154 REPORT — 1870. 



grating wheel and indices would necessarily go backward. If, however, 

 the steam, as is usual, acts on the opposite side of the piston when the 

 piston's motion is reversed, the integrating wheel will be moved to the 

 opposite side of the centre of the disk, so that the integrating wheel and 

 indices wiU be moved in the same direction as before, and the quantity 

 of motion through the receding stroke of the engine will again be propor- 

 tionate to the pressure of the steam on the piston during that return 

 stroke. Here, therefore, is provided a means of moving the indices during 

 each stroke of the engine through a space proportionate to the sum of tlie 

 moments of pressure exerted during that stroke, or, in other words, a 

 means of indicating the amount of jiower developed during that stroke. 

 The relative proportions adopted for the several working parts in the pre- 

 sent instrument are such that each division on the dial represents one 

 thousand foot-pounds of duty for each circular inch of the piston of the 

 steam-engine. These proportions may be varied. Thus the parts of the 

 indicator may be so arranged that the readings on the dial shall represent 

 the number of horse-powers given out during any required period of time. 

 By closing the tap connecting one end of the indicator-cylinder with the 

 corresponding end of the steam-engine cylinder and opening the small 

 drij)-tap to admit air freely to the disconnected end of the indicator-cylin- 

 der, the indicator is rendered single-acting, and will show the manner 

 of working and the amount of work done by one end of the steam-engine 

 cylinder alone. By opening the closed taps and closing the open ones the 

 indicator is reversed, and the manner of M'orking and the amount of work 

 done by the other end of the steam-engine cylinder ascertained. In the 

 case of a non-condensing engine, the integrating wheel would not return to 

 the centre of the rotating disk during the back or return stroke of the en- 

 gine, by a distance proportionate to the back pressure opposing the motion 

 of the steam-engine piston, the effect being that, during the return stroke, 

 the integrating wheel and indices would be wound back by an amount of 

 motion proportionate to the loss of power by back pressure. Also, if the 

 valves of the engine are opened or closed too early or too late, the integrating 

 wheel will be seen to move backward at the beginning or end of each stroke, 

 thereby showing work undone by an amount of motion proportionate to the 

 loss of power by such " cushioning " or too late admission of the steam or 

 too late exhausting of it. The instrument can be so constructed that paper 

 diagrams may be taken indicating the action of the steam in each end of the 

 steam-engine cylinder, or in both ends conjointly. 



FoEMirLA POR SHOWING THE EeLATIVE CoITNEXION OE THE DIMENSIONS OF THE 

 VARIOUS PARTS OE THE PoWER-MeTER. 



Let w == the weight in lbs. required to distend or compress the spring one inch, d = dia- 

 meter of indicator-cylinder in inches, D = diairieter of integi-ating wheel in inches, 

 I = number of teeth in the long pinion, w, = number of teeth in wheel geared in long 

 pinion, n — number of teeth in worm-wheel or first index-wheel, x = diameter of driving- 



pulley on disk-shaft ; then d'^ = the area of the cylinder in circular inches, and -35 = the 



pressure in pounds of steam per circular inch on the piston, to distend or compress the 



spring one inch. 



One revolution of the disk with the integrating wheel one inch from the centre will 



2 

 drive the integrating wheel =- revolutions. Then 



of - of - 

 D m n 



