458 REPORT— 1889. 



choked later on at + 2° Fahr. I do not think that in any case which 

 I met with there would have been any trouble from choking had the 

 exhaust pipes been properly arranged. As it was, they were merely the 

 ordinary vertical exhaust pipes of a steam engine, quite suitable for their 

 original and for their intended purpose, but singularly unfitted for the 

 purpose to which I was putting them. 



Summarising now the whole matter as regards efficiency, it may be 

 said that the result of m.y detailed investigations is to show that the 

 compressed air transmission system in Paris is now being carried on on a 

 large commercial scale in such a fashion that a small motor four miles 

 away from the central station can indicate in round numbers 10 horse- 

 power for 20 indicated horse-power at the station itself, allowing for the 

 value of the coke used in heating the air, or for 25 indicated horse-power 

 if the air be not heated at all. Larger motors than the one I tested (and 

 there are a number of such in Paris) may work somewhat mox'e, and 

 smaller motors somewhat less, economically. The small rotary motors 

 would of course be much less economical. The figures which I have 

 given are, however, such as can be reached by any motor of between five 

 and 25 indicated horse-power if worked at a fair power for its size. 

 M. Victor Popp himself, and the engineers of the company, by no means 

 content with the results already obtained, are experimenting in various 

 directions with a view to greater economy, and I have not the least doubt 

 that they will attain their end. But although I made several experiments 

 on new appai'atus, I prefer to leave their results here undiscussed, 

 confining myself as strictly as possible to the work which has been already 

 carried out and the economy of actual present working, rather than 

 giving any credit for the result of improvements which, however certain, 

 are not yet actually carried out in practical work. 



A system of transmission which has actually been carried out on a 

 large commercial scale in such a way as to have an indicated efficiency of 

 50 jDcr cent, between prime mover and secondary motor, four or five miles 

 apart, is one which needs no adventitious aids to commend it to notice, 

 especially whei'e its uses are so numerous and so varied, and its con- 

 venience so extremely great, as are those of compressed air. Both 

 M. Victor Popp, who has organised and carried through the work of the 

 Paris company, and Mr. James Paxman, who has designed and made the 

 greater part of the machinery used, are to be heartily congratulated on 

 the results which have attended their work. 



While, however, I am unwilling to lay stress on possibilities which are 

 not yet actualities, there can be no harm in saying that I have no doubt 

 whatever that with mere improvement of existing methods and 

 appliances, and without the adoption of any new or untried methods 

 whatever, the new plant of the Paris company now being constructed 

 can be made to have an indicated efficiency of 67 per cent, instead of 50 

 per cent., and to give about 0'54 effective horse-power at the motor for 

 each indicated horse-power at the central station in the case of such a 

 motor as that on which I expei'imented. Under these cii'cumstances the 

 air used per indicated horse-power at the motor would be 520 cubic feet, 

 or 650 cubic feet per brake horse-power. I have the less hesitation in 

 giving these hypothetical figures because the more important imperfec- 

 tions of M. Popp's transmission system arise from such a very obvious 

 cause. Nothing indeed can be easier (as was evident on the recent visit 

 of the Institution of Mechanical Engineers to St. Fargeau) than to 



