Residual charge : comparison of resistances 255 



If the spheroid agdm does not differ much from a sphere, and ab does not 

 differ much from ad, the surface afea is nearly 



equal to the circumference of gm x ab x - j^ , 



^surface 

 the -! thickness of the part under water was 



Icomp. pow. 



( 62 (-5-3 



| -0127, and that of the part above J -0179, and the 

 1 6200 1.375 



comp. power of the whole part below top of coating 6575, the specific gravity 

 of the glass being supposed 2-68. 



Therefore inc. el. by comp. pow. = 1-78. 



523] As it appears from the above experiments that the Florence flask 

 contains more electricity when it continues charged for a good while than when 

 charged and discharged immediately, it was tried whether the white globes 

 would do the same. 



This was done by putting the globe 3 on positive side and the white cylinder 

 and trial plate 6 on negative side, and first charging and discharging them in 

 the common manner, and then discharging the magazine and charging it again, 

 while the end c of the wire Cc rested on Bb, while the end C was prevented 

 from resting on A a by a silk string. When the magazine was charged, and had 

 continued so for a little time, the end C was let down on Aa and the wire Cc 

 immediately drawn up again so as to discharge the globe &c. The event was 

 as follows, 



in common way, wh. cyl. + 6 20 sep. near i diam. pos. 



globe elect, first, +6-24 D. 



in common way, +6 47 D neg. 



globe elect, first, +6-48 D. 



By these experiments the globe contains 45 inc. el. or about ^ 1 T less when 

 electrified in the common way than when charged before the rest, which is as 

 much as is contained in i inch in length of the uncoated part of the neck (the 

 whole neck being ij inches), so that supposing the experiment exact it seems 

 as if the globe contained rather more electricity when it continued charged a 

 considerable time than when charged and discharged immediately *. 



524] Diminution of shock by passing through different liquors^. 

 Tried in November [1772]. 



The electricity was made to pass through 42 inches of a saturated solution 

 of sea salt in a thermometer tube of a wide bore, and the two jars charged in 



* [These phenomena are connected with the "residual charge." A careful in- 

 vestigation of them has been made by Dr Hopkinson, Phil. Trans, vol. 167 (1877), 

 P- 599'] {Reprinted in his collected Scientific Papers.} 



f [This is the first experiment on electric resistance.] 



