Mat/t '-/:'<■;>, riments voiih !*• n<lnhinb~<L otromek r. 388 



The mean of our measurements gives for the ratio of den- 

 sities at middle and at end of cylinder, 1 :2*27, which is sub- 

 stantially the sam* onlomb's ratio of 1 :2*3, 



Measurements of Quantity <o«t Potential 



The quantity and potential of the charge on a sphere of 



known radius are readily measured by the pendulum-electrom- 

 eter, as shown by the following experiment-. 



The charged sphere, of 1 cm. radius, was brought in contact 

 with the electric pendulum, and the force in dynes exerted on 

 the latter was 7*058. The distance apart of centers of spheres 

 was 74 cms. This gives for the quantity (Q) on the pendulum, 



Q = ^7*058 X 74 = 10-7 units of electricity. 



A- Boon as the readings of the deflection of the pendulum 

 and the distance apart of centers of spheres were obtained, the 

 sphere on the rod, of 1 cm. radius, was removed and a charged 

 >phere of the 4 6 cm. radius was brought opposite the charged 

 pendulum. The deflection of the latter was now 3*5 cms. ; the 

 distance of centers of spheres, 28 '5 cms., and the force of deflec- 

 tion in dynes, 10*29. The quantity, Q', on larger sphere is 



, x . fD* 10-28X812-25 



Q= Q = - 19-7 = 424 ' 26 



units of quantity. 



As the potential (V) of the larger sphere is equal to the 

 quantity (Q') of its charge divided by its capacity (C), or 

 raaius in centimeters, we have 



Q' 424 



V = -=■ = — = 92*2 units of potential. 

 O 4*6 p 



The foregoing experiments show that the pendulum-electrom- 

 eter gives the law of inverse squares, serves to determine the 

 law of dissipation of electric charge, and with it one may make 

 measures of the electrical distribution on conductors and de- 

 termine quantity and potential. In short, this simple apparatus 

 affords an inexpensive and ready means, of presenting clearly 

 to students the nature of measurements of static electricity, and 

 allows one to make these measures in absolute units before a 

 class with ease and dispatch. 



Stevens Institute of Technology, Hoboken, N. J. 



