118 . Presents. [June 11, 



On comparing the tractive force of the cobalt with that of iron, 

 each with 5 amperes of current, it will be seen from the table that it 

 was still very high, being no less, for the iron, than 0'437 Ib. = 

 222 Ibs. per square inch of section, or more than 12,000 times its own 

 weight. Although this amount of tractive force is greater than any 

 so far recorded for iron, yet the magnetising force was not sufficient 

 to break down the property of the increase of magnetic force of the 

 heated cobalt. - It is well, however, that I should point out that the 

 property only pertains in the highest degree to the metal when in a 

 state of purity, as several of the specimens experimented upon, from 

 different sources, only exhibit the property in a feeble manner, the 

 diminution being due to the presence of iron in the cobalt. 



As the determination of the limit of the magnetisability of iron by 

 different methods is of some importance to magnetical science, an 

 experiment was made on a cylinder of annealed charcoal iron wire 

 0'2 inch long, O'Oo inch in diameter, and f grain in weight. The 

 cylinder was driven up the end of a thick copper wire for the purpose 

 of suspension as in the previous experiments. The tractive force of 

 this specimen of iron at 13 C., with 40 amperes of current, was 

 0*75 Ib., which is equal to 381 Ibs. per square inch of section, or 

 7000 times the weight of the iron. 



That the limit of magnetisability was virtually arrived at in this 

 experiment was shown by reducing the current to 20 amperes, when 

 the tractive force remained at 0*734 Ib. = 373 Ibs. per square inch of 

 section, or only 8 Ibs. less per square inch than the tractive force 

 obtained with 40 amperes of current. 



Presents, June 11, 1891. 

 Transactions. 



Bremen : Naturwissenschaftlicher Verein. Abhandlungen. Band 

 XII. Heft 1. 8vo. Bremen 1891. The Society. 



Kharkoff: Section Medicale de la Societe des Sciences Experi- 

 mentales, Universite de Kharkow. Travaux. 1890. [Russian.] 

 8vo. Kharkow 1891. The Society. 



London : British Association. Report. 1890. 8vo. London 

 1891 - The Association. 



London Mathematical Society. Proceedings. Vol. XXI. Nos. 

 395398. 8vo. London 1891. The Society. 



Photographic Society of Great Britain. Journal and Transac- 

 tions. Vol. XV. No. 8. 8vo. London 1891. 



The Society. 



University of London. Calendar. 1891-92. 8vo. London 

 1891 - The University. 



