444 Mr. T. T. P. B. Warren on Electrification. 



If the discharge after one minute's contact and one minute's 

 insulation be 180, and the immediate discharge 200, the dura- 

 tion of contact being also one minute, the total effect for electri- 

 fication at the end of the minute's insulation will be 95 per cent, 

 of what it would have been if connected to the same battery for 

 two minutes. 



By taking these considerations into account, the formula of Pro- 

 fessor Fleeming Jenkin,R==( ^ ) x 10 6 , may be rendered 



strictly applicable for deducing from the loss of static charge in 

 time t the resistance for the same period of contact in absolute 

 measure, or in terms of that system which makes R and K func- 

 tions of each other ; and we may expect that the capacity K can 

 be eliminated from this formula when R is known, if we can 

 determine the constant for electrification for the interval of time 

 during which the core is held free. 



In this formula, if the test is performed in the manner here 

 indicated, t will be 60, and the value obtained for R will be the 



C 



resistance at the end of the second minute more nearly as — ap- 

 proaches 1. This resistance has then to be divided by a number 

 which expresses the ratio between the first and second minute's 

 contact ; approximately, and on short lengths of core, this may 

 be obtained as follows : — Recharge the core, after being kept to 

 earth for some hours, maintaining contact with the battery for 

 two minutes before noting the loss ; then by dividing the per- 

 centage of loss in the first experiment by the percentage of loss 

 given in the second experiment, we shall obtain a number by 

 which, if R be divided, the resistance corresponding to one mi- 

 nute's contact maybe found. 



The following ratio expresses the rate of increase in resistance 

 on prolonged contact : — Let D be the deflection at the end of the 

 first period of contact, and d the deflection at the end of the nth. 

 period, then D : d : : d : deflection at the end of n 2 minutes ; or 

 the deflection after the first period of contact is to the deflection 

 for any other period of contact as this deflection is to the deflec- 

 tion at the period of contact corresponding to the square of the 

 intervals. 



I have to acknowledge my obligation to Mr. Hooper for pla- 

 cing at my disposal the necessary instruments and cores for the 

 subject of this paper. 



