Missing $GLOBALS SCRIPT_URI

I am writing some php code that requires the $GLOBALS['SCRIPT_URI'] variable. When I access the code under its encrypted (https) location it is available without issue. However, when I try to access the code under its unencrypted (http) location it is not available. In fact, phpinfo() shows that there are a lot less $GLOBALS available under the http location than there are under the https location. I am using Apache 1.39 with Php 4.2.3. Your comments are greatly appreciated. Respectfully, Gary