in Terms of the Mechanical Equivalent of Heat. 33 



For, let E be the difference of potential of the ends of the 

 coil, e the E. M. F. of polarization, E and r the resistances of 

 coil and water respectively. Then the current in the coil is 



C= - and the current in the water is c= 



R r 



The energy converted into heat is 



<**.-W:W)] 



In the first method of calculation above the energy is com- 

 puted as 



In the second method it is computed as 



(C+c) 2 B= ^[1 + ^(1-^)] + smaller terms. 



E was over 6 volts, e is about 1*5 volts. Hence the second 

 result is larger than the first, which agrees with the facts, and 

 the error of the first is less than one-fourth of the difference 

 between the two. The discussion shows that the first 

 method of calculation is to be preferred, and I therefore take 

 J = 42,055,000 O as the result. * 



Since the completion of my experiments, a 10 ohm Elliott 

 standard in the possession of the University has been compared 

 with the Cambridge standards and found correct at 20°'9 C. 

 My standard has been compared with this with the following 

 result : 



W. M. & C.'s coil, _ ^ 1878 



Elliott s coil, 



« « = 1-00170 " 1882 



= 1-00173 " 1883 

 In these comparisons the Elliott coil was taken at 16 0, 3 C, as 

 marked. Also we have 



Elliott coil at 20°-9 _ 



Elliott coil at 16°'3 

 1-0017 

 Hence O = j^kt\ = 1-0003 B.A. units and J = 42,068,000 x 



value of B. A. unit in earth -quadrants per second. 



Rowland* has discussed Joule's values and reduced them to 

 the air thermometer and the latitude of Baltimore. The mean 

 of the best results from the friction of water, in 1850 and 

 1878, thus becomes 426-55 kilogram-meters or 41,805,000 C.G.S. 

 at 14 - 1° C. This, according to Rowland's results for the tem- 

 * Proceedings of American Academy of Arts and Sciences, 1880. 



Am. Jour. Sci. — Third Series, Vol. XXX, No. 175. — July, 1885. 

 3 



