Electrical Discharge. 357 



different metals introduced into the ball of the thermometer 

 evince heating effects in this same reciprocal proportion. Thus 

 in the ordinary case of the electrical discharge, silver and copper 

 are with a given quantity of electricity the least heated, and lead 

 the most ; gold, zinc, platinum, iron, tin, &c. come in due place 

 between these extremes ; whilst the degree of effect indicated on 

 the scale taken inversely, approximate very closely to the com- 

 parative values of these relative conducting powers. It is espe- 

 cially remarkable that the conducting powers of copper and lead, 

 as thus determined, have precisely the same relative value as 

 given in the numbers of M. Becquerel*. The numbers for other 

 metals do not differ considei'ably when we take into the account 

 the great variety of circumstances liable to derange the result. 

 These, and other experimental facts which might be quoted, 

 favour the conclusion, that the simple degree of movement of 

 the fluid in the stem of the instrument, without further coi-rec- 

 tion, is after all the best measure of the force of the current in 

 the wire ; it at least furnishes approximations sufficiently near 

 as to leave no doubt on the mind of the laws we seek to discover. 

 All we require, therefore, in the use of this instrument is a care- 

 ful manipulation, and due attention to the dimensions of the 

 wire in the ball, and other conditions of the experiment. Taking 

 these several facts, to which I have called attention, into con- 

 sideration, I am not disposed to allow the justness of M. Riess's 

 criticisms on my original inquiries, or that the course of experi- 

 ment pursued by Prof. Riess, and to which M. De la Rive devotes 

 so large an amount of i^onside/ation, is so perfect as that which 

 he condemns. 



26. It is not without regret that I observe M. Riess's system- 

 atic disparagement of what I have effected at various times in 

 this department of science. Until my several papers first ap- 

 peared, we had really few, if any, available quantitative processes 

 in electricity. In the course of these papers I was the first to 

 point out and furnish practical methods of quantitative measure- 

 ment, and illustrate thereby many important laws of electrical 

 action. Many of these processes have been virtually adopted by 

 others. " L'electrometre a poids," figured at p. 160, vol. ii. of 

 M. De la Rive's woi'k, together with the process he there de- 

 scribes, is really a bad adaptation of my electrical balance described 

 in the Philosophical Transactions for 1834, and it will be found 

 practically inaccurate. The exceptions taken by M. Riess to my 

 several instruments and my methods of research are without any 

 good foundation whatever. In alluding to my " unit measure," 

 (Poggendortf's Annalea, vol. xl.p. 323), M. Riess observes, "the 

 measure of electricity by the revolutions of the electrical machine 

 * Traits experiment ale, torn. iii. p. 91. 



