28 CAVENDISH. 



laid aside Chemistry for other departments of physics. In 1771 he 

 published an elaborate paper on the theory of the principal phe- 

 nomena of electricity ; and in 1776 appeared the curious and inter- 

 esting account of his attempts to imitate the effects of the torpedo, 

 by an apparatus constructed in imitation of the living fish, and 

 placed in connection with a frictional electrical machine and a 

 Leyden battery. In this imitation he succeeded so well, that all 

 doubts were removed as to the identity of the torpedinal benumb- 

 ing power with common electricity. In 177(3 Cavendish was se- 

 lected by the Royal Society, in whose ' Transactions' all his previous 

 papers had been published, to describe the various meteorological 

 instruments which were made use of in their apartments ; and the 

 succeeding year to this marks the period when he commenced his 

 most important chemical researches, entitled ' Experiments on Air,' 

 which were carried on with frequent and sometimes long interrup- 

 tions until 1788, no part of them, however, having been published 

 before the year 1783. They led to the discovery of the constant 

 quantitative composition of the atmosphere, the compound nature 

 of water, and the composition of nitrio acid. To solve the impor- 

 tant problems, whether the atmosphere is constant in its composi- 

 tion, and if so, what is its composition? Cavendish experimented 

 in 1781 for some sixty successive days, making many hundred 

 analyses of air. The honour of the discovery of the compound 

 nature of water, by which perhaps his name has become most 

 famous, is also claimed by James Watt. Cavendish, however, seems 

 at all events entitled to the honour of having first supplied the 

 data on which that discovery was founded, whilst Watt appears to 

 have supplied the conclusion. 



Between the years 1783 and 1788, Cavendish published his papers 

 on ' Heat,' and his ' Experiments on Air ;' the former are three in 

 number, and relate chiefly to the phenomena of congelation, and 

 embody some of the results of experiments made as early as the 

 year 1764. The first of these papers refer to quicksilver, demon- 

 strating the true freezing-point of this metal to be 39 or 40 below 

 zero, while the second and third refer to the freezing of the mineral 

 acids and of alcohol. 



His experiments on air, which led to the important results already 

 referred to, supplied materials for four papers, besides leading to 

 the observation of many phenomena which were never made pub- 

 lic. With the last of these papers published in 17H8, Cavendish 

 closed his chemical researches, his remaining publications referring 

 to meteorology and astronomy. 



In 1798 appeared the celebrated enquiry into the density of the 

 earth, communicated by Cavendish, in a paper to the Eoyal Society, 

 in which he determined, by means of an apparatus contrived by the 

 Kev. John Mitchell, the density of our globe to be 5'4, or, in other 

 words, nearly five-and-a-half times heavier than the same bulk of 



