372 Mr. H. Tomlinson on the Temperature at which 



or less than with gratings only experience can prove. Cer- 

 tainly, if the method is capable of giving exact results, it is in 

 the hands of one able to obtain them from it. 



In closing this paper I can only express my sincerest gra- 

 titude to the various friends who have done all in their power 

 to facilitate my work, and especially to Professor W. A. 

 Rogers, who has been tireless in his endeavours to determine 

 the true value of the standards of length ; to Mr. J. S. Ames, 

 Fellow in this University, who has given me invaluable aid 

 in the work with metal gratings ; and to Professor Rowland, 

 who has furnished all possible facilities and under whose 

 guidance the entire work has been carried out. 

 Physical Laboratory, 

 Johns 'Hopkins University, 

 March 1888. 



XLVIII. The Temperature at which Nickel begins to lose sud- 

 denly its Magnetic Properties. By Herbert Tomlinson, 

 B.A* 



IT has long been known that nickel, like iron, begins at a 

 certain temperature to rapidly lose its magnetic properties, 

 and that the critical temperature for the former metal is much 

 lower than for the latter. According to Faraday, nickel loses 

 its magnetic permeability about 330° to 340° C. ; according 

 to Becquerel, about 400° C. ; according to Pouillet, about 

 350° C. ; and according to Chrystal, about 400° C. Berson, 

 however, seems to have been the first t to publish a curve 

 showing the relation between magnetic induction and tempe- 

 rature right up to the point at which the former ceases prac- 

 tically to exist. The author has also, independently of Berson, 

 drawn up curves of a similar kind which have not as yet been 

 published, and which he ventures to offer to the Physical 

 Society, because they not only supplement Berson's results, 

 but they seem also to partly explain why different observers 

 have obtained such widely differing temperatures for the point 

 of nil permeability $. 



In the axis of a magnetizing solenoid, and perpendicular to 

 the magnetic meridian, was placed a nickel wire, 30 centim. 

 in length and 0*0053 square centim. in section. The solenoid 

 consisted of cotton-covered copper wire of ^ inch in diameter, 

 wrapped in a single layer of 8*25 turns to the centimetre 



* Communicated by the Physical Society: read February 25, 1888. 

 t Ann. de Phys. et de Chink vol. vii. (1886). 



\ That is practically nil. The experiments of Faraday seem to show 

 that the permeability never entirely vanishes. 



