510 SPECIAL METHODS OF DISCOVERY. 





1804, found a new star, which he soon was led to consider 

 as a planet. Grauss and Burckhardt also calculated the 

 elements of its orbit, "and the planet was named Juno.' 

 ' After this discovery Olbers sought the sky for additional 

 fragments of his planet with extraordinary perseverance. 

 He conceived that one of two opposite constellations, the 

 Virgin or the Whale, was the place where its separation 

 must have taken place ; and where, therefore, all the orbits 

 of all the portions must pass. He resolved to survey, three 

 times a year, all the small stars in these two regions. This 

 undertaking, so curious in its nature, was successful. On 

 March 29, 1807, he discovered Vesta, which was soon 

 found to be a planet. And to show the manner in which 

 Olbers pursued his labours, we may state that he after- 

 wards published a notification that he had examined the 

 same parts of the heavens with such regularity, that he 

 was certain no new planet has passed that way between 

 1808 and 1816.' l 



It was by means of his hypothesis of the propagation of 

 light by undulations that Huyghens was led to discover 

 the law which regulates extraordinary refraction in doubly- 

 refracting substances ; and that Brewster, Biot, Fresnel, 

 and Arago were enabled to explain the more complex 

 phenomena of this kind in biaxial crystals. It was by 

 assuming that polarization of light might be produced 

 by other means than those already known that Biot and 

 Seebeck were led to discover that tourmaline, instead of 

 giving, by double refraction, two images oppositely polar- 

 ized, gives a single polarized image ; and that Brewster 

 discovered a partially similar property in agate. 



In order to test the commonly believed hypothesis that 

 the yellow or most luminous of the sun's rays were the 



1 Wliewell, History of the Inductive Sciences, vol. ii. 3rd edit. p. 179. 



