Proceedings of the Polytecenic Association. 913 



the pressure of the steam or by the force due to the continued action 

 of steam and of a partial vacuum at the same times and to the same 

 degree in proportion to its area as the piston of the steam-engine. 

 The piston-rod of the indicator is connected with a spiral spring, 

 which controls the action of the indicator-piston, the said spring 

 resisting the movement of the said piston in either direction from 

 tlie position of equilibrium, which is at about the center of the cylin- 

 der, the spring being made about proportionate to the area of the 

 piston and to the pressure acting thereon. On the piston rod is 

 mounted by a friction-wheel or pinion, to which a variable rotary 

 motion is imparted during the working of the engine by a disk, the 

 surface of which is in contact with the circumference of the said 

 friction-wheel. The disk is caused to rotate alternately in opposite 

 directions, the rotation being derived from the engine similarly as in 

 the case of the barrel of the ordinary indicator, or in any suitable 

 manner, the disk rotating to a suitable extent in one direction during 

 the forward or upward stroke of the piston of the engine, and in the 

 reverse direction during the return stroke thereof. 



Mr. Emery remarked that this invention is of American origin, 

 but it has defects which are obviated by more improved apparatus. 



Mr. G. H. Babcock remarked that about four years ago he invented 

 such an apparatus as was described. It is said to be a recent English 

 invention. It is not new; it has, in fact, been invented several times. 

 After he invented it, he found he had been anticipated. An indicator 

 similar to it was exhibited at the fair of the American Institute in 

 1855 or 1856, invented by Mr. George H. Reynolds. It is not of 

 much value, because of the inaccuracies developed by friction, the 

 registering wheel requiring to be slid in the line of its axis, by the 

 indicator piston. A good instrument that can be relied upon for this 

 purpose is much wanted. In an early edition of Bourne on the steam 

 engine, published in 1846, attention is called to this subject, and it 

 is remarked that an instrument for this purpose would be very valu- 

 able. Some years ago Gooch invented one in which a series of 

 diagrams was taken in succession upon a strip of paper, which had 

 a regularly progressive motion. On the French steamers coming to 

 this port this instrument is still used ; but the area of all the cards 

 must be computed to determine the power. Another invention for 

 the same purpose, the inventor of which he could not then name, has 

 been made, in which a ratchet-wheel received a series of impulses 

 from a vibrating link, which was so connected with the piston of 



[Inst.] 58 



