Relation by Measure of Common and Voltaic Electricity. 359 



times the thickness, only twelves inches in length, and soaked 

 in dilute acid (298.). With the thick string the charge 

 passed at once; with the thin string it occupied a sensible time, 

 and with the thread it required two or three seconds before 

 the electrometer fell entirely down. The current therefore 

 must have varied extremely in intensity in these different cases, 

 and yet the deflection of the needle was sensibly the same in 

 all of them. If any difference occurred, it was that the thin 

 string and thread caused greatest deflection ; and if there is 

 any lateral transmission, as M. Colladon says, through the 

 silk in the galvanometer coil, it ought to have been so, be- 

 cause then the intensity is lower and the lateral transmission 

 less. 



366. Hence it would appear that if the same absolute quan- 

 tity of electricity pass through the galvanometer, whatever may 

 be its intensity, the deflecting force upon the magnetic needle is 

 the same. 



367. The battery of fifteen jars was then charged by sixty 

 revolutions of the machine, and discharged, as before, through 

 the galvanometer. The deflection of the needle was now as 

 nearly as possible to the eleventh division, but the graduation 

 was not accurate enough for me to assert that the arc was ex- 

 actly double the former arc ; to the eye it appeared to be so. 

 The probability is, that the deflecting force of an electric cur- 

 rent is directly proportional to the absolute quantity of electri- 

 city passed, at whatever intensity that electricity may be*. 



368. Dr. Ritchie has shown that in a case where the inten- 

 sity of the electricity remained the same, the deflection of the 

 magnetic needle was directly as the quantity of electricity 

 passed through the galvanometer f. Mr. Harris has shown 

 that the heating power of common electricity on metallic wires 

 is the same for the same quantity of electricity whatever its in- 

 tensity might have previously been J. 



369. The next point was to obtain a voltaic arrangement 

 producing an effect equal to that just described (367.). A 

 platina and a zinc wire were passed through the same hole of 

 a draw-plate, being then one eighteenth of an inch in diame- 

 ter; these were fastened to a support, so that their lower ends 



* The great and general value of the galvanometer, as an actual mea- 

 sure of the electricity passing through it, either continuously or inter- 

 ruptedly, must be evident from a consideration of these two conclusions. 

 As constructed by Professor Ritchie with glass threads (see Philosophical 

 Transactions, 1830, p. 218, and Quarterly Journal of Science, New Series, 

 vol. i. p. 29.), it apparently seems to leave nothing unsupplied in its own 

 department. 



f Quarterly Journal of Science, New Series, vol. i. p. 33. 



% Plymouth Transactions, page 22. 



