But what about the direction of the other spokes of the wheel? With them the plumb line will not help us. We must get a straight stick, say the handle of the stable broom. If we hold this along the direction of either of the spokes, nearest to the center one, we shall find that when the handle touches the ground, it will be at a point further off from the hub, and not at a right angle to the ground but at an acute angle. If we try the same experiment with the next spoke, we may need a longer stick, for the point where it reaches the ground will be still further from the hub, and the angle of direction will be still more acute. If we follow on to the next spoke, we shall probably find that its direction, when extended, does not reach the ground. It points above it. Perhaps it hits the barn wall; and then again comes the question: does it hit the wall at a right angle or at an acute angle? The answer to this, if you think a moment, will depend upon the position, not only of the spoke, but also of the wall. For example, the spoke may point directly at the wall, so that when you stand at the corner of the barn and run your eye along the wall, the spoke will make a right angle with the wall’s vertical direction. But the wall has another direction--a horizontal one; and this may slope away from the direction of the spoke, so that if you stand in front of the wall, your stick makes with it an acute angle. Evidently under some circumstances a single direction may make with the surface of the wall both an acute and a right angle.