142 



MALUS. 



this point then, they would say, that Wollaston was de- 

 ceived.' The object which Malus proposed in his memoir 

 was to submit this point to a decisive experimental test. 

 He chose a substance, beeswax, whose refractive power 

 could be measured in the transparent state, and in the 

 opaque state by the method of Wollaston. He applied 

 to the angles of disappearance corresponding to these two 

 conditions, and sufficiently different one from the other, 

 the formulas of the Mecanique Celeste, and he found there 

 would result refractive powers perfectly identical. This 



For refraction; by an analogous construction, the circles which 



spread in the denser medium. are smaller than those in the first, the 

 radii being diminished in the ratio of the velocities or inversely as the 

 densities. Thus when the new wave originating at o' has spread to vt, 

 that from o will have spread to double the same radius at v. The com- 

 mon tangent or front of the refracted waves will be inclined at an angle 



t v, which is easily determined by drawing the parallel through t of 

 the incident tight, whence we have (i and r being the angles of inci- 

 dence and refraction) u t=o t sin. i, and o v=o t sin. r; but o v and u t 

 being the radii of waves in the two media, are in the constant ratio of 

 the densities =^5 hence sin. i =/* sin. 7', which is the experimental 



1 aw of refraction. 



