292 THE POPULAR SCIENCE MONTHLY. 



will have a value of 772 x 1*8 = 1,390 foot-pounds). Now, this much 

 having been gained in fixing the principle of our calculations, let us go 

 back to our steam-boiler, and to the coal we feed it with. It has been 

 experimentally determined that, if the entire quantity of heat given 

 off during the burning of one pound of pure coal could be applied 

 without loss to heating water, it would suffice to raise the temperature 

 of one pound of water 7,900 C. ; or, what is the same thing, differ- 

 ently stated, it would be sufficient to raise the temperature of 7,900 

 pounds of water one degree. The possible mechanical duty of the 

 " theoretically perfect " steam-engine is found by simply multiplying 

 the quantity which expresses the thermal equivalent of coal by the 

 quantity which expresses the mechanical equivalent of heat, and the 

 result would be the true value of one pound of coal burned in the 

 boiler in " foot-pounds." Performing this simple arithmetical opera- 

 tion, we obtain (7,900 x 1,390 =) 10,980,000 foot-pounds ; or, to put it 

 more simply, suppose we convert these foot-pounds into horse-power, 

 which we can do by another simple arithmetical operation of dividing 

 them by 33,000, and we shall have as a result that one pound of pure 

 coal, burned in the perfect boiler in one minute, would, if we could 

 apply it with absolute economy to the performance of work, exert a 

 force of (-^^(nf- =) 332 horse-power during one minute; or, if 

 burned during an hour, then one sixtieth of 332, or 5*5 horse-power. 



With a perfect boiler, therefore, we ought to get 5*5 horse-power 

 per hour out of every pound of coal burned on the grate-bars. Now, 

 let us inquire, What do we get in practice ? Surely, you will say, our 

 scientific mechanics and engineers have succeeded in getting a goodly 

 percentage out of this possible figure ; and the splendid engines, of 

 massive construction, that work so beautifully as to excite our wonder 

 and admiration at their smoothness and ease of their movements, must 

 be very near perfection. Alas for the vanity of human expectations ! 

 Instead of getting 5 # 5 horse-power out of every pound of coal we 

 burn in the boiler, the very best boiler and engine that have ever been 

 constructed require two and a half pounds of coal to give out one 

 horse-power : which means that, in spite of the vaunted progress of the 

 mechanic arts in our times, the best engineering talent applied to the 

 improvement of the steam-engine, from the time of James Watt down 

 to Corliss, has only succeeded in making it yield a duty of 15 per cent, 

 of what it ought to do, leaving an enormous margin of 85 per cent, for 

 future improvements. 



In the foregoing remarks I have, I fear, inadvertently been unjust to 

 our engine-builders, for by far the greater portion of this 85 per cent, 

 of wasted power is chargeable directly to the steam-boiler, and but a 

 comparatively small proportion thereof to the engine. In considering 

 the question of the duty of steam-motors, however, we must take the 

 whole machine (engine and boiler), as a single apparatus. If our 

 boiler-makers could do as well as our engine-builders the two indus- 



