Intelligence and Miscellaneous Articles. 399 



A mirror in the prolongation of the torsion-thread permitted the 

 measurement of the displacements of the moveable ball, and, at the 

 same time, of the torsion of the thread. 



The two balls were at first connected with each other and with 

 the earth ; afterwards they were charged permanently by the nega- 

 tive pole of a pile of Daniell's elements, the positive pole being led 

 to the earth. 



Here are the details of an experiment, the units adopted being 

 the millimetre and the milligramme : — 



Position of equilibrium of the moveable ball (the two 1 

 balls connected together and with the earth) . . . . j 



The two balls communicating with the negative polel i^^.c ' 

 of a pile of 65 Daniell's elements j 



The communication with the earth reestablished. . . . 82*75 



178-5-82-87 = 95-63. 



The equation J2^^°® 9 = ^^0 gives the quantity q of electricity 



■which is found on each ball. 



d is the distance between the two balls. To find its value, a tele- 

 scope placed at a measured distance permitted the angle to be mea- 

 sured under which the centres of the two balls were seen ; <?=32*6 

 millims. when the two balls communicate with the negative pole of 

 the pile. 



/, length of the gum-lac spindle, 70 millims., reckoned from the 

 point of suspension from the torsion-thread to the centre of the ball. 



n represents the force necessary to twist the thread an arc equal 

 to the radius. This quantity is obtained by causing the thread to 

 oscillate after replacing the stick of gum lac by a metallic spindle of 

 known weight and length. The thread of the balance was 30 cen- 

 tims. long ; w=5'47 ; with the units employed it required a force of 

 5 "47 milligrammes, applied at the distance of 1 millim., to twist the 

 thread an arc equal to the radius. 



<p is the angle of torsion. The rule being divided into millimetres 



and placed at 3*13 metres from the mirror, 0= • 



a, the distance- angle; 



-=13° 28'; cos- =0-97. 

 2 2 



We obtain ^^=2'77, ^ = 1*76. This is the quantity of electricity 

 which was found upon each of the two balls. The potential will be 



"y; r, the radius of one of the balls, 8'3 millims. ; 4" = 0255. -^ 



therefore represents the density of the electricity distributed upon 

 the sphere, taking for unit of surface in measuring the density the 

 surface of the sphere which has the unit of length for its radius. 



In this case a sphere of I millim. radius, communicating with the 

 negative pole of the pile of 65 elements, is charged with a quantity of 

 electricity which produces upon an equal mass concentrated at the 



