KINETIC OR MECHANICAL VIEW OF NATURE. 23 



have unequal properties in different directions ; and ilie 

 process of revealing it was termed polarisation. Huygens 

 had discovered this property, which he found was given 

 to rays of light if they passed through certain crystals, 

 notaljly througli Iceland spar, which has the capacity 

 of di^^ding the rays so that objects seen througli tliem 

 appear double. He could not explain it on his 

 hypothesis of undulations, though he had invented a geo- 

 metrical construction of the double refraction which had 

 led him to its discovery. Malus showed in 1808 that 

 double refraction was not a necessary accompaniment of 

 polarisation, l)ut that ordinary reflexion was enough tu 

 give these sides to rays of light. Although the projectile 

 theory gave no complete explanation of this property, 

 still the supposition that this one- or many-sitledness 

 was owing to certain geometrical shapes of the i»ro- 

 jected particles suggested that double refraction might 

 be explained by the different attraction or repulsion 

 which these particles suffered according to tlie aspect 



determining the course of the ordl- liglit " (Works, vol. i. |i. 247). And 



uary and extraordinary rays in Ice- Plains himself, in writing to Young 



land spar, described the pheno- as Foreign Secretary of the Royal 



menon fully, admitting at the same Society, by whom he had been 



time that he could not explain it. awarded the Rumford Medal, >ay8 : 



When Malus discovered that light " Je ne regarde pa.s la connaissance 

 might acquire this peculiar pro- , de ces phononienes counue plus 



perty by reflexion, Young wrote 

 in a review ('Quarterly Review,' 

 May 1810): "The discovery . . . 

 appears to us to be by far the most 

 important and interesting that has 

 been made in France, concerning 



favorable au sj'stome de roniis.sion 

 qu'h celui des ondulations. lis do- 

 montrent ^galement linsuffisanoe 

 des deux hypotheses ; en etlet com- 

 ment expliijuer dan.s I'une ou dans 

 I'autre pounjuoi un rayon polarii«^ 



the properties of light, at least since ' pent traverser sous uiie certaine 



the time of Huygens ; and it is so inelinaison uu corps diaphnne, eu 



much the more deserving of notice, se ddrobant totalement k la n.^- 



as it greatly influences the general flexion partielle qui a lieu h la sur- 



balance of evidence in the com- face de ces corps dans les ciui ordi- 



parison of the undulatory and the naires ?" (quoted l>y Peacock, 'Life 



projectile theories of the nature of of Young,' p. 248 note). 



