170 Dr. C. Iv. Alder Wright on the Determination of 



Earth -quadrant 

 per second. 



Coil No. 1. B.A. unit, by Elliot . . .0-99257 

 „ 2. 10-ohm coil, „ ... 0-98963 



„ o. 10-ohm coil, by Warden, Mur- \Q.oqi 99 



head, and Clark ... j 

 „ 4. 100 „ „ „ 0-99098 



Mean 0*99112 



Hence, on the whole, Eowland's experiment indicates an error 

 in the B.A. unit of 0*00888 = 0*888 per cent, in deficiency. 



Weber's determinations, on the other hand, indicate that 

 the B.A. unit is nearly correct, the slight error being one of 

 excess, and that the value of J is somewhat above that deduced 

 from Joule's water-friction experiments. Thus he obtained 

 the following values for J in gravitation measure ; the annexed 

 values in ergs are calculated on the supposition that at Zurich 

 the value of g is 981*5. 



Gravitation ■**■ , 



Megalergs. 

 measure. D 6 



Value derived from calculations based on 



the different specific heats of a gas, I jqo.q- 49.1 n 



from experimental determinations by 



Begnault and Eontgen . . . 

 Value derived from experiments by H. 



F. Weber, on the heat developed by a 



known current whilst passing through 



a resistance measured in absolute mea- 

 sure by himself * 



y 428*15 42*02 



Taking the mean of these values for J ( = 428*55 in gravi- 

 tation measure), and determining the heat produced by a 

 measured current in a circuit the resistance of which was 

 measured by himself in absolute units, Weber obtained a mean 

 value for the Siemens unit of resistance of 0*9550 x 10 9 

 C.G.S. units, employing a coil (No. 1914) obtained from W. 

 Siemens as standard. By two other different methods (one 

 depending on the determination of the rate of oscillation of a 

 magnetic needle in a coil, the other on the measurement of 

 the current induced in a given coil by opening a known cur- 

 rent in an adjacent circuit) the resistance of this same standard 

 coil was found to be respectively 0*9545 x 10 9 and 0-9554 x 10°, 

 giving as final average of the three series of observations, 

 0*9550 x 10 9 C.G.S. units. Unfortunately Weber did not com- 

 pare his standard Siemens unit with any copy of the B.A. unit: 

 assuming, however, that the Siemens unit used by him bore 



