442 Mr. T. T. P. B. Warren on Electrification. 



of the insulator. Battery-contact being still maintained, the 

 deflection falls very rapidly at first, and gradually becomes reduced 

 for some time after. 



The shorter the length of cable and the lower the degree of in- 

 sulation, the less defined will be the differences in the deflections 

 after a few minutes' contact. 



Great care must be taken, when making these experiments, 

 that the cable has not been previously charged ; should the cable 

 have been charged, it must be connected to earth for some hours 

 before testing. The battery must be in very good condition, and 

 unsteady deflections totally discarded. 



The ratio between the deflections for equal periods of contact 

 is independent of the length, and is greater or less according to 

 the specific resistance of the dielectric. 



The ratio is unaltered under different electromotive forces so 

 long as constancy is maintained during the time of observation 

 and the deflection itself the same with the different electromotors 

 at the end of the first period of contact ; but when, with different 

 electromotive forces, the deflections at the end of the first period 

 of contact are not the same, we may obtain the deflections which 

 should be given on prolonged contact if we know the deflection 

 for a corresponding period by any electromotive force, since the 

 deflections for the first period of contact will have to one another 

 the same ratio which the deflections at any other period of con- 

 tact have : thus if with a given electromotive force we obtain at 

 the end of the first minute's contact a deflection of 84, which at 

 the end of the second minute is reduced to 76, and with a dif- 

 ferent electromotive force we have a deflection of 70 at the end of 

 the first minute's contact, the deflection at the end of the second 

 minute will have the same ratio to 76 which 70 has to 84. 



Under different temperatures the resistances corresponding to 

 one, two, three, &c. minutes' contact follow the same law of varia- 

 tion. Thus if R = r x constant * represent the resistance after 

 one minute's contact, then 



ft/ =r f x constant t = resistance after 2nd minute. 

 B/' =r" „ „ „ 3rd „ 



KiT?'"m " " " 4th " 



ft — r „ „ „ 5 th. „ 



R» =i* „ „ „ nth 



r 9 r\ r n , r'", r uu , r n are the resistances determined after 1, 2, 3, 4, 

 5, n minutes' contact respectively, and ft, ft', ft", ft'", ft"", ft" the 

 required resistances for the same differences of temperature t, and 

 at the end of 1, 2, 3, 4, 5, n minutes' contact. 



If at any temperature T we obtain a deflection G after one 

 minute's contact, which at the end of the second minute falls to 



