var balloon = $('div.balloon'),
		x = 0,
		y = 0,
		dir = 1,	// direction
		alt = 1		// altitude

	function animate_balloon(){
		// increment x axis
		x = x + (1 * dir);

		// increment y axis
		y = y + (1 * alt);

		balloon.css({
			'margin-top' : y + 'px',
			'margin-left' : x + 'px'
		});

		if(x == 10){
			dir = -1;
		} else if(x == 0){
			dir = 1;
		}

		if(y == 15){
			alt = -1;
		} else if(y == 0){
			alt = 1;
		}

		setTimeout(animate_balloon, 250);
	}

	animate_balloon();