Trouble Retrieving Window Location From A Previously Opened Window ?

I am trying to open up a new window and then get the current url/location
back from the (win_1) window and display the url in an alert box.

Here is the code I am using :-

<script type="text/javascript">
var mywin_1 = open ("http://www.anysite.com/index.htm", "win_1",
"height=640, width=820, left=200, top=0, scrollbars, status, location");
var temp = mywin_1.location;
alert (temp);
</script>

Where am I going wrong?