Cua. VI., § 5.] 
published it more than thirty years after, when cer- 
tainly it was not calculated to advance science in a 
perceptible degree. An essay on Heat and Climate, 
read at the meetings of the Royal Society of London 
in 1798, had not a more favourable reception; and 
HEAT.—SIR JOHN LESLIE—PICTET. 
943 
Heat, in 1804; the latter by his appointment to the 
chair of mathematics in the University of Edinburgh 
in 1805, I shall first say a few words on his cha- 
racter as a mathematician. 
Mathematics were, as has been stated, his earliest 646.) 
though published twenty-six years later in Thomson’s 
pursuit, and he cultivated them with great industry Mathemati- 
Annals, it was refused a place in the Philosophical 
and success. His adviser, Playfair, was attached ag 
(645.) 
Publishes 
his Essay 
on Heat. 
Transactions. The author, no doubt, attributed these 
rejections to the boldness with which he criticised 
opinions currently received, and to the novelty of 
the views which were shadowed forth ; but something 
is, no doubt, to be allowed for the real immaturity of 
these works, the involved and even inflated style in 
which they were written, and the questionable evi- 
dence for some of the conclusions. In these, and in 
some subsequent scattered papers in Nicholson's 
Journal, we observe, with all the faults, yet many of 
the merits of those researches which afterwards made 
him justly famous. We find acute observation, in- 
genious, if not close reasoning, considerable inven- 
tiveness in imagining experiments and in constructing 
apparatus, and a general tendency to express physi- 
cal Jaws in a mathematical form. It must be con- 
fessed, that these merits were united to a good deal 
to the methods of the foreign mathematicians; and 
Leslie no doubt acquired from him, as well as from 
his continental friends, a taste for the notation of 
Leibnitz, then hardly employed in this country, but 
which he uses in his work on Heat, and elsewhere. 
Nevertheless, his real preference appears to have 
been decidedly geometric. He almost always pre- 
fers demonstrations, whether in mathematics or na- 
tural philosophy, in the manner of Huygens and 
Newton. He could hardly be called a discoverer in 
mathematics ; but his work on Geometrical Analysis 
and the Higher Curves shows much taste and know- 
ledge, and is justly commended by Chasles and other 
foreign writers. His attempt to replace Euclid’s Ele- 
ments by a new work on Elementary Geometry was 
not more successful than such attempts have usually 
been, 
of dogmatism, and a somewhat supercilious judgment = Unquestionably, the bent of Leslie’s mind was _ (647-) 
. . . * * ° » Growing 
of persons eminent in science whose years and at- to physical research, in which he showed a peculiar importanee 
tainments should have commanded respect. This, 
however, is a fault which many ardent students not 
very conversant with the world have had abundant 
occasions to regret at leisure. Whether or not he 
believed Sir William Herschel to have had some 
share in the refusal of his paper by the Royal So- 
ciety I do not know, but it is difficult, on other 
grounds, to understand the bitterness with which he 
expressed himself as to that eminent person, in con- 
nection with his experiments on heat. 
One of the circumstances which most contributed 
to encourage Mr Leslie’s taste for experiment, was 
his engagement for above two years as tutor and 
companion in the family of the ingenious Mr Wedg- 
wood, Another was the opportunities which he 
found or made for himself of foreign travel. With 
or without companions he visited, in the early period 
of his career, America, and most of the northern 
countries of Europe, particularly Holland, Germany, 
Switzerland, Sweden, and Norway. He also medi- 
tated a journey to Egypt and the Hast, a project 
reluctantly abandoned, and to which he reverted even 
in the last years of his life; but it was never carried 
into effect. Nothing, perhaps, fosters so surely a 
taste for science as such extended tours; and the 
acquaintance made under the most agreeable cir- 
cumstances with foreign philosophers, and the fami- 
liarity gained with their language and experiments, 
contributes to it in no small degree. 
We have now come to the period of Mr Leslie’s 
life when his character and position became esta- 
blished, the first by the publication of his Hwperi- 
mental Inquiry into the Nature and Propagation of 
talent; and his selection of Heat was, 
as we have of the sub- 
hinted, well-timed; since there appeared a con- ject of ra- 
vergence of attention to the subject, such as usually 
heralds some eminent discovery. The doctrines of 
heat in combination, of which we have already spoken, 
had engaged the attention of Black, Cavendish, and 
Lavoisier; the subject of meteorology, in which Leslie 
took the greatest interest, was becoming a science in 
the hands of De Saussure and Deluc; whilst Pictet 
repeated (without being aware of the anticipation) 
the curious observation of Porta on the apparent con- 
centration of cold by a concave mirror. As this ex- 
periment really opened anew the subject of radiant 
heat, we shall dwell for a moment on Pictet’s labours 
and their results. : 
diant heat. 
Geneva was at this time nearly in the zenith of its _(648.) 
reputation as a nursery of the sciences. The most 
eminent and independent of its citizens were proud 
of being also amongst its instructors, and the office 
of professor was then, as it still is, considered one of 
the most honourable in the state. About 1790 De 
Saussure, the most eminent physical geographer of 
his time, was in the vigour of his intellect, and amongst 
his friends and coadjutors Marc-Aveuste Picrer 
held a conspicuous place. The latter was professor 
in the Academy, and being a person of popular man- 
ners and great information, was known and esteemed 
by the learned throtghout Europe. He was the 
author of numberless papers in a scientific jour- 
nal which he edited ; but his work on fire—Zssai sur 
le Feu—published in 1791, was his principal pub- 
lication. It contains some good observations on latent 
and specific heat ; and on the power of different kinds 
Pictet of 
Geneva. 
