■NOVEMBEK 10, IfSS.?.] 



SCIENCE. 



645 



known as the Z ilvnanio, and is installed for 

 ■what is called a H circuit. It has its fiekl- 



magiiets vertical (fig. 6), and its armature re- 

 volves on a horizontal axis in the magnetic 

 field. The field-magnets are arranged on what 

 is called a ' derivation ' from the commutator, 

 placing it in the circuit, as in the Siemens 

 system. In adopting and utilizing known 

 principles and devices, 

 Edison has worked out 



the details to a state of r 



perfection simply admir- 

 able. Wherever liic eye 

 rests, it is pleased b}- cor- 

 rect proportions, sound 

 mechanical ideas, and 

 agreeable outlines. 



The armature, on 

 Siemen^'s principle, is 

 mounted on a wrought- 

 iron shaft. About the 



shaft, and concentric with it, are circular c^'l- 

 inders of wood, separating copper plates, as 

 shown in fig. 7. IJetween the plates a and h. 



and also between c and d, there are annular 

 disks of copper, insulated from cacli other. 

 Between the plates b and c are similar but 

 very thin annular disks of iron, separated 

 from each other b}- tissue-paper. This 

 built-up cylinder is then bolted together 

 longitudinally ; the bolls passing tiirough 

 the thin iron and coi)per disks without 

 touching tlicm, but clamping them be- 

 tween the thiclc plates. Wire bundles or 

 bars are jilaced equidistant from each 

 other longitudinally-, around the cylinder, 

 connecting each a pairof the copper disks, 

 i.e., one at each cud; and these bars or 

 bundles generate the current. 



Bars of brass or copper, separated 

 by thin sheets of mica, e,e, are dove- 

 tailed into the projecting end of the 

 cylinder, which forms tlie commutator. 

 The resistance of tiie generator is thus 

 small, and allows great subdivision of 

 the current in multiple arc. 



To preserve the uniformity of the cur- 

 rent, an adjustable resistance-box is 

 placed in the circuit of the field-mag- 

 nets ; and, when a number of lamps are 

 extinguished, additional resistance may 

 be added to the field by a switch on this 

 resistance-l)ox, whcreb3- tlie internal and 

 external resistauces are balanced, pre- 

 serving not only the uniform briglituess 

 of the lamps, but also the economy of 

 the machine. A test-lamp is suspended 

 on the dynamo ; and the fireman, who 

 ' oils the engine, regulates the resistance 

 according to the brightness of this lamp. 

 Automatic regulators have been devised ; but 

 as it is necessarj- to employ a man to run the 

 engine and dynamo, and as the incandescence 

 is more frequently altered by slipping of belts 

 than hy the sudden turuiug-out of a large num- 

 ber of lamps, the same man can attend both : 



consequently the sim[)le resistance-box answers 

 every pur|)ose on board ship. 



( Tv he continued.) 



