470 



Messrs. A. W. Porter and D. K. Morris. [Mar. 21, 



oscillatory discharge, are hence unsiiited for discriminating between 

 the two causes : to test whether true hysteresis exists it is essential 

 to so arrange the experiment that all viscous effects shall have had 

 time to subside before any measurement of charge is made. Hence 

 the interesting experiments made during the last three years by 

 Riccardo Arno,* in which a dielectic cylinder begins to rotate when 

 placed in a rotating electrostatic field, as well as the experiments 

 made by P. Janet,f and by one of us using oscillatory discharges, do 

 not serve as test experiments on this question. 



The arrangement which we adopted to test for hysteresis is as 

 follows : 



Condenser 



Rheostat 



Batten/ 



A battery (E.M.F. = 11 volts) is connected permanently in simple 

 circuit with the ends of a rheostat of 850 ohms resistance. The 

 condenser terminals can be put in contact by means of a two-way 

 switch, with one end A, and an intermediate point B of the rheostat. 



The position of the point B is capable of continuous adjustment, 

 and hence also is the difference of potential between the condenser 



* Published in the ' Eendiconti della E. Accademia dei Lincei/ October 16, 

 1892, p. 284, April 30, 1893, p. 341, November 12, 1893, p. 260, March 18, 1894, 

 p. 272, June 17, 1894, p. 585, November 18, 1894, p. 294. For translations vide 

 1 The Electrician ,' March 3, June 23, December 29, 1893, and January 18, 1895. 



t " Sur les Oscillations ^lectriques de Periode Moyenne," ' Journ. de Phys.,' 

 August, 1893. For other recent literature on the subject vide A. Hess, " Sur les 

 Dielecbriques Heterogenes," 'Journ. de Phys./ Jpril, 1893; Steinmetz, 'The 

 Electrician/ April 8, 1892 (from the 'Electrical Engineer ' of New York). 



