2 Introduction 



These calculations relate to the equivalent values of his trial plates 

 when drawn out to different numbers of divisions. There is no date nor 

 any part of the original letter. 



The memoranda of some experiments similar to those in Art. 588, on 

 the time of discharge of electricity through different bodies, are on the 

 back of the usual Notice of the election of the Council and Officers of the 

 Royal Society on the Thirtieth of November, 1774 (being St Andrew's 

 Day) at Ten o'Clock in the Forenoon at the House of the Royal Society 

 in Crane Court, Fleet Street. The address on the back of this letter is 



To 



The Hon Henry Cavendish 



Gr* Marlborough Street. 



Dr Thomas Thomson, who was acquainted with Cavendish, says in 

 his interesting sketch of him*, 



During his father's life-time he was kept in rather narrow circumstances, 

 being allowed an annuity of 500 only, while his apartments were a set of 

 stables, fitted up for his accommodation. It was during this period that he 

 acquired those habits of economy and those singular oddities of character which 

 he exhibited ever after in so striking a manner. 



The whole of the electric researches of which we are to give an account 

 were made before the death of Lord Charles Cavendish, which took place 

 in 1783. We must therefore suppose that they were made in Great Marl- 

 borough Street, and probably in the set of stables mentioned by Dr 

 Thomson. He speaks of a "fore room and a back room" in Art. 469, and 

 in Art. 335 he compares the size of the room in which he worked to that 

 of a sphere 16 feet in diameter. The dimensions of his laboratory are of 

 some importance in determining the electric capacity of bodies hung up 

 in it, and by the foot-note to Art. 335 it would appear that the room was 

 probably 14 feet high, which is somewhat lofty for "a set of stables," 

 but I believe not much more than the height of some of the rooms in the 

 dwelling-houses in Great Marlborough Street. 



Let us then suppose that we have been admitted by Cavendish into 

 his laboratory in Great Marlborough Street, as it was arranged for his 

 electrical experiments in 1773, and let us make the best of an opportunity 

 rarely, if ever, accorded to any scientific man of his own time, and 

 examine the apparatus by which the electric fluid, instead of startling us 

 with the brilliant phenomena, new instances of which were then every 

 day being discovered, was made to submit itself, like everything else 

 which entered that house, to be measured. 



The largest piece of apparatus was the "machine for trying simple 

 bodies" of which we have a description and sketch in Art. 241, and plans 



* History of Chemistry, vol. i. p. 336, quoted in Wilson's Life of Cavendish, p. 159. 



