by Dr Thomas Young 439 



7. Report of the Committee appointed to consider of the best Method of adjusting 

 Thermometers. (Phil. Trans. 1777, p. 816.) This paper is signed by Mr Cavendish 

 and six other members, but it is principally a continuation of the preceding. 

 It contains very accurate rules for the determination of the boiling point, and 

 tables for the correction of unavoidable deviations from them: establishing 

 29-8 inches as the proper height of the barometer for making the experiment, 

 if only steam be employed, and 29-5 if the ball be dipped in the water; but 

 with all precautions, occasional variations of half a degree were found in the 

 results. 



8. An Account of a New Eudiometer. (Phil. Trans. 1783, p. 106.) Mr Cavendish 

 was aware of the great difference in the results of eudiometrical experiments 

 with nitrous gas, or nitric oxyd, according to the different modes of mixing the 

 elastic fluids; and he justly attributes them to the different degrees of oxy- 

 genization of the acid that is formed. But he found that when the method 

 employed was the same, the results were perfectly uniform; and he ascertained 

 in this manner that there was no sensible difference in the constituent parts of 

 the atmosphere under circumstances the most dissimilar: the air of London, 

 with all its fires burning in the winter, appearing equally pure with the freshest 

 breezes of the country. He also observed the utility of the sulphurets of potass 

 and of iron for procuring phlogisticated air; but he does not seem to have 

 employed them as tests of the quantity of this gas contained in a given mixture. 



9. Observations on Mr Hutchins's Experiments for determining the degree of 

 Cold at which Quicksilver freezes. (Phil. Trans. 1783, p. 303.) In experiments 

 of this kind, many precautions are necessary, principally on account of the 

 contraction of the metal at the time of its congelation, which was found to 

 amount to about ^ of its bulk; and the results which had been obtained were 

 also found to require some corrections for the errors of the scales, which reduce 

 the degree of cold observed to 39 below the zero of Fahrenheit, or 71 below 

 the freezing point, answering to 39-4 of the centesimal scale. In speaking 

 of the evolution of heat during congelation, he calls it "generated" by the sub- 

 stances, and observes, in a note, that Dr Black's hypothesis of capacities 

 depends "on the supposition that the heat of bodies is owing to their containing 

 more or less of a substance called the matter of heat; and as" he thinks "Sir 

 Isaac Newton's opinion, that heat consists in the internal motion of the particles 

 of bodies, much the most probable," he chooses "to use the expression heat is 

 generated," in order to avoid the appearance of adopting the more modern 

 hypothesis; and this persuasion, of the non-existence of elementary heat, he 

 repeats in his next paper*. It is remarkable that one of the first of Sir Humphry 

 Davy's objects, at the very beginning of his singularly brilliant career of refined 

 investigation and fortunate discovery, was the confirmation of this almost 

 forgotten opinion of Mr Cavendish; and for this purpose he devised the very 

 ingenious experiment of melting two pieces of ice by their mutual friction in 

 a room below the freezing temperature, which is certainly incompatible with 



* [See the account of Cavendish's dynamical manuscripts, at the end of the second 

 volume of this edition.] 



