To add the external js file there is no native function in magento. But you can add the js file through layout by following code

<reference name="head">
 
    <block type="core/text" name="unique-name">
 
        <action method="setText"><text><![CDATA[<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.0/jquery.min.js"></script>]]></text></action>
 
    </block>
 
</reference>

To add the external js file there is no native function in magento. But you can add the js file through layout by following code

<reference name="head">
    <block type="core/text" name="unique-name">
        <action method="setText">
            <text><![CDATA[<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.0/jquery.min.js"></script>]]></text>
        </action>
    </block>
</reference>