es in little more than 12 hours.[10] In the high desert
plains of Central Asia the extremes are said to be even greater.[11]
Again, in his _Universal Geography_, Reclus states that in the Armenian
Highlands the thermometer oscillates between 13 deg. F. and 112 deg.F. We may
therefore, without any fear of exaggeration, take it as proved that a
fall of 100 deg. F. in twelve or fifteen hours not infrequently occurs where
there is a very dry and clear atmosphere permitting continuous
insolation by day and rapid radiation by night.

[Footnote 10: Keith Johnston's 'Africa' in _Stanford's Compendium._]

[Footnote 11: _Chambers's Encyclopaedia_, Art. 'Deserts.']

Now, as it is admitted that our dense atmosphere, however dry and clear,
absorbs and reflects some considerable portion of the solar heat, we
shall certainly underestimate the radiation from the moon's surface
during its long night if we take as the basis of our calculation a
lowering of temperature amounting to 100 deg. F. during twelve hours, as not
unfrequently occurs with us. Using these data--with Stefan's law of
decrease of radiation as the 4th power of the temperature--a
mathematical friend finds that the temperature of the moon's surface
would be reduced during the lunar night to nearly 200 deg. F. absolute
(equal to-258 deg. F.).

_More Rapid Loss of Heat by the Moon._

Although such a calculation as the above may afford us a good
approximation to the rate of loss of heat by Mars with its very scanty
atmosphere, we have now good evidence that in the case of the moon the
loss is much more rapid. Two independent workers have investigated this
subject with very accordant results--Dr. Boeddicker, with Lord Rosse's
3-foot reflector and a Thermopile to measure the heat, and Mr. Frank
Very, with a glass reflector of 12 inches diameter and the Bolometer
invented by Mr. Langley. The very striking and unexpected fact in which
these observers agree is the sudden disappearance of much of the
stored-up heat during the comparatively short duration of a total
eclipse of the moon--less than two hours of complete darkness, and about
twice that period of partial obscuration.

Dr. Boeddicker was unable to detect any appreciable heat at the period
of greatest obscuration; but, owing to the extreme sensitiveness of the
Bolometer, Mr. Very ascertained that those parts of the surface which
had been longest in the shadow still emitted heat "to the amount of one
per cent. of the