1879.] L. Schwendler— On Electric Light Measurements. 
10 L 
This increase of current for low speeds is more than proportional to 
the speed; afterwards it becomes proportional; and for high speeds the 
increase of current is less than proportional to the speed. 
The current has, however, no maximum for any speed, but reaches its 
greatest value at an infinite speed. 
This same law, as the total resistance in circuit is supposed to be 
constant, of course holds good also for the electro-motive of the dynamo- 
electric machine. 
Influence of External resistance. See Appendix XII. 
Keeping the speed constant, the electro-motive force of any dynamo- 
electric machine decreases rapidly with increase of external resistance. 
This decrease is more rapid, the smaller the internal resistance of the 
dynamo-electric machine is made. 
Hence the currents must decrease much more rapidly than propor¬ 
tional to the total resistance in circuit. 
As in the case of speed, the electro-motive force has no maximum for 
a certain external resistance, but approaches permanently its greatest value 
for an external resistance equal ‘Nil.’ 
It appears that the function which connects E. M. F. and speed, is 
the same as that which connects E. M. F. and external resistance. 
We have only to substitute for speed the inverse of resistance and 
vice versa. 
Maximum worlc ly a current in the resistance K. 
As the current decreases much more rapidly than the total resistance 
in circuit increases, this resistance R should invariably be made smaller 
than the remaining resistance of the circuit, i. e., smaller than the internal 
resistance of dynamo-electric machines plus resistance of leading wires. 
See Appendix XI and the special proof attached. 
The Electro-motive force of a Eynamo-Electric Machine as a function 
of the resistance and speed. 
It appears that the following two formulre are most probably correct 
for all Dynamo-Electric Machines, if the loss of current by transmission 
is taken into account:— 
E the E. M. F. 
m the internal resistance, and r the external resistance, including 
resistance of leading wire. 
