private HitRecord getHitSpherePt(Vector3D start, Vector3D direction, double tmin,
			double tmax){
		HitRecord record = null;
		double distance = tmax;
		for(Sphere bubble : scene.getBubbleSphList()){
			HitRecord hit = bubble.hitNearestPoint(start, direction, tmin, tmax);
			if(hit != null && hit.getDistance() < distance){
				record = hit;
				distance = hit.getDistance();
			}
		}
		return record;
	}