134 



POPULAR EKROKS. 



against truth in single combat in the absence of ex- 

 citement or self interest. 



General Pleasanton''s experiments were sug- 

 gested by the previous experiments of others upon 

 the same subject which had given unsatisfactory 

 and contradictory results. Sir Isaac Newton, in 

 1666, had analyzed the sun's rays by means of a 

 prism into the three primary colors, blue, yellow, 

 and red. Sir John Herschel had studied the effects 

 of these different rays in chemical decomposition 

 and on vegetation. Others had tried the same 

 thing, not only with the colored rays of the spec- 

 trum, but also with light of different colors, pro- 

 duced by different colored glass and liquids. The 

 results disagreed not only with different observ- 

 ers, but also with the same observer in different 

 plants ; and it was also found that the effect of the 

 blue light of the spectrum differed somewhat from 

 that produced by blue glass or liquids. 



One of the earliest and best established facts re- 

 garding the effect of light on vegetation is that its 

 absence favors the germination of seeds. Its 

 presence does not, however, appear to be very in- 

 jurious. Professor Tracy, of Michigan, found that 

 seeds germinated with greatest vigor in pots left 

 uncovered, followed by those covered by blue, clear 

 glass, red, and orange, in the order named. While 

 the seeds, therefore, germinated much better under 



