CHAP. V., 5.] 



OPTICS. SIR DAVID BREWSTER. 



113 



To complete our biographical notice, we will here 

 just allude to M. Arago's principal researches un- 

 connected with optics. One was on the magneti- 

 zation of iron filings, and the formation of a tempo- 

 rary magnet, by means of a helical conductor of elec- 

 tricity ; l the other was the important observation of 

 the seeming magnetism of copper, and other non-mag- 

 netic metals, when put in rapid rotation near a per- 

 manent magnet. Neither of these happy experiments 

 was carried out by their author. The former was left 

 in the hands of Ampere, Sturgeon, and Henry ; the 

 latter was only rightly understood and valued when it 

 was engrafted by Mr Faraday on his splendid series 

 of researches on Magneto-Electric Induction. 2 



Arago is fairly entitled to be regarded as having 

 proved the long-suspected connection between the 

 aurora borealis and the freely suspended magnet ; and 

 this in the face of urgent contestation. 3 His contri- 

 butions to Meteorology (founded rather upon the ob- 

 servations of others than upon his own) were of con- 

 siderable importance, and several of his popular pa- 

 pers, appended to the smaller Almanac (Annuaire) 

 of the Board of Longitude, contain a great deal of 

 well-digested and curious information. 



As Secretary of the Academy of Sciences in the 



Mathematical Department (in which office he sue- Arago as 

 ceeded Fourier, in 1830), the duty devolved on him * * 

 of writing the biographies of eminent deceased mem- ^emy of 

 bers of the Academy. He bestowed extraordinary Sciences, 

 pains on these compositions, and strove to render 

 them popular without sacrificing their scientific cha- 

 racter. In this difficult attempt he was not always 

 successful. Abrupt transitions, piquant anecdotes, 

 paradoxical arguments, and political allusions, appear, 

 at least to the English reader, to be unacademical 

 adjuncts to the history of contemporary discovery. 

 The special pleader is too often visible, and even the 

 occasional sacrifices of the strong spirit of nation- 

 ality by which he was commonly actuated, to some 

 chivalrous adjustment of the rights of discovery, 

 do not always carry conviction to the mind of the 

 reader. The Eloge of Watt, probably the most po- 

 pular, appears to us far from being the best of these 

 biographies. Those of Sir W. Herschel and of Dr 

 Young are ably executed, and display much research 

 and candour. 



After having been for three years almost with- (518.) 

 drawn from science by lingering disease, and nearly His death 

 complete blindness, Arago expired at the Observatory 

 of Paris, on the 2d October 1853, aged 67. 4 



5. SIR DAVID BREWSTER Progress of Experimental Optics Laws of Polarization Double 

 Refraction produced by Heat and Compression Discovery of Biaocal Crystals Laws of Me- 

 tallic Reflection Absorption of Light ; and Lines of the Solar Spectrum ; FRAUNHOFER. 

 Seebeck ; M. BIOT. 



C519.) We have pleasure in ranking amongst the fore- 



Sir David most promoters of the science of optics in its sur- 

 Brewster. p r i s j n g revival in the earlier part of this century, 

 a philosopher who still lives amongst us and pur- 

 sues with ardour the investigations of his youth. 

 (520.) Sir DAVID BREWSTER was born at Jedburgh, in 



His early Scotland, on the llth December 1781. He was 

 studies. educated for the Scottish Church, and having en- 

 tered the University of Edinburgh at a very early 

 age, pursued his studies under Robison, Playfair, 

 and Stewart, and formed the friendship of those 

 eminent men. Amongst fellow-students of no 

 common distinction who at that time frequented the 

 college lectures, and of whom not a few were destined 

 to signalize themselves in literature, science, and the 

 career of politics, he formed the particular acquaint- 

 ance of Mr, now Lord Brougham, and through him 

 was led to study the inflection of light, and to repeat 

 Newton's experiments. This was in 1799 ; nor did 

 he afterwards lose sight of a science which he was 

 so signally to improve. The distraction of other 

 occupations, the calls of his profession, and his 

 indifferent health prevented, however, any very 

 constant application to optics : and the part of 



the subject he then principally studied was rather 

 connected with the use and theory of instruments than 

 with physical optics in the sense in which we have 

 explained it. This is evident from his first separate 

 publication in 1813, " on new Philosophical Instru- 

 ments," which, though containing many ingenious 

 and valuable suggestions, fell short of the importance 

 of his subsequent publications. 



Sir David Brewster's genius was first called forth (521.) 

 by the announcement of Malus's great discovery Directs his 

 in 1808 of the polarization of light by reflection, ph^"" 

 But for the unfortunate political relations of France optics. 

 and England at the time, which prevented, to a 

 degree which now appears almost incredible, the 

 transmission of even the most interesting scientific 

 facts from one country to the other, our country- 

 men would have borne a larger share in the dis- 

 coveries which immediately followed ; and it would 

 have been an easier task to apportion with his- 

 torical accuracy what was due to each. As the 

 French philosophers remained long in ignorance of 

 the discoveries of Davy, and were anticipated in 

 every important step in voltaic science, so Malus and 

 Arago pursued and published researches and bril- 



1 See Electricity 4 2 Electricity, 5. 



3 No doubt the fact 'had been already distinctly noticed by Hjorter and Celsius at Upsala in 1741. See Hansteen, Mag* 



nttismus der Erde. . . , 



* The article POLARIZATION OF LIGHT in this Encyclopaedia, the production of Arago, contains an excellent review ot many 



of the topics of this Section. 



