120 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



ticity at each point in the plane of the disk, one of which is 

 directed towards the centre of this disk. 



Soret and Sarasin have investigated the rotatory power 

 of quartz, extending their observations to the ultra-violet 

 rays as far as the line II, using in general the method of 

 Foucault and Fizeau, modified by that of Mascart. The 

 numbers obtained agree well with those calculated by Boltz- 

 mann's formula. 



Henri Becquerel lias submitted a large number of sub- 

 stances to the influence of magnetism, and examined them 

 with polarized light, to determine whether the magnetic ro- 

 tatory polarization of these bodies sustained any relation to 

 their other physical properties. He finds that this magnetic 

 rotation in general increases with the refractive index of the 

 body, nearly as n 2 (n 2 1), and draws a number of important 

 facts from this conclusion. 



ELECTRICITY. 



1. Magnetism. 



Wild has examined the properties of a nickel- magnet 

 made by Joseph Wharton, of Philadelphia, and given by 

 him to Kotschubey, of the Russian commission. The mag- 

 net was 155 millimeters long, 9.5 wide, and 2 thick, the ends 

 being pointed. It weighed 25 grams. Its magnetic mo- 

 ment, determined in the usual way, was, per gram, 112,000 

 as received, and 186,000 after remagnetizing; while that of 

 a nearly similar steel magnet w r as 245,000 and 368,000 re- 

 spectively. On analysis by Butlerow, the only impurity 

 was iron, of which there was present one third of one per 

 cent.; traces of cobalt were also detected. Wild concludes, 

 1st, pure nickel, unlike iron, takes considerable permanent 

 magnetism, but the amount is only from one half to one 

 third of that taken by different sorts of hardened steel; 2d, 

 the magnetism remaining in nickel is less permanent than in 

 hardened steel ; 3d, the temperature-coefficient is less in the 

 case of nickel than in that of hardened steel ; and, 4th, the 

 temporary magnetism acquirable by nickel, though about 

 twice its permanent magnetism, is only half that .which 

 hardened steel and only one fourth of that which soft iron 

 is capable of acquiring. 



