338 ELECTRICITY DURING THE NINETEENTH CENTURY. 



steel magnet. A wire touched the periphery of th<> disk :it a selected 

 position with respect to the magnet and another was in connection with 

 the axis. These wires were united through a galvanometer or instru- 

 ment for detecting electric current. A current was noted as present 

 in the circuit so long as the disk was turned. Here, then, was the 

 embryo dynamo. The century closes with single dynamo machines of 

 over 5,00(J horsepower capacity and with single power stations in which 

 the total electric gen<M"ation by such machines is 7.'),<MM» to l(H),(i(>0 horse- 

 power. So perfect is the modern d3'namo that out of l.ooo horsepower 

 expended in driving it 95t) or more may be delivered to the electric line 

 as electric energy. The electric motor, now so common, is a machine 

 like the dynamo, in which the principle of action is simph' reversed; 

 electric energy delivered from the lines becomes again mechanical 

 motion or power. 



Soon after Faraday's discovefies in magneto-electricity attempts 

 were made to construct generators of electricity from power; but the 

 machines were small, crude, and imperfect, and the results necessaril}^ 

 meager. 



Pixii, in Paris, one year after FaradaA^'s discovery was announced, 

 made a machine which embodied in its construction a simple commu- 

 tator for giving the currents a single direction of flow. This is the 

 prototype of the conunutators now found on what are called contin- 

 uous-current dynamos. After Pixii followed Saxton, Clarke, Wheat- 

 stone and Cooke, Stohrer. and others, but not until 185-1 was any very 

 notal)le improvement made or suggested. In that year Soren Hjorth, 

 of Copenhagen, (lescri))ed in a patent speciiication the principle of 

 causing the electric currents generated to travei'se coils of wire so 

 disposed as to reenforce the magnetic field of the machine itself. A 

 year subsequently the same idea was again more clearly set out by 

 Hjorth. This is the principle of the modei'n self-exciting dynamo, the 

 field magnets of which, very weak at the stjirt, are built up or strength- 

 ened by the currents from the armature or revolving pait of the 

 machine in which power is consumed to produce electricity. 



In 1S56 Dr. Werner Siemens, of Berlin, well known as a great pio- 

 neer in the electric arts, brought out the Siemens armature, an inno- 

 vation more valuable than any other made up to that time. This was 

 subsequently used in the powerful machines of Wilde and Ladd. It 

 still survives in magneto call-bell apparatus for such work as telephone 

 signaling, in exploders for mines and blasting, and in the simpler 

 types of electroplating dynamos. 



The decade between 1860 and 1870 opened a new era in the construc- 

 tion and working of d\'namo machines and motors. It is notable for 

 two advances of very great value and importance. Dr. Paccinotti, of 

 Florence, in 1860, described a machine by which true continuous cur- 

 rents resembling battery currents could be obtained. Up to that time 



