image1 = new Image();
image1.src = "images/maps/rainfall.gif"; 
image2 = new Image();
image2.src = "images/maps/sunshine.gif"; 
image3 = new Image();
image3.src = "images/maps/temp_jan.gif"; 
image4 = new Image();
image4.src = "images/maps/temp_july.gif"; 

function change(){
document.image_name.src=eval(document.Myform.Myselect.options[document.Myform.Myselect.options.selectedIndex].value);
}