ON A CONSTANT INDICATOR FOR STEAM-ENGINES. 



319 



I 



Spring No. 4, (cast steel, length 40 inches) mean value of A = -0489. 



In the interval of two months between the two sets of experiments, of 

 which the results are given in the first of the above tables, the springs had 

 been for some days worked in the indicator upon Mr. Fairbairn's engine at 

 Mill-wall. At the time of the first series they were fresh from the hands of the 

 workmen. It will be observed, that whilst no change whatever has taken 

 place in the elasticity or the law of the deflection (the mean value of A re- 

 maining the same), a change, or set of -004 inch, has been produced in the 

 initial, or permanent separation of the springs. This set was to be expected. 

 The error which might result from it is perfectly corrected (the mean value 

 of X remaining the same) by an equivalent alteration of the position of the 

 integrating wheel upon the rod, for which alteration an adjusting screw is 

 provided. 



The deflection of the spring No. 2 is greater than that theoretically due to 

 the dimensions assigned to it ; this error has resulted from a fault in the con- 

 struction, the piece which forms the centre of the spring, and is pierced by 



