ELEMEN TAR 7 MA GNETISM. 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 his spectra 
giving the general impression of a reversal of the solar 
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 Kirchhoff's 
speculations are founded, had not an accident withdrawn 
me from the investigation. But Kirchhoffs 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 
