gorous and enterprising life upon Mars."

We then started upon our return home, and on the way I drew M'Allister's
attention to the smaller size of the sun as we saw it now as compared
with the size it appeared to us when on the earth. I told him that Mars
was then about 131,000,000 miles from the sun, so the sun's apparent
diameter was only about 22-1/4 minutes.

On the earth that day the sun's apparent diameter would be about 32
minutes. So to the Martians the sun only appeared about two-thirds the
size it appeared to the people on the earth.

When, on 13th August this year, Mars was at its "perihelion," or nearest
point to the sun, the latter was 129,500,000 miles distant, and would
appear rather more than 22-1/2 minutes in diameter.

At the opposite point of its orbit, where it will be in "aphelion," or
farthest from the sun, the sun will only appear about 19 minutes in
diameter.

I then explained that, although the sun is so distant, Mars receives a
very much larger percentage of the total heat and light available than
we do on the earth, because of the thinness and generally cloudless
condition of the atmosphere. It is estimated that our atmosphere and
clouds shut out nearly 50 per cent. of the light and heat which would
otherwise reach us in the course of the year. On the other hand, their
"blanketing" effect considerably lessens the amount of heat radiated
into space; thus, by keeping in the heat we have received, compensating
to some extent for the original loss in quantity.

But, owing to its thin clear atmosphere, Mars receives nearly 99 per
cent. of the total amount of heat and light proceeding to it from the
sun; so that, although the sun is more distant from the planet, the
warmth on Mars does not compare so unfavourably with the warmth on the
earth as many have imagined it to do.

M'Allister replied that "He had expected to find it very cold indeed
upon Mars in consequence of its distance from the sun, but was surprised
to find it so warm," and added, "what you have now told me, Professor,
explains why this is so, and I can only say that at present I find the
climate a delightful one--pleasantly warm, yet bracing and invigorating.
Even in the tropical regions, although it is hot, it is not the
oppressive and enervating heat that I have experienced in the tropics on
our own world."

He then remarked that "He knew the planets all moved through space and
had read that some of the stars did too, and