Sir W. Snow Harris on new Phanomena of Electrical Force. 207 



of electricity, but on the number of attracting points called into 

 operation bv wbat is usually considered as the attracted body. Two 

 circular discs of very light wood, of 5 inches diameter, bemg care- 

 fully prepared in a lathe, were divided into sis concentric rmgs, 

 including a central plate of about an inch m diameter. The attract- 

 ive force on each pair of rings was determined by means of the 

 electrical balance and carefully noted ; the force was as the several 

 opposed areas ; and when the series was combined into one plate, the 

 force was the sum of the forces of the respective rings; when the 

 attractive forces of circular plates equal in area to the several rings 

 respectively were examined, the force was the same as that exhibited 

 by the two" rings whose area was the same ; hence it is inferred that 

 whether the charge operates from the circumference or near the 

 centre, the attractive force is the same. Two rings combined exhibit 

 forces equal to the sum of the forces taken separately ; and when 

 the force is examined between the plates or the several rings and a 

 plane circular area of large and continuous surface, the forces are no 

 greater than that between two plates or rings of equal area. When 

 the distances between the attracting surfaces or the quantities of the 

 electrical accumulation varied, then the force was as the square of tjie 

 accumulation directly, and as the square of the distances inversely. 



The author extends these experiments to spheres of different 

 diameters. He had shown in a former paper, that, taking the attract- 

 ive force to be as the areas directly, and as the squares of the 



distances inversely, according to the expression Fgc ^3, two points 

 might be determined within the hemispheres in which all the force 

 may be conceived to be collected, and to be the same as if proceeding 

 from every point of the hemisphere. If Z=the distance of either 

 point, Of/ taken within the hemisphere, ?-=radius, and a=distance 

 between the near or what may be termed the touching points of the 



spheres, then we have 1 = ^^"""^^^ ~" ; and if A=the surface, we 



have F ex \i - When both hemispheres are equal, and distance 

 (a + 22) 



=a variable, then we have also Fa ^,^„+2ry '^^'^ ""*^'"' '"^ " ^°'*" 

 mer paper had applied these formulae to the limited induction of a 

 sphere of an inch radius ; he now extends the inqmry to spheres 

 varvin'' from an inch to 5 inches or more in diameter, and finds the 

 results" conformable to the formute. He gives a table contammg 

 the results of a series of experiments with four spheres whose areas 

 regularly increased, and the radii of which were from 1 to 2 inches 

 in diameter. These were examined by the electrical balance. Ihey 

 were first placed with the points q rj, or centres of force as calculated 

 for each at a constant distance of M of an inch, in which case the 

 weiehts requisite to balance the force with a given number ot mea- 

 sures of electricity were as the opposed areas, thus confirming the 

 preceding results deduced with plane surfaces ; when the distances 



