982 
(apparently) to what occurs when polarized light 
passes through quartz or oil of turpentine. It is 
found that a great number of solids and liquids are 
subject to the magnetic influence in the same man- 
ner as in the case of “ heavy glass,” though ‘to a 
smaller amount. 
MATHEMATICAL AND PHYSICAL SCIENCE. 
[Diss. VI. 
tion as to the physical conditions on which these 
singular phenomena depend. 
Amongst Dr Faraday’s contributions to science 837.) 
Dr Fara- 
day lique- 
Sash - fies cer- 
liquid form by cold and pressure, of which he is the tain gases. 
not connected with electricity, the most remarkable 
perhaps is the condensation of many gases into the 
(836.) Now, in reasoning on this experiment, it is to be undoubted discoverer. ‘This fact is highly interest- 
Resembles ghserved that no rotation of the ray takes place un- ing both ima scientific and practical point of view. In 
, bey less there be a medium on which the magnetism im- the latter it was early applied by the late ingenious 
but with's presses its energy.1 Some molecular change, no Sir M. I. Brunel as a new moving power (375), and 
difference. doubt, results, such as that which pressure gives to it may not improbably yet be resorted to for that 
(839.) 
Vast detail 
of the 
science of 
electricity. 
Its nume- 
rous culti- 
vators. 
glass, rendering it doubly refracting and depolariz- 
ing, or, to take a still closer analogy, when heat ap- 
plied to it conveys similar properties. Yet no one 
imagines that these experiments show a direct reac- 
tion of heat, still less of mechanical compression, upon 
light. Yet, with all abatements, Dr Faraday’s dis- 
covery is novel and singular; the more so, that this 
constrained state differs from that naturally pos- 
sessed by quartz and certain liquids. The state'mag- 
netically induced in a body causes the rotation of the 
ray to be reversed when it moves in the contrary 
direction ; that is, its rotation is right-handed when 
the ray moves from the north to the south pole, but 
left-handed when it moves from S. to N. But in 
bodies in the natural state the rotation takes place 
towards the same hand whatever be the path of the 
body. Mr Airy has shown that this peculiarity ad- 
mits of being mathematically expressed in a manner 
somewhat analogous to that imagined by Professor 
MacCullagh in the case of quartz (512); but it is 
not pretended that these formule convey informa- 
purpose. The subsequent discovery of a mode of 
solidifying carbonic acid by M. Thilorier is not only 
interesting in itself, but affords a method of produc- 
ing more intense cold for experimental purposes 
than any other previously known. . 
Dr Faraday still continues his laborious and fruit- 838.) 
His wide 
reputation. 
ful inquiries. Whilst he has attained almost every 
titular honour which the world of science has to 
bestow (including that of associate of the French 
Academy of Sciences), he has preserved a modesty 
of character and a simplicity of life which enhance 
the respect in which he is held by all who are ad- 
mitted to his nearer acquaintance. No one has more 
successfully escaped the contentions which literary 
rivalry so often produces ; and by his extraordinary 
skill in expounding the most difficult researches, 
whether made by himself or by others, he has main- 
tained (as I have already said) the early reputation 
of the Royal Institution, and has immensely enlarged 
the circle of those who are able to admire and appre- 
ciate his successes. 
§ 6. OnM—DaniELL—Mr WuEatstonE—M. Jacosi.—Laws of Electrical Conduction ;—Constant 
Battery ;—Applications of Electricity to Telegraphs—Clocks—Motive Engines—the Electrotype. 
We have traced in the last section the progress of 
electrical and of electro-magnetic discovery since the 
days of Davy and Oersted, as well exemplified in 
the pre-eminent researches of Dr Faraday. In con- 
formity with the plan of this Dissertation (13), 
(14), I have, on account of their immense interest 
and importance, analyzed them more fully than 
could possibly have been done were I to render 
similar justice to all who have distinguished them- 
selves in the same career. Thus, France has pro- 
duced in M. Becquerel one of her most inge- 
nious and indefatigable experimentalists, full of de- 
votion to science, and giving up conscientiously the 
to produce crystallized earthy and metallic com- 
pounds not obtainable by chemical means is highly 
important. Switzerland is proud of her two De la 
Rives,” and Italy of not a few disciples of Volta. In 
Germany the number of electricians is greater than 
in any other country; and as they have taken the lead 
in obtaining correct measures of the electric forces, 
andin determining (in many cases) the numerical laws 
which regulate the efficiency of batteries and conduc- 
tors, and have applied these to many important 
practical purposes, I shall devote a section to some 
account of these, as well as to the beautiful experi- 
ments of our countryman Mr Wheatstone. 
Oum’s Law of Electrical Conduction. — Gore 840.) 
Smron Oum was born in Bavaria in 1787, and was pies a 
successively professor at Cologne, Niirnberg, and jecttcal 
conduction. — 
whole of a long life to the cultivation of this parti- 
cular department. His discovery of the efficacy 
of long-continued and very feeble voltaic actions 
1 I may here record that before the year 1835, I suspected that there might be some immediate action between circularly polar- 
ized light and a magnetized body, and made experiments in consequence in May 1836, which, however, led to no result, I 
rather think, however, that these experiments deserve careful repetition under more varied circumstances. 
2 MM. Becquerel and A, De la Rive have both published elaborate works on Electricity, to which the reader is referred for 
details on this inexhaustible subject, 
