0 to 40 deg. F.) a few
hours _before_ noon. This, Mr. Very thinks, is due to the fact that the
half of the moon's face first illuminated for us has, on the average, a
darker surface than that of the afternoon, or second quarter, during
which the curve descends not quite so rapidly, the temperature near
sunset being only a little higher than that near sunrise. This rapid
fall while exposed to oblique sunshine is quite in harmony with the
rapid loss of heat during the few hours of darkness during an eclipse,
both showing the prepotency of radiation over insolation on the moon.

Two other diagrams show the distribution of heat at the time of
full-moon, one half of the curve showing the temperatures along the
equator from the edge of the disc to the centre, the other along a
meridian from this centre to the pole. This diagram (here reproduced)
exhibits the quick rise of temperature of the oblique rim of the moon
and the nearly uniform heat of the central half of its surface; the
diminution of heat towards the pole, however, is slower for the first
half and more rapid for the latter portion.

It is an interesting fact that the temperature near the margin of the
full-moon increases towards the centre more rapidly than it does when
the same parts are observed during the early phases of the first
quarter. Mr. Very explains this difference as being due to the fact that
the full-moon to its very edges is fully illuminated, all the shadows of
the ridges and mountains being thrown vertically or obliquely _behind
them._ We thus measure the heat reflected from the _whole_ visible
surface. But at new moon, and somewhat beyond the first quarter, the
deep shadows thrown by the smallest cones and ridges, as well as by the
loftiest mountains, cover a considerable portion of the visible surface,
thus largely reducing the quantity of light and heat reflected or
radiated in our direction. It is only at the full, therefore, that the
maximum temperature of the whole lunar surface can be measured. It must
be considered a proof of the delicacy of the heat-measuring instruments
that this difference in the curves of temperature of the different parts
of the moon's surface and under different conditions is so clearly
shown.

_The Application of the Preceding Results to the Case of Mars._

This somewhat lengthy account of the actual state of the moon's surface
and temperature is of very great importance in our present enquiry,
because it shows u