928 MATHEMATICAL AND PHYSICAL SCIENCE. [Diss. VI. 
make the requisite experiments. So cool a ‘wmnera- 
ment was not likely to grow warmer as age advancvl, 
Almost as indifferent to the honours of discovery as 
his stoical contemporary Cavendish, unlike him he 
enjoyed in a high degree intercourse with the conge- 
nial society which Edinburgh at that time afforded. 
He loved to converse infinitely better than to write; 
especially when he could converse intimately with 
such men as Adam Smith, David Hume, Adam Fer- 
guson, Principal Robertson, Dr John Robison, John 
Home, Clerk of Eldin, and Dr James Hutton, 
(591.) Hurron was perhaps Black’s dearest friend, and 
en may be mentioned here (episodically) as no ordinary 
intimate thinker in Natural Philosophy, as well as in Geology 
friend— and Metaphysics. Besides the “theory of the Earth,” 
his theory which will ever bear his name, and which, after va- 
of rainand . . ° : 
vapour, ious transmutations in name and form, is now by 
far the most widely prevalent, his theory of Rain 
was an ingenious and important speculation. Other 
branches of Meteorology also claimed his attention, 
particularly, as might have been expected, those 
which are connected with the temperature of the 
earth. He was one of the first who drew conclu- 
sions from the temperature of springs, with regard to 
change of climate due either to increased latitude or 
to increased height above the sea. His hygrometer, 
in which the dampness of the air was estimated 
by the coolness due to evaporation, was unquestion- 
ably the first suggestion of a method now in general 
use. His ideas on the constitution of matter were 
bold and ingenious, though not on all points tenable, 
They resembled those of Boscovich, though inde- 
pendent of them. He published a voluminous trea- 
tise on several subjects in Natural Philosophy, and 
a still more formidable one on the Principles of 
Knowledge, neither of which attracted much at- 
tention at the time, and have been long forgotten ; 
yet it is not unlikely that some of his speculations 
in metaphysics might be worth the labour of re- 
examination, His friend and commentator, Playfair, 
(whose style was as remarkable for perspicuity as Dr 
Hutton’s was the contrary) has drawn the following 
lvely contrast between the characters of Hutton and 
Great caution » his reasonings, and a coolness of 
head which even approached to indifference, were 
characteristic of Dr Black. On attending to their 
conversation, and the wa; in which they treated any 
question of science and philosophy, one would say 
that Dr Black dreaded nothag so much as error, 
and that Dr Hutton dreaded nohing so much as ig- 
norance; that the one was always afraid of going 
beyond the truth, and the other oi not reaching it. 
The curiosity of the latter was by much’ he more easily 
awakened, and its impulse most powerfu. and imperi- 
ous. With the former, it was a desire whih he could 
suspend andlay asleep foratime; with the otier, it was _ 
an appetite that might be satisfied for a moment, but 
was soon to be quickly renewed. . . . « Bach 
had something to give which the other was in vant 
of. Dr Black derived great amusement from the jj. 
vacity of his friend, the sallies of his wit, the gloy. 
and original turn of his expression; and that calm- 
ness and serenity of mind which, even in a man of 
genius, may border on languor and monotony, re- 
ceived a pleasing impulse by sympathy with more 
powerful emotions.’’ 
Black died on the 6th December 1799.? His death, 
as recorded by his kinsman, Adam Ferguson,’ was Black’ 
one of the most touching on record. It succeeded his 9***- 
customary state of health by an interval inappre- 
ciably short, and, as appeared by the accompanying 
circumstances, without the slightest physical emotion, 
The philosophic composure of his whole life was mir- 
rored in the serenity of its close, 
§ 2. CavenpisH.4—His Singular Character and Attainments—Eminent Chemical Discoveries— 
Observations on Heat and on other Branches of Physics—LavoisteR—The Calorimeter— 
Theory of Combustion and of Oxidation. 
Cuvier has justly remarked, in his biography of 
(593.) Cavendish, that he had to struggle in his scientific 
Cavendish. career against obstacles much more rarely encoun- 
tered, and perhaps less easily overcome, than those 
which beset the progress of genius cramped by poverty 
and neglect. Cavendish was the descendant of one 
of England’s noblest families, and he was likewise 
the possessor of enormous wealth; yet neither of 
1 Playfair’s Biographical Account of Dr James Hutton, Works, vol. iv. 
2 Muirhead’s Correspondence of James Watt. Introd., p. xxii. 
3 Preface to Black’s Lectures, by Robison, p. lxxiv, 
* I find an apology almost necessary for introducing at some length the biography of Cavendish into a chapter professedly on 
Heat, his positive discoveries connected with which were less notable than in some other departments. But besides that his posi- 
tion in the first rank of chemists naturally indicates his place to be between Black and Dalton, I felt a wish to bring out the 
relief of the striking intellectual characteristics of those three remarkable men, by placing them in juxtaposition. I may add 
that these three sections were the earliest written of this Dissertation, at a time when I had hoped to interweave into its compo- 
sition more of the purely biographical character of each period of scientific history than I found it afterwards practicable in all 
instances to carry out. I trust, however, that it may be found a not unwelcome variety amidst the abstruser details of science, 
In the case of Cavendish, too, so various are his claims on our notice, that it was inevitable to recur to them in different chap- 
ters, especially in those on Astronomy and Electricity, It was not, therefore, really material under which head the more strictly 
personal details were given to which I have alluded. 
