1877.] 



Residual Charge of the Leyden Jar. 



497 



2nd. Let be constant = X for a very long time T previous to time 

 i=0 ; discharge and at time t insulate and observe 



A\=A— XI \p((o)d(o ; 



There are also methods of verification ; for example : — Charge during 

 time T', reverse the charge for time T" and discharge; then after time t 



insulate and observe ^ ; we shall find 

 dt 



X |^^<0-2V'(T"+ 0+^(T"+ T'+ 0} . 



III. Experiments were tried on ten glasses. The verifications were 

 perhaps as close as could be expected, considering that no attempt was 

 made to observe at a constant temperature. The glasses were : — 



No. 1. A soda-Kme glass containing much soda. 



No. 2. A soda-lime glass coloured deep blue with oxide of cobalt. 



No. 3. "Window-glass. 



No. 4. Optical hard crown. 



No. 5. Soft crown. 



No. 6. A very light flint glass. 



No. 7. Light flint. 



No. 8. Dense flint. 



No. 9. Extra-dense flint. 



No. 10. Opal glass. 



Glasses 1, 2, and 3 agree in possessing high conductivity and also 

 large values of ^t—'B; whilst 7, 8, 9, 10 have a high resistance (thou- 

 sands of times as great as 1, 2, or 3) and small residual charge. 



TV. Electrolytic conduction may occur through the soda-lime glasses 

 at the ordinary temperature of the air. 



Summary. — The experiments appear to verify the fundamental hypo- 

 thesis, viz. that the effects on a dielectric of past and present electro- 

 motive forces are superposable. Ohm's law asserts the principle of 

 superposition in bodies in which conduction is not complicated by residual 

 charge. Conduction and residual charge may be treated as parts of the 

 same phenomenon, an after effect as regards electric displacement, of 

 electromotive force. The experiments appear to show that the principle 

 of Ohm's law is true of the whole phenomenon of conduction through 

 glass. 



2k2 



