946 
greater advantage, was mainly because he yielded to 
the guidance of an imagination which often carried 
him into fanciful speculation, yet which was strangely 
united with dogmatism in maintaining what he had 
once maintained, and a disposition to accuse others of 
misinterpreting nature, whenever they arrived at con- 
MATHEMATICAL AND PHYSICAL SCIENCE. 
[Diss. VI. 
existence of climates in the arctic regions of which 
the mean annual temperature does not exceed 0° of 
Fahrenheit, proved by Parry and his successors,— 
all these, and many other demonstrated truths in his 
own peculiar walk of science, were, we fear, practi- 
eally ignored by him throughout life. 
(659.) 
But we willingly leave the ungrateful task of indi- ese 
cating defects. Let us recollect rather with pleasure Pe" me" 
‘ c : ‘ . tal re- 
how much we owe to his beautiful discoveries. It is searches. 
clusions inconsistent with his own. 
In such sciences as those which he chiefly culti- 
(658.) A , : : 
vated, — sciences eminently progressive, imperfect, 
(661.) 
and dependent on experimental proof,—a just appre- 
ciation of the labours of others is one of the most 
essential parts of the philosophic character, whilst 
an absence of it infallibly condemns the dogmatic 
theorist to be gradually left behind, even in the paths 
which he had at first trod with the greatest distine- 
tion. With few exceptions, Sir J. Leslie carried his 
scientific views of 1804 with him to the grave. The 
possibility of the passing of heat, except solar and 
highly luminous heat, through any solid body, such 
as glass, though proved by Maycock, De la Roche, 
and Powell,—the existence of dark heating rays in the 
sunbeam, less refrangible than the red, demonstrated 
by Herschel, and afterwards confirmed by many 
others,—the doctrine of gases and vapours as laid 
down by Dalton,—the maximum density point of 
water shown so ably by Hope and Rumford,—the 
§ 6. Fourter.—Mathematical Theory of the Conduction of Heat. 
perhaps not an insignificant test of their originality, 
that though they were generally adopted (at least to 
the extent which his own experiments justified), Les- 
lie’s observations were but rarely repeated, and that 
only in the way of general confirmation and illustra- 
tion. I mean that for a great many years the path 
which he had opened, and the methods which he de- 
scribed, were not seized upon by others, as leading to 
a sure course of discovery. Until the time of Dulong, 
his experiments on cooling were perhaps never care- 
fully resumed, and a very great number of his sub- 
jects of enquiry were only taken up thirty years after 
their publication, as we shall see in a future section. 
The observations of Herschel on the Refrangibility 
of Solar Heat, I shall include in the notice of the 
experiments of Berard and De la Roche, to which 
we shall presently turn. 
Lambert; Poisson.— 
Temperature of the Earth and of Space. 
It is stated by Arago, that when the Academy of 
Theory of Sciences, above a century ago, proposed as a prize sub- 
aia ject, “La Nature et la Propagation du Feu ;” adding, 
—Lam- 
bert. 
* Ja question ne donne presque aucun prise a la géo- 
metrie,’—a majority of the candidates treated of the 
methods of preventing the burning down of houses ! 
It is true, however, that on that occasion, Euler sent 
a memoir which, though crowned, was unworthy of 
his genius. Lampert in his “ Pyrometrie,” in 1779,! 
had the rare merit of laying the foundations of the 
science of conduction, He solved correctly this ques- 
tion :—* Ifa thin conducting bar of indefinite length 
be kept with one extremity heated toa constant degree 
above the surrounding space, required the tempera- 
ture of any point in the axis of the bar?” The solu- 
tion is, that the temperatures, or rather excesses of 
temperature, diminish in a geometric ratio, at dis- 
tances reckoned in arithmetical progression, from the 
origin of the heat.? In this solution it is assumed, 
(1.) That the flow of heat along the bar, is at any point 
proportional to the rapidity with which the tempera- 
ture at that part of the bar is lessening as we recede 
from the source ; in other words, that the flow of heat 
from the hot part to the cold part, is more rapid in 
proportion as the difference of temperature of two 
sections of the bar at a given short interval is greater. 
(2.) That the bar parts with its heat to the surround- 
ing space, exactly in proportion to its excess of tem- 
perature at every part. 
This beginning, which perhaps like many of Lam- 
(660.) 
(662) 
bert’s other writings was not very generally known, Biot. 
had no sequel until 1804, when M. Biot attempted to 
find the differential equation of the general movement 
of heat on the same principles. But the form which 
he obtained, including a mathematical solecism, be- 
trayed some error in stating the conditions. Three 
years later Fourier had more success, But, conform- 
ably to the plan of this discourse, I shall premise 
some facts regarding his early career, which was far 
from commonplace. 
Josern Fourter was born in 1768, at Auxerre in 
France. He was of humble parentage, and being Fourier 
early left an orphan, was educated by the Benedic- ms oa 
tine monks who, singularly enough, conducted with 
success in that town a military school. It seemed 
his fate to become either a priest or a soldier; yet he 
was neither, though ere long familiar with camps. 
He became first a pupil of the old normal school of 
1 Pyrometrie, oder, von Maasse des Feuers und der Warme. Berlin, 4to,1779. This work was posthumous, and contains many 
riginal observations on Thermometry, Conduction, Solar Radiation, and Climate. 
2 Pyrometrie, p. 184. 
(663.) 
