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.

"That's another little wrinkle for you, and you have found it all out
through tripping over a stone!"

"Losh, mon," replied he, "I seem to have learnt something almost every
day since I have been here; even a tumble down teaches me something!"

I then drew his attention to the birds flying near us, and pointed out
that they had a much wider spread of wing than our birds have, and that
this was owing to the fact that the air being so thin a wide spread of
wing was absolutely necessary to support them in the air and enable them
to fly. I further explained that, if the gravitation upon Mars were as
great as upon the earth, the birds' wings must necessarily have been
still larger, as the pull of the planet would have been so much the
greater, and would thus have prevented the birds from flying at all in
such thin air if their wings had been small.

"M'Allister," I then remarked, "you will, no doubt, have noticed the
same thing with regard to those large and beautiful bu