330 On Resistance to JLlectric Current 



COMPARISON OF RESISTANCE OF COPPER WIRE WITH THAT OF SAT. SOL. 



636] The wire was wound on reel on bars of glass about f inch broad, the 

 distance of one round of wire from the next on same bar being -6. 



The mean circumference of reel = 46-7 x a\/2*. 



There were 8 rows of glass bars, and 28 rounds of wire on each row, and 

 on one row there was \ round over. Therefore whole length of wire 



= 93-4 x \/2 x 8 x 28 + \ = 29,623 inches. 



This weighed 2967 grains, consequently there are 9-984 inches to i grain. 

 N.B. There were many knots in the wire. 



637] The resistance of this wire was attempted to be compared with that 

 of sat. sol. in tube 17 by shock melterf as in former experiments, but without 

 success. It was therefore compared by the sound of the explosion by discharging 

 the jars by a wire without its passing through my body; but in this there was 

 considerable difficulty, as the light of the spark passed through the wire was 

 very different from that passed through the water, the first being reddish and 

 the latter white. The sound also was of a different kind, the latter being sharper. 



Distance of wires in tube 17. 



El. = 4. 



68 not sensib. diff. 



6 scarce sensib. stronger. 



55 doubtful. 



5 seemed rather greater. 



45 sensib. greater. 



9 seemed sensib. less. 

 i do. 

 1-2 sensib. less. 



- El. = 



g scarce sensib. less, 



i not sensib. less. 



1-2 seemed rather less. 



6 plainly greater. 



7 not sensib. greater 



4 not sensib. gr. 



3 seemed rather gr. 



2 plainly gr. 



8 seemed rather less. 



1-2 plainly less. 



* [The reel was probably square, with glass bars at the corners, the length of 

 the diagonal being 46-7 inches.] 

 f [See Arts. 585 and 622.] 





