마우스휠 스크롤 속도 조절

$(window).on('mousewheel', function(e){
	if(e.originalEvent.wheelDelta < 0) {
		//scroll down
		$('html, body').stop().animate({
			scrollTop : '+=250px'
		},500);
	}else {
		//scroll up
		$('html, body').stop().animate({
			scrollTop : '-=250px'
		},500);
	}

	//prevent page fom scrolling
	return false;
});