DOUBLE REFRACTION. 147 



MALUS GAIXS THE PRIZE PROPOSED BT THE ACAD- 

 EMY FOR A MATHEMATICAL THEORY OF DOUBLE 

 REFRACTION. 



On the 4tli January, 1808, the Academy proposed, as 

 the subject for a prize in physical science to be decided 

 in 1810, the following question : — 



" To give a mathematical theory, confirmed by experi- 

 ment, of the double refraction which light undergoes in 

 passing through diiferent ci'ystallized bodies." 



The memoir of Malus received the prize. Doubtless 

 fearing lest he should be forestalled by some of the com- 

 petitors, in the discovery of the singular properties of 

 light which he had observed, this eminent physicist com- 

 municated the most essential parts of his researches to 

 the Academy on the 12th December, 1808, without 

 waiting for the period at which, according to the pro- 

 gramme, the competition was to be closed. It is then to 

 the end of the year 1808 that the immortal discoveries 

 belong of which I proceed immediately to give you an 

 analysis. The commission appointed to judge of the com- 

 petitors was composed of Lagrange, Haiiy, Gay-Lussac, 



of the Mec. Celeste by which this conclusion can be considered as 

 established. 



Malus observed by Wollaston's method the angles at which the dis- 

 appearance took place in wax, solid and in fusion. Tliese angles were 

 different; and calculated in the usual way, the indices of refraction 

 resulted different also (as seen in the above tabular view). 



The same observed angles, however, calculated b}' Laplace's for- 

 mula gave the resulting index the same in both cases. 



Now Laplace, Malus, and the emissiouists, considered the identity 

 of refractive power thus resulting to be a necessary truth — why so, we 

 do not see; it is obviously, at best, a mere consequence of the assump- 

 tion made at the first. The result is no proof of its truth, and decides 

 nothing either way. Arago's laboured remarks therefore seem super- 

 fluous. — Translator. 



