DISCO VEKIES ARE NOT HAPHAZARD EESULTS. 225 



at last I found that he only meant me to move my head up 

 and down.' At any rate, till the lady had acquired the 

 notions which the technical terms convey, she could not 

 have made Bartolinus's discovery by means of his acci- 

 dent. ' By accidentally combining two rhombs in dif- 

 ferent positions,' it -is added, 1 ' Huyghens discovered the 

 polarisation of light.' Supposing that this experiment 

 had been made without design, what Huyghens really 

 observed was that the images appeared and disappeared 

 alternately as he turned the rhombs round. But was it 

 an easy or an obvious business to analyse this curious 

 alternation into the circumstances of the rays of light 

 having sides, as Newton expressed it, and into the addi- 

 tional hypotheses which are implied in the term polarisa- 

 tion ? Those will be able to answer this question who 

 have found how far from easy ifc is to understand clearly 

 what is meant by polarisation in this case, now that the 

 property is fully established. Huyghens's success de- 

 pended on his clearness of thought, for this enabled him 

 to perform the intellectual analysis, which never would 

 have occurred to most men, however often they had 

 c accidentally combined two rhombs in different positions.' 

 By accidentally looking through a prism of the same 

 substance, and turning it round, Malus discovered the 

 polarisation of light by reflection. Malus saw that, in 

 some positions, the light reflected from the windows of the 

 Luxembourg, thus seen through the prism, became dim. 

 Another man would have supposed this dimness the result 

 of accident ; but his mind was differently constituted and 

 disciplined. He considered the position of the window, 

 and of the prism ; repeated the experiment over and over ; 

 and, in virtue of the eminently distinct conceptions of 



1 Edinburgh Review, No. cxxxiii. p. 121. 

 Q 



