60 



E. S. Brough — On a Case of Lightning. 

 But VS = Q 



[Fe 



■-=1 = ^'V^^^ -U'*- 



_J,-a 



X log € — 





d— '^ d^ — a" 

 which is the expression for the potential of the discharge. 

 Now in the particular case under consideration 

 r = 1'500 c. m. 

 K = 3-000 c. m. 

 d = 2-250 c. m. 

 andfl^ = 0-125 cm. 

 Hence F = 396 X 10^ grammes per sq. centimetre. 



14 Q = ^0586-5 I ^i^g^i^^g electrostatic 0. G. S. units. 



Changing the units to the ordinary ones in practical use, we find 

 14 Q = 16-86 microfarads. 

 V = 216810 volts. 



Assuming the sparking distance to increase as the square of the potential, 

 it can be calculated from the experimental results obtained by Messrs. 

 Warren de la Rue and Muller (Proc. Roy. Soc. Jan. 1876,) namely, that 1000- 

 rod chloride of silver cells give a spark 0-009166 inch, that a difference of 

 potentials of 216810 volts would produce a spark in air between two elec- 

 trodes at a distance of about 36 feet aj^art. This is of course a relatively 

 very short distance, but it must be remembered that we have only taken 

 into consideration that portion of the energy of the discharge which was 

 employed in breaking the 14 insulators, and have neglected all that was 

 spent in heat, light, &c. 



The reading of the following papers was postponed — 

 1. — ITote on the Variation of the Barometrio Tides in connection icith 

 diurnal Land and Sea Breezes. By Henry F. Blanford. 

 2. — The Kaimur Range. By Chai^drasekhara Banurji. 

 The Meeting then adjourned. 



( 



