CHAP. \'IL, 8.] ELECTRICITY (MAGNETISM). BARON HUMBOLDT GAUSS. 



195 



Baron ology and Magnetism than upon any others which he 

 cultivated. His conception of Isothermal Lines and 

 Meteoro- ^is treatment of the subject of Climatology in his re- 

 logy iso- markable paper of 1817 1 gave a new impulse to the 

 thermal former subject. His magnetical observations in his 

 voyage to the Equator have already been adverted to. 

 Magnetism. Besides this we are indebted to Baron Humboldt for 

 directing attention to the simultaneous and seemingly 

 accidental disturbances of the magnetic needle which 

 take place over vast portions of the area of the globe. 

 He commenced observations on this subject in con- 

 junction with M. Oltmanns as early as 1806 ; and 

 during his residence in Paris he no doubt encouraged 

 his friend Arago in those elaborate observations on 

 the hourly variations of the needle which, to the 

 irreparable loss of science, remained unpublished 

 whilst they might have been most useful. 2 In 1829 

 simultaneous observations were made in Germany 

 and Russia, and compared by MM. de Humboldt, 

 Dove, and others, with interesting results. 3 It is 

 probable that the results then obtained instigated 

 Gauss to the enlarged enquiry to which I shall imme- 

 diately refer. M. de Humboldt had already addressed 

 the Russian Government on the same subject, sug- 

 gesting the registration of hourly observations in their 

 vast territories; and these, the first systematic ob- 

 servations of the kind, have been continued ever 

 since. The suggestion of " Term Days" of continuous 

 registration of the Declination Needle was also due 

 to Baron Humboldt. In 1836 he addressed the 

 President of the Royal Society of London on the same 

 subject, and his letter formed the basis of the exten- 

 sive undertakings which have formed the contribu- 

 tion of the British Government to this great enquiry. 

 (895.) Baron Humboldt still lives at Berlin, enjoying the 

 respect of all who know him, and the distinguished 

 favour of his Sovereign. 



CARL FRIEDRICH GAUSS, late Professor of Astro- 

 nomy at Gbttingen, belonged to that group of cele- 

 brated geometers who illustrated the commencement 

 of this century, and of which he was for some years 

 the last survivor ; but he too has now passed 

 away. , 



(897.) Gauss was born at Brunswick on the 30th April 

 His early 177*7 O f humble parents, and was indebted for a 



history and , ., , , . . , . , , . . 



mathema- liberal education to the notice which his talents pro- 

 tical works, cured him from the reigning duke. His earliest 

 original researches were in the theory of numbers. 

 His Disquisitiones Arithmetics were published in 

 1801, and were as profound and original as they 

 have always been considered obscure even by those 

 devoted to such studies. Gauss demonstrated the 

 possibility of geometrically inscribing a regular poly- 



gon of 17 sides within a circle ; the only extension 

 of geometry in this direction since the time of Euclid. 

 His Theoria Motus Corporum Ccelestium, published 

 in 1809, is a very remarkable treatise on the geome- 

 trical theory of the planetary orbits; in which it 

 was shown for the first time how the elliptic ele- 

 ments of a heavenly body may be deduced from 

 three observations only of longitude and latitude, 

 an important extension of Newton's celebrated de- 

 monstration in the case of parabolic cometary orbits. 

 In the same work the method of least squares 

 (85) was fully unfolded in its applications to astro- 

 nomy. 



These and many other important labours all con- (898.) 

 nected with the higher mathematics, had obtained Researches 

 for Gauss an exalted place among the men of science t^ja^maff*- 

 of his time, long before he commenced those re- netism. 

 searches on Terrestrial Magnetism, in virtue of 

 which his name is introduced into the present sec- 

 tion. It can hardly be doubted, however, that by 

 these scarcely begun before he had entered on his 

 55th year he will be hereafter chiefly remembered. 

 His first work on the theory of magnetism 4 was pub- 

 lished in 1833, and excited very general notice, as it 

 contained a remarkable application of the Theory of 

 Attractions to the distribution of magnetism in a 

 steel bar, a singularly ingenious and rigorous proof 

 of the primary law of the magnetic force, and like- 

 wise a new and practical application of a suggestion Magnetic 

 thrown out by Poisson, of a method by which the f rc< j in 

 magnetic directive force of the earth itself may be measur e. 

 expressed in absolute measure, irrespectively of the 

 constancy of the magnetism in the bar which is in 

 the first instance used to estimate it. For this purpose 

 two kinds of observation are required, 1 st, By vibrat- 

 ing a needle or bar of known weight and dimensions, 

 and observing the time of its oscillation, the force 

 pulling it into the meridian is ascertained in terms 

 of the ordinary dynamical units. The time depends 

 jointly on the magnetic force of the earth, and on 

 that of the bar, or it varies inversely as the product 

 of the two. 2dly, Another bar, B, is suspended like 

 the first, A, in the magnetic meridian. A is then 

 brought to act upon B, so as to draw it permanently 

 out of the meridian. The position in which B rests 

 determines the ratio of the magnetic force of the 

 earth and of the bar A. But quantities whose pro- 

 duct and whose ratio are given in known measures, are 

 also known ; whence the separate intensities of the 

 earth's and the bar's magnetism may be eliminated. 5 



Having thus fairly entered on a career of mag- (899.) 

 netic experiments, Gauss proceeded, in conjunction J^^J! 

 with an experienced physicist of Gb'ttingen, Professor s truments. 

 Wilhelm Weber (420), to invent new apparatus for 



i Memoires d'Arceuil, torn, iii., p. 462. 2 Posthumously published in his (Euvres. 



3 See abstract in Bibliotheque Universelle, Aout 1832. 



* Intensitas vis magneticce terresiris ad mensuram absolutam revocata. Gott. 1833. 



6 The unit offeree to which these intensities are referred is that force (in grains) which acting on unit of mass through unit 

 ef time (a second) generates in it unit of velocity (a foot). 



2c 



