1879.] 
L. Schwendler— On Electric Light Measurements. 
103 
force transmitted, current and magnetism received are constant, is very 
short indeed, especially for the strong currents, which alone are made use 
of for lighting. 
Formula, for controlling the Test-results. —As the power which is 
represented by the measured current working through a given resistance 
can never exceed the original power transmitted to the machine, we can, 
from current, resistance, and force measurements, frame a formula which 
checks the probability of the results. 
This formula is :— 
0 
0-33 
J 
W—•w' 
r + m 
W' is the total power consumed by any dynamo-electric machine 
when producing the observed current -C in a circuit of resistance r + m. 
w' is the power consumed by the dynamo-electric machine when 
producing no current (i. e., driven empty; circuit open ; external resistance 
infinite). 
r is the external resistance, and m the internal resistance. 
In the above formula C is in webers, W' and w' in meg-ergs per 
second, and r and m in S.U. 
Of late, exaggerated statements of the performance of dynamo- 
electric machines have been made, the absurdity of which would have 
become evident at once if the above formula had been applied as a check 
to the results. 
Co-efficient of transmission. —If all the work (W 7 —w') were trans¬ 
formed into available current in the external circuit then:— 
^ = unity, where W is the total work performed by the observed 
current in the circuit of known resistance. 
In practice it will be found however that 
W'—w' 
W 
-7 
1 (for many reasons). 
This expression, 
W'—w' 
W ’ 
I have called :— 
The co-efficient of Transmission and designated it by the letter k. 
k is different for the different dynamo-electric machines, which have 
been tried, and decreases with increase of current. 
Producing currents above 24 webers, the following average values of 
k have been obtained:— 
