Infinite Loop Through Images?

I am trying to do the following: I have written a simple programm that loops through an array of images when the user clicks a button. I have used a for loop to do this. The program works fine, however when I get to the end of the array, the condition created in the for loop is "true" therefore the button no longer changes the image. How do I start the loop again to create an infinite loop (i.e. every time the button is clicked, the image will change)?The script I have written is as follows:

var mySpheres=new Array("sphere.gif","sphere2.gif");
function changeSphere(){
mySphere=document.getElementById("sphere");[code]....