function preLoad() {
    s1 = new Image()
    s1.src = "images/nav1on.png"
    s2 = new Image()
    s2.src = "images/nav2on.png"
    s3 = new Image()
    s3.src = "images/nav3on.png"
    s4 = new Image()
    s4.src = "images/nav4on.png"
    s5 = new Image()
    s5.src = "images/nav5on.png"
    s6 = new Image()
    s6.src = "images/nav6on.png"
    s7 = new Image()
    s7.src = "images/nav7on.png"
}