EXAMPLES OF PREDICTED DISCOVERIES. 231 



matter was also predicted by Herschel. In his 6 Prelimi- 

 nary Discourse on Natural Philosophy,' 1831, page 234, 

 he suggests that liquids and gases ' will ultimately turn 

 out to be separated by no sudden line of demarcation, but 

 shade into each other by insensible gradations. The late 

 experiment of Baron Cagnard de la Tour may be regarded 

 as a first step towards a full demonstration of this.' The 

 sagacity of the same eminent astronomer enabled him also 

 to anticipate theoretically one of the greatest discoveries 

 of Faraday, viz. that of the rotation of the plane of a beam 

 of polarised light by means of a magnet. 1 



Eelying on the strength, of Bode's law, and the conse- 

 quent probable existence of a planet between Mars and Jupi- 

 ter, the Grerman astronomers even formed themselves into 

 an association for discovering it, and wrote on the subject 

 of the long-expected planet. Instead, however, of a single 

 large planet only, a large number of small ones have been 

 found, by watching that particular part of the heavens. In 

 this way Ceres and Pallas were discovered between the 

 years 1801 and 1804 ; Vesta, in 1807 ; and a great many 

 since. One was discovered in 1845 ; three, in 1847 ; one, 

 in 1848 ; three, in 1850 ; two, in 1851 ; eight, in 1852 ; 

 four, in 1853; six, in 1854; four, in 1855; and so on, 

 and altogether about 158 have already been found. Some 

 of these are not more than about four miles in diameter, 

 whilst others are as much as about 35 miles. 



6 As soon as Wheatstone had proved experimentally 

 that the conduction of electricity occupied time, Faraday 

 remarked in 1838, with wonderful sagacity, that if the 

 conducting wires were connected with the coatings of a 

 large Ley den jar, the rapidity of conduction would be 

 lessened. This prediction remained unverified for sixteen 



1 Life of Faraday ', by Dr. H. B. Jones, vol. ii. p. 205. 



