CINXE.COM

Encyclopedia - Britannica Online Encyclopedia

<!doctype html> <!--[if lt IE 7 ]> <html lang="en" class="no-js ie ie6 browse-html bps-html"> <![endif]--> <!--[if IE 7 ]> <html lang="en" class="no-js ie ie7 browse-html bps-html"> <![endif]--> <!--[if IE 8 ]> <html lang="en" class="no-js ie ie8 browse-html bps-html"> <![endif]--> <!--[if IE 9 ]> <html lang="en" class="no-js ie ie9 browse-html bps-html"> <![endif]--> <!--[if (gt IE 9)|!(IE)]><!--> <html lang="en" class="no-js browse-html bps-html"> <!--<![endif]--> <head><script type="text/javascript" src="/_static/js/bundle-playback.js?v=HxkREWBo" charset="utf-8"></script> <script type="text/javascript" src="/_static/js/wombat.js?v=txqj7nKC" charset="utf-8"></script> <script>window.RufflePlayer=window.RufflePlayer||{};window.RufflePlayer.config={"autoplay":"on","unmuteOverlay":"hidden"};</script> <script type="text/javascript" src="/_static/js/ruffle/ruffle.js"></script> <script type="text/javascript"> __wm.init("https://web.archive.org/web"); __wm.wombat("http://www.britannica.com:80/bps/widget-tool?topicId=186603","20110426170437","https://web.archive.org/","web","/_static/", "1303837477"); </script> <link rel="stylesheet" type="text/css" href="/_static/css/banner-styles.css?v=S1zqJCYt" /> <link rel="stylesheet" type="text/css" href="/_static/css/iconochive.css?v=3PDvdIFv" /> <!-- End Wayback Rewrite JS Include --> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=7,chrome=1"> <title>Encyclopedia - Britannica Online Encyclopedia</title> <meta property="og:image" content="https://web.archive.org/web/20110426170437im_/http://school.eb.com/bcom/images/facebook-logo.png"/> <meta property="og:title" content="Encyclopedia - Britannica Online Encyclopedia"/> <meta property="og:type" content="article"/> <meta property="og:url" content="https://web.archive.org/web/20110426170437/http://www.britannica.com/bps/error404?topicId=186603"/> <meta name="description" content="Explore the updated online encyclopedia from Encyclopaedia Britannica with hundreds of thousands of articles, biographies, videos, images, and web sites."> <meta name="keywords" content="britannica, reference, online, encyclopedia, encyclpaedia, store, dictionary, thesaurus"> <script type="text/javascript"> document.write('<link rel="stylesheet" href="/static/bps-static-content/20110414-1809/css/min-bps.css" type="text/css" media="screen"/>'); </script> <noscript> <link rel="stylesheet" href="/web/20110426170437cs_/http://www.britannica.com/static/bps-static-content/20110414-1809/css/bps-noscript.css" type="text/css" media="screen"/> </noscript> <script src="/web/20110426170437js_/http://www.britannica.com/static/bps-static-content/20110414-1809/js/libs/modernizr-1.6.min.js"></script> <script> var config = { basePath:'', baseUrl:'https://web.archive.org/web/20110426170437/http://www.britannica.com', cssPath:'/css/', resourcePath:'/static/bps-static-content/20110414-1809', resourceServer:'', cachedResourceServer:'https://web.archive.org/web/20110426170437/http://cache.britannica.com', alternateResourceServer:'https://web.archive.org/web/20110426170437/http://www.britannica.com', imagesPath:'/images/', mediaPath:'media.web.britannica.com', mediaServers:'media-1.web.britannica.com,media-2.web.britannica.com,media-3.web.britannica.com', cachedMediaServers:'cache-media.britannica.com', hasBpsPermission:false, userEmailAddress:'anonymous@eb.com', userDataConfig:{"UA":false,"accountId":0,"activities":{"STDCOMMUSERINVITE":0,"COMMPUB":0,"DOCRTG":0},"adPattern":null,"annoywareConfig":null,"anonymous":true,"bcomID":"62937830811934366411303836738073","bolProduct":null,"coBrand":null,"coBrandBanner":null,"countryCode":"US","currencyCode":"USD","darwinCoBrandHeight":null,"displayName":"ANONYMOUS","ebscoGistLength":0,"editor":false,"editorialToolAccessAllowed":false,"gistLength":0,"instAccountId":null,"interstitialMax":0,"interstitialTimeout":0,"melingoConfig":"{active:false}","memberSince":null,"preAdTestId":null,"registered":false,"searchUpsellTestId":null,"seatCount":null,"showBing":false,"showEbscoGist":false,"showGist":false,"showInterstitial":false,"showSharedBook":false,"showVideoAd":false,"sidebar":null,"skipWelcomePage":false,"stats":false,"statsProduct":null,"statsUrl":null,"storeTestId":null,"subscribed":false,"tempUser":false,"testId":null,"testVersion":null,"typeGratis":"GIST","uaProduct":null,"upsellTestId":null,"userAnonymous":true,"userType":"guest","videoAdType":"","yahooUserType":"Consumer"}, trackingConfig:{memberSince:"",loggedIn:"false"}, ebAnalyticsDomain: "britannica.com", includeEbAnalytics: "true", activities:{hideUpsell:"false",hideAds:"false"}, worldDataPath:'https://web.archive.org/web/20110426170437/http://world.britannica.com', includeNextAction:true, includeGoogleAnalytics:true, includeKontera:false, includeInfolinks:true, includeAdaptv:true, adaptvKey:'nj232', includeYahooWebAnalytics:true, includeGoogleMaps:true, isSecured:false, statsURL:'school.eb.com', copyright:'', showDialog:'' ,topicBrowsePage:true }; </script> </head> <!-- --> <body class="browse-body bps-body "> <!--INFOLINKS_OFF--> <nav id="eb-header-navigation"> <ul class="eb-horizontal-list"> <li><a href="/web/20110426170437/http://www.britannica.com/" rel="nofollow">HOME</a></li> <li><a data-track="{n:'05',d:'HDR - Browse',p:'query'}" href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha" rel="nofollow">BROWSE</a></li> <li> <a id="nav-dashboard-link" rel="nofollow" href="/web/20110426170437/http://www.britannica.com/bps/dashboard/workspace ">WORKSPACE</a> </li> <li><a data-track="{n:'02',d:'HDR - Shop'}" href="https://web.archive.org/web/20110426170437/http://britannicastore.com/" target="_blank" id="navigation-link-shop" rel="nofollow">SHOP</a></li> <li><a data-track="{n:'06',d:'HDR - Blog'}" href="https://web.archive.org/web/20110426170437/http://www.britannica.com/blogs" rel="nofollow">BLOG</a></li> <li><a data-track="{n:'66',d:'HDR - Advocacy'}" href="https://web.archive.org/web/20110426170437/http://advocacy.britannica.com/" rel="nofollow">ADVOCACY</a></li> <li><a data-track="{n:'102',d:'HDR - Help'}" href="https://web.archive.org/web/20110426170437/http://help.eb.com/premium/index.htm" target="_blank" rel="nofollow">HELP</a></li> <li id="nav-login-link"><a data-track="{n:'07',d:'HDR -Log In'}" href="#">LOG IN</a></li> </ul> </nav> <div id="bps-advanced-search" class="x-hidden bps-js-required"> <form id="bps-advanced-search-form" class="UI-Form" action="/web/20110426170437/http://www.britannica.com/bps/search" method="get"> <label for="queryAll">With all of these words</label><input class="UI-Form-Field" type="text" id="queryAll" name="queryAll" data-separator="AND" data-pre=""/> <label for="queryExact">With the exact phrase</label><input class="UI-Form-Field" type="text" id="queryExact" name="queryExact" data-separator="" data-pre=""/> <label for="queryAny">With any of these words</label><input class="UI-Form-Field" type="text" id="queryAny" name="queryAny" data-separator="OR" data-pre=""/> <label for="queryWithout">Without these words</label><input class="UI-Form-Field" type="text" id="queryWithout" name="queryWithout" data-separator="AND NOT" data-pre="NOT"/> <input class="bps-advanced-search-go UI-Form-submitButton" type="submit" value=""/> </form> </div> <div id="hp-login" class="UI-Multiview "> <div id="upsell-login" class="UI-Multiview-View"> <div class="anonymous-upsell "> <div id="" class="bps-advertisement bps-advertisement-placeholder" data-options="{&quot;vendor&quot;:&quot;adtech&quot;,&quot;pid&quot;:1371258,&quot;cid&quot;:3603,&quot;ifw&quot;:291,&quot;ifh&quot;:42}"></div> <noscript><a href="" target="_blank"><img src="/web/20110426170437im_/http://www.britannica.com/bps/widget-tool?topicId=186603"></a></noscript> </div> </div> <div id="enter-login" class="UI-Multiview-View"> <div id="enter-login-close" class="eb-close-button-12-white"></div> <form id="login-form" class="enter-login-box UI-Form" action="https://web.archive.org/web/20110426170437/https://www.britannica.com/bps/login" method="post"> <div> <label for="log-username">Username:</label> <input type="text" id="log-username" class="UI-Form-Field UI-Form-Field" name="username"> </div> <div> <label for="log-password">Password:</label> <input type="password" id="log-password" class="UI-Form-Field" name="password"> </div> <a href="#" id="log-go" class="UI-Form-submitButton login-go-button"></a> <div> <input type="submit" class="hide-on-js" name="noJsLogin" value="Log In"/> </div> <div class="log-functions"><input type="checkbox" id="log-remember" name="remember" value="true"><label for="log-remember">Remember me</label><a href="#" id="log-forgot" class="hp-login-link">Forgot your password?</a></div> <div class="UI-Form-ValidationMessageWrapper"> <div class="UI-Form-ValidationMessage"></div><a href="#" id="login-help-link" class="hp-login-link">Help</a> </div> <input type="hidden" name="target" value="/bps/error404?topicId=186603"/> </form> </div> <div id="login-help-msg" class="UI-Multiview-View"> <div class="eb-close-button-12-white" id="login-close-help"></div> <p>"<b>Email</b>" is the e-mail address you used when you registered.</p> <p>"<b>Password</b>" is case sensitive.</p> <p>If you need additional assistance, please contact <a href="https://web.archive.org/web/20110426170437/http://corporate.britannica.com/help/index.html" target="_blank" class="hp-login-link" rel="nofollow">customer support</a>.</p> </div> <div id="enter-forgot-password" class="UI-Multiview-View bps-js-required"> <div class="eb-close-button-12-white" id="login-close-forgot"></div> <form id="forgot-password-form" action="/web/20110426170437/http://www.britannica.com/bps/email-password" method="post" class="UI-Form"> <div> Enter the e-mail address you used when enrolling for Britannica Premium Service and we will e-mail your password to you. </div> <div class="forgot-password-enter"> <input id="forgot-password-field" class="UI-Form-Field UI-Form-email" type="text" name="email"/> <a href="#" id="forgot-go" class="UI-Form-submitButton login-go-button"></a> </div> <div class="UI-Form-ValidationMessage"></div> </form> </div> <div id="login-user-info" class="UI-Multiview-View bps-js-required"> </div> </div> <div id="bps-header" class="headerSeparator"> <div id="bps-header-search"> <form id="bps-header-search-form" action="/web/20110426170437/http://www.britannica.com/bps/search" method="get" autocomplete="/bps/opensearch/eb/topic"> <label for="query">Search Site: </label> <input class="bps-default-text" type="text" id="query" name="query" autocomplete="off" title="Search Site" value="Search Site"/> <input class="bps-header-search-right" id="reset_search" type="reset" value=""/> <input class="bps-header-search-go" id="header_go" type="submit" value=""> </form> <ul id="bps-search-toolbar" class="UI-Toolbar bps-js-required"> <li id="bps-advanced-search-link" data-track="{n:'60',d:'Advanced Search',q:'query'}"> <a href="#"><span>Advanced Search</span></a> </li> </ul> </div> <div id="bps-header-top" class="bps-header-top"> <a class="bps-header-logo" href="/web/20110426170437/http://www.britannica.com/"> <span>Home</span> </a> </div> </div> <!--INFOLINKS_ON--> <div> <div id="bps-sidebar" class="sidebarB sidebar-browse"> <div class="toggle"><input type="radio" name="sidebarToggle" value="browse" id="sidebarToggle-browse" checked="checked"/><label for="sidebarToggle-browse">Browse</label></div> <div class="toggle"><input type="radio" name="sidebarToggle" id="sidebarToggle-researchTools" value="researchtools"/><label for="sidebarToggle-researchTools">Other Research Tools</label></div> <h4 style="margin-top:10px">Browse:</h4> <ul id="sidebar-tools" class="sidebar-tools"> <li><a id="bps-az-link" class="" title="" href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha">A-Z</a></li> <li><a id="bps-biography-link" class="" title="" href="/web/20110426170437/http://www.britannica.com/bps/biography-browse">Biographies</a></li> <li><a id="bps-contributor-link" class="" title="" href="/web/20110426170437/http://www.britannica.com/bps/contributor-browse">Contributors</a></li> <li class="two-line"><a id="bps-primary-link" class="" title="" href="/web/20110426170437/http://www.britannica.com/bps/browse/primary-source">Ebooks &amp;<br/>Primary Sources</a></li> <li><a id="bps-magazine-link" class="" title="" href="/web/20110426170437/http://www.britannica.com/bps/browse/magazine">Magazines</a></li> <li><a class="" title="" href="/web/20110426170437/http://www.britannica.com/bps/media-browse">Media Collection</a></li> <li><a id="bps-quotations-link" class="" title="" href="/web/20110426170437/http://www.britannica.com/bps/quotations-browse">Quotations</a></li> <li><a id="bps-subject-link" class="" title="" href="/web/20110426170437/http://www.britannica.com/bps/subject-browse">Subjects</a></li> </ul> <div id="sidebar-upsell"> <div id="" class="bps-advertisement-placeholder" data-options="{&quot;vendor&quot;:&quot;adtech&quot;,&quot;pid&quot;:1371363,&quot;cid&quot;:5,&quot;ifw&quot;:120,&quot;ifh&quot;:90}"></div> </div> </div> </div> <div id="bps-main"> <div id="main"> <div id="errorMain"> <span class="errorHeader">Sorry, page not found.</span> <p>You can browse an alphabetical list of the topics on this site: </p> <ul> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/a">A</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/b">B</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/c">C</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/d">D</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/e">E</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/f">F</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/g">G</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/h">H</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/i">I</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/j">J</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/k">K</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/l">L</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/m">M</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/n">N</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/o">O</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/p">P</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/q">Q</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/r">R</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/s">S</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/t">T</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/u">U</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/v">V</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/w">W</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/x">X</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/y">Y</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/z">Z</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/bps/browse-alpha/0-9">0-9</a></li> </ul> <p>Visit the <b><i>Britannica Online Encyclopedia</i></b> <a href="/web/20110426170437/http://www.britannica.com/">home page</a> to access additional features and content.</p> <!-- siteapp20--> </div> </div> </div> <!--INFOLINKS_OFF--> <!--INFOLINKS_OFF--> <div id="media-overlay" class="bps-js-required"> <table width="100%" height="100%"> <tr> <td width="100%" height="100%" valign="middle" align="center"> <div id="media-overlay-content-wrapper" class="media-overlay"> <div class="overlay-corner overlay-dialog-bl"></div> <div class="overlay-corner overlay-dialog-br"></div> <div class="overlay-corner overlay-dialog-tl"></div> <div class="overlay-corner overlay-dialog-tr"></div> <a id="media-overlay-close" class="eb-close-button-16"></a> <div id="media-overlay-content-container" style="display: block;"> <div class="media-overlay-slideshow "> <div class="media-overlay-slideshow-gradient"></div> </div> <div id="media-overlay-content"> <div id="media-overlay-previous"></div> <div id="media-overlay-next"></div> <div id="media-overlay-content-loaded"> </div> </div> <div id="media-overlay-sidebar" class="bps-js-required"> <div id="magic-zoom-big"></div> <div class="assembly-header"> <div class="left-assembly-header"></div> <ul id="assembly-toolbar" class="UI-Toolbar UI-Toolbar-no-shadow"> <li id="assembly-print-tab"><a target="_blank"><span id="assembly-print">&#160;</span>PRINT</a></li> <li id="assembly-email-tab"><a href="#"><span id="assembly-email">&#160;</span>E-MAIL</a></li> <li id="assembly-share-tab"><a href="#"><span id="assembly-share">&#160;</span>SHARE</a></li> </ul> <div class="right-assembly-header"></div> </div> <div id="media-overlay-sidebar-links"> <ul> <li id="media-overlay-save"> <a>Save to My Workspace</a> </li> <li id="media-overlay-download"> <a target="_blank" title="Right click or option-click the link and choose &quot;Save As...&quot; to download this file.">Download <span class="mo-video">Video</span><span class="mo-audio">Audio</span><span class="mo-image">Image</span></a> </li> <li id="media-overlay-submit-image"> <a>Submit an image to Britannica</a> </li> <li id="media-overlay-submit-video"> <a>Submit a video to Britannica</a> </li> <li id="media-overlay-submit-audio"> <a>Submit audio to Britannica</a> </li> </ul> </div> <div id="media-overlay-sidebar-help"> <ul> <li id="media-overlay-sidebar-media-help" class="media-overlay-sidebar-help-message">All of the media associated with this article appears on the left. Click an item to view it.</li> <li>Mouse over the caption, credit<span id="media-overlay-help-links">, links</span> or citations to learn more.</li> <li id="media-overlay-sidebar-image-help" class="media-overlay-sidebar-help-message">You can mouse over some images to magnify, or click on them to view full-screen.</li> <li id="media-overlay-sidebar-video-help" class="media-overlay-sidebar-help-message">Click on the Expand button to view this full-screen. Press Escape to return.</li> <li id="media-overlay-sidebar-audio-help" class="media-overlay-sidebar-help-message">Click on audio player controls to interact.</li> </ul> </div> <div id="media-overlay-sidebar-ad"> <div id="bps-companion-ad" class="bps-advertisement bps-advertisement-rectangle bps-advertisement-rectangle-wrapper bps-advertisement-placeholder" data-options="{&quot;vendor&quot;:&quot;adtech&quot;,&quot;pid&quot;:1375457,&quot;cid&quot;:170,&quot;ifw&quot;:300,&quot;ifh&quot;:250}"></div> </div> </div> </div> </div> </td> </tr> </table> </div> <!--INFOLINKS_ON--> <div id="bps-community-registration" class="x-hidden bps-js-required"> <!-- Join / Login buttons --> <div id="bps-community-registration-switch"> <a href="#" id="bps-community-join-button" class="selected"><span>JOIN COMMUNITY</span></a> <a href="#" id="bps-community-login-button"><span>LOGIN</span></a> </div> <!-- Main Multiview --> <div id="bps-community-multiview" class="UI-Multiview"> <!-- Registration Dialog --> <div id="bps-community-join-view" class="UI-Multiview-View"> <em>Join Free Community</em> <p>Please join our community in order to save your work, create a new document, upload <br/>media files, recommend an article or submit changes to our editors. </p> <form id="bps-community-join-form" class="UI-Form" method="post" action="/web/20110426170437/http://www.britannica.com/bps/community"> <table cellpadding="0" cellspacing="0"> <tr> <td><label for="bps-community-join-firstName">First Name:</label></td> <td><input id="bps-community-join-firstName" class="UI-Form-Field" type="text" name="firstName"/></td> <td><label for="bps-community-join-lastName">Last Name:</label></td> <td><input id="bps-community-join-lastName" class="UI-Form-Field" type="text" name="lastName"/></td> </tr> <tr> <td><label for="bps-community-join-email">Email:</label></td> <td><input class="UI-Form-Field UI-Form-email" type="text" id="bps-community-join-email" name="emailAddress"/></td> <td><label for="bps-community-join-password">Password:</label></td> <td><input class="UI-Form-Field" type="password" id="bps-community-join-password" name="password"/></td> </tr> </table> <div> <input id="bps-community-join-cb1" name="britOptOut" type="checkbox"/> <label for="bps-community-join-cb1">Please send me periodic email about new product updates and exclusive offers from Britannica.</label> </div> <div> <input id="bps-community-join-cb2" name="optintwo" type="checkbox"/> <label for="bps-community-join-cb2"> By checking this box, I confirm that I accept the terms of the <a href="https://web.archive.org/web/20110426170437/http://corporate.britannica.com/termsofuse.html" target="_blank">Britannica Usage Agreement</a>.</label> </div> <div class="bps-community-join-buttons"> <a id="bps-community-join-submit" class="UI-Button UI-Form-submitButton"><span>Join</span></a> <a id="bps-community-join-cancel" class="UI-Button"><span>Cancel</span></a> </div> <div class="UI-Form-ValidationMessage"></div> <input name="json" type="hidden" value="true"/> </form> </div> <!-- Login dialog --> <div id="bps-community-login-view" class="UI-Multiview-View"> <em>Premium Member/Community Member Login</em> <div id="bps-community-login-multiview" class="UI-Multiview"> <div id="bps-community-login-enter-login" class="UI-Multiview-View"> <form id="bps-community-login-form" class="UI-Form" method="post" action="https://web.archive.org/web/20110426170437/https://www.britannica.com/bps/login"> <table cellspacing="0" cellpadding="0"> <tr> <td><label for="bps-community-login-username">Email:</label></td> <td><input type="text" class="UI-Form-Field UI-Form-email" id="bps-community-login-username" name="username"/></td> </tr> <tr> <td><label for="bps-community-login-password">Password:</label></td> <td><input type="password" class="UI-Form-Field" id="bps-community-login-password" name="password"/></td> </tr> </table> <div class="bps-community-login-cb"> <input id="bps-community-login-remember" class="UI-Form-Field" type="checkbox" name="remember" value="true"/> <label for="bps-community-login-remember">Remember me</label> </div> <div id="bps-community-login-forgot-link"> <a href="#">Forgot your password?</a> </div> <div class="bps-community-login-buttons"> <a class="UI-Button UI-Form-submitButton" id="bps-community-login-submit"><span>Login</span></a> <a class="UI-Button" id="bps-community-login-cancel"><span>Cancel</span></a> </div> <div class="UI-Form-ValidationMessage"></div> <div id="bps-community-login-help" class="x-hidden"> <p>"<b>Email</b>" is the e-mail address you used when you registered. "<b>Password</b>" is case sensitive.<p/> <p>If you need additional assistance, please contact <a href="https://web.archive.org/web/20110426170437/http://corporate.britannica.com/help/index.html" target="_blank" rel="nofollow">customer support</a>.<p/> </div> <input type="hidden" name="target" value="/bps/error404?topicId=186603"/> </form> </div> <!-- Forgot password view --> <div id="bps-community-login-send-password" class="UI-Multiview-View"> <p> Enter the e-mail address you used when registering and we will e-mail your password to you. (or click on Cancel to go back). </p> <form id="bps-community-email-password-form" action="/web/20110426170437/http://www.britannica.com/bps/email-password" method="post" class="UI-Form"> <label for="bps-community-email-password">Email Address:</label> <input id="bps-community-email-password" class="UI-Form-Field UI-Form-email" type="text" name="email"/> <div> <a href="#" class="UI-Button UI-Form-submitButton"><span>Send Password</span></a> <a id="bps-community-email-password-cancel" href="#" class="UI-Button"><span>Cancel</span></a> </div> <div class="UI-Form-ValidationMessage"></div> </form> </div> </div> </div> </div> </div> <div id="snippets-save" class="bps-js-required"> <a href="#">Save to My Workspace</a> </div> <div id="UI-modal-curtain" class="bps-js-required"><span></span></div> <div id="UI-wait-box" class="bps-js-required"><div class="UI-wait-box-msg"></div><div class="UI-wait-box-progress"></div></div> <div id="bps-share-wrap" class="x-hidden bps-js-required"> <div id="bps-share-dialog"> Share the full text of this article with your friends, associates, or readers by linking to it from your web site or social networking page.<br/><br/> <b>Permalink</b> <input type="text" readonly="readonly" id="share-link"/> <div> <ul id="bps-share-links"> <li> <a rel="http://www.facebook.com/share.php?u=%url&amp;t=%title" title="Add Facebook bookmark." target="_blank"> <img src="/web/20110426170437im_/http://www.britannica.com/static/bps-static-content/20110414-1809/images/darwin/share-dialog/facebook_32.png" border="0" title="Add Facebook bookmark." alt="Facebook"/> </a> </li> <li> <a rel="http://twitter.com/share?url=%url&amp;text=%title" title="Send a Tweet." target="_blank"> <img src="/web/20110426170437im_/http://www.britannica.com/static/bps-static-content/20110414-1809/images/darwin/share-dialog/twitter_32.png" border="0" title="Send a Tweet." alt="Twitter"/> </a> </li> <li> <a rel="http://www.linkedin.com/shareArticle?mini=true&amp;url=%url&amp;title=%title&amp;source=Encyclop忙dia+Britannica" title="Share on LinkedIn." target="_blank"> <img src="/web/20110426170437im_/http://www.britannica.com/static/bps-static-content/20110414-1809/images/darwin/share-dialog/linkedin_32.png" border="0" title="Share on LinkedIn." alt="LinkedIn"/> </a> </li> <li> <a rel="http://del.icio.us/post?url=%url&amp;title=%title" title="Add del.icio.us bookmark." target="_blank"> <img src="/web/20110426170437im_/http://www.britannica.com/static/bps-static-content/20110414-1809/images/darwin/share-dialog/delicious_32.png" border="0" title="Add del.icio.us bookmark." alt="Del.icio.us"/> </a> </li> <li> <a rel="http://www.google.com/bookmarks/mark?op=add&amp;bkmk=%url&amp;title=%title" title="Add Google bookmark." target="_blank"> <img src="/web/20110426170437im_/http://www.britannica.com/static/bps-static-content/20110414-1809/images/darwin/share-dialog/google_32.png" border="0" title="Add Google bookmark." alt="Google"/> </a> </li> <li> <a rel="http://reddit.com/submit?url=%url&amp;title=%title" title="Submit to Reddit." target="_blank"> <img src="/web/20110426170437im_/http://www.britannica.com/static/bps-static-content/20110414-1809/images/darwin/share-dialog/reddit_32.png" border="0" title="Submit to Reddit." alt="Reddit"/> </a> </li> <li> <a rel="http://www.stumbleupon.com/submit?url=%url&amp;t=%title" title="Add StumbleUpon bookmark." target="_blank"> <img src="/web/20110426170437im_/http://www.britannica.com/static/bps-static-content/20110414-1809/images/darwin/share-dialog/stumbleupon_32.png" border="0" title="Add StumbleUpon bookmark." alt="StumbleUpon"/> </a> </li> <li> <a rel="http://digg.com/submit?phase=2&amp;url=%url" title="Digg it." target="_blank"> <img src="/web/20110426170437im_/http://www.britannica.com/static/bps-static-content/20110414-1809/images/darwin/share-dialog/digg_32.png" border="0" title="Digg it." alt="Digg"/> </a> </li> <li> <a rel="http://myweb2.search.yahoo.com/myresults/bookmarklet?u=%url&amp;t=%title" title="Add Yahoo bookmark." target="_blank"> <img src="/web/20110426170437im_/http://www.britannica.com/static/bps-static-content/20110414-1809/images/darwin/share-dialog/yahoo_32.png" border="0" title="Add Yahoo bookmark." alt="Yahoo!"/> </a> </li> </ul> </div> <a id="bps-share-link-copy" class="UI-Button"> <span>Copy Link</span> </a> </div> </div> <div id="bps-assignments-wrap" class="x-hidden bps-js-required"> <div class="assignment-note"> Britannica needs you! Become a part of more than two centuries of publishing tradition by contributing to this article. If your submission is accepted by our editors, you'll become a Britannica contributor and your name will appear along with the other people who have contributed to this article. <a href="https://web.archive.org/web/20110426170437/http://corporate.britannica.com/submission.html" target="_blank" rel="nofollow">View Submission Guidelines</a> </div> <div id="assignments-grid"> <div class="wrapper-header"> <div class="grid-header"> <a class="grid-header-column" id="col-assignments-type"><div>Type</div></a> <a class="grid-header-column" id="col-assignments-change-needed"><div>Description</div></a> <a class="grid-header-column" id="col-assignments-submit"><div></div></a> </div> </div> <div id="assignments-content" class="grid-content"> </div> </div> </div> <div id="bps-comment-wrap" class="x-hidden bps-js-required"> <div id="bps-comment-dialog-email" class="bps-comment"> <p>Have a comment about this page?<br/>Please, <a id="comment_contact" href="#">contact us</a>. If this is a correction, your suggested change will be reviewed by our editorial staff.</p> </div> </div> <div id="bps-email-wrap" class="x-hidden bps-js-required"> <div id="bps-email-dialog" class="bps-email"> <form class="UI-Form" id="emailForm" action="/web/20110426170437/http://www.britannica.com/bps/email" method="post"> <div> <label for="toEmail">To</label> <input class="UI-Form-Field UI-Form-email" type="text" id="toEmail" name="toEmail"/> </div> <div> <label for="fromEmail">From</label> <input class="UI-Form-Field UI-Form-email" type="text" id="fromEmail" name="fromEmail"/> </div> <div> <label for="emailSubject">Subject</label> <input class="UI-Form-Field" type="text" id="emailSubject" name="emailSubject"/> </div> <input type="hidden" id="urlLink" name="urlLink"/> <textarea class="UI-Form-Field" autocomplete="off" cols="85" id="emailComments" name="emailComments"></textarea> <span class="bps-comment-limit">(Please limit to 900 characters)</span> <a href="#" class="UI-Button UI-Form-submitButton"><span>Send</span></a> <div class="UI-Form-ValidationMessage"></div> </form> </div> </div> <div id="add-widget-to-webpage" class="x-hidden bps-js-required"> <p>Copy and paste the HTML below to include this widget on your Web page.</p> <form> <input type="text" name="htmllink" id="widget_html_link" readonly="true" htmlval="<iframe width='100%' src='targetUrl' height='330' scrolling='no' frameborder='no'></iframe>"/> </form> <a href="#" class="UI-Button" id="bps-widget-dialog-copy"><span>Copy Link</span></a> </div> <div id="bps-browse-store" class="bps-js-required"> <h5><a href="https://web.archive.org/web/20110426170437/http://britannicastore.com/" class="bstore" data-track="{n:'101', d:'Shp - B Store'}">The Britannica Store</a></h5> <ul id="bps-browse-store-categories"> <li><a href="/web/20110426170437/http://www.britannica.com/store/educational-learning-books.html" data-track="{n:'10', d:'Shp - Books'}">Books</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/store/reference-software.html" class="software" data-track="{n:'11', d:'Shp - Software'}">Software</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/store/dvd-documentaries.html" class="dvd" data-track="{n:'12', d:'Shp - DVDs'}">DVDs</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/store/puzzles-games.html" class="toys-and-games" data-track="{n:'13', d:'Shp - Toys &amp; Games'}">Toys &amp; Games</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/store/foreign-language-learning.html" class="foreign-language" data-track="{n:'14', d:'Shp - Foreign Language'}">Foreign Language</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/store/student-child.html" class="kids" data-track="{n:'15', d:'Shp - Kids'}">Kids</a></li> <li><a href="/web/20110426170437/http://www.britannica.com/store/globe-map-anatomy.html" class="globes-and-maps" data-track="{n:'17', d:'Shp - Globes &amp; Maps'}">Globes &amp; Maps</a></li> </ul> </div> <div id="UI-Tooltip" class="bps-js-required"><div class="UI-Tooltip-tl UI-Tooltip-border"></div><div class="UI-Tooltip-top UI-Tooltip-border"></div><div class="UI-Tooltip-tr UI-Tooltip-border"></div><div class="UI-Tooltip-left UI-Tooltip-border"></div><div class="UI-Tooltip-middle"><div></div></div><div class="UI-Tooltip-right UI-Tooltip-border"></div><div class="UI-Tooltip-bl UI-Tooltip-border"></div><div class="UI-Tooltip-bottom UI-Tooltip-border"></div><div class="UI-Tooltip-br UI-Tooltip-border"></div><a href="#" class="UI-Tooltip-close eb-close-button-12"></a></div> <div id="UI-Tooltip-arrow" class="bps-js-required"></div> <div id="UI-ModalBox" class="UI-ModalBox-border bps-js-required"></div><a href="#" id="UI-ModalBox-close" class="eb-close-button-12"></a> <div id="UI-ModalBox-MessageBox" class="bps-js-required"> <div id="UI-ModalBox-MessageBox-message"></div> <div class="UI-ModalBox-MessageBox-buttons"> <a id="UI-ModalBox-MessageBox-bt1" class="UI-Button" href="#"><span></span></a> <a id="UI-ModalBox-MessageBox-bt2" class="UI-Button" href="#"><span></span></a> <a id="UI-ModalBox-MessageBox-bt3" class="UI-Button" href="#"><span></span></a> </div> </div> <div id="UI-Form-Bubble" class="bps-js-required"><div class="UI-Form-Bubble-tl"></div><div class="UI-Form-Bubble-bl"></div><div class="UI-Form-Bubble-tr"></div></div> <div id="UI-Form-Bubble-content" class="bps-js-required"></div> <div id="project-share-dialog" class="project-dialog bps-js-required"> <h3>Share This <span class="shared-object-name"></span></h3> <div>Other users can view this <span class="shared-object-name"></span> at the following URL:</div> <input type="text" readonly="readonly" id="project-share-url"/> <a href="#" class="UI-Button" id="project-share-ok"><span>Copy</span></a> </div> <div id="project-create-dialog" class="project-dialog bps-js-required"> <h3>Create New Project</h3> <form action="/web/20110426170437/http://www.britannica.com/bps/dashboard/my-documents-tagging?action=createProject" class="UI-Form" id="project-create-dialog-form"> <table> <tr><td><label for="project-create-dialog-title">Title:</label></td><td><input type="text" maxlength="40" class="UI-Form-Field" id="project-create-dialog-title" name="name"/></td></tr> <tr><td><label for="project-create-dialog-description">Description:</label></td><td><input type="text" class="UI-Form-Field" id="project-create-dialog-description" name="description"/></td></tr> </table> <a href="#" class="UI-Button UI-Form-submitButton"><span>Done</span></a> <div style="text-align:center; margin-top:6px"><span class="UI-Form-ValidationMessage"></span></div> </form> </div> <div id="project-rename-dialog" class="project-dialog bps-js-required"> <h3>Rename This Project</h3> <form action="/web/20110426170437/http://www.britannica.com/bps/dashboard/my-documents-tagging?action=updateProject" class="UI-Form" id="project-rename-dialog-form"> <table> <tr><td><label for="project-rename-dialog-title">Title:</label></td><td><input type="text" maxlength="25" class="UI-Form-Field" id="project-rename-dialog-title" name="name"/></td></tr> <tr><td><label for="project-rename-dialog-description">Description:</label></td><td><input type="text" class="UI-Form-Field" id="project-rename-dialog-description" name="description"/></td></tr> </table> <a href="#" class="UI-Button UI-Form-submitButton"><span>Done</span></a> <div style="text-align:center; margin-top:6px"><span class="UI-Form-ValidationMessage"></span></div> <input type="hidden" id="project-rename-dialog-id" name="tagId"/> </form> </div> <div id="project-edit-dialog" class="project-dialog bps-js-required"> <h3>Add or Remove from Projects</h3> <table> <tr> <td>Add to project:</td> <td> <form action="/web/20110426170437/http://www.britannica.com/bps/dashboard/my-documents-tagging?action=tag" class="UI-Form" id="project-edit-add-dialog-form"> <select id="project-edit-dialog-add" name="tagId"> </select> <a id="project-edit-dialog-do-add" href="#" class="UI-Button UI-Form-submitButton"><span>Add</span></a> <input type="hidden" name="userContentKey" id="project-edit-add-key"/> </form> </td> </tr> <tr> <td>Remove from Project:</td> <td> <form action="/web/20110426170437/http://www.britannica.com/bps/dashboard/my-documents-tagging?action=untag" class="UI-Form" id="project-edit-remove-dialog-form"> <select id="project-edit-dialog-remove" name="tagId"> </select> <a id="project-edit-dialog-do-remove" href="#" class="UI-Button UI-Form-submitButton"><span>Remove</span></a> <input type="hidden" name="userContentKey" id="project-edit-remove-key"/> </form> </td> </tr> </table> <div style="text-align:center"><span class="UI-Form-ValidationMessage" id="project-edit-dialog-error"></span></div> </div> <div id="project-copy-dialog" class="project-dialog bps-js-required"> <h3>Copy This Project</h3> <form action="/web/20110426170437/http://www.britannica.com/bps/dashboard/my-documents-share?action=copyProject" class="UI-Form" id="project-copy-dialog-form"> <table> <tr><td><label for="project-copy-dialog-title">Title:</label></td><td><input type="text" maxlength="25" class="UI-Form-Field" id="project-copy-dialog-title" name="projectName"/></td></tr> </table> <a href="#" class="UI-Button UI-Form-submitButton"><span>Copy</span></a> <div style="text-align:center; margin-top:6px"><span class="UI-Form-ValidationMessage"></span></div> <input type="hidden" id="project-copy-dialog-id" name="shareKey"/> </form> </div> <div id="project-import-dialog" class="project-dialog bps-js-required"> <h3>Import Projects</h3> <div class="project-import-disclaimer">Please enter your user name and password<br/>that you use to sign in to your workspace account on<br/>Britannica Online Academic.</div> <form action="/web/20110426170437/http://www.britannica.com/bps/wsImport?action=importWorkspace" class="UI-Form" id="project-import-dialog-form"> <table> <tr><td><label for="project-import-dialog-username">Username:</label></td><td><input type="text" class="UI-Form-Field" id="project-import-dialog-username" name="username"/></td></tr> <tr><td><label for="project-import-dialog-password">Password:</label></td><td><input type="password" class="UI-Form-Field" id="project-import-dialog-password" name="password"/></td></tr> </table> <div class="project-import-buttons"> <a href="#" class="UI-Button UI-Form-submitButton"><span>Import</span></a> <a href="#" class="UI-Button" id="project-import-cancel"><span>Cancel</span></a> </div> </form> </div> <div id="my-documents-context-menu" class="bps-js-required"> <div id="my-documents-context-menu-close" class="eb-close-button-12"></div> <ul> <li><span id="md-ctx-open"><b>Open</b> this item</span></li> <li><span id="md-ctx-delete"><b>Delete</b> this item</span></li> <li><span id="md-ctx-share"><b>Share</b> this item</span></li> <li><span id="md-ctx-add-remove-project"><b>Add/Remove</b> this from a project</span></li> <li><span id="md-ctx-insert"><b>Insert</b> this into my edited document</span></li> <li><span id="md-ctx-submit"><b>Submit</b> this to the editors of Britannica</span></li> </ul> </div> <script src="//web.archive.org/web/20110426170437js_/http://ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js"></script> <script>!window.jQuery && document.write(unescape('%3Cscript src="/static/bps-static-content/20110414-1809/js/libs/jquery-1.5.1.min.js"%3E%3C/script%3E'))</script> <script src="/web/20110426170437js_/http://www.britannica.com/static/bps-static-content/20110414-1809/js/bps-ext.js"></script> <script type="text/javascript" src="/web/20110426170437js_/http://www.britannica.com/static/bps-static-content/20110414-1809/js/min-bps-browse.js"></script> <!--INFOLINKS_ON--> <script>na_ci='';na_oi='';na_ov='';na_sc='';na_pc='';na_nb='';na_fn='';na_ln='';na_zc='';na_cy='';na_st='';na_a1='';na_a2='';na_em='';na_ev='';</script> <script src="https://web.archive.org/web/20110426170437js_/http://e.nexac.com/e/a-887/s-1711.js"></script> <noscript> <iframe src="https://web.archive.org/web/20110426170437if_/http://f.nexac.com/e/a-887/s-1711.xgi" name="naframe2" height="0" width="0" frameborder="0"></iframe> </noscript> <script> var _gaq = [['_setAccount', 'UA-6636134-2'], ['_trackPageview']]; (function(d, t) { var g = d.createElement(t), s = d.getElementsByTagName(t)[0]; g.async = true; g.src = ('https:' == location.protocol ? 'https://web.archive.org/web/20110426170437/https://ssl' : 'https://web.archive.org/web/20110426170437/http://www') + '.google-analytics.com/ga.js'; s.parentNode.insertBefore(g, s); })(document, 'script'); </script> <script> var ebaJsHost = (("https:" == document.location.protocol) ? "https://" : "http://"); document.write(unescape("%3Cscript src='" + ebaJsHost + "britannica.com/webstats/1287677973370/stats.js' type='text/javascript'%3E%3C/script%3E")); document.write(unescape("%3Cscript src='" + ebaJsHost + "britannica.com/webstats/Math.uuid.js' type='text/javascript'%3E%3C/script%3E")); </script> <div id="ebstats-hidden-div" style="display:none;">&nbsp;</div> <script type="text/javascript"> try { writeStat("", {hostnameOverride: 'britannica.com', accountId: config.userDataConfig.accountId}); } catch(err) {} $("body").bind("ajaxComplete", function(event,request, settings){ try { writeStat("", { hostnameOverride: 'britannica.com', hitCount: 2, accountId: config.userDataConfig.accountId, requestUrl: config.baseUrl + settings.url, referrerUrl: document.location.href }); } catch(err) {} }); </script> <script type="text/javascript"> var groupid = Math.round(Math.random() * 1000); var isrc = "https://web.archive.org/web/20110426170437/http://adserver.adtechus.com/adiframe|3.0|5308.1|1371251|0|170|ADTECH;target=_blank;grp=" + groupid + ";kvsource=;kvtopicid=;kvchannel="; var jsrc = "https://web.archive.org/web/20110426170437/http://adserver.adtechus.com/addyn|3.0|5308.1|1371251|0|170|ADTECH;target=_blank;grp=" + groupid + ";kvsource=;kvtopicid=;kvchannel=;misc=" + new Date().getTime(); var adaptvCompanionAdTag = '<iframe allowtransparency=true hspace=0 noresize=true vspace=0 frameborder=0 height=250 marginheight=0 marginwidth=0 scrolling=no width=300 src="' + isrc + '"><scr' + 'ipt src="' + jsrc + '"></scr' + 'ipt></iframe>'; </script> <span id="ywa-test"></span> <!-- Yahoo! Web Analytics - All rights reserved --> <script type="text/javascript" src="https://web.archive.org/web/20110426170437js_/http://d.yimg.com/mi/ywa.js"></script> <script type="text/javascript"> Darwin.Tracking.logPageSubmit("Browse page", "Browse"); </script> <noscript> <div> <img src="https://web.archive.org/web/20110426170437im_/https://a.analytics.yahoo.com/p.pl?a=1000737262638&amp;js=no" width="1" height="1" alt=""/> </div> </noscript> <!-- End of Yahoo! Web Analytics Code --> <script type="text/javascript"> Darwin.Tracking.trackStats('query'); </script> <!-- Start Quantcast Delivery Tag --> <script type="text/javascript"> _qoptions={ qacct:"p-fePJXh17dNmkk" }; </script> <script type="text/javascript" src="https://web.archive.org/web/20110426170437js_/http://pixel.quantserve.com/seg/p-fePJXh17dNmkk.js"></script> <!-- End Quantcast Delivery Tag --> <!-- Start Quantcast Measurement Tag --> <script type="text/javascript"> var channel = ""; _qoptions={ qacct:"p-fePJXh17dNmkk", labels:channel }; </script> <script type="text/javascript" src="https://web.archive.org/web/20110426170437js_/http://edge.quantserve.com/quant.js"></script> <noscript> <img src="https://web.archive.org/web/20110426170437im_/http://pixel.quantserve.com/pixel/p-fePJXh17dNmkk.gif" style="display: none;" border="0" height="1" width="1" alt="Quantcast"/> </noscript> <!-- End Quantcast Measurement Tag --> <!-- siteapp20 --> </body> </html> <!-- FILE ARCHIVED ON 17:04:37 Apr 26, 2011 AND RETRIEVED FROM THE INTERNET ARCHIVE ON 06:51:44 Nov 27, 2024. JAVASCRIPT APPENDED BY WAYBACK MACHINE, COPYRIGHT INTERNET ARCHIVE. ALL OTHER CONTENT MAY ALSO BE PROTECTED BY COPYRIGHT (17 U.S.C. SECTION 108(a)(3)). --> <!-- playback timings (ms): captures_list: 0.583 exclusion.robots: 0.025 exclusion.robots.policy: 0.015 esindex: 0.01 cdx.remote: 21.147 LoadShardBlock: 280.17 (3) PetaboxLoader3.resolve: 200.721 (3) PetaboxLoader3.datanode: 221.103 (4) load_resource: 154.048 -->

Pages: 1 2 3 4 5 6 7 8 9 10