% Sir H. Davy on the Magnetic Flucnomena [Jan. 



charged with a mixture of nitric acid and water, so as to exhibit 

 a considerable intensity of electrical action, and the relative 

 conducting powers of silver and platinum in air and water ascer- 

 tained by means of it. In air, b' inches of wire of platinum of 

 ^\y discharged only 4 double plates, whilst 6 inches of silver wire 

 of the same diameter discharged the whole combination : the 

 platinum was strongly ignited in this experiment, whilst the 

 silver was scarcely warm to the touch. On cooling the platinum 

 wire by placing it in water, it was found to discharge lU double 

 plates. When the intensity of the electricity is very high, how- 

 ever, even the cooling powers of fluid media are of little avail; 

 thus I found that fine wire of platinum was fused by the dis- 

 charge of a conmion electrical battery under water ; so that the 

 conducting power must always be diminished by the heat gene- 

 rated, in a greater proportion as the intensity of the electricity 

 is higher. 



It might, at first view, be supposed, that when a conductor 

 placed in the circuit left a residuum of electricity in any battery, 

 increase of the power of the battery, or of its surface, would not 

 enable it to carry through any additional quantity. This, how- 

 ever, is far from being the case. 



When saline solutions were placed in the circuit of a battery 

 of 20 plates, though they discharged a veiy small quantity only 

 of the electricity, when the troughs were only one quarter full, 

 yet their chemical decomposition exhibited the fact of a much 

 larger quantity passing through them, when the cells were filled 

 wit'h fluid. 



And a similar circumstance occurred with respect to a wire 

 of platinum, of such a length as to leave a considerable residuum 

 in a battery when only half its surface was used ; yet when the 

 whole surface was employed, it became much hotter, and never- 

 theless left a still more considerable residuum. 



VIII. 1 found long ago, that in increasing the number of alter- 

 nations of similar plates, the quantity of electricity seemed to 

 increase as the number, at least as far as it could be judged of 

 by the effects of heat upon wires ; but only within certain limits, 

 beyond which the number appeared to diminish, rather than 

 increase the quantity. Thus the 20U0 double plates of the 

 London Institution, when arranged as one battery, would not 

 ignite so much wire as a single battery of 10 plates with double 

 copper. 



It is not easy to explain this result. Does the intensity mark 

 the rapidity of the motion of the electricity i or merely its dimi- 

 nished attraction for the matter on which it acts ? and does this 

 attraction become less in proportion as the circuit through which 

 it psusses, or in which it is generated, contains a greater number 

 of alternations of bad conductors ? 



Mr. Children, in his account of the experiments made with 

 his battery of large plates, has ingeniously referred the heat 



