LIFE AND LABORS OF HENRY GUSTAVUS MAGNUS. 229 



submitted to luminous radiations. According to Magnus, rock-salt is 

 not in the least atliermocbroic, that is to say, diathermal, under any 

 kind of heat; it is, on the contrary, monothermal, emitting and absorbing 

 only a very limited number of simple radiations; just as incandescent 

 sodium emits only a few of the yellow radiations and excludes all other 

 kinds of light. This result, certainly very curious and unexpected, 

 should be investigated in regard to other bodies. 



Magnus, as we have said, especially applied himself to the study of 

 heat, but he enriched other branches of science with numerous observa- 

 tions, all of which bear the imprint of his acute and accurate under- 

 standing. We will say a few words only upon his researches in thermo- 

 electricity. Taking up the experiments of M. Becquerel, who attempted 

 to show that in an homogeneous circuit heated at one point, electricity is 

 produced because the heat emitted on both sides of this point differs in 

 quantity, Magnus demonstrated that the production of electricity in 

 the connected wire should not be attributed to the unequal transmission 

 of heat in the two portions of this wire, but to an alteration in its molec- 

 ular condition. After having confirmed the fact announced by Matteucci, 

 that there is no production of electricity when two masses of mercury 

 are brought in contact at different temperatures, he showed that an 

 abrupt change of diameter, either in a column of mercury, or in a per- 

 fectly homogeneous wire, does not necessarily give rise to a current of 

 electricity, but on the other hand, electricity may always be excited by 

 heating the point of contact of two heterogeneous portions of a single 

 wire, for instance, when one part is hammer hardened, and the other 

 annealed. 



This sketch would be incomplete without some notice of the numerous 

 articles published by Magnus in the memoirs and monthly issues of the 

 Academy of Berlin, and also in the Annales de Poggendorff^ many of 

 which have reappeared in the "Archives,'^ either translated or reviewed. 

 We must, however, confine ourselves to a mere mention of his researches 

 upon the movement of liquids ; upon the deviation in the rotary motion 

 of projectiles ; upon the temperature of the earth at great depths ; upon 

 the tension of mixed vapors ; upon the electrolysis ; upon the action of 

 the brace of magnets, and upon the diffraction of light in a vacuum. Such 

 were some of the various subjects which engaged his attention and which 

 he pursued with unceasing accuracy and care. 



But it was not only by his numerous and laborious investigations that 

 Magnus advanced the cause of science ; he filled the office of Professor; 

 was, in fact, the leader of the university. He loved youth, and knew 

 how to make himself beloved while imparting a taste for that science to 

 which he had consecrated his life ; and we m ay, without exaggeration , say 

 that he exercised an important influence upon thQ scientific generation 

 which has succeeded him. He received many testimonials of the confi- 

 dence he inspired in the young men of the university ; among others, we 

 may mention, that in the troubles of 1848, to him, a man preeminently 



