ON THE EXPERIMENTS ON STEAM-ENGINES. 91 



the 10,000dth part of a second may be easily discerned, is the invention of 

 M. Poncelet, carried into execution by M. Morin. 



On examining the machine, it was found necessary to make some few re- 

 paii's of injuries it had received in carriage, and also some alterations to fit it 

 for the particular purpose it was proposed to apply it to. These were done 

 by Mr. Holtzapffel. 



The instrument, when put in order, was first tried at King's College, a 

 variable motion being given by a small carriage made to descend an inclined 

 plane. The correspondence of the velocity shown by the machine, with that 

 deduced by the known laws of dynamics, was such as to give great confi- 

 dence in its accuracy ; and after a few minor alterations suggested by fre- 

 quent trials, it was removed to the East London Water Works, Old Ford, 

 and, by the kind permission of Mr. Wicksteed, the engineer, was attached to 

 the Cornish engine at work there. This was considered a very favourable 

 engine to experiment upon, inasmuch as the constants involved in its work- 

 ing had been so accurately ascertained by Mr. Wicksteed in his previous ex- 

 periments, and so amply confirmed by the long trial of the constant indicator 

 upon it by your Committee during the years 1841 and 1842. 



After several preparatory trials and adjustments, some diagrams were taken 

 on the 8th of August, and the velocities calculated from these have been ex- 

 pressed in the form of geometrical curves, whose abscissae represent the 

 spaces passed over by the piston of the engine, and whose ordinates indicate 

 the corresponding velocities at the different points of the stroke. 



Plate XXVI. shows diagrams which represent the velocities of the piston 

 both in the descending and ascending strokes of the engine, or as they are tech- 

 nically termed, the in-door and out-door strokes. The velocity of the in-door, 

 or descending stroke of the piston, is taken from the mean of three experi- 

 ments, differing very little from each other. The velocity begins from zero, 

 accelerating as the piston descends, until at about four feet of the stroke it 

 attains a maximum of about lO'i feet per second. This is the point where the 

 pressure of the steam in the cylinder has, by expanding, become exactly equal 

 to the resistance opposed to the motion of the piston ; and from this point the 

 velocity gradually decreases as the steam becomes more attenuated, until the 

 piston is gradually brought to rest by the exhaustion or expenditure of the whole 

 of the work accumulated in the moving mass (in the shape oivis viva) during 

 the early part of the stroke, while the steam power exceeded the resistance. 



The velocity of the out-door, or pumping stroke, is much less than that of 

 the former, the greatest velocity being only about 3*8 ft. per sec. 



Plate XXVII. contains diagrams of the spaces and times constructed in a 

 similar manner ; the abscissae of the curves representing, as in the former case, 

 the spaces passed over by the piston, and the corresponding ordinates indi- 

 cating the times in which those spaces are described. 



It will be seen that the whole in-door stroke is performed in about 1 1 se- 

 cond, and the out-door stroke in about 4 seconds. As a check to these re- 

 sults, the time occupied in the strokes was observed directly with a stop-watch, 

 and was found perfectly to agree with the indications of the machine. The 

 observed times were, as nearly as could be ascertained. 



In-door sti'oke 1'5 second. 



Short pause between the in-door and out-door strokes* '5 ,, 



Out-door stroke 4 „ 



Pause 2 „ 



Total 8 seconds. 



* This is not usual in the engines at work in the Cornish mines ; in most of these the 



