70 



Royal Society 



tained in circular plates and globes, together with their respective 

 intensities for diameters varying from '25 to 2 inches; a circular 

 plate of an inch diameter and ^th of an inch thick being taken as 

 unity, and supposed to contain 1 00 particles or units of charge. 



Diameters, 



or 



units of charge. 



Circle. 



Globe. 



Particles. 



Intensity. 



Particles. 



Intensity. 



0-25 

 0-50 

 0-75 

 1-00 

 1-25 

 1-40 

 1-50 

 1-60 

 1-75 

 2-00 



25 



50 

 75 

 100 

 125 

 140 

 150 

 160 

 175 

 200 



0-062 

 0-250 

 0-560 

 1-000 

 1-560 

 . 1-960 

 2-250 

 2-560 

 3-060 

 4-000 



35 

 70 

 105 

 140 

 175 

 196 

 - 210 

 224 

 245 

 280 



0-124 



0-500 

 1-120 

 2-000 

 3-120 

 3-920 

 4-500 

 5-120 

 6-120 

 8-000 



13. The experimental investigations upon which these elementary 

 data depend, constitute a second part of this paper. The author 

 here enters upon a brief review of his hydrostatic electrometer, as 

 recently perfected and improved, it being essential to a clear com- 

 prehension of the laws and other physical results arrived at. 



In this instrument the attractive force between a charged and 

 neutral disk, in connexion with the earth, is hydrostatically coun- 

 terpoised by a small cylinder of wood accurately weighted, and 

 partially immersed in a vessel of water. The neutral disk and its 

 hydrostatic counterpoise are freely suspended over the circumference 

 of a light wheel of 2*4 inches in diameter, delicately mounted on 

 friction-wheels, so as to have perfectly free motion, and be suscep- 

 tible of the slightest force added to either side of the balance. Due 

 contrivances are provided for measuring the distance between the 

 attracting disks. The balance-wheel carries a light index of straw 

 reed, moveable over a graduated quadrantal arc, divided into 90° on 

 each side of its centre. The neutral attracting plate of the electro- 

 meter is about 1^ inch in diameter, and is suspended from the 

 balance-wheel by a gold thread, over a similar disk, fixed on an insu- 

 lating rod of glass, placed in connexion with any charged surface the 

 subject of experiment. The least force between the two disks is 

 immediately shown by the movement of the index over the gradu- 

 ated arc in either direction, and is eventually counterpoised by the 

 elevation or depression in the water of the hydrostatic cylinder sus- 

 pended from the opposite side of the wheel. The divisions on the 

 graduated quadrant correspond to the addition of small weights 

 to either side of the balance, which stand for or represent the 

 amount of force between the attracting plates at given measured dis- 

 tances, with given measured quantities of electricity. This arrange- 

 ment is susceptible of very great accuracy of measurement. 



The experiment requires an extremely short time for its develop- 

 ment, and no calculation is necessary for dissipation. The author 



