324 REPORT — 1841. 



Spring No. 2, A = 0-68. 

 U = 24*566 m N — -3018 L (common engine). 

 U = 24-566 m N — -3018 (\ + — ") L (Cornish engine). 



SpringNo. 3, A =-1115. 

 U = 14"982 »i N — '3018 L (common engine). 

 U = 14-982 wN — -3018 (\ + — ^ L (Cornish engine). 



Spring No. 4, A = -0489. 

 U = 34" 162 m N — -SOlS L (common engine). 

 U = 34-16'2m N - -3018 A + -L'j L (Cornish engine). 



The values of U, obtained from the above formula, being multiplied by the 

 number of square inches in the surface of the piston of the engine, will give 

 the whole number of units of work yielded by it during the time of the ex- 

 periment. 



It will be observed, that no account is taken in these formula of the weight 

 (3 lbs. 0| oz.) of the pistons, the integrating wheel, and the rod to which these 

 are attached. The influence of this weight is, in fact, allowed for when, the 

 springs being placed in the indicator, and therefore loaded with it, and sus- 

 taining no other pressure, the integrating wheel is moved to such a position 

 upon the rod as that its circumference may coincide with the apex of the 

 cone. The springs are then just so much deflected as by their elasticity to 

 sustain this weight, and that initial deflection remaining superadded to any 

 additional deflection to which they may be subjected by the additional strain 

 thrown upon them, the weight of the pistons, &c. will in every position be 

 accurately balanced by it, and the additional strain thrown upon the springs 

 will produce precisely the same deflections as though no such weight existed. 



In conclusion, the Committee are desirous to express their obligations to 

 Mr. Button, foreman to Mr. Fairbairn at Manchester, for a valuable sugges- 

 tion made by him, and adopted by them* ; to Mr. Holtzappfel for the excel- 

 lent workmanship of the machine ; and to include in this acknowledgement 

 their sense of the valuable services of his di-aughtsman, Mr. Timme, whose 

 name is several times mentioned in this Report, and whose intelligent and 

 persevering attention have greatly facilitated its construction. 



They regret that the construction of the instrument has been attended by 

 numerous delays, and that it has not been so far completed as to admit of 

 being applied to an engine for a trial until within one week of the date of 

 this Report. By the kindness of Messrs. Fairbairn and Murray they were then 

 allowed to place it on their engine at Mill-wall. The object of that trial 

 was simply to determine whether the mechanical difficulties opposed to its 

 construction, on which much stress had been laid, and in res'ject to which 

 a failure had been pi-edicted, had in reality been overcome ; on this point 

 the trial supplied a decisive answer. Every part of the instrument performed 

 the mechanical functions assigned to it with entire precision and accuracy, 

 except the pistons, which have been replaced by others more accurately fitted 

 to the cylinders. 



* It was at the suggestion of Mr. Dutton that a single cylinder was replaced by two 

 cylinders ; the instrument was thus made to assume a more compact and convenient form, 

 and much was gained, practically, in that correctness and facility of workmanship which re- 

 sults from making the cylinders themselves the guides of the piston-rod, and dispensing with 

 the stuffing-boxes. 



