548 THE POPULAR SCIENCE MONTHLY. 



mon was preached in the West Kirk of Edinburgh, one of the largest 

 churches in Scotland, before an unusually crowded congregation ; and 

 he preached frequently for some time afterward. His ministrations 

 "seem always to have been most acceptable from the beauty and 

 earnestness of his style, and his well-known gift of creating interest 

 out of the driest subjects." But he was excessively nervous, and his 

 efforts were attended with intense suffering, in the shape of a nervous 

 faintness, which only occurred when he was making a public appear- 

 ance. For this reason he finally desisted from preaching. 



His regular philosophical studies began in 1799, when, at the sug- 

 gestion of his friend Brougham, he repeated Newton's experiments in 

 the inflection of light, and in connection with them made his first dis- 

 covery. His after-life was one of almost uninterrupted research. Plis 

 investigations were to a large extent parallel with those which Malus 

 and Fresnel and others were carrying on during the same period in 

 France, and in some cases room was left for question as to priority of 

 discovery. But in no case is Brewster's claim to independence in re- 

 search and originality impaired. Professor Forbes has summarized 

 the most important subjects of Brewster's inquiries at this time, as the 

 laws of polarization by reflection and refraction, and other quantita- 

 tive laws of phenomena ; the discovery of the polarizing structure in- 

 duced by heat and pressure ; the discovery of crystals with two axes 

 of double refraction, and many of the laws of their phenomena, includ- 

 ing the connection of optical structure and crystalline forms ; the laws 

 of metallic refraction, and experiments on the absorption of light. Of 

 his discoveries, primary importance belongs to those of the connection 

 between the refractive index and the polarizing angle, of biaxial crys- 

 tals, and of the production of double refraction by irregular heating. 



In 1816 he devised the kaleidoscope, which became at once very 

 popular, and spread his name widely among all classes of people. The 

 patent which he took out for it was of little value to him, for the 

 authorized manufacturers seem to have wholly failed to supply the 

 demand for the instruments, and the device was speedily patented by 

 enterprising adventurers who made their fortunes out of it. He after- 

 ward made earnest and long-continued eft'orts to promote reforms in 

 the patent laws that should make them more just to inventors. 



Several years later, in 1849-'50, he perfected the stereoscope, the 

 principle of which had been discovered and applied by Wheatstone in 

 1838. Wheatstone employed mirrors to effect the merging of the 

 binocular pictures into one ; Brewster substituted lenses for the mir- 

 rors, and gave us the instrument substantially as it is. 



For the improvements that were made in lighthouses during the 

 second decade of this century, the credit must be divided between 

 Brewster and the Frenchman Fresnel. Both worked independently, 

 and arrived in some cases at nearly identical results. Sometimes 

 Brewster, sometimes the Frenchman, was ahead on a particular point. 



