404 



SCIENCE. 



[N. S. Vol. VII. No. 169. 



leigh, Ayrton & Perry, Mather, Swinburne, 

 Cardew and Weston. 



Magneto - electric and dynamo - electric 

 generators and motors have now become 

 so common that we are apt to forget that 

 their introdactiou on an extensive scale has 

 only taken a few years. Faraday's disc 

 dynamo was, as has already been stated, 

 produced in 1831, and a machine for gener- 

 ating electricity was made by Pixii in the 

 following year. Pixii's machine consisted of 

 a horseshoe permanent magnet which was 

 rotated in such a way that its poles passed 

 alternately in front of the poles of a similar 

 electro-magnet. An alternating current 

 was thus induced in the circuit which in- 

 cluded the coils of the electro-magnet. 



This machine was improved by Clai'ke, 

 who removed the coils and put a commuta- 

 tor on the axis. Other machines were made 

 or suggested by various physicists, and an 

 important observation, which has since been 

 frequently overlooked, was made at this 

 time by Jacobi, who pointed out the im- 

 portance of making the cores of the coils 

 short. Sturgeon, in 1836, made a dynamo 

 with a shuttle-shaped armature ; a similar 

 form has long been identified with the name 

 of Siemens. AVoolrich made a multipolar 

 magneto machine in 1841 for electroplating, 

 and Wheatstone about this time produced 

 his small multipolar magneto, long used for 

 telegraph purposes. In 1845 "Wheatstone 

 and Cooke patented the use of electro-mag- 

 nets in place of the permanent magnets, and 

 Brett suggested, in 1848, that the current 

 from the machine might be made to pass 

 round a coil surrounding the magnet and 

 thus increase its strength. A similar sug- 

 gestion was independently made in 1851 by 

 Sinsteden. In 1849 Pulvermacher proposed 

 the use of thin laminte of iron for the cores 

 of the magnet, a proposition which has 

 since, but probably for a different reason, 

 been almost universally adopted . Sinsteden 

 used iron wire cores and made a number of 



experiments on the effect of varying the 

 pole face. About this time another class 

 of machines were proposed by Ritchie, Page 

 and Dajardin. In these machines both the 

 magnets and the coils were to be stationary, 

 but the magnetism was to ba varied by re- 

 volving soft iron pieces in front of the poles. 

 Modern representatives of these machines 

 are to be found in the dynamos of Kingdon, 

 Stanley and others. All the machines up 

 to this time had been of very small dimen- 

 sions In 1849 Nollet began the construc- 

 tion of an alternating machine on a larger 

 scale, but died before it was completed. 

 Machines of Nollet's type were afterwards 

 made by Holmes and by the Compagnie 

 1' Alliance of Paris, the latter being called 

 the Alliance machine. These machines were 

 used for lighthouse purposes. Holmes's 

 earlier machines were continuous current, 

 but later he left out the commutator, and 

 still later again introduced it on part of the 

 coils for the purpose of obtaining current to 

 excite his field magnets. This latter plan 

 was introduced after the self-exciting prin- 

 ciple had been introduced by Siemens and 

 Wheatstone. A remarkable machine his- 

 torically was patented in 1848 by Hjorth. 

 In this machine a combination ®f the per- 

 manent and electro-magnet was used, 

 the first to give magnetism enough to 

 produce a current with which to excite 

 the other. A similar idea was developed 

 fifteen years later by Wilde with the difi"er- 

 ence that the permanent magnet part was a 

 separate machine. The idea of using part 

 of the current from the armature to excite 

 or j)artially excite the field magnets was 

 at this time in the minds of a number of 

 workers, and some remarkable machines 

 were patented by the brothers Varley, one of 

 which containing both a shunt and a series 

 winding has been held by some to antici- 

 pate the compound winding now in use. 

 In 1867 it seems to have occurred inde- 

 pendently to Wheatstone and E. Werner 



