616 SCIENTIFIC RECORD FOR 18S3. 



the original resistance; with flint-glass the difference is still more 

 striking; 2d, moderate annealing, causing the elasticity due to harden- 

 ing to partially disappear, destroys only in part the action of this 

 hardening on the resistance; and 3d, the resistance of a glass recently 

 annealed continues to increase slowly for some time. (C. R., March) 

 1883, xcvi, 785.) 



The rapidity with which light modifies the resistance of selenium is 

 well shown by an experiment of Bellati and Romanese. A Breguet 

 photophonic receiver received the light of a petroleum lamp after pass- 

 ing a solution of alum. This receiver and a rheostat, in the circuit of 

 ten Bnnsen cells, were placed on the two circuits of a differential gal- 

 vanometer. Between the light and the receiver a disk, pierced with 

 holes, rotated. Though the speed of rotation was widely varied no 

 appreciable change was observed in the mean resistance of the selenium, 

 which could hardly have been the case unless the effect of the light on 

 the selenium was instantaneous. {TINuovo Cimento, III, xi, 5; J. Phys., 

 November, 1883, II, n, 518.) 



Bidwell has submitted selenium cells to direct examination in order 

 to test the truth of Moser's hypothesis that their change of resistance 

 was an effect of heat. He finds the very reverse to be the fact; that 

 with a single exception all the cells in his possession rise in their 

 resistance as their temperature rises; reaching a maximum and then 

 decreasing. Exposed to sunlight a selenium cell does not become per- 

 ceptibly warm to the touch; but the amount of dark heat required to 

 effect the same reduction in its resistance would certainly render it too 

 hot to handle. {Phil. Mag., January, 18S3, V, xv, 31.) 



' Fritts has described a new form of selenium cell in which he has suc- 

 ceeded in diminishing materially the resistance, and in which the light 

 is made to strike the cell in the same direction as that in which the 

 current passes. These cells are far more sensitive to light than any 

 before made, falling in resistance from twenty to forty-four times when 

 placed in sunlight. He has also observed a change in resistance on re- 

 versing the current, and on varying the strength of the battery. To 

 make these sensitive cells it is necessary to use selenium which has been 

 very carefully purified. {Am. J. Sci., December, 1883, III, xxvi, 4G5.) 



Gray has published a valuable paper on the size of conductors re- 

 quired for the distribution of electric energy, considering the questions 

 of economy, safety, and regulation. {Phil. Mag., September, 1883, V, 

 XVI, 187.) 



Thompson has given an ingenious method for representing graphi- 

 cally the law of efficiency of an electric motor. {Phil. Mag., February, 

 1883, V, XV, 124; J. Phys., March, 1883, II, II, 131.) 



The complete report upon the experiments made at the Paris Elec- 

 trical Exhibition by the special committee appointed for the purpose, 

 consisting of Allard, Le Blanc, Joubert, Potier, and Tresca, has been 



