THE 

 LONDON, EDINBURGH AND DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



OCTOBER 184-0. 



XXXV. Comparative Measure of the Action of two Voltaic 

 Pairs, the one Copper-zinc, the other Platina-zinc. By 

 M. JACOBI*. 



I HAVE the honour to communicate to the Imperial Aca- 

 demy of Sciences, the result of my comparative experi- 

 ments, concerning the force of two different voltaic pairs with 

 partitions, the one copper-zinc, charged with sulphate of 

 copper and sulphuric acid dilute with six parts by volume 

 of water ; the other platina-zinc, and charged, according to 

 the recommendation of Mr. Grove, with concentrated nitric 

 acid, and with the same diluted sulphuric acid. The first pair, 

 copper-zinc, had 36 square inches of surface, the pair platina- 

 zinc had only 2| square inches. To measure the force of the 

 current, I employed M. Becquerel's electro-magnetic balance. 

 This instrument is valuable for accurate measures, provided 

 the helices be so disposed as to be able to fulfil the conditions 

 of stable equilibrium, which necessarily ought to exist in a 

 balance. This is attained by making the repulsion only act 

 between the magnetic bars and helices. For this purpose, 

 one of the helices ought to be fixed below, the other above 

 the said bars. This last helix is traversed by the rod, by 

 which the bar is suspended from the beam of the balance. 

 It is still necessary that a correction be adapted to the cur- 

 rents measured by the balance. This correction, of which 

 other synchronous investigations have shown the necessity, is 

 in proportion to the square of the force of the current. For 



* Read before the Imperial Academy of Sciences of St. Petersburg!], 

 on the 31st of January, 1840. 



Phil. Mag. S, 3. Vol. 17. No. 110. Oct. 184-0. B 



