REPORT ON OPTICS. 
311 
It will afford a curious insight into the character of great 
minds, and at the same time a striking proof of the fallibility 
and even the weakness of the loftiest intellects, to study the 
conduct of Newton and of Huygens in reference to their mu¬ 
tual discoveries. We have already seen that Huygens rejected 
Newton’s doctrine of the different refrangibility of light, and 
also his analysis of the spectrum; and it is well known that he 
opposed the theory of universal gravitation. The discoveries 
of the Dutch philosopher were received by our illustrious 
countryman with equal if not greater distrust. Newton not 
only rejected the undulatory theory which Huygens had so 
ably expounded, but he rejected also the mathematical law of 
extraordinary refraction, which was established by direct ex¬ 
periment,—a law the truth of which was independent of the 
hypothesis from which it was deduced. Anxious, no doubt, to 
avoid controversy, Newton did not formally attack the law of 
Huygens, nor did he call in question the accuracy of his expe¬ 
riments ; but without noticing this law he brings forward a new 
one of his own, without the sanction of any general principles, 
and without a single experiment in its support. “ The un¬ 
usual refraction,” says Newton, “ is performed by the fol¬ 
lowing rule,” which he proceeds to describe minutely with 
the aid of a diagram. Now this rule, investigated by the first 
genius of the age, and with all the powers of the inductive 
philosophy, has been universally rejected as erroneous ; while 
the law of Huygens, explored by a less gifted mind, and origi¬ 
nating in a bold hypothesis, enjoys the splendid triumph of 
having not only laid the foundation of one of the noblest 
branches of knowledge, but of having led, by its application, to 
the establishment of that very hypothesis from which it sprung. 
Historical truth, however, requires us to add that Huygens 
did not see the universality of his own law, and that in his 
investigation of the double refraction of rock crystal, both 
his experiments and his hypothesis utterly failed him. He 
announced that the double refraction of this mineral was regu¬ 
lated by two spherical emanations, one of which was a little 
slower than the other. This strange mistake had however a 
very natural origin. Taking it for granted that the extraor¬ 
dinary ray must always be the least refracted one, as in Iceland 
spar, Huygens appears to have measured only the refraction of 
the least refracted ray, which he found to be regulated by the 
ordinary law of Snellius. This result was perfectly correct; 
but he had been working only with the ordinary ray, having 
assumed most improperly that the other ray would have the 
same properties as the corresponding one in Iceland spar. By 
