LAWS OF STATICAL ELECTRICITY. 



219 



16. The superficial dimensions of a given conductor, or the quantity of electricity 

 disposed on it, being varied, considerable differences are observed to arise in the 

 attractive force ; and of these, the instruments above described (7.) (8.) are extremely 

 susceptible : by carefully pursuing the inquiry under these conditions, I arrived at 

 very interesting results : the most important of these are the following : 



A given quantity, divided upon two perfectly similar conductors, was found to 

 exert upon external bodies, only a fourth part of the attractive force apparent when 

 disposed upon one of them. 



When divided upon three perfectly similar conductors, the force upon either is 

 only one ninth of the force apparent when disposed upon one of them, and so on ; 

 that is, the quantity being constant, the force is as the square of the surface inversely ; 

 or the surface being constant, as the square of the quantity directly. 



17. The following experiments may be adduced as illustrative of the above laws : 

 (c.) Three or four perfectly similar and equal conductors, a, h, c, fig. 8, of a cylindri- 

 cal form, being well insulated, a given quantity of electricity was communicated to one 

 of them by means of the charged jar D (14.), and the attractive force measured by the 

 electrometer, fig. 2, with the contact ball of which it was subsequently made to com- 

 municate, as in fig. 8. The electrified bodies being now reduced to a neutral state, a 

 second equal quantity was again communicated to the same conductor as before ; 

 after which it was caused to touch one of the others, so as to divide the charge on 

 both. In this case, each conductor was observed to be, on transferring it to the elec- 

 trometer, equally charged ; the force, however, after making the requisite correction 

 for distance between the attracting bodies m f, fig. 2, (8.) amounted only to the one 

 fourth of the previous force. This process, repeated with three and with four similar 

 conductors, reduced the force to the one ninth and one sixteenth part of the first 

 respectively. The actual results of a series of experiments, conducted under extremely 

 favourable conditions of the air, are given in the following Table : 



Table I. 



quite impossible to insure accuracy in a moist atmosphere, or with imperfect insulation. Flame of all kinds 

 should be studiously removed from near the subject of experiment ; the dissipation of a charge being rapid 

 under the influence of a lamp or a candle. When, however, the system of insulation is perfect, the electricity 

 remains stationary on the conductors for a much longer time than is requisite for patient observation ; and the 

 electricity abstracted from the charged jar, upon an insulated plate of metal, will pass off again from the plate, 

 without dissipation, in a sharp spark. 



