SOLAR LIGHT. 395 



Whether rays of heat differ from rays of light, by a differ- 

 ence in the lengths of the transversal vibrations of ether ; or 

 whether they are identical with rays of light, but that a 

 certain velocity in the vibrations which generates very high 

 temperatures, is requisite to excite the impression of light in 

 our organs, the Sun, as the main source of light and heat, must 

 nevertheless, be able to call forth and animate magnetic 

 forces on our planet, and more especially in the gaseous 

 strata of our atmosphere. The early knowledge of thermo- 

 electrical phenomena in crystallized bodies (such as tourma- 

 line, boracite, and topaz), and Oersted's great discovery (1820) 

 that every conducting body charged with electricity exerts a 

 definite action on the magnetic needle during the continua- 

 tion of the electrical current, afforded practical evidence of 

 the correlation of heat, electricity, and magnetism. Basing 

 his deductions on the idea of such an affinity, Ampere, 

 who ascribed all magnetism to electrical currents which lie in 

 a plane at right angles to the axes of the magnet, advanced 

 the ingenious hypothesis that terrestrial magnetism (the 

 magnetic charge of the Earth) was generated by electrical 

 currents, circulating round the planet from east to west; and 

 that the horary variations of the magnetic declination are on 

 this account consequences of the fluctuations of heat, varying 

 with the position of the Sun, by whose action these currents 

 are excited. These views of Ampere have been confirmed 

 by Seebeck's thermo-magnetic experiments, in which diffe- 

 rences of temperature of the points of contact of a circle 

 composed of bismuth and copper, or other heterogeneous 

 metals, affect the magnetic needle. 



Another recent and brilliant discovery of Faraday's, the 

 notice of which has been of almost simultaneous occurrence 

 with the printing of these pages, throws an unexpected light 

 on the same important subject. Whilst the earlier researches 

 of this great physicist showed that all gases are diumuguctic, 



