14 On the Determination of the B.A. Unit. 



puted as 



*o + .j-f[iiI(f-i)].. 



In the second method it is computed as 



(C + c) 2 R= ^|"l+ ^( 1 ~ |)1 + smaller terms. 



E was over 6 volts, £ 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 differ- 

 ence between the two. The discussion shows that the first 

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

 J = 42,055,000 as the result. 



Since the completion of my experiments, a 10-ohm Elliott 

 standard in the possession of the University has been com- 

 pared with the Cambridge standards and found correct at 

 20 o, 9 C. My standard has been compared with this, with the 

 following result: — 



W. M. & C.'s coil ,. nA1 £ Q . i Q7Q 



™ lr +o m — = 1*00168 in 1878, 



Jiilliott s coil * 



„ „ =1-00170,, 1882, 



„ „ =1-00173 „ 1883. 



In these comparisons the Elliott coil was taken at 16°*3 C, 

 as marked. Also we have 



Elliott coil at 20°-9 -i-QOU 

 Elliott coil at HF3 



Hence 0=^So =1'0003 B.A. units and J = 42,068,000 x 

 1-0014 ' > 



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 42655 kilogram- meters or 41,805,000 



C.G.S. at 14°-] C. This, according to Rowland's results for the 



temperature- variation, corresponds to 41,608,000 at 26°, the 



mean temperature of my experiments. Rowland's value at 26° 



is 41,720,000. Combining the mean of these, 41,664,000, 



with my result, I find 1 B.A. unit= .' -Vn nn == '9904 earth- 

 quadrant per second. 



This research cannot compare in weight with the elaborate 

 determinations of the ohm by direct methods which have been 



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



