184 



MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



(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. 



(836.) Now, in reasoning on this experiment, it is to be 

 Resembles observed that no rotation of the ray takes place un- 

 the action j egg ^^ k e a me( ^ um on w hi c h the magnetism im- 

 of quartz, . i c< TIT. 



but with a presses its energy. 1 borne molecular change, no 



difference, doubt, results, such as that which pressure gives to 

 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 formulae convey informa- 



tion as to the physical conditions on which these 

 singular phenomena depend. 



Amongst Dr Faraday's contributions to science (837.) 

 not connected with electricity, the most remarkable Dr F f 

 perhaps is the condensation of many gases into the fi * 

 liquid form by cold and pressure, of which he is the tain gases. 

 undoubted discoverer. This fact is highly interest- 

 ing both in a scientific and practical point of view. In 

 the latter it was early applied by the late ingenious 

 Sir M. I. Brunei as a new moving power (375), and 

 it may not improbably yet be resorted to for that 

 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.) 

 ful inquiries. Whilst he has attained almost every His wi( ^ e 

 titular honour which the world of science has to re P utatlon> 

 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. OHM DANIELL Mr WHEATSTONE M. JACOBI. Laws of Electrical Conduction; Constant 

 Battery; Applications of Electricity to Telegraphs Clocks Motive Engines the Electrotype. 



vators. 



(839.) ^ We have traced in the last section the progress of 

 Vth electrical and of electro-magnetic discovery since the 



science of days of Davy and Oersted, as well exemplified in 

 electricity, the pre-eminent researches of Dr Faraday. In con- 



i- formit y with the P lan 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 

 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 



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, 2 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, 

 and in 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. 



OHM'S Law of Electrical Conduction. GEORG (840.) 

 SIMON OHM was born in Bavaria in 1787, and was Ohm>8 

 successively professor at Cologne, Niirnberg, and e jg t ^ c 1 

 conduction 



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. 



fl 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. 



