Jquery :: Grouping Existing Top Level Functions Inside Closure

I'm trying to group some existing top-level functions inside a closure (to avoid polluting the global namespace) but I'm not quite getting it to work. First, all the JS works outside my anonymous function, but once I put it in the anonymous function I get an error of "crossfade is not defined". I'm not quite getting why the the setInterval/crossfade works outside the anonymous function but not inside. Anything inside start() should be able to see vars/functions outside start() and it should all be protected in the closure created by the top-level anonymous function? I'm not trying to access anything *within* crossfade(), I'm just trying to execute it.

Code:
(function($) {
//vars up here that internal functions can access
//also using some jquery inside here, so using $
function crossfade() {
//body here
}
//other functions
function start() {
//body here
cInterval = setInterval('crossfade()', 5000);
}
})(jQuery);