To Edward Nairne (unpublished)
On his Patent Electrical Machine, and the Effects of Lightning on the Eyes, &c. of Animals killed by it.
Passy, Oct. 18, 1783.
Dear Sir,

I received your favor of August 14, by Mr. Sykes, with the book of directions for using your patent electric machine. The machine itself is also come to hand in good order, after some delay on the road; and I think it very ingeniously contrived indeed: I wish your success in the sale may be equal to its merits. The experiments in your pamphlet gave me pleasure, and I shall be glad to see the account you mention of the shortening of the wires by lightning.

What you have heard of the eyes of sheep forced out by a stroke of lightning which killed them, puts me in mind of having seen at Philadelphia six horses all killed by lightning in a stable, every one of whom appeared to have bled at the eyes, nose, and mouth; though I do not recollect that any of their eyes were out.

You are so good as to consider how much my time has been taken up, and to excuse on that account my being a bad correspondent. Near three years ago I began a letter to you on the subject of hygrometers. I had written three folio pages of it when I was interrupted by some business; and before I had time to finish it I had mislaid it. I have now found it, and having added what I suppose I had intended to add, I enclose it. You can judge better than myself whether my idea of such an instrument is practicable and may be useful.

If you favor me with another line, let me know how Mrs. Nairne does, and your amiable children. With great esteem, &c. I am,

B. Franklin.

[Enclosed in the foregoing.]
Proposal for a Slowly Sensible Hygrometer for Certain Purposes.
Passy, near Paris, Nov. 13. 1780
Sir,
The qualities hitherto sought in an hygrometer, or instrument to discover the degree of moisture and dryness in the air, seems to have been an aptitude to receive humidity readily from a moist air, and to part with it as readily to a dry air. Different substances have been found to possess more or less of this quality; but when we shall have found the substance that has it in the greatest perfection, there will still remain some uncertainty in the conclusions to be drawn from the degree shown by the instrument, arising from the actual state of the instrument itself as to heat and cold. Thus if two bottles or vessels of glass or metal being filled, the one with cold, the other with hot water, are brought into a room, the moisture of the air in the
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