var cl = document.getElementById('column_left');  
var clh = cl.offsetHeight; 
var cr = document.getElementById('column_right');  
var crh = cr.offsetHeight; 
if(crh<750){crh=750;}



var spacerspot = document.getElementById('spacer');
var spacer =(crh-clh)+22;
document.getElementById('spacer').style.height = spacer+'px';