854 KEPORT— 1892. 



able, where there is cheap water-power, and the possibility of constructing high- 

 level storage reservoirs, then hydraulic transmission can be adopted with success 

 for distributing power for ordinary manufacturing purposes. But neither telo- 

 dynamic transmission nor hydraulic transmission has proved suitable as methods 

 for the general distribution of motive power from central stations. Distribution 

 by steam and distribution by hente^ water have both been tried in the United 

 States, but not witli very remarkable success. Only two other methods are 

 available — distribution by compressed air and distribution by electricity. 



For many years compressed air has been used to distribute power in tunnelling 

 and mining operations to considerable distances. It is only recently that it has 

 been used as a general method of distributing power to many consumers. la 

 many installations the machinery has been rough and unscientitic, and the waste 

 of energy very considerable. It is through experience gained and improvements 

 carried out in the remarkable system now at work in Paris, and known as the 

 Popp system, that the great advantages of compressed air distribution have been 

 proved. The Paris system has very gradually developed. About 1870 a small 

 compressing station was ei-ected to actuate public and private clocks by intermittent 

 pulses of air conveyed along pipes chiefly laid in the sewer.s. In 1889 about 8,000 

 clocks were thus driven. Meanwhile the compressed air had also been applied to 

 drive motors for small industries. The demand for power thus supplied grew so 

 rapidly that a second compressing station was built in the Rue de Saint Fargeau. 

 In 1889 steam air compressors of 2,000 horse-power were at work, and additional 

 compressors were under construction. The pressure at that time was five atmo- 

 spheres, and the largest air mains were 12 inches in diameter. Ingenious and 

 .simple rotary machines were used as air motors for small powers, and for larger 

 powers any ordinary steam-engine was converted into an air motor. Professor 

 Kennedy made tests in 1889, which were communicated to this Association. He 

 found that a motor four miles from the compressing station indicated 10 horse- 

 power for 20 indicated horse-power expended at the compressing station, an efficiency 

 of 50 per cent only. There were then 22-5 motors worked from the air mains. 



Since 1889 more extended investigations have been made by Professor lliedler, 

 of Berlin, and the chief part of the waste of work has been traced to inefficiency 

 of the air compressors. Compound air compressors of much higher efficiency have 

 now been constructed. The plant at the Saint Fargeau station has been increased 

 to 4,000 horse-power. A new station has been erected on the Quai de la Gare, 

 intended ultimately to contain compressors of 24,000 horse-power. Compressors 

 of 10,000 horse-power are already under construction. 



Compressed air transmission, whether or not it is the most economical system, 

 is undoubtedly applicable for the distribution of power on a very large scale and 

 to very considerable distances. There is nothing in any of the appliances which 

 is noyel or imperfectly understood. The air is used in the consumer's premises in 

 machinery of well-understood types, and old steam engines can be converted into 

 air motors without difficulty and without alteration of existing transmissive 

 machinery in the factories. Not least important, the air can be measured with 

 accuracy enough for practical purposes by simple meters, and charged for in 

 proportion to the power consumed. Air compressors and air motors are not as 

 efficient as dynamos and electric motors, but in one respect distribution by air and 

 electricity are similar. For distances which are not more than a few miles the loss 

 of energy in transmission is small enough to be insignificant. 



There is yet one other mode of power distribution which promises to become 

 the most important of all, and which, in tlie case of transmission to very great 

 distances, if such transmission becomes necessary, has undoubtedly great advantages 

 over every other method. 



About electrical distribution of power I shall not venture to say much, partly 

 Ijecause I am not an electrical expert, partly because it has been lately pretty fully 

 discussed. In the United States there has been an enormous development of 

 electric tramways, which are essentially cases of electric power distribution. In 

 this country we have the South London and some other railways worked electri- 

 cally. There are others also on the Continent. But electrical power distribution 



