ON A CONSTANT INDICATOR FOR STEAM-ENGINES. 101 



the Committee to the British Association of Science at their last meeting, 

 when reduced* by the substitution in it of the particular values assigned to 

 the constants in these experiments, is as follows : — 



U = 161-4474 N - -09051 L, 

 where N represents the number registered by the indicator during the period 

 for which the work of the engine is to be determined, L the space in feet de- 

 scribed by the piston of the engine during that time, and U the number of 

 units of work (in lbs. one foot high) done by the steam upon each square 

 inch of the piston of the engine during that time. The second term of the 

 formula is exceedingly small as compared with the first, and is a correction 

 for the influence of the friction of the indicator on the number registered by it 

 The mean number registered by the indicator per stroke of the engine 

 between the 28th of January and the 18th of February being -7451 ; the 

 mean work done by the steam (in lbs. one foot high) on each square inch of 

 the piston per stroke during that time (according to the indicator) was, by 

 the above formula, 



161-4474 X -7451 — 10 x -09051 = 119-3883. 



Also the mean stroke of the engine, during that time, was (by the measure- 

 ment of the engineer) 9 ft. 10§ in., or 9*875 ft., so that the mean effective press- 

 ure of the steam upon each square inch of the piston was, by the indicator, 



119-38S3 lonnll . 

 ~— = 12-09 lbs.f 



The whole number of units of work done upon each square inch of the pis- 

 ton, between the 28th of January and the 15th of February, was, by the in- 



dlcator ' 21,464,067-1727. 



This number multiplied by the number of square inches in the piston, which 

 is 5019-5, gives the whole number of units of effective work done by the 

 steam upon the piston of the engine during the time of the experiments, or 

 the whole number of lbs. of water which would have been raised one foot 

 high by the engine during that time, had it not been for friction and other 

 prejudicial resistances. This number is 



• 107,738,885,310-4. 



During this time 1226j cwt. of coals were consumed by the engine ; whence 



* The general formula as proved in the report is, 



U = 1-67052 Q£\ N - -3017 (l - -~\ L, 



where m represents the ratio of the space described by the piston of the engine to that de- 

 scribed in the same time by the circumference of the pulley of the indicator ; A the additional 

 deflexion of the springs, in inches, for each additional lb. in the strain upon them ; p the 

 number of times the engine expands. 



Now (by the measurement of Price the engineer) the cord passing over the pulley of the 

 indicator described 37? inches, whilst the piston of the engine made a stroke of 10 feet, so 



120 

 that m — —J = 3-2215 ; also (by the experiment of Mr. Timme, Mr. Holtzapffel's draughts- 



3 1 



man) the springs deflected exactly 3 inches under a strain of 90 lbs., so that X = — = — , 



whence it follows that 1-67052 (^-) = 161-4474 ; also the steam was cut off at 3 ft. 6 in. 



10 2' „ , 2 / 2 \ 



.-.p=5T •••— =-7.-.l = -3.-. -3017 ( 1 ) = -09051. 



d ? . P P \ P / 



t This is the mean pressure of the steam above the vacuum resistance. 



