As we were walking home next day, M'Allister suddenly tripped over some little projection and fell prone to the ground. John ran to his assistance and raised him up, at the same time asking "If he were hurt?"
"No, not at all," said M'Allister; "I seemed to fall so lightly that I scarcely felt it when I touched the ground."
"Ah, M'Allister!" I exclaimed, "if you had fallen like that upon our earth, I think you would not have come off quite scatheless. You see, upon Mars the gravitation is much less than on the earth, being only three-eighths of what it is there, so one does not fall so swiftly, nor so heavily, as on the earth.
"You can prove that very easily. Just take up a stone and hold it out higher than your head, and let it fall; at the same time note, by the second hand of your watch, how long it takes for the stone to reach the ground."
He did so, and said that "As near as he could tell, the stone was just about one second of time in passing from his hand to the ground."
"Just so," I replied. "On Mars a falling body only moves through a space of about six feet in the first second of time. On the earth, however, the gravitation is so much greater that a falling body passes through a space of a little over sixteen feet during the first second.
"In addition to that, although you weighed twelve stones when on the earth, you only weigh about four and a half stones here upon Mars. Now you can understand why it was you seemed to fall so lightly."
"Yes, Professor," he replied, "and I'm glad I fell here, and not upon the earth!"
Then, picking up the stone again and throwing it high in the air, he watched its fall, and turning to me, remarked, "Professor, you were quite right; that stone seemed to be quite a long time coming down again, much longer than it would have been on our own world."
"Well, M'Allister," I replied, "now you know for certain that upon a small planet gravitation really is much less than upon a larger planet of the same kind.