1074 DR. C. W. SIEMENS ON THE DYNAMO-ELECTRIC CURRENT. 
coils of greatly increased weight and dimensions; at the same time the helix wire had 
to be increased in diameter to give room for the aggregate current, but in reality I found 
it advantageous to increase the diameter of the same in a much greater proportion. 
These general conditions having been determined by preliminary experiment, Mr. 
Lauckert, electrician engaged at my works, undertook a series of comparative 
experiments which are given in the appendix attached to this paper, and the results 
are given numerically and exhibited in curves. On examining the curves it will be 
remarked : 
1. That the electro-motive force instead of diminishing with increased resistance, 
increases at first rapidly, then more slowly towards an asymptote. 
2. That the current in the outer circuit is actually greater for a unit and a-half 
resistance than for one unit. 
3. With an external resistance of one unit, which is about equivalent to an electric 
arc when 30 or 40 webers are passing through it, 2'44 horse-power is expended, of 
which 1 ‘29 horse-power is usefully employed : an efficiency of 53 per cent, as compared 
with 45 per cent, in the case of the ordinary dynamo machine. 
4. That the maximum energy which can be demanded from the engine is 2‘6 horse¬ 
power, so that but a small margin of power is needed to suffice for the greatest possible 
requirement. 
5. That the maximum energy which can be injuriously transferred into heat in 
the machine itself is 1'3 horse-power, so that there is no fear here of destroying the 
insulation of the helix by excessive heating. 
6. That the maximum current is approximately that which would be habitually used, 
and which the commutator and collecting brushes are quite capable of transmitting. 
Hence I conclude that the new machine will give a steadier light than the old one, 
with greater average economy of power, that it will be less liable to derangement, and 
may be driven without variation of speed by a smaller engine ; also that the new 
machine is free from the objection of having its currents reversed when used for the 
purpose of electro deposition. 
The same peculiarity also enables me to effect an important simplification of the 
regulator to work electric lamps, to dispense with all wheel and clock-work in the 
arrangement, as shown in Plate 40. The two carbons, being pushed onward by 
gravity or spring power, are checked laterally by a pointed metallic abutment, situated 
at such a distance from the arc itself that the heat is only j ust sufficient to cause the 
gradual wasting away of the carbon in contact with atmospheric air. The carbon 
holders are connected with the iron core of a solenoid coil, of a resistance equal to 
about fifty times that of the arc, the ends of which coil are connected with the two 
electrodes respectively. The weight of the core, which has to be maintained in 
suspension by the attractive force produced by the current, determines the distance 
between the electrodes, and hence the electric resistance of the arc. The result is 
that the length of the arc is regulated automatically so as to maintain a uniform 
resistance, signifying a uniform development of light- 
