ELECTRICITY. 



453 



Pc*criptive 

 Electricity. 



When the 

 two globes 

 are equal. 



Exp. 3. With the same Globes. 



Repulsive force. 



Globe touched at 90 from the point of contact 20* 

 Globe touched at ISO from the point of contact 19 

 Globe retouched at 90 from the point of contact 17 

 Globe retouched at 1 80 from the point of contact 18 



Hence taking the three first observations, the density 

 at 90 is to that at 180 as 19 to 18^, or as 1 to 0.98 



Taking the three last, it is to that at 180" as 



18| to 17, eras .............. 1 to 0-92 



Mean 1 to 0.95 



Exp. 4. With the tame Globes. When the globes are 

 touched at 20, or at any point below it, no electricity 

 appears. 



By comparing the 2d, 3d, and 4th experiments, we 

 shall have for the ratio of the electrical densities at ,"0 

 and 90, 4.83, the mean of which and 4.72 formerly 

 found, is 4.78. 



The following Table will show at one view the re- 

 suits of the preceding experiments. 



Ratio of the electrical 

 densities. 



Distances from the 

 point of contact. 



. 



. 



1 . 



3.72 

 4.78 

 5.03 



. 20 



. 30 

 . 60 

 . 90 

 180 



When the When the globes were unequal, and the one half the 

 two globes diameter of the other, the density of the small globe 

 re unequal. was a i most nothing till the distance was 30. 



From 60 to 90 it increases in the ratio of 10 to 17. 

 From i>0 to 180 it increases in the ratio of 75 to 100. 



When the small globe was only J the diameter of 

 the other, the density of the small globe increased 



Increase. Distances from contact. 



from OtoO OtoSO 



01 SO 45 



14 45 90 



4 5.72 90180 



In the large globe of 8 inrfces, the density was no- 

 thing tn tli Hh or 5th degrees from the point of con- 

 tact. It then increased rapidly, and from 3O to 1 80* 

 it was almo,t uniform. 



Central re- From these cxpe rimcnts we may conclude in general, 

 ult, that the more the globes are unequal, the more does the 



density of the small globe vary from the point of con- 

 tact to 1 SO", and the more does the distribution of the 

 electric matter on the great globe approach to uniformi- 

 ty, increasing rapidly from the point of contact, where 

 it is nothing, to the 7th or 8th degree from this point, 

 and being uniform over all the rest of its surface. 



In order to compare these experiments with the 

 theory of the distribution of electricity after the law of 

 the inverse duplicate ratio of the distance, Coulomb 

 found it necessary to make some subsidiary experi- 

 ments, which are well worthy of being detailed as ge- 

 neral facts. 

 Two globes fp t 1 . Having placed between two electrified globes 



ne below* 1 ^ **" 8ame 8 ' ze a sma ^ g'be, whose diameter was less 

 than the sixth part of the diameter of either, so that all 

 the three were in contact, he found that the small globe, 

 when presented to a very sensible electrometer, gave 



no signs of electricity, and that hftwevw small the middle Descriptive 

 globe was it possessed no negative electricity. Electricity. 



Exp. 2. When three equal globes, two inches in ^^7"^ 

 diameter, were placed in contact in a right line, one a i obes in 

 of the globes, supported by the pincers Fig. 3, was contact. 

 placed successively between the two others, and on each 

 side of both. In these different positions it was pre- 

 sented to the great torsion balance, and the quantity of 

 electricity being measured, it was found, that when it 

 was placed in the middle it took more electricity than 

 when it was placed at either of the sides in the ratio of 

 100 to 134. This result is the mean of the experi- 

 ments made ai'ter equal intervals, for the purpose of 

 correcting the error arising from the dissipations. 



Exp. 3. Hitherto we have seen that when two globes 

 were in contact, the density at the point of contact 

 and in the adjacent parts was nothing, and was never 

 negative when the two globes were positively electrifi- 

 ed. But the moment the two globes are separated, then 

 if one of the globes is smaller than the other, and if the 

 distance of the two globes is not great, the point of the 

 little globe which was in contact with the great globe, 

 will become negative, till they are separated to a cer- 

 tain distance. At tins distance, the electricity is again 

 nothing, and, by increasing the distance, the same point 

 becomes afterwards positive. 



Exp. 4. Having insulated a globe of 1 1 inches dia- 

 meter, and also another globe of a smaller size, electri- 

 fy them and bring them into contact. Let the small 

 globe be then taken to a different distance, and, by means 

 of a very small ball of lead suspended by gum lac, or 

 by means of a circle of gilt paper, touch the small 

 globe at the point where it touched the great globe, and 

 examine in the small torsion balance the nature of the 

 electricity of that point. 



When the Targe globe is 1 1 inches in diameter, and 

 the small one 8 inches, and both positively electrified, 

 the point of contact of the great globe is always posi- 

 tively electrified, whatever be the distance between the 

 two. The point of contact of the small globe, how- 

 ever, will be negatively electrified, till the distance of 

 the two is one inch. At this distance it becomes nothing, 

 and beyond it its electricity is positive. 



If the small globe is only 4 inches in diameter, the 

 other remaining the same, the phenomena are precisely 

 the same ; but they take place at 2 incites instead of 1 

 inch. 



When the small globe is only 2 inches in diameter, 

 or less than 2 inches, the other remaining the same, 

 the same phenomena take place, but at the distance of 

 2 inches and 5 lines. 



The following Table contains some curious results, 

 shewing the relation between the mean density D of 

 the largest of two globes after its separation from the 

 small globe, to the density d of the point of the small 

 globe with which it was in contact, II being the radius 

 of the large globe, and r that of the small one. 



Ratio of the Badii, 



R 

 or 



r 



Ratio of the Elec- 

 trical densities, or 

 d 



D 



1 1.27 



2 1.55 



4. 2.35 



8 3.18 



Infinite 4-00 



