$(document).scroll(function() {
 
var pos = $(window).scrollTop();
var wheight = $(window).height();
var fold = wheight + pos;
 
var offset = $("#art1").offset();
 
if(offset.top <= fold) {
 
 
          var _x = '0 '
                  
          var bpos = _x + -(pos/7) + 'px';
          
                   $('#art1').css({'backgroundPosition':bpos})
                   
               }
               
               
var offset2 = $("#art2").offset();
 
if(offset2.top <= fold) {
 
 
          var _x2 = '0 '
                  
          var bpos2 = _x2 + -(pos)/10 + 'px';
          
                   $('#art2').css({'backgroundPosition':bpos2})
                   
               }
               
 
               
               var offset3 = $("#art3").offset();
 
if(offset3.top <= fold) {
 
 
          var _x3 = '50% '
                  
          var bpos3 = _x3 + -(pos)/14.5 + 'px';
      
                   $('#art3').css({'backgroundPosition':bpos3})
                   
               }
 
               var offset4 = $("#art4").offset();
 
if(offset4.top <= fold) {
 
 
          var _x4 = '50% '
                  
          var bpos4 = _x4 + -(pos)/18 + 'px';
      
                   $('#art4').css({'backgroundPosition':bpos4})
                   
               }
 
});