60 PROCEEDINGS OF THE AMERICAN ACADEMY 



The preceding values of d y, H are directly proportional to the 

 values of the electromotive forces. The formula for the electromotive 

 force is E^kRd, in which k is the constant of the galvanometer, R 

 is the resistance of the circuit, and d is the tangent of the deflection 

 of the galvanometer needle. 



The constant of the galvanometer was determined by means of a 

 small gas battery. The electromotive force of the gas battery was 

 found, by means of Thomson's electrometer, to be .285 of a Daniell 

 element. The electromotive force of a Daniell element = 1.079 

 volts, hence that of the gas battery = 1.079 X -285 =: .307515 volts 

 = 30751500 absolute units, since one volt = 10^ absolute units, in 

 the C. S. G. system. The formula for the constant is 



" — R'd' 



where E' = the electromotive force of the battery, R' the whole re- 

 sistance of the circuit, and d the tangent of the deflection of the gal- 

 vanometer needle, 



"" — R'd' 



Consequently the preceding formula for the electromotive force 

 E = k R tan a becomes 



The constant by which the preceding results in the tables are to be 

 multiplied in order to reduce the electromotive force to absolute units 



is then ^^7^, = k. 

 R'd 



It was found that when R' = 12000 d' = 45.0. 

 " " " R' = 11000 d' = 50.5. 



The first gives for k = 56, 9 ; the second 55.3 ; mean value of 

 it =56.1. 



Hence to obtain the absolute values of the electromotive forces the 

 values oi d y^ R given by the tables must be multij^lied by 56.1. 



After the preceding experiments a still lower temperature was ob- 

 tained by means of solid carbonic dioxide and ether. Two experi- 

 ments were made, the temperatures in the first being measured by an 

 ether thermometer, in the second by an air thermometer. In both 

 the same metals, copper and nickel, employed in the previous experi- 

 ment, were used. 



