Saturday Morning 7.A.M.
My dear Mrs Pollock,
Welcome home! When your kind husband2 called to see me yesterday I had some hope of being able to speak my welcome last night instead of writing it now. But I was thus employed:—
The moon was bright and I returned swiftly from St. John’s Wood3 to the Institution. My men were gone; but I could not afford to lose the chance of observing the moon’s radiation. I have a platform on the house top over seventy feet above the floor of the laboratory. I ascended to this platform fifteen times from the laboratory—now seventy multiplied by fifteen makes a height of one thousand and fifty feet! This I climbed last night between 8.15 and 10.30 o'clock.
The result opposed all my notions and ought to make me humble. I have often ridiculed the idea of the moon’s beams being cold; but last night the result was exactly equivalent to this. My face was colder when I looked at the moon than when I looked upwards at the same inclination towards any other part of the heavens. Of course in such a case I did not trust my sensations—indeed they could tell me nothing, but I have hard figures for the result which is quite certain.
Now ask your husband to account for this; and do not mention it to any body else. I am almost certain that you will puzzle him.
Yours always | John Tyndall.
RI MS JT/1/TYP/6/2218
Please cite as “Tyndall1814,” in Ɛpsilon: The John Tyndall Collection accessed on