ELECTRICITY DURING THE NINETEENTH CENTURY. 339 



machines gave either rapidly alternating or fluctuating- currents, not 

 steady currents in one direction. The Paccinotti construction, in 

 modified forms, is now almost universally employed in dynamo 

 machines, and even where the form is now quite different the Pacci- 

 notti type has been at least the forerunner and has undergone modifi- 

 cations to suit special ends in view. Briefly, Paccinotti made his 

 armature of a ring of iron with iron projections, between which the 

 coils of insulated wire are wound. Although full descriptions of Pac- 

 cinotti-s ring armature and commutator were given out in 1864, his 

 work attracted but little attention until Gramme, in Paris, about 1870, 

 brought out the relatively perfect Gramme machine. In the mean- 

 time the other great development of the decade took place. 



Although Hjorth had, as stated before, put forward the idea that a 

 dynamo generator might itself furnish currents for magnetizing its 

 own magnets, this valuable suggestion was- not apparently worked out 

 until 1866, when a machine was constructed for Sir Charles Wheat- 

 stone. This appears to have been the first self -exciting machine in 

 existence. Wheatstone read a paper before the Royal Society in Feb- 

 ruary, 1867, "On the augmentation of the power of a magnet by the 

 reaction thereon of currents induced by the magnet itself." This 

 action later became known as the reaction principle in dynamo 

 machines. 



As often happens, the idea occurred to other workers in science 

 almost simultaneously, and Dr. Werner Siemens also read a paper in 

 Berlin about a month earlier than that of Wheatstone, clearh^ describ- 

 ing the reaction principle. Furthermore, a patent specification had 

 been filed in the British patent office by S. A. Varley, December 24, 

 1866, clearly showing the same principle of action, and he was, there- 

 fore, the first to put the matter on record. The time was ripe for 

 the appearance of machines closely resembling the types now in such 

 extended use. Gramme, in 1870, adopting a modified form of the 

 Paccinotti ring and commutator, and emplo}' ing the reaction principle, 

 first succeeded in producing a highly efficient, compact, and durable 

 continuous-current dynamo. The Gramme machine was innnediately 

 recognized as a great technical triumph. It was in a sense the culmi- 

 nation of many years of development, beginning with the early 

 attempts immediately following Faraday's discovery already referred 

 to. Gramme constructed his revolving armature of a soft iron wire 

 ring, upon which ring a series of small coils of insulated wire were 

 wound in successive radial planes. These coils were all connected 

 into a continuous wire, and from the junctions of the coils one with 

 another connections were taken to a range of copper bars insulated 

 from each other, constituting the commutator. In 1873 Von Hefner 

 Alteneck, in Berlin, modified the ring winding of Gramme, and pro- 

 duced the " drum winding," which avoided the necessity for threading 



