230 THE DEVELOPMENT OF ELECTRICAL SCIENCE. 



to this time had been of very small dimensions. In 1849 Nollet began 

 the construction of an alternating machine on a larger scale, but died 

 before it was completed. Machines of JSTollet's type were afterwards 

 uipde by Holmes and by the Gompagnie 1' Alliance, of Paris, the latter 

 being called the Alliance machine. These machines were used for 

 light-house purposes. Holmes's earlier machines were continuous cur- 

 rent, but later he left out the commutator, and still later again intro- 

 duced 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 principle had been introduced by Siemens and Wheat- 

 stone. A remarkable machine, historically, was patented in 1848 by 

 Hjorth. In this machine a combination of the permanent and electro 

 magnet was used, the first to give mechanism enough to produce a 

 current with which to excite the other. A similar idea was developed 

 fifteen years later by Wilde, with the difference that the permanent- 

 magnet part was a separate machine. The idea of using part of the 

 current from the armature to excite, or partially excite, the field mag- 

 nets was at this time in the minds of a number of workers, and some 

 remarkable machines were patented by the brothers Yarley, one of 

 which, containing both a shunt and a series winding, has been held by 

 some to anticipate the compound winding now in use. In 1867 it seems 

 to have occurred independently to Wheatstone and E. Werner Siemens 

 that the permanent-magnet part of the Hjorth and Wilde machines 

 might be dispensed with, the residual magnetism being used to start 

 the action. Siemens gave the name dynamo-electric machine to this 

 type, and it has stuck. In order to diminish the fluctuations in the 

 strength of the current during one revolution of the armature Pacinotti 

 devised his multigrooved armature in 1864. This machine did not 

 receive the notice it deserved for a number of years, and in the mean- 

 time Gramme produced his smooth-ring armature, in 1870. Gramme's 

 machine was soon recognized as being of great merit, and its gradual 

 introduction gave rise to increased activity. In 1873 the Hefner- 

 Alteneck improvements on the Siemens armature were introduced and 

 in the remaining seventies quite a number of forms of dynamo were 

 invented, the Lontin type, introduced in 1875 with improvement in 

 subsequent years, being one of the best. The early eighties saw 

 tremendous activity; the patent offices in Europe and America were 

 flooded with inventions of various types of dynamos and motors, of 

 lamps for electric lighting, etc. It is curious how few of those machines 

 have stood the test of time and how well the old types of Pacinotti, 

 Gramme, Siemens Alteneck, and Lontin in some one of their modifica- 

 tions hold the field. Great progress has been made in the last fifteen 

 years. Machines have assumed enormous proportions and the number 

 of branches of industry to which they have been applied is now very 

 large. Much has been learned during this time, particularly with 

 regard to alternating currents and their application to the transmission 



