456 



REroRT — 1889. 



revolutions per minute, used 890 cubic feet of air per indicated horse-power 

 per hour. (Its indicator diagrams are shown in Fig. 4, their area being- 

 represented by K N O in Fig. 3.) The work which this quantity of air, 

 at the given pressure and temperature, is theoretically capable of doing 

 behind a jjiston, expanding down to atmospheric pressure, is equivalent 



to 1"27 horse-power for an hour. The in- 

 dicated efficiency of the motor (the ratio 

 expressing loss by rounding of courses, by 

 insufficient expansion, by back pressure, 

 &c.) is therefore 0'79. This figure gives 

 us a check on the ratios already worked 

 out, for if they are right the air actually 

 used should be -^ times as great as the 696 



cubic feet already allowed for. This would 

 be 880 cubic feet, which represents of course 

 a most satisfactory check. It will, however, 

 be recognised that this agreement checks 

 the figures only so far as they apply to air 

 actually used, and would not be vitiated or 

 in any way affected by losses by leakage. 



The vital measurement of all the ex- 

 periments was, of course, that of the quan- 

 tity of air used. The air was passed through 

 one of the fan meters already described, 

 readings of which were taken every quarter 

 of an hour. After the experiments were 

 over air was passed through the same meter 

 at exactly the same pressure, and in as 

 nearly as possible the same quantity, and 

 then passed, at atmospheric pressure, 

 through two large standard wet gas 

 meters. The readings of these were taken 

 as correct, and the multiplier for the fan 

 meter determined from them. I found 

 from numerous experiments on several fan 

 meters that this multiplier varied both 

 with pressure and with quantity, but that 

 the latter pariation was very small within 

 the limits of my experiments. I have no 

 doubt that the air quantities which I shall 

 give you are correct within about 2 per 

 cent, plus or minus. 



It will be seen that the total indicated 

 efficiency of transmission, with cold air, is 

 0'39 (see Table) ; in other words, that work 

 requires to be done at the rate of 2'6 indi- 

 cated horse-poAver at the central station per indicated horse-power at the 

 motor. The motor was worked on a brake, and its mechanical efficiency 

 was found to be 067, so that (see Table), in round numbers, four indi- 

 cated horse-power were required at St. Fargeau per brake horse-power at 

 the motor. 



To examine the economy due to heating the air before using it, I used 



