GUSTAV ROBERT KIRCHHOFF. 373 



tion, the details of which I may be permitted to pass over, it comes out 

 that the different combinations in which the metals have been tried, the 

 variety of chemical processes in the different flames, and their vast dif- 

 ference of temperatures, exert no influence on the position of the lines 

 in the spectrum of the same metal." 



The last subject introduced into the Gesammelte Abhandlungen is 

 the history of spectrum analysis and the analysis of the sun's atmos- 

 phere. It rarely happens to any great epoch in science that it comes 

 wholly unheralded. Kirchhoff has candidly reviewed the various 

 claims which have been advanced as anticipations of his discovery. 

 Some of them were merely conjectures ; others failed from too great 

 generality and looseness of statement ; the best circulated from mouth 

 to mouth, were not published, and could not have been known to 

 Kirchhoff previous to his own discovery ; and all relied on inadequate 

 experiments, unsupported by mathematical demonstration. Every 

 great discovery in science, after it has been clearly proved and publicly 

 announced, throws back a light upon its antecedents which they did not 

 and could not originate. Spectrum analysis, with its far reaching con- 

 sequences, was in the air : a few great minds felt it and predicted it ; 

 Kirchhoff demonstrated it. 



In 1874, Kirchhoff published the Vorlesungen iiber Mathemati&che 

 Physik, or " Lectures on Dynamics." These lectures, thirty in num- 

 ber, relate to the mechanics of solids and liquids, the theory of light, 

 electricity and magnetism, and special subjects in hydro-dynamics and 

 electro-dynamics. As Kirchhoff informs his readers in the Preface, he 

 discusses what the phenomena are, and not their causes. Other writers 

 are accustomed to define mechanics as the science of forces, and force 

 as the cause which produces or strives to produce motion. Kirchhoff 

 admits the usefulness of this definition in the development of mechanics, 

 and to the student when it is illustrated by the experiences of ordi- 

 nary life ; but he thinks that there always clings to it an obscurity 

 from which the idea of cause and resistance cannot be extricated. This 

 obscurity manifests itself in the different views taken of the laws of 

 inertia and the parallelogram of forces, whether they are the results 

 of experience, axioms, or laws which can and must be known logically. 

 Kirchhoff aimed to remove this obscurity from mechanics, even if it 

 were only possible by a limitation of its propositions. He would 

 describe, fully and in the simplest manner, the motions occurring in 

 nature, ignoring their cause. Starting with the conception of space, 

 time, and matter, he would arrive by purely mathematical paths at the 

 general equations of mechanics. The notion of force comes in, but it is 



