Whats the porpuse of i = 1; on this function?

JavaScript
1 
var image = ['a','b', 'c', 'd','e'];

var i = image.length;

function nextImage(){
    	if (i<image.length) {
    		i= i+1;
    	}else{
    		i = 1;
    	}
    	  slider_content.innerHTML = "<img src="+image[i-1]+".jpg>";
    }