230 GENERAL CONDITIONS OF SCIENTIFIC RESEARCH. 



throw the point of greatest heat to a considerable distance 

 beyond the vjsible part 'of the spectrum ; an anticipation 

 which experiment fully confirmed, by placing it as much 

 beyond the dark limit of the red rays as the red part is 

 distant from the bluish-green band of the spectrum.' l 



Sir Humphry Davy, in the year 1802, conjectured 

 that all electrical decompositions might be polar, i.e. the 

 separated elements might be divided into positive and 

 negative. In the year 1806, he tried to test this, and, by 

 numerous experiments, proved his conjectures to be cor- 

 rect, and showed that when a liquid was decomposed by an 

 electric current, it was separated into two classes of bodies, 

 positive and negative, and c that chemical and electrical 

 attractions were produced by the same cause, acting in 

 the one case on particles, in the other on masses.' It was 

 also with the object of supporting this theory that he 

 tried to decompose potash and soda by the aid of an 

 electric current, and succeeded. 



Anticipating that a piece of iron changing in tempe- 

 rature whilst under magnetic influence would produce an 

 electric current by magneto-electric induction, I heated 

 an iron wire to redness in the axis of a coil of insulated 

 copper wire, the ends of which were attached to a galva- 

 nometer, and allowed the iron to cool whilst in contact 

 with the poles of a magnet, and obtained the expected 

 current. 2 



Mitscherlich, knowing the law of expansion of calc- 

 spar by heat, predicted that its double-refracting power 

 for light would decrease as the temperature of the spar 

 was raised, and this was proved to be correct by experi- 

 ment. The continuity of the liquid and gaseous states of 



1 Mrs. Somerville, Connection of the Physical Sciences, 2nd edit, 

 p. 247. 



2 See Proceedings Royal Society, 1869, No. 108. 



