GALVANISM. 



[Continued from page 423 of the Report ol 1855.] 



SECTION FOURTH. 



GALVANIC PHENOMENA OF LIGHT AND HEAT. 



§ 54. Production of heat hy the galvanic current — The laws of the; 

 development of heat produced by the galvanic current in metallic^ 

 wires, have been investigfated bv Joule, (Phil. Magazine, Oct., 1841,) 

 and by Lenz, (P. A. LIX, pp. 203 & 407, LXI, p. 18.) 



The memoir of Joule not being within my reach, I shall only report i 

 on the researches of Lenz, and this will be sufficient, since the results 

 of the Russian and of the English physicist agreee. 



The first two sections of the memoir of Lenz, in vol. LIX of Pog. . 

 Ann., contain only introductory matter, to which we shall but briefly v; 

 refer. 



To measure the strength of the current Lenz made use of a Nerv- 

 ander's tangent compass, which was most carefully constructed and 

 tested. He found by accurate experiments that up to 40° the strengths 

 of the currents are proportional to the tangents of the angles of de- 

 flection. 



Lenz also compared his tangent compass with the decomposition of 

 water. It results, from his numerous and accurate experiments, that i 

 the tangent of the observed angle of deflection is to be multiplied by ' 

 39.3 in order to obtain the reduced quantity of detonating gas from i 

 the same current per minute, expressed in cubic-centimetres. Lenz '. 

 takes for his unit a current which causes a deflection in his tangent t 

 compass of 1°, and this produces 0.686 c, c. of the mixed gases in at 

 minute. Since our unit of current is that which gives 1 c. c. per ' 

 minute, it is evident that Lenz's values of strength of current must ; 

 be multiplied by 0.686 to reduce them to our unit. In what follows i 

 I shall always make use of the reduced values for the strength of cur- • 

 rent, instead of those of Lenz. 



As the unit of resistance Lenz takes the resistance of one wind of ' 

 his rheostat (agometre) of Grerman silver, which, according to his 

 statement, is equal to the resistance of a copper wire of 6.358 English 

 feet in length, and 0.0336 English inch in diameter. Hence, it appears 

 that this unit of resistance is equal to 2.66 of our own ; the values of 

 Lenz mu«t therefore be multiplied by 2.66 to reduce them to our 

 unit. 



