3*4 SCIENCE PROGRESS. 



tions per minute, with ten poles and a commutator five feet 

 in diameter. In the dynamos which the same firm has 

 built more recently, a feature of interest is that the separate 

 commutator is discarded, and the numerous sets of brushes 

 bear directly on the peripheral surface of the ring winding ; 

 the outer portion of each loop is a copper piece wedge- 

 shaped in section, and is mounted so that the entire number 

 forms in effect a gigantic commutator. At the Spandauer 

 Strasse station there are four engines, each of iooo horse- 

 power, driving two dynamos which are mounted at 

 either end of the engine crankshaft : each dynamo has ten 

 poles and gives 2000 amperes at 140 volts when running at 

 60 revolutions per minute, whence each combined set is 

 capable of lighting as many as 7000 lamps of 8 candle- 

 power : while at the Mauer Strasse and Schiffbaudamm 

 stations, there are three and six equally large double steam 

 dynamos. The above gives an idea of the size to which 

 the demand for electric light in towns has raised the con- 

 tinuous-current dynamo. Machines of the same type as 

 above described are also to be found at Copenhagen and 

 Stockholm. 



The Schuckert dynamo for central-station work is of 

 an entirely different construction, but again is multipolar. 

 It has a large ring armature of a fiat discoidal shape, 

 flanked on either side by numerous poles facing the arma- 

 ture core : opposite poles are of the same sign and in effect 

 form a common polar surface. In recent machines, the 

 armature is adjustable end-ways, so that it may be set 

 exactly central between the poles on either side ; all thrust 

 or pull on the core, due to the fields on one side being 

 stronger than those on the other, is thereby obviated. At 

 Hanover there are triple expansion engines of 400 and 600 

 horsepower, each coupled directly to their dynamos : the 

 armatures, owing to their large diameter of 10 ft. and their 

 high peripheral speed, serve as flywheels : the commutators 

 are of huge size, 6 ft. 6 in. in diameter, and have as 

 many as 840 sections. At Dtisseldorf the dynamos have 

 14 poles and give 400 volts and 1000 amperes at 90 revolu- 

 tions per minute, and again the armatures are 10 ft. in 



