40 PROCEEDINGS OF THE AMERICAN ACADEMY 



of Professor J. D. Forbes, and say : " His scientific glory is different in 

 kind from that of Young and Fresnel ; but the discoverer of the law of 

 polarization, of biaxial crystals, of optical mineralogy, and of double 

 refraction by compression, will always occupy a foremost rank in the 

 intellectual history of the age." His theory of only three primary 

 colors, which he proposed as a substitute for the seven primary colors 

 of Newton, though plausible and well sustained by his experiments, 

 has suffered more from neglect than from criticism, Helmholtz alone 

 having seriously undertaken to refute it. Outside of the range of Op- 

 tics, Brewster's most important contribution to science was a paper, pub- 

 lished in 1821, on the mean temperature of the globe and the close co- 

 incidence between the poles of maximum cold and maximum magnetic 

 dip. His first appearance, in 1806, before the commonwealth of science, 

 was with a criticism upon the demonstrations of the lever, as furnished 

 by Galileo, Huyghens, De la Hire, Newton, Maclaurin, Landen, and 

 Hamilton. The solution which he himself gives of this fundamental 

 problem in statics, if not unexceptionable, is certainly ingenious, and 

 indicates a mind well adapted for mechanical research. 



Brewster's scientific labors sometimes assumed a practical turn. In 

 1831 he published, in the Transactions of the Royal Society of Edin- 

 burgh, a memoir on the construction of Polyzonal Lenses for Light- 

 houses. As early as 1748, Buffbn had proposed a similar device 

 for burning-glasses. The execution of it was postponed for thirty 

 years, and then proved a failure even in the hands of Rochon. Con- 

 dorcet, in his eulogy upon Buffbn, pronounced in 1788, suggested a 

 modification of his plan, which consisted in building the lens up of sep- 

 arate rings. We next hear of the subject from Brewster in 1811. 

 But the British government were not ready to take the hint from 

 their scientific advisers until after Fresnel had presented to the French 

 Academy of Sciences, in 1822, his memoir on Lighthouses, and his 

 lamp and lens shot forth a blaze of light from the headlands of France. 



The Kaleidoscope, which Brewster invented in 1817, delighted and 

 instructed all Europe at the time. Fashion may have dethroned it, 

 though once the ornament of the fair sex : but it has not outgrown its 

 popularity in the nursery, and time never can exhaust the fertility of 

 this invention in devising patterns for the manufactory. No less won- 

 derful, no less charming, is the Stereoscope, which, though invented by 

 Wheatstone, has been remodelled by Brewster in a way which has 

 brought it into the homes of millions, to delight, refine, and civilize all 

 ages and all classes. 



