Irregular 
dilatation 
of glass. 
(723.) 
Dulong 
and M. 
Regnault 
on the elas- 
ticity of 
steam. 
(724.) 
M. Reg- 
nault on 
latent heat. 
(725.) 
(728.) 
Galvani. 
(729.) 
His posi- 
tion as a 
discoverer 
difficult to 
estimate. 
958 
the great difficulties not only of these enquiries, but 
generally, in constructing comparable thermometers. 
It varies so much with the composition of the glass 
as to leave a serious amount of uncertainty in the 
measure of temperatures above that of boiling water. 
M. Regnault has had the perseverance himself to 
graduate the thermometers which he uses. 
These enquiries were in some measure introductory 
to the determination of the elasticities of steam at 
different temperatures, which had been already ascer- 
tained with so much care by Dulong (nominally in 
conjunction with Arago and other academicians), as 
to leave little need for their repetition, except on the 
ground of the uncertainty of the indications at high 
temperatures of the thermometers which they used. 
All M. Regnault’s results are most carefully expressed 
in terms of temperatures measured on an air thermo- 
meter corrected for the expansion of glass. They agree 
well with those previously ascertained by Dulong. 
In connection with this subject, the important law 
of the latent heat of steam at different temperatures 
has been correctly ascertained for the first time by M. 
Regnault. Watt maintained that the sum of the 
sensible and latent heats of steam is constant at 
all temperatures : Southern and others, on the con- 
trary, believed that the latent heat has a constant 
value, whatever be the temperature of vaporization. 
M. Regnault shows that the true law is intermediate. 
The latent heat diminishes as the sensible heat of steam 
increases, but in a slower proportion. 
Our author also followed the steps of his prede- 
MATHEMATICAL AND PHYSICAL SCIENCE. 
[Diss. VI. 
cessor Dulong in verifying the law of Mariotte and Law of 
Boyle on the compressibility of the gases. He found Mariotte 
it to be indeed very approximately true, yet not ab- 
solutely so for any gas. For atmospheric air and for 
most other gases the compression increases rather 
faster than the strict proportionality to the pressures 
would assign. In hydrogen gas the contrary is the 
case. This result, together with that on the dilatation 
of different gases, shows (if fully confirmed hereafter) 
that mere simplicity or uniformity of result is not by 
any means a sure ground of induction as to a law of 
nature. That simplicity often appears to be predi- 
cable only of some abstract condition of matter which 
we may assign or imagine, but which we rarely if 
ever find realized amongst the bodies around us. 
The preceding investigations, the result of an 
amount of minute and assiduous labour almost fear- 
ful to contemplate, are to be found collected in the 
21st volume of the Memoirs of the French Academy 
of Sciences, which they entirely oceupy. 
M. Regnault has elsewhere published analogous 
researches on the Specific Heat of a great variety of 
substances, and on the theory and practice of Hygro- « 
metry, both of which are highly interesting and im- Heat and 
portant, but which I have not here space to analyze, Hygrome- 
He is also favourably known as the author of an 
excellent treatise on chemistry, and in fact sits in the 
Institute as a member of the Chemical Section. He 
now directs the manufactory of porcelain at Sevres; 
and being still in the prime of life, much may yet be 
hoped from his devotion to science. 
CHAPTER VII. 
ELECTRICITY—MAGNETISM—ELECTRO-MAGNETISM. 
§ 1—GALVANI.—Discovery of Galvanism ; Proper Animal Electricity—The subject revived by 
Nobili—MM. Matteucci and Du Bois Reymond. 
Tuer are few discoverers in science whose posi- 
tion it is more difficult to assign with aceuracy than 
Galvani. Attaining at first, by a curious observa- 
tion patiently reflected on and carefully repeated in 
detail, to the rank of the founder of a new science, 
he was so far outstripped in its applications, that his 
merit was soon in a measure overlooked, and his un- 
questionable discoveries ascribed to capricious acci- 
dent. 
We find that a concurrence of circumstances con- 
tributed to this result. Galvani was advanced in 
years, and, it would appear, somewhat exhausted in 
constitution, when he made his famous observation 
on muscular contractions. He was an anatomist, 
far more than either a chemist or physicist;—no 
blame, surely, is to be attributed to him on that 
account! His discovery was chiefly interesting in 
his eyes, as illustrating the laws of sensation and 
the source of nervous irritability. It was calculated 
to throw great light on these most abstruse enquiries. 
Groping to find the thread which should reveal to 
him that labyrinth, is it surprising that he devoted 
himself exclusively to those effects which gave him a 
real promise of success ?—a promise held out still by 
the same facts—still the envied goal of physiologists 
—yet how little realized by the unremitting labours 
of two subsequent generations! 
Again, the almost irresistible temptation of con- 
verting successful philosophers into heroes, at the pace + of 
expense of their contemporaries, added to a less par- .43 Volta, 
donable wish to relieve the tedium of scientific dis- 
cussion, by the introduction of a lively, though ques- 
tionable anecdote, has induced the eulogists of Volta 
to exalt his ungestionable claims by the deprecia- 
tion of those of his less widely known and less for- 
tunate countryman, Galvani. Their contrasts in cha- 
and Boyle. 
(726.) 
(727.) 
M. Reg- 
nault on 
pecific 
try. 
(730.) 
alvani 
