$(document).ready(
    function externalLinks() {   
        if (!document.getElementsByTagName) return;   
            var anchors = document.getElementsByTagName("a");   
            for (var i=0; i<anchors.length; i++) {   
				var anchor = anchors[i];   
				if (anchor.getAttribute("href") && anchor.getAttribute("rel") == "external") anchor.target = "_blank";   
    		}
});