. Electric railway gazette . he re- rotallon. This resistance to the mechanicaleffort of the steam engine is really the measure ofthe work the dynamo is performing, so the elec-trical resistance opposed by the counter electro-motive force of the motor is a measure of thework the motor Is doing. Prof. Silvanus Thompson, in his great work onDynamoElectric Machinery, cites an examplewhich very well shows how the current that amotor will take decreases with the speed of itsarmature. He used a small Immisch motor withseparately excited fields and connected it up withwith a primary battery and amper
. Electric railway gazette . he re- rotallon. This resistance to the mechanicaleffort of the steam engine is really the measure ofthe work the dynamo is performing, so the elec-trical resistance opposed by the counter electro-motive force of the motor is a measure of thework the motor Is doing. Prof. Silvanus Thompson, in his great work onDynamoElectric Machinery, cites an examplewhich very well shows how the current that amotor will take decreases with the speed of itsarmature. He used a small Immisch motor withseparately excited fields and connected it up withwith a primary battery and ampere meter. Atdifferent speeds, the following figures were ob-tained: Speed Revs,per Minute. 0 60 100 CurrentAmperes. 20 16,2 Speed Revs. per Miuute. 160 I 180 1 195 CurrentAmperes. Thus at its maximum speed it took only aboutone-fourth of the current that it took when thearmature was held at rest. In this case . am-peres were required to overcome the friction ofthe armature. Had the friction be en less, the. rof Thompson and the subsequent remarks, theamount of current that a motor will take Is onlythat which is absolutely necessary to do the workwhich it is called upon to do. That is to say, itit has no other work to do than to overojme Itsown friction, its armature will automaticallyattain such a speed as to generate a counterelectromotive force or back pressure such thatonly sufficient effective electromotive force remainsto force through the motor sufficient current tomove the armature against this resistance. Ifnow an additional load is thrown on the motor,the speed of Its armature will be at once retarded,less counter electromotive force will be gener-ated, and consequently more current will passand the motor at once adjusts itself to this newlo ad. SAFETY IN STREET RAILWAY TRAFFIC. Tnere is a great deal of common sense in thefollowing extract of a veto message of MayorHaynes of Newark: No passenger has been injured while in hislegitimate place, nor on a
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Keywords: ., bookcentury1800, bookdecade1890, bookidelectricrail, bookyear1895
