function showAdd() {
	new Effect.Appear('overlay', { duration: overlayDuration, from: 0.0, to: 0.5});
	new Effect.Appear('advert', { duration: overlayDuration * 2.0 , from: 0.0, to: 1.0});
}

function hideAdd() {
	new Effect.Fade('advert', { duration: overlayDuration});
	new Effect.Fade('overlay', { duration: overlayDuration});
}