Rosse considered that his results show that the heat from
the moon is mainly _obscure, radiated_ heat; the _reflected_ heat,
according to him, being much less in amount.
A moment's thought will show that the moon's heat must consist of two
portions. First, there will be _reflected solar heat_. The amount and
character of this will depend in no way upon the temperature of the
moon's surface, but solely upon its reflecting power. And it is to be
noted that moon-_light_ is only a part of this reflected radiant
energy, differing from the invisible portion of the same merely in
having such a wave-length and vibration period as to bring it within
the range of perception of the human eye.
The second portion of the heat sent us by the moon is that which she
emits on her own account as a warm body--warmed, of course, mainly, if
not entirely, by the action of the sun. The amount of _this_ heat will
depend upon the temperature of the moon's surface and its radiating
power; and the temperature will depend upon a number of things
(chiefly heat-absorbing power of the surface, and the nature and
density of the lunar atmosphere, as well as the supply of heat
received from the sun), being determined by a balance between give and
take.
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