Проблема setInterval в классе.

[Dr.XxX]

class Timer {
	private var onEnterFrame:Function;
	public static var nTimer:Number = null;
	public static var nInterval:Number = null;
	public static function init() {
		nTimer = 20;
		trace(nTimer);
		nInterval=setInterval(this, "onTimer", 100);
	}
	public function onTimer() {
		trace(nTimer);
		nTimer--;
	}
}

Выдаёт ошибку Line 8: 'this' is not accessible from this scope. nInterval=setInterval(this, "onTimer", 100);
Почему ?