826 



disappeared, but after the next meal the effect of the tartrate of 

 potash was again apparent. 10 drachms of tartrate of potash taken 

 in three days produced but little, if any effect, on the acidity of the 

 urine twenty -four hours after the last dose was taken. 



2. " On the direct production of Heat by Magnetism." By 

 W. R. Grove, Esq., M.A., V.P.R.S. &c. 



The author recites the experiments of Messrs. Marrian, Beatson, 

 Wertheim and De la Rive on the phenomenon made known some 

 years ago, that soft iron when magnetized emitted a sound or musical 

 note. 



He also mentions an experiment of his own. published in January 

 1845, where a tube was filled with the liquid in which magnetic 

 oxide had been prepared, and surrounded by a coil ; this showed, 

 to a spectator looking through it, a considerable increase of the 

 transmitted light when the coil was electrized. 



All these experiments the author considers go to prove that when- 

 ever magnetization takes place a change is produced in the molecu- 

 lar condition of the substances magnetized ; and it occurred to him 

 that, if this be the case, a species of molecular friction might be 

 expected to obtain, and by such molecular friction heat might be 

 produced. 



In proving the correctness of these conjectures difficulties pre- 

 sented themselves, the principal of which was, that with electro- 

 magnets the heat produced by the electrized coil surrounding them, 

 might be expected to mask any heat developed by the magnetism. 

 This interference, after several experiments, the author considers 

 he entirely eliminated by surrounding the poles of an electro-magnet 

 with cisterns of water, and by this means and by covering the 

 keeper with flannel, and other expedients, he was enabled to produce 

 in a cylindrical soft-iron keeper when rapidly magnetized and de- 

 magnetized in opposite directions a rise of temperature several degrees 

 beyond that which obtained in the electro-magnet, and which there- 

 fore could not have been due to conduction or radiation of heat from 

 duch magnet. A series of experiments with this apparatus is given. 



By filling the cisterns with water colder than the electro-magnet, 

 the latter could be cooled by the water while the keeper was being 

 heated by the magnetization. 



The author subsequently obtained distinct thermic effects in a 

 bar of soft iron placed opposite to a rotating permanent steel mag- 

 net, using a delicate thermo-electrical apparatus placed at his disposal 

 by Mr. Gassiot. 



To eliminate the effects of magneto-electrical currents, the author 

 then made similar experiments with non -magnetic metals and with 

 silico-borate of lead, substituted for the iron keepers, but no thermic 

 effects were developed. 



He then tried the magnetic metals nickel and cobalt, and obtained 

 thermic effects with both, and in proportion to their magnetic in- 

 tensity. 



Some questions of theory suggested by the above experiments 



