PHP Include Does Not Work Well
===

I'm working with two files - a.php which contains the class Background, and b.php which includes a.php .
*In a.php , out of the class scope , there's a echo statement " background check" .

When I load b.php  , I can see the output "background check" , but when I try to create a background object the next warning message appears : 

    Fatal error: Class 'Background' not found in ....

Here's a code sample from b.php :

    <?php
    		include ('http://localhost/wT/sf/a.php');
    		$url2="http://www.google.com";
    		$b = new Background($url2);
    ?>

Any suggestion would be helpful , 
Thanks 