102 
L. Schwendler —On Electric Light Measurements. [March, 
k and a arc independent of m and r, and are functions of the speed of 
the induction cylinder, and contain also the construction co¬ 
efficients. e is the basis of the natural logarithm. 
Further:— 
E' the E. M. F., and v the speed of the induction cylinder. 
k and a! are independent of v, and are functions of m and r only. 
These two functions, E and E', correspond to all the characteristics of 
the curves found by experiment, and they also fulfil the limit conditions. 
In Appendices IX and X, the question has been gone into fully. 
Resistance and.Electro-motive force of the Electric arc. 
There appears to be no doubt that an appreciable E. M. F. in the arc 
is established which acts in opposite direction to the electro-motive force 
of the dynamo-electric machine. 
This E. M. F. of the arc increases with the current, passing through 
the arc. 
The resistance of the arc for constant length is also a function of the 
current passing through it, i. e., the resistance of the arc decreases with 
the current, see the following table :— 
Current 
in Webers. 
Resistance of 
the Arc in S.U. 
E.M.F. of the 
Arc in Y olts. 
28-81 
0-91 
2 02 
23-87 
1-72 
191 
16-27 
1-97 
1-86 
See Appendix XI. The E.M.F. in an electric arc, opposite to the electro¬ 
motive force of the dynamo-electric machine, constitutes another reason 
against the unlimited divisibility of the electric light. 
Regularity of the production of Currents by Dynamo-Electric Ma¬ 
chines at different periods .—If the brushes are well set, and if they are 
placed as nearly as possible in the neutral line of the commutator, the 
production of current is perfectly regular, and measurements taken through 
the same external resistance at the most distant periods agree most per¬ 
fectly with each other, supposing the correction for variation in speed and 
internal resistance are applied. 
Disregarding the heating of the dynamo-electric machine by the 
current, the time required to arrive at dynamic equilibrium, i. e., when 
