or 300 deg.
F. under solar radiation, however long continued.
It must, in fact, be considered at present extremely doubtful whether
any portion of the moon's surface ever reaches a temperature as high
as -100 deg..
The subject, undoubtedly, needs further investigation, and it is now
receiving it. Professor Langley is at work upon it with new and
specially constructed apparatus, including a "bolometer" so sensitive
that, whereas previous experimenters have thought themselves fortunate
if they could get deflections of ten or twelve galvanometric divisions
to work with, he easily obtains three or four hundred. We have no time
or space here to describe Professor Langley's "bolometer;" it must
suffice to say that it seems to stand to the thermopile much as that
does to the thermometer. There is good reason to believe that its
inventor will be able to advance our knowledge of the subject by a
long and important step; and it is no breach of confidence to add that
so far, although the research is not near completion yet, everything
seems to confirm the belief that the radiated heat of the moon,
instead of forming the principal part of the heat we get from her, is
relatively almost insignificant, and that the lunar surface now never
experiences a _thaw_ under any circumstances.
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