178 



MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



(801.) 

 Seebeck. 

 Discovery 

 of thermo- 

 electricity. 



(802.) 

 Invention 

 of the 

 galvan- 

 ometer 

 Schweig- 

 ger and 

 Nobili. 



(803.) 

 Oersted's 

 history 

 continued. 



Whilst Ampere, Arago, Davy, the two De la 

 Rives, and Mr Faraday, were throwing light on 

 the causes, and developing the consequences of 

 Oersted's experiment, SEEBECK of Berlin discovered 

 in 1822 a new source of electric excitement, 

 which has since become indirectly of very great im- 

 portance. This was Thermo-Electricity. He found 

 that when heterogeneous metals are united, either 

 by soldering or pressure, and the junction heated, a 

 current of electricity is established. The order of 

 metals which produces the most energetic combina- 

 tions, is wholly unlike the arrangement of the vol- 

 taic series, and has no apparent reference to any 

 other known property of those substances. Bismuth 

 and antimony stand at the opposite extremities of 

 the scale, and a pair formed of them is consequently 

 the most powerful which can be made. When heat- 

 ed at the junction, positive electricity passes from 

 bismuth to antimony. In 1823, Oersted, then on 

 a visit to Paris, united with Fourier in making 

 experiments on this subject, and was probably the 

 first who constructed thermo-electrical piles. Un- 

 questionably, the most important application of these 

 was to the construction of an instrument for measur- 

 ing the effects of radiant heat, by Nobili and Melloni, 

 of which an account has already been given, Art. 

 (709). 



An application of electro-magnetism of extreme 

 importance, was the Multiplier or Galvanometer, 

 contrived by Schweigger of Halle. In it the idea 

 was first realized of measuring the power of an 

 electric current by its effect in deviating a mag- 

 netic needle. Schweigger perceived that he could 

 multiply the action of one and the same current, by 

 causing it to traverse successive parallel coils of the 

 conducting wire carried round the needle. Its sensibi- 

 lity was still farther, and almost indefinitely increased 

 by Nobili' s invention of rendering the needle astatic, or 

 diminishing its natural directive power in any required 

 degree. This he did by connecting it firmly with a 

 second needle parallel to the first, of nearly equal 

 strength, with its poles placed in an inverted posi- 

 tion relatively to the other, and moving freely in a 

 plane altogether exterior to the coil, so that whilst 

 the directive effect of the earth's polarity is almost 

 neutralized, the electro-magnetic effect of the coil 

 tends to produce a similar deviation in both needles. 

 This is one of the most precious philosophical instru- 

 ments ever invented. It has been employed for 

 thirty years in almost every electrical research or 

 application. One of its best forms for many pur- 

 poses (though hitherto little used) is the Torsion 

 Galvanometer of Ritchie. 



Oersted, of course, interested himself in this new 

 application of his own great discovery. Indeed, hav- 

 ing the good fortune to survive that discovery for 

 more than thirty years, with a full enjoyment 

 of his intellectual vigour, he had the gratifica- 

 tion of contemplating a body of science entirely 



new as its results, and a variety of useful ap- 

 plications scarcely less astonishing, which might, 

 in one sense, be called his own creation. The dis- 

 coveries of Ampere, Seebeck, and Mr Faraday, were 

 all based upon his; and during those thirty years, this 

 elegant and interesting branch of experimental phy- 

 sics underwent an almost uninterrupted extension, 

 such as hardly any other affords an example of. The 

 Electric Telegraph is one of its most direct and practi- 

 cal results ; nor should we omit that Oersted himself 

 proposed, as far back as 1818, the application of elec- 

 tricity to blasting rocks by the very same process in 

 which it has of late years been so usefully applied, 

 namely, that of heating a fine wire to incandescence. 



Though Oersted was the author of numerous (804.) 

 papers connected with science down nearly to His experi 

 the close of his life, they do not contain any impor- ment8 n 

 tant discovery, and with reference to electro-mag- *^ ~ 



1 1 1 1 i / 



netism, he appears to have contented himself pnnci- water. 

 pally with repeating and expounding the observations 

 of his contemporaries. But some of his experiments on 

 other subjects deserve mention, especially those on the 

 compressibility of water. This fact, which the Flo- 

 rentine Academicians had vainly sought to establish 

 in the 17th century, had been clearly demonstrated 

 by Canton in the middle of the 18th, but Oersted 

 first devised a compendious and effective apparatus 

 for producing and measuring it more effectually. His 

 result, that the compression amounts to46-millionths 

 of the bulk, for a pressure equal to one atmosphere, 

 agrees almost precisely with Canton's. In 1845, he 

 considered that he had established that the heat de- 

 veloped by the same amount of compression is -0203 

 of a centigrade degree. He also made some experi- 

 ments on the Law of the Compressibility of Air and 

 upon other subjects. 



The desideratum of a clear expression of the mani- (805.) 

 fest alliance between Electricity and Magnetism had rste< | re 

 been so long and so universally felt, that the discovery p r j ze O f 

 placed its author in the first rank of scientific men. the Insti- 

 There was not even, so far as I am aware, a sus- tute of 

 picion that he had been, however remotely or dimly, 

 anticipated. The prize of the French Institute which 

 had been awarded to Davy for his galvanic discoveries, 

 was bestowed upon Oersted, and so far as I am inform- 

 ed, has not been since adjudicated. He was elected first 

 Correspondent, and finally Associate of the Academy 

 of Sciences. He was personally known to many of 

 the philosophers of Europe, having made repeated 

 journeys in France, Germany, and England. His His stien- 

 agreeable manners and general information rendered tificcharac 

 him popular. Sir H. Davy, who visited him at Co- ter * 

 penhagen, describes him as " a man of simple man- 

 ners, of no pretensions, and not of extensive re- 

 sources." Niebuhr, however, who viewed his cha- 

 racter in a different light, says, " I scarcely know 

 another natural philosopher with so much intellect, 

 and freedom from prejudice and esprit de corps" His 

 writings were indeed too discursive. Professor Forch- 



