n1 = new Image();
n1.src = "pic/dot1.gif";
h1 = new Image();
h1.src = "pic/dot2.gif";

n2 = new Image();
n2.src = "pic/dstrich1.gif";
h2 = new Image();
h2.src = "pic/dstrich2.gif";

function bw(nr,n)
 {
  window.document.images[nr].src = n.src;
 }