WILLIAM SIEMENS, F.R.S. 399 



and round, forming as it were electrical eddies which must be 

 productive of heat. 



Those losses, however, can be diminished almost indefinitely by 

 iiinvasing the size and conductivity of the wires, and as regards 

 thr iron, a form of armature has been devised, which is best 

 illustrated in the machine before us the Gramme machine the 

 original conception of which is due to Dr. Pa'cinotti in 18G1. 

 This consists in putting the iron, in the form of wire coiled round 

 and round a non-conducting body, which is surrounded in its 

 turn by the insulated copper wire forming the coils of the rotating 

 armature. The iron wires being surrounded by a non-conducting 

 material, electric eddies cannot circulate in the direction in which 

 they would occur, viz., transversely to that of the wires, whereas 

 the magnetic -poles induced by the field-magnets are free to 

 advance within the iron wires at the rate of the rotative motion 

 imparted to them. 



We have here another armature which is not entirely according 

 to Pacinotti's idea, but involves it an armature such as is now 

 largely used in dynamo-machines. On a wooden bobbin are 

 wound coils of insulated wire in a direction parallel to its longi- 

 tudinal axis, according to a plan due to Von Heftner Alteneck. 

 Each coil of wire thus wound is brought successively into metallic 

 connection with one of these laminae, through which the current 

 produced within the coil in passing through the magnetic field is 

 conveyed by the commutator and its contact brushes, into the 

 wire constituting the outer circuit, and the coils of the field 

 magnets. A succession of currents is thus set up, all flowing in 

 the same direction and constituting in their aggregate a con- 

 tinuous flow. The chief advantage claimed for this arrangement 

 is that the whole of the wire upon the armature, except where it 

 crosses from side to side at the end, is effective ; whereas in the 

 Pacinotti ring the copper returns on the inside of the iron ring, so 

 that only one half of its length receives inductive effect in passing 

 through the magnetic field. 



Professor "Wheatstone in his Paper mentioned a very significant 

 fact. He said : "If I make a cross-connection between the 

 circuit passing round the armature and the field, I get a momen- 

 tary very powerful effect." This cross-connection really severe 

 the current into two parallel circuits, one portion passing at once 



