Load external javascript files

You should always use wp_enqueue_script() only, so other scripts can rely on yours or bundle all scripts in one file.

Do not load another jQuery; WordPress comes with a built-in jQuery, and other plugins and the core depend on exactly that version.

wp_enqueue_script() accepts any valid URL as source file, external or internal. If something doesn’t work check your browser’s error console. Note you have to use jQuery, not $ in your scripts to access the global jQuery object.