In answer to your letter of the 2nd inst. [instant], (which I return to you for convenience of reference), I cannot find any published description of the instruments you inquire about, but I have inquired of one or two Fellows and have now the pleasure to send an answer by Prof. Silvanus Thompson, which appears to be fairly satisfactory. In case you should care to correspond with the people whom he mentions, I subjoin thir addresses: -
R. H. Scott, Esq., F.R.S. [Fellow of the Royal Society], Meteorological Office, 63 Victoria Street, S.W.
Chas. [Charles] Tomlinson, Esq., F.R.S., 7 North Road, Highgate, N.
I am, yours truly,
Asst. Sec. R.S. [Assistant Secretary, Royal Society]'.