242 THE SCIENTIFIC PAPERS OF 



It is a remarkable circumstance in favour of the electric 

 transmission of power, that while the motion of the electro- 

 magnetic or power-receiving machine is small, its potential of 

 force is at its maximum, .and it is owing to this favourable 

 circumstance that the electric train starts with a remarkable 

 degree of energy. With the increase of motion the accelerating 

 power diminishes until it comes to zero, when the velocity of the 

 magneto or driven machine becomes equal to that of the dynamo 

 or current-producing machine. Between the two limits of rest 

 mid maximum velocity the driving power regulates itself accord- 

 ing to the velocity of the train ; thus, on an ascending gradient 

 the speed of the train diminishes, but the same effect is automati- 

 cally produced which results from the turning on of more steam 

 in the case of the locomotive engine. When running on the level, 

 the velocity of the train should be such that the magneto-electric 

 machine should make one-half to two-thirds as many revolutions 

 per minute as the dynamo-electric. When descending, the speed 

 of the magneto-electric machine will be increased, in consequence 

 of the increased velocity of the train, until it exceeds that of the 

 dynamo-electric machine, from which moment the functions of 

 the two machines will be reversed ; the machine on the train will 

 become a current generator, and pay back, as it were, its spare 

 power into store, performing at the same time the useful action of 

 a brake in checking further increase in the velocity of the train. 

 If two trains should be placed upon the same pair of rails, the one 

 moving upon an ascending portion, the other upon a descending 

 portion of the same, power will be transmitted through the rails 

 from the latter to the former, which may therefore be considered as 

 connected by means of an invisible rope. 



The effects obtained with dynamo-electric machines under 

 varying circumstances of load and velocity have been very fully 

 investigated and brought forward by Dr. Hopkinson, F.R.S., in two 

 papers read by him recently before the Institution of Mechanical 

 Engineers, so that it would be superfluous for me to dwell upon 

 this portion of the subject on the present occasion. Suffice it to 

 say, thaj; in transmitting the power of a stationary engine to a 

 running train, the proportion of power actually transmitted varies 

 with the resistance to, or speed of the train, reaching practically a 

 maximum when the velocity of the machine on the train is about 



