if (document.images)
{
  pic1= new Image(900,190); 
  pic1.src="images/main_1.jpg";

  pic2= new Image(900,190); 
  pic2.src="images/main_2.jpg";

  pic3= new Image(900,190); 
  pic3.src="images/main_3.jpg";
  
  pic4= new Image(900,190); 
  pic4.src="images/main_4.jpg";
}