1880.] on Ap2)li cat Ions of the Dynamo-Electric Current. 335 



from electric currcut back into mechanical force, was clearly demon- 

 strated. 



Tlie utilization of the induced current had, however, been a work 

 of mucli time and thought on tlie part of those who followed in the 

 wake of the great discoverer. One of the first attempts to utilize the 

 magneto-electric current in telegraphy was made by Whcatstono in 

 18-44:, when he brought out his magneto-electric step-by-step instru- 

 ment. But, notwithstanding the great ingenuity displayed in tlic 

 same, the current induced was found practically insufficient to movo 

 the receiving instrument with a sufficient degree of certainty. 



An important step towards aggregating magneto-electric currents 

 was made by Dr. Werner Siemens in 1856, who constructed an arma- 

 ture resembling in section a double-headed rail, or double I , into the 

 hollow of which the insulated wire was wound longitudinally. In 

 mounting this armature upon bearings, and giving it a rapid rotation 

 between the poles of a series of permanent magnets, an accumulative 

 eflect was produced through the simultaneous action of each perma- 

 nent magnet in setting up a current in one and the same coil ; thus a 

 succession of currents was set up, which, when directed by means of 

 a commutator into an outer metallic circuit, was capable of producing 

 a continuous current of considerable power. A magneto-electric 

 step-by-step instrument constructed on this principle was shown in 

 operation, and also a more powerful arrangement of the same descrip- 

 tion for exploding mines, and for igniting platinum wire. It was 

 also shown that in turning the handle of such a machine, and con- 

 necting its leading wires to another similar machine, motion was set 

 up in the latter, and sufficient force was obtained to work a ventilator 

 with considerable efifect. 



The magneto-electric machines of Holmes and Wilde were next 

 passed in review, which it was shown marked a further step towards 

 the attainment of powerful effects by the accumulation of magneto 

 currents when steam power was employed for their production. 



The dynamo-electric principle attributable to Werner Siemens 

 and Wheatstone was next adverted to, and the first machine con- 

 structed on this principle by the lecturer, and brought by him before 

 the Royal Society in 1867, was shown in operation. This machine 

 differed from magneto-electric arrangements in the substitution of 

 electro - magnets for permanent or steel magnets, which electro- 

 magnets were excited by the current produced by the rotation of 

 the helix or armature of the machine itself. The advantage of the 

 machine consisted in the accumulative action it evolved, giving rise to 

 currents of considerable magnitude which were strictly proportionate 

 to the mechanical power expended. 



The adaptations of this accumulative principle by Professor 

 Pacinotti, by Gramme, by von Heftner-Alteneck, and others, were 

 alluded to, leading up to a recent modification of the dynamo-electric 

 machine by the lecturer, by which a further increase in the strength 

 of current and improved steadiness of action could be realized. The 



