Letter from Alexander Graham Bell to Samuel P. Langley, January 28, 1901
January 28, 1901.
Dear Prof. Langley: —
Look at Nature, for December 20, 1900, Vol. 63, p. 180. There is a very suggestive letter there from W. J. Knight, entitled “Can Spectroscopic Analysis Furnish us with Precise Information as to the Petrography of the Moon”.
The absorption of radiant energy by “limestone, basalt, &c.” would probably affect the infra-red portion of the spectrum much more than the visible part, and hence it is probable that the effects could be most easily detected by the bolometer.
It has occurred to me that here is a most excellent field of research for your astro-physical observatory. The bolometer is the instrument, and you are the man to discover and make known absorption bands in the infra-red characteristic of various substances at normal temperatures. Then, by applying the knowledge thus gained and examining the infra-red spectrum of sun-light reflected from various parts of the surface of the moon — why might you not hope to give us information concerning the nature of the materials composing the surface of the moon.
Here is a great field of research that belongs to you — and so far as I can see, to you alone.