archematics/public/jelts/book1/joyceDefI2.html
Glen Whitney e7361f94a7 feat: Produce an archematics plugin that works in Firefox (#38)
With this loaded in under the Firefox debugger, one can see linked WRL files and Java Geometry Applets on arbitrary web pages.
This represents significant progress on #28, but getting more controls and getting it to work in other browsers is still on deck.

Reviewed-on: #38
Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Co-committed-by: Glen Whitney <glen@studioinfinity.org>
2023-10-05 06:19:11 +00:00

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<html><head>
<meta http-equiv="content-type" content="text/html; charset=windows-1252">
<title>Euclid's Elements, Book I, Definition 2</title>
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<script src="joyceDefI2_files/elements.js"></script>
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<div id="header"><a class="hover" href="https://mathcs.clarku.edu/%7Edjoyce/java/elements/elements.html"><h1>Euclid's Elements</h1></a><a class="hover" href="https://mathcs.clarku.edu/%7Edjoyce/java/elements/bookI/bookI.html"><h1>Book I</h1></a></div>
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<div class="theorem">
<h1>Definition 2</h1>
<div class="statement">A <i>line</i> is breadthless length.</div>
</div>
<a name="guide"><h2>Guide</h2></a>
“Line” is the second primitive term in the <i>Elements.</i> The
description, “breadthless length,” says that a line will have one
dimension, length, but it wont have breadth. The terms length and
breadth are not defined in the <i>Elements.</i> In <a href="https://mathcs.clarku.edu/%7Edjoyce/java/elements/bookI/defI5.html">I.Def.5</a> a surface is defined with the two dimensions length and breadth, and in <a href="https://mathcs.clarku.edu/%7Edjoyce/java/elements/bookXI/defXI1.html">XI.Def.1</a> a solid is defined with the three dimensions length, breadth, and depth.
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<p>One cannot tell from this definition what kind of line is meant by
line, but later a straight line defined to be a special kind of line.
One can conclude, then, that lines need not be straight. Perhaps
“curve” would be a better translation than line since Euclid meant what
is commonly called a curve in modern English, where a curve may or may
not be straight.
</p><p>Also, from the next definition, it is apparent that Euclids
lines may have ends, so they are line segments or curve segments. But
they need not have ends in all cases since the entire circumference of a
circle is an example of a line. Indeed, lines need not be finite in
all cases; there are a few instances in the <i>Elements</i> where a line is not bounded, and that is usually indicated by the language. See, for example, proposition <a href="https://mathcs.clarku.edu/%7Edjoyce/java/elements/bookI/propI12.html">I.12</a>.
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<div id="ap1">
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<img src="joyceDefI2_files/defI2.gif" alt="java applet or image">
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<param name="title" value="I.39">
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<param name="e[3]" value="C;point;free;190,100;0">
<param name="e[4]" value="D;point;free;280,50;0">
<param name="e[5]" value="BC;line;connect;B,C">
<param name="e[6]" value="E';point;perpendicular;B,C;0;0">
<param name="e[7]" value="M;point;midpoint;A,B;0;0">
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<param name="e[12]" value="N;point;midpoint;C,D;0;0">
<param name="e[13]" value="F'';point;perpendicular;N,C;0;0">
<param name="e[14]" value="F;point;intersection;C,F',N,F'';0;0">
<param name="e[15]" value="CND;sector;sector;F,C,D;0;0;black;0">
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<script>
if (!navigator.javaEnabled()) document.getElementById('ap1').innerHTML =
'<img src="defI2.gif" hspace=10 vspace=10 alt="I.Def.2">';
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<p>One piece of terminology that Euclid did not mention explicitly in a
definition is a phrase to indicate when a line passes through a point.
That would be a primitive relation that could hold between a line and a
point. Postulates would be included as well to give meaning to the
phrase as they are in modern treatments of elementary geometry.
</p><div id="footer"><br><p></p><hr size="6"><p></p><center><table><tbody><tr valign="top"><td>Next: <a href="https://mathcs.clarku.edu/%7Edjoyce/java/elements/bookI/defI3.html">I.Def.3</a> &nbsp; &nbsp; &nbsp; &nbsp; </td><td><form name="PropForm"><select name="select1" size="1" onchange="if (options[selectedIndex].value){ location = options[selectedIndex].value }"><option value="" selected="selected">Select from Book I</option><option value="bookI.html">Book I intro</option><option value="defI1.html">I.Def.1</option><option value="defI2.html">I.Def.2</option><option value="defI3.html">I.Def.3</option><option value="defI4.html">I.Def.4</option><option value="defI5.html">I.Def.5</option><option value="defI6.html">I.Def.6</option><option value="defI7.html">I.Def.7</option><option value="defI8.html">I.Def.8</option><option value="defI9.html">I.Def.9</option><option value="defI10.html">I.Def.10</option><option value="defI11.html">I.Def.11-12</option><option value="defI13.html">I.Def.13-14</option><option value="defI15.html">I.Def.15-18</option><option value="defI19.html">I.Def.19</option><option value="defI20.html">I.Def.21</option><option value="defI22.html">I.Def.22</option><option value="defI23.html">I.Def.23</option><option value="cn.html">Common Notions</option><option value="post1.html">I.Post.1</option><option value="post2.html">I.Post.2</option><option value="post3.html">I.Post.3</option><option value="post4.html">I.Post.4</option><option value="post5.html">I.Post.5</option><option value="propI1.html">I.1</option><option value="propI2.html">I.2</option><option value="propI3.html">I.3</option><option value="propI4.html">I.4</option><option value="propI5.html">I.5</option><option value="propI6.html">I.6</option><option value="propI7.html">I.7</option><option value="propI8.html">I.8</option><option value="propI9.html">I.9</option><option value="propI10.html">I.10</option><option value="propI11.html">I.11</option><option value="propI12.html">I.12</option><option value="propI13.html">I.13</option><option value="propI14.html">I.14</option><option value="propI15.html">I.15</option><option value="propI16.html">I.16</option><option value="propI17.html">I.17</option><option value="propI18.html">I.18</option><option value="propI19.html">I.19</option><option value="propI20.html">I.20</option><option value="propI21.html">I.21</option><option value="propI22.html">I.22</option><option value="propI23.html">I.23</option><option value="propI24.html">I.24</option><option value="propI25.html">I.25</option><option value="propI26.html">I.26</option><option value="propI27.html">I.27</option><option value="propI28.html">I.28</option><option value="propI29.html">I.29</option><option value="propI30.html">I.30</option><option value="propI31.html">I.31</option><option value="propI32.html">I.32</option><option value="propI33.html">I.33</option><option value="propI34.html">I.34</option><option value="propI35.html">I.35</option><option value="propI36.html">I.36</option><option value="propI37.html">I.37</option><option value="propI38.html">I.38</option><option value="propI39.html">I.39</option><option value="propI40.html">I.40</option><option value="propI41.html">I.41</option><option value="propI42.html">I.42</option><option value="propI43.html">I.43</option><option value="propI44.html">I.44</option><option value="propI45.html">I.45</option><option value="propI46.html">I.46</option><option value="propI47.html">I.47</option><option value="propI48.html">I.48</option></select></form></td></tr><tr valign="top"><td>Previous: <a href="https://mathcs.clarku.edu/%7Edjoyce/java/elements/bookI/defI1.html">I.Def.1</a></td><td><form name="BookForm"><select name="select2" size="1" onchange="if (options[selectedIndex].value){ location = options[selectedIndex].value }"><option value="" selected="selected">Select book</option><option value="../bookI/bookI.html">Book I</option><option value="../bookII/bookII.html">Book II</option><option value="../bookIII/bookIII.html">Book III</option><option value="../bookIV/bookIV.html">Book IV</option><option value="../bookV/bookV.html">Book V</option><option value="../bookVI/bookVI.html">Book VI</option><option value="../bookVII/bookVII.html">Book VII</option><option value="../bookVIII/bookVIII.html">Book VIII</option><option value="../bookIX/bookIX.html">Book IX</option><option value="../bookX/bookX.html">Book X</option><option value="../bookXI/bookXI.html">Book XI</option><option value="../bookXII/bookXII.html">Book XII</option><option value="../bookXIII/bookXIII.html">Book XIII</option></select></form></td></tr><tr valign="top"><td><a href="https://mathcs.clarku.edu/%7Edjoyce/java/elements/bookI/bookI.html">Book I</a></td><td><form name="TopicForm"><select name="select3" size="1" onchange="if (options[selectedIndex].value){ location = options[selectedIndex].value }"><option value="" selected="selected">Select topic</option><option value="../elements.html">Introduction</option><option value="../toc.html">Table of Contents</option><option value="../usingApplet.html">Geometry applet</option><option value="../aboutText.html">About the text</option><option value="../Euclid.html">Euclid</option><option value="../web.html">Web references</option><option value="../trip.html">A quick trip</option><option value="../subjindex.html">Subject index</option></select></form></td></tr></tbody></table></center><hr size="6"><p><font size="-1"><a href="https://mathcs.clarku.edu/%7Edjoyce/java/elements/copyright.html">©1996</a><br><a href="http://aleph0.clarku.edu/%7Edjoyce/">David E. Joyce</a><br><img src="joyceDefI2_files/dj.gif"><br><a href="http://www.clarku.edu/departments/mathcs/">Department of Mathematics and Computer Science</a><br><a href="http://www.clarku.edu/">Clark University</a><br>Worcester, MA 01610</font></p></div>
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