418 ELECTRICITY. 



TABLE for determining the lost of Electricity along impcrf telly Insulating Elutrici: 

 rillST SET OF EXl'EHI.Mr.VIX 

 May 28M. 



from the 



preceding 



Ttblc. 



Conclusions It appear* from the preceding Table, that the dimi- 

 nution of electricity is at first much more rapid when 

 the electrical density is considerable, than it ought to be 

 if it were produced solely by the contact of the air; and 

 when this density is reduced to a certain tlegree, the 

 diminution of electricity becomes precisely the same as 

 it is when the insulation is perfect, or as it is when the 



' ion is entirely due to the contact of the air. 

 It follows, therefore, from this observation, that the 

 silken fibre 15 inches long is a perfect insulator when 

 the reciprocal action of the two balls is measured in the 

 first set of experiments in the preceding Table by a force 

 of torsion of 40 or under, since the loss of electricity 

 is then only-j'jd per minute, the very same dissipation 

 that took place on the same day, and that was due sole- 

 ly to the contact of the air. . 



It results likewise, that in the second set of experi- 

 ments in the above Table, the silk fibre 15 niches long 

 insulated perfectly when the repulsive action of the two 

 balls was 70 or under, for then the dissipation was 

 3Tjth, the very same that was obtained on the same day, 

 :'iid that was due solely to the conducting power of 

 the air. 



Since the repulsive forces are measured at a constant 

 distance, by the product of the densities of the two equal 

 balls, the next object of Coulomb was to a-scut/un tin- 

 relation between the primitive density, and the differ- 

 ent degrees of density of the ball supported by the 

 o 



silken fibre, when the silk fibre begins to insulate the 

 ball in a perfect manner. 



In the first set of experiments in the preceding Ta- Dctermina. 

 ble, the two kills were equally electrified. The ball tionofthe 

 a upon the needle insulated by means of gum lac lost dr. trie di-n- 

 2XTr=T I Tf its electricity per minute, solely by the sit > *' }>en , 

 Conducting power of the ambient air. The other !^ ".;" 

 ball supported by the silken fibre, dissipated its electri- to ' insulate 1 

 city not only by the contact of the air, but also by its perfectly, 

 imperfectly insulating support; and it was not till 

 10 h W that the siik fibre began to insulate completely 

 the second ball, at which time the repulsive force of 

 the two balls was 40. But at 10 h , the bi-ginnin'.: of 

 the experiment, the repulsive force of the two balls 

 equally electrified was 180. Since the action at a con- 

 stant distance is always proportioned to the product of 

 the' densities, and since the densities at the first expe- 

 riment were equal, the electric density of each ball is 

 proportional to ^/180 at 10 h 0'. But we have already 

 seen, (p. 416. col. 1.) that the dissipation of electricity 



from the contact of air was -. =r ml, where d is the den- 



d 



sity at the end of any time t, and m=2 X V' = sV ln co '- 

 7. of the first set of experiments in the preceding Table. 



D 4343 

 Now the fluent of the above formula is log. -,=. -' . 



<1 o 



D being the primitive density of the ball, and 0.4343 



