300 



. KNOWLEDGE ♦ 



[Nov. 10, 1882. 



tlie historj- of uiy conntxtion with the matter. 1 know 

 ::othint; »bout the asUonomical inagaziiie in which Mr. 

 Ljnn stxms to have announct- d his (or Mr. Prince's) con- 

 clusions to a sekvt circle of readers ; but Mr. Maunder 

 i-*!! scarcely exf»H.t sucli magazine to enjoy an absolute 

 wonopoly of discussion of a question wliich has previously 

 been privately debated as tliis question lias U'en. 



WiLLi.\M Noble. 

 For«t Ltdge, Mareslield, Uck6eld. 



wliich consists of a li.xod ring of malleable cast iron, about 



2| inches long and 2 inches in dii 

 paratively tliicli wire .ire wounil < 



THE GRISCOM ELECTRO-MOTOR. 



rpm.S little piece of apparatus illustrates a principle 

 X of the utmost importance to those whose business or 

 pleasure it is to deal with matters electrical. It may be i 

 remeuiWred that seme few months since we explained the j 

 principles of dynamo electric generators. It was shown ] 

 that the armature or coil of wire revolvin-,' before the poles I 

 of tJie large electro- or lield magnets, had a series of 

 electric impulses induced in it With a large machine, j 

 having an armature revolving at a high rate, the current , 

 induced as the result of the force expendtd in the steam- 

 engine would l>e proportionately large, and capable of being 

 ajiplitd to lighting, electrotyping, or any other of the many 

 applications of electricity. But now we have to refer to a 

 still further development of the principles of electric 

 induction. If we pass the current produced in a 

 dynamo machine, or its equivalent galvanic battery, into 

 another sin)ilar machine, its armature will be found to 

 revolve at a rate and with a force proportioned to the , 

 current traversing the coils. The explanation is simple 

 — when the current enters the machine, a magnetic field 



eter. Two coils of com- 



. the oi>posito sides of tli' 



ring to within about an inch of each other, top and bottom. 

 C represents the commutator, which, of course, runs on the 

 same axis as the armature. Itconsistsof a drum of insulating; 



i« <T»at«^, and, a« a consequence, the movable armature 



' ' -i V^fore the pole* of the lield-magnet Tliis, then, 



■ i» known as the " revcmibility of the dynamo 



The motor we are dencribing is only a small 



... -.iia r(9ii*taiice of aliout ony Ohm, and is worked 



by a UtU-ry giving an el««tro motive jKiwer of about 



I'l voltA. Fig. 1 u a p«:nipective view, and Fig. 2 



a v»?rtic*l sectional vi»rw. A imall SiemenH" armature 



(Fig, 2, A A), can be i«cn iniiide the Held magnet (IJ 15), 



material on to which a split-ring (PP) is attached. InsteatI 

 of the ordinary filit-springs to complete the circuit through 

 thr> commutator, little rollers (RR) are used. One pole of 

 the battery (D) is shown as being connected to the comnau- 

 ttttor, the other to the field-magnet. The binding-screws 

 used for this purpose are shown in Fig. I on the left-hand 

 side, while at the opposite side is to be seen the little 

 driving-wheel from which a band passeB over the wheel of 

 the sewing-machine, lathe, ic. 'J'lie little bolt and nut 



