94 Galvanism, from Galvani to Ohm. 



explained by supposing that small plates give a small quantity 

 of the electric fluid with a high velocity, while large plates 

 give a larger quantity with no greater velocity. Shocks, 

 which were supposed to depend on the velocity of the fluid 

 alone, would therefore not be intensified by increasing the size 

 of the plates. 



The effect of varying the conductors which connect the 

 terminals of the pile was also studied. Nicolas Grautherot 

 (b. 1753, d. 1803) observed* that water contained in tubes which 

 have a narrow opening does not conduct voltaic currents so 

 well as when the opening is more considerable. This experi- 

 ment is evidently very similar to that which Beccaria had 

 performed half a century previously! with electrostatic 

 discharges. 



As we have already seen, Cavendish investigated very 

 -completely the power of metals to conduct electrostatic 

 discharges; their power of conducting voltaic currents was 

 now examined by Davy.J His method was to connect the 

 terminals of a voltaic battery by a path containing water 

 (which it decomposed), and also by an alternative path 

 consisting of the metallic wire under examination. When the 

 length of the wire was less than a certain quantity, the water 

 ceased to be decomposed ; Davy measured the lengths and 

 weights of wires of different materials and cross-sections under 

 these limiting circumstances ; and, by comparing them, showed 

 that the conducting power of a wire formed of any one metal 

 is inversely proportional to its length and directly proportional 

 to its sectional area, but independent of the shape of the cross- 

 section.! The latter fact, as he remarked, showed that voltaic 

 currents pass through the substance of the conductor and not 

 along its surface. 



Davy, in the same memoir, compared the conductivities of 

 various metals, and studied the effect of temperature : he found 



* Annales de China., xxxix (1801), p. 203. t See p. 53. 



% Phil. Trans., 1821, p. 433. His results were confirmed afterwards by 

 Becquerel, Annales de Chiiuie, xxxii (1825), p. 423. 

 6 These results had been known to Cavendish. 



