1S99]. SELLERS — TRANSMISSION OF ENERGY BY ELECTRICITY. 61 



and economy made by the projector. He even went so far as to say 

 that in case of transmitting power from a central station to an out- 

 lying electric light plant he would use compressed air for the pur- 

 pose, using air to drive the engines connected to the dynamos at 

 the lighting stations, instead of transmitting electricity ready for 

 immediate use. Among his various plans of using compressed air, 

 besides operating air motors, elevators and the like, he had pub- 

 lished a long list of uses to which it was applicable; he also sub- 

 mitted to the Government his cold storage scheme. In the event 

 of foreign invasion and the investment of Paris, when local indus- 

 tries might be stopped, he stated that by using the compressed air 

 from part of his compressing plant to drive the engines that oper- 

 ated the compressors of the other part, and utilizing the exhaust 

 from these air-driven compressors in the Government storehouses, 

 he could thus lower their temperature to the required degree, on the 

 principle of refrigeration by rarefaction of air after having exerted 

 force, as discussed by Prof. Henry on March 2, 1825, and as after- 

 ward toward 1S50 used for the artificial production of ice. 



The alternate-current lighting plant of Deptford, London, 

 established in 1889, was predicated on the possible generation of 

 electricity in large units of 10,000 volts pressure. I spent much 

 time in watching this experiment, which was in 1891 far from 

 meeting the expectations of its promoters. The 10,000 horse- 

 power engines and direct connected 10,000 horse-power dynamos 

 were never finished. 



In Rome I found the most promising scheme under way to utilize 

 the water power at Tivoli to generate a single-phase, alternate cur- 

 rent, to be transmitted a distance of twenty-five miles to the gates 

 of Rome by overhead cables, at a pressure of about 5000 volts, with 

 perhaps twelve per cent, loss in transmission. The Roman plant 

 was interesting, ^as in it the question of rate of alternation per 

 second had been considered, and Ganz & Co., of Budapest, 

 had recommended the lo\vest periodicity, forty-two full alternations 

 per second, as adapted to arc and incandescent lights on the same 

 feeders. If the rate of alternation per second be less than forty- 

 two full periods arc lights will pulsate, while in the case of incan- 

 descent lights by alternating current the rate of alternation may be 

 carried as low as twenty per second, depending upon the thickness 

 of the filament, with no perceptible effect on my eyes. But in 

 common practice seventy-two full periods per second has been 



