ELEMENTARY MAGNETISM. 261 



for 1855, he indicates that the rays which a body absorbs 

 are precisely those which it can emit when rendered 

 luminous. In another place, he speaks of one of hisspectrn 

 giving the general impression of a reversal of the solai 

 spectrum. Foucault, Stokes, and Thomson, have all been 

 very close to the discovery; and, for my own part, the 

 examination of the radiation and absorption of heat by 

 gases and vapors, some of the results of which I placed 

 before you at the commencement of this discourse, would 

 have led me in 1859 to the law on which all KirchhofFs 

 speculations are founded, had not an accident withdrawn 

 me from the investigation. But Kirchhoff's claims are 

 unaffected by these circumstances. True, much that I 

 have referred to formed the necessary basis of his dis- 

 covery; so did the laws of Kepler furnish to Newton 

 the basis of the theory of gravitation. But what Kirch- 

 hoff has done carries us far beyond all that had before 

 been accomplished. He has introduced the order .of 

 law amid a vast assemblage of empirical observations, 

 and has ennobled our previous knowledge by showing 

 its relationship to some of the most sublime of natural 

 phenomena. 



CHAPTER XV. 



ELEMENTARY MAGNETISM. 



A LECTURE TO SCHOOLMASTERS. 



WE HAVE no reason to believe that the sheep or the dog, 

 or indeed any of the lower animals, feel an interest in the 

 laws by which natural phenomena are regulated. A herd 

 may be terrified by a thunderstorm; birds may go to roost, 

 and cattle return to their stalls, during a solar eclipse; 

 but neither birds nor cattle, as far as we know, ever think 

 of inquiring into the causes of these things. It is other- 

 wise with man. The presence of natural objects, the 

 occurrence of natural events, the varied appearances of the 

 universe in which he dwells, penetrate beyond his organs of 

 sense, and appeal to an inner power of which the senses 

 are the mere instruments and excitants. No fact is to 

 him either original or final. He cannot limit himself to 

 the contemplation of it alone, but endeavors to ascertain 



