F., while during the night it falls nearly or quite to the freezing point--a difference of 118 degrees 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.