102 REPORT — 1842. 



it follows, that by the indicator the duty done by the steam upon the piston 

 for each cwt. of coals consumed, Mas 



87,852,427-049*. 



Comparison of the Results given by the Indicator with the Expemnetits of 

 Mr. Wicksteed. t 



The effective work done by the steam per square inch of the piston per 

 stroke of the engine, as determined by the experiments of Mr. Wicksteed 

 (Experimental Inquiry, p. 22), was 



129-4 -7-30f = 122-1. 



In Mr. Wicksteed's experiments the engine was assumed to make a mean 

 stroke of 10 feet. At the time of the experiments with the indicator, the 

 mean stroke of the piston was 9 ft. \0\ in. (by the measurement of the en- 

 gineer). The mean stroke being thus 1^ in. short of its former length, the 



]i 1 



work done per stroke is to be diminished by the r-^rth part, or the -^rth part. 



This deduction being made, we obtain 



Work per stroke per square inch by experiment 1 20-574 ; 



1 20 - 574 

 Mean pressure by experiment = 12*21. 



The duty done per cwt. of coals, consumed between the 28th of January 

 and 1 5th of February, estimated by the water raised, was, by Mr. Wicksteed's 

 calculation, 81-627,471. 



On the whole, therefore, we have 



lbs. one foot high per square inch per stroke by experiment 120*5741 

 lbs. one foot high per square inch per stroke by indicator 1 19*388 J 

 Mean effective pressure of steam per sq. in. of piston by experiment 12-21 lbs. \ 

 Mean effective pressure of steam per sq. in. of piston by indicator 12-09 lbs. J 

 Duty done at pumps with 1 cwt. of coals, as shown by water raised 81,627,471. 

 Duty done by steam on piston with 1 cwt. of coals, as shown by in- 

 dicator 87,852,427. 



Variations in the Registration. 



The greatest variations from the mean registration per stroke, as shown by 

 the table, occur on the 6th and the 1 1th of February. The latter differs from 

 the mean by -032, which is equivalent by the formula to 4*26 units of work. 



These variations are due, — 1st, to a variation in the length of the stroke, 



2 1 

 amounting to 2| in. at least, and giving a variation of the -r^th part, or the 



1 199-1 



— -th in the work per stroke, which variation is equivalent to — — , or 2*543 

 48 48 



units of work per square inch of the piston. 



* The coals used were small coals of the worst quality, Mr. Wicksteed having, it is well 

 known, adopted the excelleut expedient of contracting with the coal-merchant, on the part 

 of the company, to pay not according to the quantity or quality of the coals supplied, but 

 according to the pounds of water which the engine is made to raise by them one foot high ; 

 i. e. to pay the coal-merchant so much per unit of work doue by the coals. Had the best 

 Welch coals (such as are used in Cornwall) been used on this occasion, the duty would have 

 been 110 millions per cwt. 



f The work expended per stroke on the vacuum resistance is here deducted to get the 

 effective work, which is evidently that shown by the indicator. 



