1864.] 



of Electrical Force. 



369 



12. The author calculates from these laws of charge for circles and 

 globes, a series of circular and globular measures of definite values, taking 

 the circular inch or globular inch as unity, and calling, after Cavendish, a 

 circular plate of an inch in diameter, charged to saturation, a circular inch 

 of electricity ; or otherwise charged to any degree short of saturation, a 

 circular inch of electricity under a given intensity. In like manner he de- 

 signates a globe of an inch in diameter a globular inch of electricity. 



In the following Table are given the quantities of electricity contained in 

 circular plates and globes, together with their respective intensities for dia- 

 meters 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 

 100 particles or units of charge. 



Diameters, 

 or 



units of charge. 



Cir 



cle. 



Globe. 



Particles. 



Intensity, 



Particles. 



Intensity. 



0-25 



25 



0062 



35 



0-124 



0-50 



50 



0-250 



70 



0-500 



0-75 



75 



0-560 



105 



1-120 



1-00 



100 



1-000 



140 



2-000 



1-25 



125 



1-560 



175 



3-120 



1-40 



140 



1-960 



196 



3-920 



1-50 



150 



2-250 



210 



4-500 



1-60 



160 



2-560 



224 



5-120 



1-75 



175 



3-060 



245 



6-120 



2-00 



200 



4-000 



280 



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 comprehension 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 counterpoised 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 susceptible of the shghtest 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 electrometer is 

 about 1^ inch in diameter, and is suspended from the balance-wheel by 

 a gold thread, over a similar disk, fixed on an insulating 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 



