May 1, 1885. 



SCIENCE. 



365 



and unusually detailed discussion. Mr. Mair lias been 

 one of the earliest and most earnest advocates of this 

 system of 'independent engine-tests,' and has fol- 

 lowed closely upon the steps of Messrs. Farey & Don- 

 kin, and of Sir Frederick Bramwell, in carrying out 

 this undoubtedly correct method. 



By this system, the power of the engine, and the 

 distribution and variations of weight of steam in the 

 steam-cylinder, are determined by the indicator in 

 the usual way ; while, at the same time, the discharge 

 of heat into the condenser of the engine is measured 

 by introducing a weir at the discharge from the hot- 

 well, and, by the use of properly disposed thermome- 

 ters, calculating from the readings so obtained the 

 number of thermal units of heat-energy thus carried 

 away from the engine. The sum of the quantities 

 of heat carried off, the heat converted into power 

 and utilized as mechanical energy, and the heat 

 wasted in various ways in its passage through the 

 machine, should evidently be equal to the heat re- 

 ceived from the boiler. The latter quantity is usually 

 capable of easy determination; and the power of the 

 engine as shown by the indicator, and the losses in 

 the condensing water, are the other important quan- 

 tities, and these are also readily ascertainable. The 

 comparison thus made is that of the heat produced at 

 the generator, with the power derived from it; and, 

 this comparison being effected, it becomes easy to 

 calculate, from the data thus obtained, what is the 

 actual efficiency of the engine; what are the wastes, 

 and in what direction they occur; and, finally, in 

 what direction improvement may be looked for, and 

 to what extent it is possible. 



Mr. Mair's trials were made with several engines, 

 and in some cases with the same engine under vary- 

 ing conditions. Of the engines tested, one was a 

 single-cylinder beam-engine, one was a 'Bull-Cornish 

 engine,' and the others were Woolf arrangements of 

 the compound engine. With the first of these en- 

 gines, steam was carried at from 56 to 59 pounds' 

 pressure, measured from vacuum. The speed of pis- 

 ton was from 222 to 240 feet per minute, and the ratio 

 of expansion varied from 2 to 4.33. The steam used 

 was practically dry, containing, by observation, but 

 one per cent of water. The amount passing through 

 the jacket was from 4.4% to 4.9%, except on one oc- 

 casion, when the jacket-steam was entirely shut off. 

 The power of the engine was from 120 to 125 horse- 

 power, as shown by indicator. 



The proportion of water condensed in the cylinder, 

 up to the point of cut-off, varied from 15% to 30%, 

 as the ratio of expansion increased from 2 to 4.33, 

 and was brought up to 37 % at the ratio 3.84 by shut- 

 ting off the jacket. The heat supplied to the engine, 

 measured in British thermal units, varied from 416 

 to 516 per horse-power per minute; the best work 

 being done, and most economy exhibited, at a ratio of 

 expansion of 3.16. When the jacket-steam was shut 

 off, the consumption of heat amounted to 516 units 

 per minute. The consumption of steam amounted to 

 from 21 to 26.5 pounds per horse-power per hour. The 

 theoivt ical efficiency was from 25 % to 27 %, while the 

 actual efficiency was from 8% to 10%, or from 33 % to 



37% of that estimated on the assumption of perfect 

 freedom from wastes other than the necessary thermo- 

 dynamic waste of the perfect engine. 



Comparing these figures, it will be seen that the 

 cylinder waste amounts, in this engine, to about ten 

 or twelve hundredths the ratio of expansion, in per- 

 centage of the total heat or steam supplied in the 

 cases of trial of the jacketed cylinder. Throwing off 

 the jackets brings up"the waste to a percentage equal 

 to nearly fifteen-hundredths the ratio of expansion. 



The 'Bull-Cornish engine' is a pumping-engine in 

 which the steam-distribution is effected as in the or- 

 dinary Cornish engine; but the beam is dispensed 

 with, and the cylinder is inverted and set directly 

 over the shaft and pump-rod. It is thus impossible 

 to use safely as large a ratio of expansion as in the 

 common form of Cornish engine, the distribution of 

 weights being less capable of a wide range of adjust- 

 ment. In this ca c e, the engine was worked with 55 

 pounds' absolute steam-pressure, at a piston-speed of 

 244 feet per minute, using dry steam at a ratio of 

 expansion of 1.75. In this case, the amount of con- 

 densation at cut-off was 17%; the power was 175 

 horse-power; the heat used was about 624 thermal 

 units per minute, and the steam 32 pounds per 

 horse-power per hour; the theoretical efficiency was 

 23 %, the actual 7 %, and the latter was 30 % of the 

 former. The ' Bull-Cornish engine ' is thus seen to 

 be substantially equal to the single-cylinder, jacketed 

 beam-engine in waste by condensation, but, on the 

 whole, to be inferior to the latter in its consumption 

 of heat and of steam under substantially equivalent 

 conditions. 



The Woolf compound engines were worked with 

 steam varying from 67 to 78 pounds' pressure, absolute, 

 with piston-speeds from 284 to 368 feet per minute, 

 and at ratios of expansion varying between 10 and 

 16.5. Their power ranged from 133 to 215 horse- 

 power, and the amount of heat supplied ranged from 

 296 to 324 thermal units per horse-power per hour. 

 The cylinder-condensation ranged from 24% to 31%, 

 or about eight times the square root of the ratio 

 of expansion, in per cent, of steam supplied. The 

 engines used from 15.12 to 16.6 pounds per horse- 

 power and per hour. The efficiencies, theoretical and 

 actual, were from 25 % to 30 %, and from 13 % to 14 % ; 

 the latter quantity being nearly one-half the former. 

 The consumption of steam, on these trials, is extraor- 

 dinarily low, — the lowest on record, probably, — and 

 should be checked by repeated experiment. 



On the whole, these reports present the class of 

 data that the engineer greatly needs, both for the 

 purpose of determining the direction and the limita- 

 tions of further improvement of the steam-engine, 

 and for the purpose of securing a more practically 

 applicable theory of the real, as distinguished from 

 the ideal heat-engine. K. H. Thurston. 



METEOROLOGICAL NOTES. 



The Russian meteorologist, Woeikof, known in 

 this country from his share in the final preparation 



