SOS REPORT — 1841. 



throwing the indicator of a trial engine into gear at any such portion of the 

 line, and thus registering tlie amount of work necessary to carry the engine 

 over that particular portion of the line; passing too over the value of the 

 purely scientific data which would result from the extensive accumulation of 

 records such as these, the Committee are desirous more particularly to point 

 out the importance of the knowledge it might supply, not only as to the eco- 

 nomical loorking of marine engines, but as to their construction, and the build 

 or construction of steam-boats. In the existing state of our knowledge, it is 

 impossible to divide with certainty between the builder of the boat and the 

 builder of its engine, the responsibility which belongs to their several parts 

 in giving speed to it. A registration such as that here spoken of would, 

 however, at once make this division. It would determine the merits of the 

 engine independently of the properties of the boat, and the properties of the 

 boat separately from the merits of the engine. 



There are other points of view in which the value of such a method of 

 registration, if by any means it might be attained, is perhaps equally ap- 

 parent ; enough, however, has been said to justify the Association in appoint- 

 ing a committee to inquire into the possibility of effecting such a registra- 

 tion, and placing at their disposal a grant of 100/. to cover the expense of 

 such trials as they might recommend to be made. 



Watt's Indicator. 



The only instrument at present used for determining the work done by the 

 steam on the piston of an engine, is that well known as the indicator of Watt. 

 Its insufficiency for the purpose of a registration, such as that the Committee 

 proposed to themselves, was at once apparent to them. It determines the 

 work only at a single stroke of the engine ; the desideratum was a registration 

 of the work continued to any number of strokes, and under such variations 

 of the resistance as should render the work done at any one stroke no cor- 

 rect representative of the work done at any other. The indicator of Watt 

 presents its registration of the work thus done at a single stroke, under the 

 form of a certain small area, bounded by a curved line, which is traced by a 

 pencil fixed to a small piston sustaining the pressure of steam from the 

 cylinder of the engine, and made by means of a spiral spring to deviate from 

 its position of repose by spaces which are directly proportional to the pres- 

 sures sustained ; the paper which receives the trace of the pencil receiving 

 meanwhile a lateral motion, constantly proportional to the motion of the pis- 

 ton itself. 



Were it not that the first objection, the want of continuity, was fatal to this 

 method of registration for the object proposed to the consideration of the 

 Committee, the great inaccuracies to which it is liable in the mechanical 

 tracing of the curve, and the geometrical determination of the area it bounds, 

 would have led them to seek for some more certain method of registration, 

 and one more easy of application, to place in the hands of the working 

 engineer. 



The labours of the Committee were with this view specially directed to the 

 application of a principle of dynamometrical admeasurement, first proposed by 

 M. Poncelet, the illustrious President of the Institute, described by him in his 

 work, entitled ' Mecanique Industrielle,' and in the work of M. Morin, ' De- 

 scription d'Appareils Dynamometriques' (published at Metz in 1838). 



Morin's Compteur. 



This principle will be best understood by the example of an application 

 which M. Morin has made of it, to the construction of an instrument for re- 



