firstChild is undefined

firstChild is undefined

jQuery: jquery-1.9.1.min.js
IE: 9
Visual Studio 2010
 
I'm starting out with jQuery and am walking through a book's example but am having problems with firstChild being undefined.  Here's the code:
 
SiteMaster:

<%

@ Master Language="C#" AutoEventWireup="true" CodeFile="Site.master.cs" Inherits="SiteMaster" %>

<!

DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<

html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">

<

head runat="server">

<title></title>

<script type="text/javascript" src="Scripts/jquery-1.9.1.min.js"></script>
< link href ="~/Styles/Site.css" rel ="stylesheet" type ="text/css" />
etc..
 
Default.aspx

<%

@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"

CodeFile="Default.aspx.cs" Inherits="_Default" %>

<

asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">

<script type="text/javascript">

$(document).ready(

function () {

$(

"input[id$=join_list]").click(function () {

$(

"email_error").firstChild.nodeValue = "Entry is invalid.";

});

});

</script>

</

asp:Content>

<

asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">

<label for="email_addresss">Email Address:</label>

<input type = "text" id="email_address" />

<span id="email_error">*</span><br />

<label>&nbsp;</label>

<input type="button" id="join_list" value="Join our List" />

</

 

asp : Content >
 
 
I put a break point on the click function and see that $("email_error") is defined but firstChild is not.
 
Why is firstChhild undefined?