140 Mr. Julius Frith on 



The most conclusive of these experiments are those of 

 Von Lang and Arons. 



Von Lang,* with an apparatus represented in Fig. 1, 

 using carbons 5 mm. in diameter and 3 mm. apart, with a 

 current of 4*3 amperes, found the back E.M.F, to be 

 39 volts. 



Arons-j- worked with a Wheatstone bridge, of which 

 two branches, P and Q, Fig. 2, contained fixed resistances, 

 the third a variable resistance R, the fourth in series, a 

 battery B, Key K, variable resistance S, ammeter C and an 

 arc lamp L, the carbons of which can be short circuited by 

 the Key K'. 



Fig. 2. 



Centralblatt fur Elektrotechnik, vol. 7, p. 443 (1885). 

 t Wied. Ann. Vol. XXX., p. 95 (1887). 



