1880.] 



On the Dynamo-Electric Current. 



209 



which dynamo- electric machines worked on the shunt principle can be 

 made to give maximum results. A series of tables and diagrams are 

 given, the results of experiments conducted by Mr. Lauckert, elec- 

 trician, employed at the author's works, which lead up to the conclusion 

 that, in constructing such machines on the shunt principle, the resist- 

 ance on the rotating helix has to be considerably reduced by increas- 

 ing the thickness of the wire employed, and that on the magnets has to 

 be increased more than tenfold, not by the employment of thin wire, 

 but by augmenting the length and weight of coil wire employed. 



The results of this mode of distributing the resistances is sum- 

 marised as follows : — 



1. That the electro-motive force, instead of diminishing with in- 

 creased resistance, increases at first rapidly, and 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 equiva- 

 lent to an electric arc, when thirty or forty webers are passing through 

 it, 2'44 horse-power is expended, of which 1*29 horse-power is usefully 

 employed, proving 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 T3 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 the author concludes 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 

 all objection when used for the purpose of electro-deposition. 



This construction of machine enables the author to effect an im- 

 portant simplification of the regulator to work electric lamps, enabling 

 him to dispense with all wheel and clockwork in the arrangement. 

 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 just sufficient to 

 cause the gradual wasting away of the carbon in contact with atmo- 

 spheric air. The carbon holders are connected to the iron core of a 

 solenoid coil, of a resistance equal to about 50 times that of the arc, 

 the ends of which coil are connected to the two electrodes respectively. 



