332 Mayer — Experiments with Pendulum electrometer. 



inches in diameter. I made a similar cylinder of wood neatly 

 covered with thick tin-foil. With it I made the following 

 experiments to test the value of the pendulum -electrometer 

 from measurements that could be compared directly with those 

 made by Coulomb with his torsion-balance. 



To do this I had first to determine the fraction of the charge 

 lost by this cylinder per minute. This I did by transferring, 

 at intervals of three minutes, a proof-plane from the charged 

 cylinder to the stationary sphere of the pendulum- electrometer, 

 and made a series of experiments similar to those given under 

 " Experiments to determine the law of the loss of electricity, 

 "etc." It was found that the charged cylinder lost *04 of its 

 charge in one minute. 



The following experiment, ~No. 9 of the series given, will 

 show the manner of procedure in making a measure of electric 

 density at a point on the cylinder. 



Proof-plane carried from contact with middle of cylinder 

 to stationary sphere of pendulum-electrometer gave a deflec- 

 tion of the pendulum of 3*55 cms., with distance of centers of 



spheres of 5*55 cms. \/3*55 X 5*56 = 1043 = charge on middle 

 of cylinder. After an interval of two minutes the following 

 measure was obtained from charge of proof -plane conveyed to 

 electrical-pendulum from contact with the end of the cylinder : 



Deflection of pendulum = 6-7 cms. 

 Distance of centers of spheres = 8-7 cms. 



V^V X 8 m 1 = 22'53, 22-53 + (22'53 X '08)= 24*33, 



- 10-43 



and = 1:2-33. 



24-33 



That is, the ratio between the electric density on the middle of 

 the cylinder to that on the end is as 1 to 2*33. 



The following measures were made in the above manner : 





Density on Middle. 



Density on 



End. 





Density on Middle. 



Density on End 



1 



1-00 



2-42 





1 



1-00 



2-21 



2 



u 



2-36 





8 





2*31 



3 



a 



2-20 





9 





2-33 



4 



it 



222 





10 





2-23 



5 



4. 



2-26 





11 





2-26 



6 



Mean = 1 



2-20 





12 





2 21 





2-27 



Coulomb gives' for the distribution on this cylinder the fol- 

 lowing ratios : 



At middle of cylinder TOO 



" 2 ins. from end 1*25 



" 1 in. " end _ 1*8 



" end 2-3 



