Electric Residue in the Lei/den Jar. 481 



§12. 



With respect to the meaning of the three constants p, b and 

 m, b is found to be connected with the resistance which the 

 glass opposes to the external influence of the electricity, so that 

 its magnitude may be different for different kinds of glass, whilst 

 m has reference to the time in which this resistance is gradually 

 overcome. The circumstance that m has the same magnitude 

 for the different glasses of the differently-shaped charging appa- 

 ratus, seems to indicate that the function of the time, which dif- 

 fers little from the square root, was justly introduced into the 

 formula, and that the resistance is a mechanical one, proceeding 

 from the molecular forces on each particle of glass, as in the 

 analogous case of elastic secondary action. The number p ex- 

 presses what part of the charge which is then present could be 

 detained by the electric moment of the glass if the state of equi- 

 librium were attained. The magnitude oi 'p depends, therefore, 

 on b, and at the same time on the thickness of the glass. As 

 the relation between p and b is still unknown, it does not appear 

 possible at present to obtain the equation of the residue with 

 only two constants. 



Whatever opinion may be entertained with respect to these 

 constants, or even to what has here been termed an electric mo- 

 ment, this much is at least certain, the electric residue can be 

 calculated from the equation III. As soon as, for any particular 

 jar, the constants shall have been determined according to § 11, 

 we can give an equation for its disposable charge, which, if not 

 strictly expressive of the precise law, will at any rate secure an 

 approximation sufficiently correct for pi'actical purposes. Prac- 

 tice, for example, may demand the calculation of the disposable 

 charge, which, in a given time after a known charge had been 

 imparted to the jar, was employed for some purpose or other, 

 without being able directly to observe its magnitude. On the 

 other hand, the magnitude of the disposable charge being known, 

 that of the original charge, which was suddenly imparted to a 

 jar at a certain earlier period, may be required. \Yc will deduce 

 the equation, and at the same time consider a jjarticular example, 

 from the data furnished by the jar a, and given in the Tables a, 

 a', a« and a'". 



According to the calculation of these observations, we have 

 (see Table «'", and the calculation of Table a" given in Aj)pen- 

 dix III.) — 



Qo=0-4742; V = 0-0109; F = 228086 ; <^ = 30-767 ; 

 T = 080; ;> = 0-4289; /> = 00397 ; m= -0-5744. 



llerelti T is the lime at which the jar was first discharged. 



Phil. May. S. 4. No. 48. Suppl. Vol. 7. 2 K 



