Add a jQuery UI library to a Drupal 7 site via template.php

template.php

/**
 * Preprocess variables for html.tpl.php
 */
function themename_preprocess_html(&$variables) {
  drupal_add_library('system', 'ui.slider');	
}

Usage

Usage
-----
Place the 'themename_preprocess_html()' function in your theme's template.php file.

Rename 'themename' to your theme's actual name,
e.g. for 'bartik' the function name would be changed to 'bartik_preprocess_html'.

Change 'ui.slider' to whichever jQuery UI library you want to add.
In Drupal 7, jQuery UI library files are stored in '/misc/ui'.
See: http://api.drupal.org/api/drupal/includes--common.inc/function/drupal_add_library/7 for reference.