31 Sackville St <1>
You were enquiring about portable instruments and contrivances, there is one which I will mention that I found very useful; it was intended to supply the place of a stand for a large Achromatic Telescope which I took with me to Italy more for stargazing in a fine climate than for making astronomical observations; The Telescope is a 5 ½ feet achromatic with a 4 ½ inch object glass, consequently belongs to
the a class of instruments which few would reckon portable.
The stand being excessively ponderous, was of necessity left at home; & the London opticians assured me it was impossible to supply its place; but as I was unwilling to abandon my intentions I adopted the following plan which succeeded perfectly: a brass bar was made which lengthened
and or shortened itself by means of a screw, of 3 feet length, and carrying a sliding socket. The bar being placed horizontally in any window, was then screwed longer, until its ends pressed against the sides of the window frame, when a few turns more made it as immoveable as a rock. The telescope tube carried a ball, which was placed in the socket on the bar, and suspended it in equilibrio, making its management a thing of perfect facility – The apparatus was put up anywhere in five minutes or less. My bar was made unnecessarily strong; I think it would almost have borne a piece of Ordnance. This contrivance on a much smaller scale; or even quite slightly made, I recommend as a stand for any species of instrument; resting on the walls of the house it is unaffected by the tremors of the floor, & will even sustain a violent accidental shock, without injury to the instrument it supports –
Believe me Dear Sir, with many thanks for your kindness in shewing us your machine <2>
Yours most truly
H. F. Talbot
C. Babbage Esq –
5 Devonshire Street <3>
1. 31 Sackville Street, London residence of the Feildings, often used as a London base by WHFT.
2. That is, the calculating engine.