hr style='width: 20%;' />
+
+<p class="center"><b>Every Boy Should Make Electrical Toys.</b></p>
+<hr />
+
+<p class="t1"><b>A MOTOR THAT CAN DO THINGS</b></p>
+
+<p><small>The "St J. Motor No. 1" (List No. 2201) is designed for students and
+others who want a small motor for experimental purposes as well as for
+all of the work that any small motor can do. We believe this to be the
+best small motor made, and we know that it can be used in more ways than
+any other motor of equal cost ever built. It has four
+binding-posts,&mdash;making it possible to energize the field or armature
+separately,&mdash;and so it can be used in circuits with reversers and
+rheostats for experiments. The speed and direction of rotation can be
+changed at will, thus adapting it for running toys, etc. As the
+binding-posts are mounted upon the frame, this motor can be taken from
+the base for remounting and using in many ways, and as it has a
+three-pole armature it will start promptly in any position. The shaft
+carries a pulley, and a fan can be added at any time. One cell will give
+a high speed, and more cells may be added, according to the work it has
+to do.</small></p>
+
+<p><small>Motor No. 1 stands 3&frac12; inches high. It is finished in black enamel
+with nickel-plated trimmings,&mdash;strong and well made. With it are
+furnished three nickel-plated connecting-straps, which are to be used
+for connecting the field and armature in "series" or "shunt." So much
+can be done with this motor that it is simply impossible to tell it
+here; in fact, it is used as the basis for a whole book of 60
+experiments called "The Study of Electric Motors by Experiment," and,
+when used in connection with the other parts of the Motor Outfits, it
+will give a practical knowledge of motors that no other plan can give.</small></p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/ad9.jpg" width="500" height="423" alt="No. 2201" title="" />
+<span class="caption">No. 2201</span>
+</div>
+
+<p><small>These motors and motor outfits have been highly praised by electrical
+experts and educators as being invaluable to students. They can do
+everything the big motors can do, and if used with the rheostats,
+reversers and other apparatus in the outfits, the student will have a
+whole motor laboratory.</small></p>
+
+<p><small>Why not get a motor that has brains and that can do tricks and
+experiments? Any good motor will go when you turn on the power; but that
+doesn't mean much when it comes to understanding things.</small></p>
+
+<p><small>No. 2201&mdash;"St. J. Motor No. 1," with Wiring-Diagrams $1.35</small></p>
+
+<p><small>If sent by mail, postage extra, shipping weight one pound.</small></p>
+<hr />
+
+<p class="t1"><b>"ST. J." ELECTRIC MOTOR OUTFIT</b></p>
+
+<p><small>These outfits have been designed for students and others who want to do
+real experimental work with motors, so as to get right down to the
+bottom of the matter and thoroughly master the foundation principles of
+the subject. It is simply astonishing to see how much can be learned
+with one of these outfits, especially if the work be done as fully
+detailed in "The Study of Electric Motors by Experiment." Every
+electrical laboratory should have one of these sets, and the more you
+know about motors the more you will appreciate an outfit of this kind.</small></p>
+
+<p><small>Don't simply read about motors&mdash;get right down to the practical part of
+it and experiment for yourself. Every experiment will settle an
+important point in your mind.</small></p>
+
+<p><small>ELECTRIC MOTOR OUTFIT No. 2226X contains everything needed for sixty
+interesting and profitable experiments. With the improved apparatus that
+we now give we feel that this is the most complete set ever sold for the
+money. The following articles are included, packed in a wooden box:</small></p>
+
+<p><small>THE "ST. J." MOTOR, fully described on another page, is well called "A
+motor that can do things."</small></p>
+
+<p><small>THE FIVE-POINT RHEOSTAT is used as a "starting-box" in the
+armature-circuit and in various other ways to regulate speed. (See cut.)</small></p>
+
+<p><small>THE ELEVEN-POINT RHEOSTAT is used to regulate the "field-magnetism," as
+one method of speed-regulation, and for other purposes. (See cut.)</small></p>
+
+<p><small>THE DOUBLE-KEY CURRENT REVERSER is, really, a key, a two-point switch,
+and a current-reverser combined. On this account it can be used in many
+ways, shown in numerous wiring-diagrams. (See cut.)</small></p>
+
+<p><small>THE HANDY CURRENT-DETECTOR is used as a current-detector and as a device
+for studying the counter-electromotive force of motor while running.</small></p>
+
+<p><small>THE TWO-POINT SWITCH is useful in quickly switching the current wherever
+it is needed, and for many other experiments.</small></p>
+
+<p><small>THE STRAP KEY protects the batteries and closes the circuit.</small></p>
+
+<p><small>THE MINIATURE ELECTRIC LAMP AND SOCKET are used in the motor-circuit to
+prove certain things and form an attractive addition to the outfit.</small></p>
+
+<p><small>THE MAGNETIC NEEDLE in the new outfits is nickel-plated and serves as a
+compass for studying the magnetism of the poles, etc.</small></p>
+
+<p><small>IN ADDITION to the articles mentioned above, the outfit contains a Set
+of Wires for Connections, a Box of Iron-Filings for studying lines of
+force, an Experimental Package containing Iron, Steel, etc., three
+Connecting-Wires, and</small></p>
+
+<p><small>THE BOOK OF INSTRUCTIONS, called "The Study of Electric Motors by
+Experiment." This contains 10 chapters, 110 pages, and over 70
+illustrations and diagrams. Bound in stiff paper.</small></p>
+
+<p>BATTERIES are not included, unless ordered extra. Three of our No. 1101
+batteries cost 36c., and extra postage for 2 lbs.</p>
+
+<p><small>No. 2226X&mdash;Complete Motor Outfit, as above (P. weight, 3 lbs.) $3.75**</small></p>
+
+<hr style='width: 20%;' />
+
+<p class="center"><b>THE STUDY OF ELECTRIC MOTORS BY EXPERIMENT</b>
+<small>contains Sixty Experiments that Bear Directly upon the Construction,
+Operation, and Explanation of Electric Motors, together with Much
+Helpful Information upon the Experimental Apparatus Required. This book
+will be a great help to those who want to do real experimental work with
+motors. It contains 10 chapters, 110 pages, over 70 illustrations and
+diagrams, and you can not afford to be without it.</small></p>
+
+<p><small>No. R57P&mdash;"Study of Motors," bound in paper, postpaid $0.35**</small></p>
+
+<p><small>No. R57C&mdash;"Study of Motors," bound in cloth, postpaid $0.60**</small></p>
+<hr />
+
+<p class="t1"><b>Fun With Telegraphy</b> <small>(PATENTED)</small></p>
+
+<p class="center"><b>TWO GREAT OUTFITS FOR STUDENTS</b></p>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/ad10.jpg" width="500" height="220" alt="Fun With Telegraphy" title="" />
+</div>
+
+<p><small>These two outfits are similar in construction, although they differ in
+details, each being designed for its special work. The "keys,"
+"sounders" and "binding-posts" are neatly mounted upon ebonized bases
+measuring 6&frac12;&times;3&frac34; in., these also serving as sounding-boards.</small></p>
+
+<p><small>"Fun with Telegraphy" is the original low-price telegraph outfit for
+students that has sold by the thousands and given universal
+satisfaction. It is considered the best 50-cent outfit ever produced,
+and, although we have made several improvements lately, the price is the
+same as before. In connection with a peculiar oscillating electro-magnet
+and a queer anvil, the sounding-board aids in giving out a loud, clear
+click that is found elsewhere only in noisy railroad sounders. This
+outfit is best adapted for a learner's set of one instrument and a
+battery to be used on the table for practising, either with or without
+the "codegraph," and not for telegraphing over wires to other stations.</small></p>
+
+<p><small>Outfit: Illustrated Book of Instructions, called "Fun with Telegraphy";
+Telegraph "Key"; Telegraph "Sounder"; Nickel-Plated "Binding-Posts";
+Insulated Wires for Connections.</small></p>
+
+<p><small>No. R8&mdash;"Fun with Telegraphy," without battery, postpaid $0.50</small></p>
+
+<p><small>No. R8, R8B&mdash;"Fun with Telegraphy," with one dry battery, postpaid, .65</small></p>
+
+<p><small>"Improved Telegraphy No. 2."&mdash;In answer to a number of requests for an
+improved outfit for regular line work between two stations a few hundred
+feet apart, we now offer this set, which is, in general, similar in plan
+to our first "Telegraphy No. 2." We have replaced the single
+electro-magnet of the old set, as shown in the cut, with two larger ones
+of superior construction, thus making the instrument much more
+sensitive. The key has also been greatly improved, and we now have a
+fine set at low cost.</small></p>
+
+<p><small>No expensive gravity batteries are needed with this ingenious
+arrangement, as it is designed to work with dry batteries which are
+clean and cheap. By means of a peculiar switch, either station may
+"call" the other at any time, even though the line is kept on "open
+circuit." There is absolutely no waste of current when the line is not
+in use&mdash;and, even then, only at the instant the dots and dashes are
+made. This is certainly a great advantage over the old-fashioned methods
+with gravity batteries which amateurs have heretofore been obliged to
+use. With this instrument you have a learner's set as well as one that
+can be used to send messages to another station. If you do not care for
+the superior advantages of "Semi-Wireless," this outfit will give entire
+satisfaction for ordinary work.</small></p>
+
+<p><small>Outfit: Illustrated Book of Instructions called "Telegraphy Number Two";
+Improved Telegraph "Key"; Telegraph "Sounder" with Double
+Electromagnets: Special "Switch" for controlling the batteries;
+Nickel-plated Screw "Binding-posts"; Insulated Wires for connections.</small></p>
+
+<p><small>No. 2307&mdash;"Improved Telegraphy Number Two" (no batteries), postpaid,
+$1.00</small></p>
+
+<p><small>No. 2307B&mdash;Same as No. 2307, but with two dry batteries, postpaid, 1.35</small></p>
+<hr />
+
+<p class="t1"><b><big>The Codegraph</big> (PATENTED)</b></p>
+
+<p class="right">
+<b>NOTE&mdash;Continental<br />
+Code sent unless<br />
+otherwise ordered</b>.<br />
+</p>
+
+<div class="figleft" style="width: 500px;">
+<img src="images/ad11.jpg" width="500" height="264" alt="Codegraph" title="" />
+</div>
+
+<p><small>The Codegraph is a brand-new scheme for thoroughly and rapidly learning
+the telegraphic code, and it has been worked out with the beginner in
+mind. This code-learning system really adapts itself to the beginner,
+and it gives a personal touch to each individual student according to
+his needs. No other system can do so much, for the student sees, hears
+and feels every letter and signal.</small></p>
+
+<p><small>The greatest trouble that every one has in learning by listening to
+regular messages is in separating the letters and words as they come in
+so fast. There is no time to think, and letters pile up in the mind. The
+codegraph avoids all confusion because every letter is under perfect
+control and may be repeated as many times as desired; hard things can be
+made easy; words and sentences can be built at will. We guarantee that
+any one of average ability can make rapid improvement with the
+codegraph.</small></p>
+
+<p><small>What It Is. A complete codegraph outfit, as shown in the cut, has three
+main parts: (1) The "plate and pen," (2) some form of "key and sounder"
+and (3) two batteries. While any key and sounder can be used with the
+plate, we wish to call especial attention to the duplex sounder shown,
+as this has been designed to do double work. If you already have "Fun
+with Telegraphy," for example, and want to order the "Codegraph Plate
+and Pen," we will include, free of charge, an extra attachment for
+connecting up your instrument.</small></p>
+
+<p><small>The Plate and Pen. When the pen is lightly drawn over the plate, the
+sounder responds and shows exactly how every letter and signal should
+sound. The student can then practise each letter until perfect. The
+surface of the plate is covered with a special insulating enamel, bare
+spots corresponding to correct dots and dashes. The polished brass plate
+measures about 6&times;8 inches and has a most elegant appearance. The book
+tells all about practising, etc.</small></p>
+
+<p><small>Duplex Codegraph Key and Sounder, as shown, has a double action and is
+the latest thing in code-learning devices. By the mere turning of a
+switch you can have the ordinary telegraph clicks or the wireless
+buzzes, making two sounders in one and at the cost of one. The
+combination sounder and a substantial key are mounted upon a finely
+finished base with nickel-plated trimmings, binding-posts, switch, etc.
+If you want to become an operator in the shortest possible time, no
+matter whether you have ever tried before or not, get one of these
+outfits and begin at once. You will be pleased right from the start,
+because you will make rapid progress right from the start.</small></p>
+
+
+<div class='table1'>
+<table border="0" cellpadding="4" cellspacing="0" summary="Codegraphs">
+<tr>
+ <td align='left'>No. 2350&mdash;"Codegraph Plate and Pen," with Book of Instructions</td>
+ <td align='right'>$1.00</td>
+</tr>
+<tr>
+ <td align='left'>If sent by mail, postage extra</td>
+ <td align='right'>12</td>
+</tr>
+<tr>
+ <td align='left'>No. 2351&mdash;"Duplex Codegraph Key and Sounder" (no batteries)</td>
+ <td align='right'>1.00</td>
+</tr>
+<tr>
+ <td align='left'>If sent by mail, postage extra</td>
+ <td align='right'>.10</td>
+</tr>
+<tr>
+ <td align='left'>No. 1102&mdash;Two Dry Batteries, as shown</td>
+ <td align='right'>.25</td>
+</tr>
+<tr>
+ <td align='left'>If sent by mail, postage extra</td>
+ <td align='right'>.10</td>
+</tr>
+<tr>
+ <td align='left'>Special&mdash;Complete Codegraph Outfit, as in cut, postpaid</td>
+ <td align='right'>2.50</td>
+</tr>
+</table></div>
+<hr />
+
+<p class="t1"><b>TELEGRAPH AND TELEPHONE SETS (LIST T)</b></p>
+
+<p><small>ORIGINAL OUTFITS that are worthy of your attention and that give fine
+results; products of hundreds of experiments and models that give best
+value for least money. A complete line of outfits beginning with "Fun
+with Telegraphy" and ending with combined "Semi-Wireless Telegraph,
+Telephone and Electric Light Signal Sets," with endless possibilities.</small></p>
+
+<p class="center"><small>Don't forget to add postage according to weight and zone.</small></p>
+
+
+<div class='table1'>
+<table border="0" cellpadding="4" cellspacing="0" summary="tele sets">
+<tr class='tr1'>
+ <td align='left'>List No.</td>
+ <td align='right'>List Price</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2302&mdash;"NEW FUN WITH TELEGRAPHY." A Book, Key, Sounder, Wires. Nicely
+mounted, sensitive, adjustable, improved, practical. (P. Wt. 1 lb.)</td>
+ <td align='right'>$0.35**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2302B1&mdash;Same as No. 2302, but with 1 dry battery. (P. Wt. 1 lb.)</td>
+ <td align='right'>$0.50**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2308&mdash;"NEW TELEGRAPHY NUMBER TWO." For regular line-work: has ingenious
+switch; uses dry batteries. Key, Sounder, Book, Wires. (P. Wt. 1 lb.)</td>
+ <td align='right'>$0.75**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2308B2&mdash;Same as No. 2308 but with two dry batteries. (P. Wt. 2 lbs.)</td>
+ <td align='right'>$1.00**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2304&mdash;"CLICKERBUZZ" TWO-STATION TELEGRAPH OUTFIT. Special value; loud,
+resonant, substantial, very neat and does several things. Complete with
+two separate No. 2580 "WONDERBUZZ" Instruments, Morse Code, Continental
+Code, Wire for short Line, Pkg. small Telegraph blanks, Instructions and
+Wiring Diagrams. (P. Wt. 2 lbs.)</td>
+ <td align='right'>$2.00**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2304B4&mdash;Same as No. 2304 but with four dry batteries. (P. Wt. 3 lbs.)</td>
+ <td align='right'>$2.50**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2350&mdash;CODEGRAPH PLATE, PEN AND BOOK. Teaches Continental Wireless Code,
+giving correct sounds on your buzzer or on ours. Original, practical,
+solves home study. (Weight 1 pound.)</td>
+ <td align='right'>$1.00**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2355&mdash;CODEGRAPH OUTFIT MOUNTED on ebonized base with High-pitch
+Nickel-plated Buzzer, Binding-posts and Key, Books and Wires. Fine set
+for practice and study. Continental Code. (Weight, 2 lbs.)</td>
+ <td align='right'>$2.75**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2355B2&mdash;Same as 2355, but with 2 batteries. (Wt. 3 lbs.)</td>
+ <td align='right'>$3.00**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2580&mdash;"SEMI-WIRELESS WONDERBUZZ," a real wonder that can actually be
+used in 40 hookups. A basic instrument around which to build
+Code-teaching Devices, Blinker Signal Systems, numerous Click
+Telegraphs, Buzz Telegraphs, Semi-wireless Telegraphs, several Telephone
+Plans, combined Telegraph and Telephone schemes over the same wire,
+actual Room-to-room Wireless, etc., etc. Can't begin to tell it all
+here. An all-useful instrument with directions. (Weight, 1 lb.)</td>
+ <td align='right'>$1.00**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2576&mdash;THE "WONDERPHONE" is a practical, inexpensive telephone set;
+sensitive, strong and well made. Outfit for one station: Receiver,
+Carbon Grain Transmitter, both with flexible wires, Combination
+Binding-post and Instrument Support, Battery Box, Wire for Connections,
+50 ft. of Line Wire, Directions. (Weight, 1 lb.)</td>
+ <td align='right'>$1.50**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2576B2&mdash;Same as No. 2576, but with 2 batteries, (Wt. 2 lbs.)</td>
+ <td align='right'>$1.75**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2582&mdash;"SEMI-WIRELESS TELEGRAPH, TELEPHONE, AND ELECTRIC LIGHT SIGNAL
+SET." A Combination of the "Wonderbuzz," the "Wonderphone," Night Signal
+Attachment, and a Lot of Extras, Line Wire, Etc. A set that beats them
+all and does most. No other system does so much for the money and no
+other can do so much for ten times the money. A wonder combination of
+usefulness. Please read about the "Wonderbuzz" and the "Wonderphone."
+The latest word in telegraphy from Cascade Ranch. (Weight, 2 lbs.)</td>
+ <td align='right'>$2.75**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2582B2&mdash;Same as No. 2582 but with 2 batteries. (Wt. 3 lbs.)</td>
+ <td align='right'>$3.00**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>No. STJC&mdash;SAVE-TIME-JIFFY-CODE. Learn to send and receive slowly in an
+hour or less. In a day you can telegraph in a jiffy, any message,
+punctuation, numbers, sentence-signals and the whole business. Every boy
+a telegrapher. Fun to make your own Cipher Codes on this as a basis.
+Complete, postpaid 6c., two for</td>
+ <td align='right'>$0.10**</td>
+</tr>
+<tr class='tr1'>
+ <td align='left'>2425&mdash;"DANDY HANDIPHONE." An inexpensive house-to-house telephone.
+Sensitive, attractive, practical, efficient. Rings bell or buzzer to
+call, using dry batteries. Will work as far as any battery-phone, and
+farther than many of them. A dandy Handiphone. In preparation.</td>
+ <td align='right'>&nbsp;</td>
+</tr>
+</table></div>
+
+<p class="center"><small>Be sure to add postage according to weight and zone.</small></p>
+
+<p class="t1"><b>THOMAS M. ST. JOHN, Cascade Ranch, East Windham, N.Y.</b></p>
+
+<p>&nbsp;</p>
+<p>&nbsp;</p>
+<hr class="full" />
+<p>***END OF THE PROJECT GUTENBERG EBOOK HOW TWO BOYS MADE THEIR OWN ELECTRICAL APPARATUS***</p>
+<p>******* This file should be named 28335-h.txt or 28335-h.zip *******</p>
+<p>This and all associated files of various formats will be found in:<br />
+<a href="http://www.gutenberg.org/dirs/2/8/3/3/28335">http://www.gutenberg.org/2/8/3/3/28335</a></p>
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+*** END: FULL LICENSE ***
+</pre>
+</body>
+</html>
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author	Roger Frank <rfrank@pglaf.org>	2025-10-15 02:38:10 -0700
committer	Roger Frank <rfrank@pglaf.org>	2025-10-15 02:38:10 -0700
commit	d4aa45a4bf556431ba5305417937d1d892c5bb68 (patch)
tree	1fa2c88865c2c7e6be8c5c3a6920e486851a1754 /28335-h