From John Frederick William Herschel   Nov. 24/61

Collingwood | Nov. 24/61.

My dear Sir,

What you state¹ about the tenacity of a vapour whose radiation you have succeeded in measuring is truly astonishing. One thing only occurs, (without calling in question either the delicacy or the precision of your means of exploration) & that is by what means it is possible to assure yourself that such is the degree of tenacity of the matter subjected to it—i.e. within 3 or 4 places of figures?

Au reste—as the air at 80 miles is only $\frac{1}{100,000,000}$ of the density at the surface, it would attain your degree of tenacity at only 10 additional miles of altitude and every 10 miles more will add another 0 to the denominator of the fraction. Still that some matter, vapour, or whatever else it may be at 100 or even at a much more considerable elevation, no one who has attended to the phenomena of the Aurora Bor. can doubt—but as to its having density enough to scatter the Sun’s light and form the Corona about the moon in an eclipse, I should be disposed to demur.

If you are satisfied that, in turning your explorator off the moon, on all sides, round its center, so as exactly to exclude the moon from its field of View, and no more, indications of greater inward radiation or increased warmth are unequivocally manifested, I can no how see how it can be accounted for by the cause you assign—or in any other way than from radiation from extra-lunar space or starry matter capable of penetrating the upper strata of our air, while the radiation from the moon is stopped by the upper air & that of the space behind the moon, in that direction, by the body of the moon—.

Be that as it may however it is evident that you are opening up a highly interesting chapter in the book of Thermotics—and will I doubt not prosecute it with effect.

Believe me | Dear Sir | Yours very truly | JFW Herschel

RI MS JT/1/H/97