wp_enqueue_script appearing not to work

Dear All,

I’m trying to include some JavaScript in the header of my plugins admin page. Any idea on why this deson’t work:

wp_enqueue_script('my-plugin-1', '/wp-content/plugins/my-plugin/javascript1.js', array('jquery'));
wp_enqueue_script('my-plugin-2', '/wp-content/plugins/my-plugin/javascript2', array('my-plugin-1'));

When this does?

wp_register_script('my-plugin-1', '/wp-content/plugins/my-plugin/javascript1.js', array('jquery'));
wp_register_script('my-plugin-2', '/wp-content/plugins/my-plugin/javascript2', array('my-plugin-1'));
wp_print_scripts('my-plugin-2');