Use the .width()
function to get the browser's width, and only execute the code if it exceeds 960:
$(document).ready(function() {
$(window).scroll(function() {
if($(window).width() > 960) {
$('.hidden').each( function(i){
var bottom_of_object = $(this).position().top + $(this).outerHeight() / 4;
var bottom_of_window = $(window).scrollTop() + $(window).height();
if( bottom_of_window > bottom_of_object ){
$(this).animate({'opacity':'1'},500);
}
});
}
});
});