Determination of law of electric force 249 



globe was taken away, that the pith balls did not sep., but if they were sepa- 

 rated before their elect, was discharged, then the pith balls would at first sep. 

 about an inch or so, but quickly closed, whereas if the inner globe was electrified 

 after the hemispheres were separated, it was found to be a great while before 

 the pith balls closed. It was found that this was owing to the sticks of glass 

 on which the hemispheres slid being electrified thereby, as the same phenomena 

 were produced by electrifying those sticks when the hemispheres were taken off. 

 N.B. These sticks were not covered with sealing wax, and as appeared by 

 this exper. suffered the electric, to run along them pretty readily. The stick 

 of glass run through the globe had all that part without the globe covered with 

 sealing wax. 



513] The same thing tried by a better machine. 



Wed. Dec. 23 [1772]. Th. 52. N. i8. 



The exper. was tried in a different manner, the hemispheres being fastened 

 by sticks of glass covered with sealing wax within wooden frames turning on 

 hinges. 



If the pith balls were made to sep. pos. about i inch before the globe was 

 elect, they separated i or two diameters on touching the globe. If they 

 separated only r inch before touching, they did not sep. at all on touching the 

 globe. If they separated negatively i or 2 inches before touching, they did 

 not sep. at all after touching. 



The event was just the same whether the wires for discharging the elect, 

 of the globes when separated were placed so as to touch the hemispheres as 

 soon as they were sep. an inch from each other, or whether they were placed 

 so as not to touch them till they were separated almost the whole distance. 



N.B. Each hemisphere was drawn back about n inches from its first 

 situation. 



It appears from hence that the inner globe was a small matter overcharged, 

 but not enough so to make the balls sep. unless they were before positively 

 electrified, so that the redundant fluid in it could hardly be ^ of that which 

 it would have received by the same degree of electrification if the outer hemi- 

 spheres had been taken away, and probably not more than \ as much. 



[Exper. rosin*.} 



514] These rosin plates were made out of a mixture of 4 parts rosin and 

 r of bees wax mixed together with a considerable heat, towards the beginning 

 of the year 1771. Towards end of 1772 some round plates were cast out of this 

 by gentle heat, which were pared to a proper size and shape and then pressed 

 out between brass plates heated in wooden box over furnace (the tin lining 

 being not then made), the bits of tinfoil were at first fastened on by just wetting 

 it in a few places with gum water and sticking it on, but as this was found not 

 to do well, the bits of tinfoil were afterwards rubbed with melted wax and 

 fastened on by keeping them some time pressed with slight weights with flannel 

 between them. 



* [See Arts. 337, 373, and 500.] 



