Oscillatory Discharges. 5 



More recent experiments are those o£ Robb *, who kept the 

 condenser in communication with the source o£ electricity for 

 intervals gradually increasing from very small values, deter- 

 mined by the duration of the contact established by two 

 steel spheres striking against one another ; but the uncertainty 

 attending this method of evaluating the duration of the time 

 of charge imparts to those experiments a merely qualitative 

 character. 



Similarly Wulf f, in an investigation on the dissipation of 

 energy in dielectrics, determined by means of an interrupter 

 moved by a falling weight the curve of residual discharge ; 

 and whereas for condensers not subject to the phenomenon of 

 charge-penetration he obtained values agreeing well with 

 those calculated from the formula T = 27T\/LC, he found 

 notable departures in the case of two paraffin-paper con- 

 densers. 



Tallqvist's J experiments afford more adequate arrangements 

 for quantitative verifications. By means of a pendulum 

 interrupter, he obtained a satisfactory verification of the 

 formulas expressing the charge of a condenser as a function 

 of time, for periods of about five-thousandths of a second ; 

 and so do Seller's similar researches, equally carried on with 

 a pendulum interrupter allowing of still more exact measure- 

 ments of the time of charge. 



Seiler first found the formula T = 27r\/LC to be verified 

 for periods ranging from 0*0012 to 0*0045 sec, L being 

 maintained constant and C taking variable values ; but he 

 failed to state a satisfactory agreement between the experi- 

 mental values of the logarithmical decrement of oscillations 

 and those derived from theory. 



Similar investigations, based upon Helmholtz and Schiller's§ 

 classical method, have recently been made — for periods 

 between 0-0000246 and 0-0000586 sec— by Webster ||, using 

 an air-condenser and two spirals wound in a suitable way, so 

 as to cause their capacity to be negligible. The interruption 

 of contacts was effected, instead of by the pendulum, by 

 means of a weight falling down from different heights (of 

 about 75 cm.) ; by starting successively two levers, this device 

 enabled — according to Webster's statements — measurements 

 of time intervals as small as 0*0000005857 sec to be made. 



* Phil. Mag-, xxxiv. p. 389 (1892). 



t Wien. Ber. cv. II. a, p. 667 (1896). 



X Ibid. lx. p. 248 (1897). 



§ Ibid. lxi. p. 30 (1897). 



|| Phys. Rev. xl p. 297 (1898). 



