if (document.images) 
{
   img1 = new Image();
   img2 = new Image();
   img3 = new Image();
   img4 = new Image();
   img5 = new Image();
   img6 = new Image();
   img7 = new Image();
   img8 = new Image();
   img9 = new Image();
   img10 = new Image();
   img11 = new Image();
   img12 = new Image();
   img13 = new Image();
   img1.src = "images/nav_r2_c3_f2.jpg";
   img2.src = "images/nav_r2_c5_f2.jpg";
   img3.src = "images/nav_r2_c8_f2.jpg";
   img4.src = "images/nav_r2_c10_f2.jpg";
   img5.src = "images/nav_r2_c12_f2.jpg";
   img6.src = "images/nav_r2_c14_f2.jpg";
   img7.src = "images/nav_r2_c15_f2.jpg";
   img8.src = "images/nav_r2_c17_f2.jpg";
   img9.src = "images/navBase_r1_c3_f2.jpg";
   img10.src = "images/navBase_r1_c8_f2.jpg";
   img11.src = "images/navBase_r1_c12_f2.jpg";
   img12.src = "images/navBase_r1_c17_f2.jpg";
   img13.src = "images/navBase_r1_c20_f2.jpg";
}