MEMOIR OF DANIEL TREADWELL. 



503 



found practicable, however, to make and use this with openings sufficiently contracted to prevent the es- 

 cape of the smaller sparks, and the apparatus of Mr. Curtis is in addition to the gauze cap as ordinarily 

 used. It consists of a round plate of iron fixed within the cap and directly over the chimney. It is formed 

 a little convex upon its underside, so as to deflect the sparks which are blown against it outwards and 

 downwards through the stream of smoke which is passing by its edges, that they may fall a little upon 

 the outside of the top of the chimney, where they are collected in a cavity formed between the bottom of 

 the cap and the chimney which projects into it. From this they are conveyed by a small pipe down out- 

 side of the chimney, and drop from its open end near the ground. 



The effect of the instrument in preventing the egress of the sparks from the chimney is not, I believe, 

 doubted by any one who has witnessed its operation ; but as an opinion has been formed by several of the 

 operative engineers that the sparker diminishes the effective power of the engine, it was decided that the 

 truth of this opinion should be tested b}* experiments. As these experiments would require that the engine 

 should run over a considerable extent of the road, and that the weight of the load, resistance, and velocity 

 should be observed, it was thought advisable to arrange the observations so as to obtain, in addition to a 

 decision of the question concerning the sparker, facts for the solution of other questions ; such as the com- 

 parative powers of engines of different dimensions and forms of construction ; the comparative power of 

 the same engine, using steam of a given elastic force, when running at different velocities ; the quantity 

 of wood required to produce a given power; the resistance of the load when passing upon a horizontal 

 plane and upon ascents of different inclinations, and likewise the effects of the curves of the railway in 

 increasing the resistance, and any other facts important to the construction, arrangement, or manage- 

 ment of railroads or locomotive engines. 



To make experiments which should give satisfaetor}- conclusions in the cases above recited, it seemed 

 to me important, first of all, to obtain an instrument by which the force of the engine in drawing the load, 

 or rather the resistance of the load, should be accurately measured. No dynamometer had as yet, to my 

 knowledge, been constructed, which, w r hen applied to an engine and its train, was not subject to such 

 wide and rapid vibrations as to render it impossible to deter- 

 mine the force upon it at any instant of time. To obviate this 

 difficulty, I contrived, and had constructed, an instrument as 



herein shown. * 



a a, a strong plate of cast iron, upon the face of which is 

 fixed b b, a cylinder, shown in section, accurately bored, c, a 

 piston one fiftieth of an inch less in diameter than the cylinder, 

 and pierced with the small hole e, one eighth of an inch in 

 diameter, d, piston rod, its top guided in the box e. f, a 

 bent lever moving upon the pin a, as a fulcrum, and its hori- 

 zontal arm attached to the piston rod by the connecting jointed 

 rod b. ggg, a powerful spring tending to raise the horizontal 

 arm of the lever f, and consequently the piston, n, a connect- 

 ing rod to be united to the tender of the engine, rf, an index 

 fixed to the upper part of the piston rod, which points upon the 

 scale, marked 10, 20, 30, 40, &c, to the force in pounds which 

 is at any time acting upon the connecting rod h. To mark or 

 divide this scale weights are hung upon the horizontal arm of 

 the lever f, the plate a a being in a vertical plane, at e, being 

 the same distance from the fulcrum a with the pin/. The de- 

 pression of the arm by the weights so placed will of course be 



Treadweix's Dynamometer. 



* Count Fambour ( TraM TMorique ef Pratique des MaehiMZ Locomotive^ pp. 101, 103, Paris, 1835) found the same diffi- 

 culty with all circular dynamometers, and abandoned that mode of determining resistance on railroads. He substituted as a 

 method of measuring these resistances, the descent of a train of cars along two inclined planes, the inclination of the second 



