I have two websites: mysite1.com and mysite2.com

On mysite1.com I store all my articles in the "library" folder as .php files (they contain nothing but the actual article content - no headers, footers, other includes, etc.). To call those articles on mysite1.com I use a "title" folder to store another .php file that contains the formatting (header, footer, other includes, etc.). Everything works just fine on mysite1.com.

Now, I want to use some of those articles on mysite2.com without having to create another article file. Unfortunately, the code returns an error for line 11, which is the call to the external .php file:
<?php include("http://www.mysite1.com/library/thearticleiwant.php"); ?>
No such file or directory in /home2/myserver/public_html/mysite2/library/titles/thearticletitle.php on line 11
What this tells me is, the code is looking inside mysite2.com for the include, not at mysite1.com. (NOTE - I also tried using "require_once" with a similar result.) Is it possible to call an external .php file?