250 THE SCIENTIFIC PAPERS OP 



motor machine could not exceed one-half that communicated to> 

 the generator. That, however, was a question which had been 

 much discussed amongst electricians, and Mr. A. Siemens had 

 adopted the safer course, of rather under than over-stating the- 

 results, which might be and had been obtained. There was by 

 no means such a limit as 50 per cent. Experiments of undoubted 

 accuracy had shown that you could obtain GO or 70 per cent., and 

 that the point of maximum effect was not limited to half the- 

 velocity ; though he quite agreed with Mr. Preece that there was. 

 a limit. If the velocities were equal theoretically, the maximum 

 result should be obtained, but the counter current produced in 

 that case was also a maximum, so that practically the maximum 

 lay between the two results of half velocity and equal velocity. 

 He had in his hand a report, received only that day, with regard 

 to the working of the little railway at Berlin, in which his brother 

 put it, as the result of observation and measurement, that 60 per 

 cent, of useful effect was realised ; but this was under very peculiar 

 conditions. And it was one of the remarkable features connected 

 with the electric transmission of power, that as the resistance to- 

 be overcome in the railway carriage increased, so did the force- 

 increase to overcome the resistance. Thus, in going on a level* 

 the power used to propel the train might be 10 h.p. ; but when 

 the train ascended a gradient of 1 in 80, which was the steepest 

 on the line, then the power necessary to drive the dynamo machine- 

 at the station increased, and the power transmitted to the carriages- 

 increased in a still greater ratio. Indeed, it was a surprise- 

 to everyone who had investigated this little railway to see with 

 what determined force the carriages ascended the incline, with 

 comparatively little decrease of velocity. Of course, in order to- 

 overcome the greater resistance, the velocity had to decrease. It 

 was stated in the paper that the velocity of the train had been 

 limited to ten miles an hour ; but, seeing the facilities with which 

 the train ran, greater speed had been allowed, and the carriages 

 had gone to the distant station and back in seven and a-half 

 minutes, which meant an average speed of about twenty-five miles 

 an hour. A difficulty had arisen, as happened with most new 

 inventions, and this difficulty was of a most peculiar kind. In 

 the Berlin railway, one rail conducted the current towards the 

 carriages, and the other took it back to the station. Now, if a 



