explanations; for none of the physical laws with which I am familiar explains how a man can lose his weight at the very surface of the earth. I suppose, though, that you have found some obscure little law, known only to scientists, which will account for your strange assumption."
"Not a bit of it, James. The law I refer to is one of which you see examples every day, and which is quite a familiar one. Have you ever seen a man riding on a street-car?"
"Well, rather! I see hundreds of them every day," replied Mr. Curtis. "But what connection is there between a man on a street-car and a man falling through the earth?"
"There is a closer connection than you would be ready to believe. Now, let us suppose that the street-car is traveling at the rate of ten miles per hour; do you know how fast the passenger himself is traveling?"
"Why, he must be traveling at the same rate—ten miles per hour, also."
"Quite true. So long as the man does n't walk toward the front or rear of the car he is necessarily traveling at the same rate as the car. Well, now, if, as you say, the man is traveling at just the same speed as the car, no matter how long he
