370 SCIENTIFIC CONGRESS OP CARLSRUHE. 



the vegetable that the saline material is decomposed. The metamor- 

 phosis takes place in the soil after the solution has penetrated it, and, 

 strange to say, it takes place precisely in the way most propitious to 

 the development of the plant. 



Saline substances, therefore, are not absorbed indifferently by the 

 roots of vegetables; before these can be reached by them, such sub- 

 stances have undergone a sort of preparation which qualifies them for 

 the part they are destined to fulfill in the act of nutrition. 



If we could allow ourselves to interpose an opinion on a question 

 handled by such a master as M. Liebig, we would say that thjs func- 

 tion of arable land might be assimilated to the act of digestion. What, 

 in natural history, distinguishes vegetables from animals is the absence 

 of a digestive tube, and yet the former feed and grow as well as the 

 latter. The interesting discovery just adverted to, justifies the admis- 

 sion that there may be digestion without a digestive tube. If nutrition, 

 in a word, implies digestion, we may say that in plants this digestion 

 is external ; while, in animals, it is internal. ' 



VI. Section oe Physics. 



Magnetic Currents Developed by Torsion — Electro-statics — Binocular Vision — Apparatus of 

 Ruhmkorff — Photo-chromatic Illumination — Mechanical Equivalent of Heat — Molecular 

 Movement in Gaseous Bodies. 



To the researches of a physical nature, which were communicated in 

 the mixed session of the 19th September, we ought to add an account 

 of some other labors, not less important, which were explained by their 

 authors in the special sessions. The first to address the meeting was 

 Professor Wiedemann, of Basle, who gave a summary of his labors on 

 magnetism in its relations with torsion ; a noble subject, whose start- 

 ing point is to be sought in an observation made some twenty years 

 since by Choron,* and which has been inaugurated by the ingenious 

 researches of M. Wertheim. Prof. Wiedemann has shown that a twisted 

 wire of iron undergoes a detorsion when it is subjected to magnetiza- 

 tion, and he is of opinion that the laws which govern the torsion are 

 applicable to the magnetization of bars of steel to such an extent that, 

 in the enunciation of those laws, we might interchange the words to 

 twist and to magnetize. He conceives that an analogous relation pre- 

 sents itself when we subject magnets to torsion, or when, inversely, 

 we magnetize twisted threads of iron. 



After M. Wiedemann, M. de Feilitzsch, Professor of Physics in the 

 University of Greifswalde, entered upon some considerations on the 

 law of currents in its relations with the law of electro-statics. Next, 



*"On the change of pole produced by torsion in an iron wire properly arranged," by M. 

 Choron ; Comptes rcndus des Seances des l\icademh des Sciences. XX., p. 1456. 



