46 



the liquors in them were weighd, & also the bottles which the liquors were 

 poured out of; by which means the quantity of liquor was known, & also 

 the weight of the snow ; the result is on the other side the leaf : the small 

 bottles were not tried." 



This entry stands in his note book subsequent to all the entries of experi- 

 ments on the heat of mixtures of "hot & cold water" — "hot water & quick- 

 silver" — " hot quicksilver & cold water"-—" hot quicksilver & cold quick- 

 silver" — "hot water & oil" — "hot quicksilver & cold spts" — "hot spts & 

 cold spts" — " hot spts & cold quicksilver" — " hot quicksilver & solut. pearl 

 ashes" — " hot quicksilver & oil vitr." — "silver sand, iron filings, lead shot, 

 powdered glass, powdered marble, tin shot, powdered charcoal, Newcastle 

 coal, brimstone, tried in tin bott. in hot water" — " cold spermaceti in warm 

 water" — " concerning heat & cold produced by hardening & melting of sper- 

 maceti" — " expts on time of evaporation of boiling water" — " exper. concern- 

 ing the cooling of water in worm-tub, by blowing air through pipe, & con- 

 cerning the heating of it by distillation"; — with the following result of the 

 latter experiments. — " Therefore heat gen. by condens. vapours = 942°." — 

 MSS. p. 71. 



At what date Black and Watt arrived at a similar result I know not. Nor 

 do I know the precise year in which Black first taught the doctrine of specific 

 heat. Dr. Thomson says, " That the specific caloric of bodies is difi'erent, was 

 first pointed out by Dr. Black in his lectures at Glasgow between 1760 & 

 1765. Dr. Irvine afterwards investigated the subject between 1765 and 1770 

 (Black's Lectures, i. 504), and Dr. Crawford published a great number of experi- 

 ments on it in his Treatise on Heat (1779), but Professor Wilcke, who pub- 

 lished the first set of experiments on the subject (Stockholm Transactions, 

 1781), introduced the term specific caloric." " I have been informed", he adds, 

 " by the late Professor Robison, that Wilcke's information was got from a 

 Swedish gentleman, who attended Dr. Black's lectures, about 1770." It ap- 

 pears probable, from what I have stated, that this unpublished series of experi- 

 ments by Cavendish is the first made upon this subject. After these, and im- 

 mediately preceding those of the date Feb. 1765, is Cavendish's determination 

 of the number of degrees of "cold gen. by thawing ice or snow," which he 

 found on an average to be 150°. In the account which Black gives, in his 

 Lectures, of his determination of the quantity of heat absorbed in the melting 

 of ice, he says, " these two experiments and the reasoning which accompanies 

 them were read by me in the Philosophical Club or Society of Professors of 

 Glasgow in the year 1762." The following is the only notice which Caven- 

 dish has given of any of his numerous and elaborate experiments on these 

 subjects. In his "Observations on Mr. Hutchins' experiments for deter- 

 mining the degree of cold at which quicksilver freezes" (Phil. Trans. 1783.), 

 he says, 



" The cause of the rise of the thermometer when the water begins to 

 freeze, is the circumstance, now pretty well known to philosophers, that 

 all, or almost all, bodies, by changing from a fluid to a solid state, or from 

 the state of an elastic to that of an unelastic fluid, generate heat ; & that 

 cold is produced by the contrary process. This explains all the circum- 



