186. =A Case in Court.=--A dashing young man driving a light phaeton ran against a heavy carriage. His father was induced by his son's representations to prosecute the driver of the carriage for driving too fast. A knowledge of motal inertia very readily decided the case. The son and his servant both declared that the shock of the carriage was so great against the phaeton that they were thrown over the horses' heads. They thus proved themselves guilty of the fast driving, for it was their own rapid motion that threw them out when the phaeton was stopped by running against the carriage. The following case is a parallel one. If two boats, the one of large size sailing slowly up stream, the other a small one sailing rapidly down, run against each other, a man standing in the bow of the one going down will be thrown much farther forward than one standing in the bow of the other. 187. =Course of Bodies Thrown into the Air.=--It results from the principle that I have illustrated that when any body, as a stone, is thrown, as we say, straight upward, it does not, in reality, go up or come down perpendicularly. If it did it would come down at a great distance from us. Suppose it takes two seconds for it to go up and to reach the ground. If we are at the equator, in that two seconds we move from the point where we threw up the stone nearly 3000 feet eastward, and therefore if the stone rose and fell perpendicularly it would fall 3000 feet westward of us. Why, instead of this, does it fall at our feet? Because that when thrown into the air it has not only the upward motion given by the hand, but also the forward motion of the earth. It is a case similar to that of the rider in Fig. 127, the horse representing the surface of the earth and the rider the stone. For the same reason a man on board of a steamboat, though it move fifteen miles an hour, tosses up his ball or orange and catches it as well as if he were on land. This he could not do if both he and his orange did not have the same forward motion that the boat does. So, also, if a man fall from a mast-head he reaches the deck at the foot of the mast when the vessel is sailing rapidly, just as he would if it were lying still at the wharf. If he did not by inertia retain the forward motion which he had in common with the vessel he would fall at some distance behind the mast.