"HECLA" Tender and Twelve Carriages. Liverpool to Birmingham, 95 miles, 3654 lbs. of coke, 2108 gallons of water. Coke per mile One pound of coke evaporates 5-63 lbs. of water. 37.16 lbs. 37.16 imperial gallons. It is to be observed that the previous statement comprises the entire quantity of coke supplied to the engine, both for getting up the steam in the morning, and for work during the day; whereas, on the other hand, the water recorded was that actually used during the two journeys. The duty of 1 lb. of coke is greater than is here assigned. Report of a Committee appointed at the Tenth Meeting of the Association, on the Construction of a Constant Indicator for Steam-Engines. Members of the Committee, the Rev. Professor MOSELEY, M.A., F.R.S., EATON HODGKINSON, Esq., F.R.S., J. ENYS, Esq. A REGISTRATION of the work done by a steam-engine made at its piston, or of the work done by the steam upon the piston, appears to offer important practical advantages, as compared with any other method of registration, in these respects; that it is applicable to every possible variety in the circumstances under which the engine is made to operate, and that it is a registration of the work of the engine absolutely, and separated from all those uncertain influences of friction, or other prejudicial resistances which intervene between the piston and the working points of the machine to which it gives motion; influences which it is impossible to eliminate from a registration of the work done at the working points, with certainty or accuracy. In proof of the advantages which would result from any method of registration of the work, and therefore of the duty of steam-engines, could it be made to assume this general character, it is sufficient to point to the history of the Cornish pumping-engines. It is entirely from the registration of their work (so easily made in respect to them by reason of the simple and constant nature of that work), that has resulted that admirable knowledge of the working properties of the steam-engine, which is so extensively diffused through the mining districts; and to the same cause is entirely due (as a consequence of this knowledge), that vast economy of power and fuel in the working of the Cornish engines, which has so recently been brought under the consideration of the Association. If a method of registration equally (or even yet more) certain and easy of application could be extended to the working of all engines, no matter how varied or how complicated, or how intermittent the nature of their operations might be to the engines, for instance, which perform the varied and intermittent labours of an engineer's workshop or a manufactory, or to the engine of a steam-boat-giving by a method beyond the control or interference of the engineer, the work of the engine of such a boat during any given time -a day, a week, or a month, and the duty which the engine does with each bushel of coals, independently of her speed through the water, and of all considerations dependent upon the form of the boat, or the direction or force of the winds or currents, or of the tides--it would at once become possible, by recording and publishing the duty of each engine periodically, to introduce precisely that competition of economy in power between the engineers in factories and the engineers in steam-boats, which has been attended with results of such advantage to the mining districts of Cornwall. If, again, we conceive the work of each of the engines of a railway company to be made thus to register itself, and the amount thus registered to be published under the form of a weekly or a monthly return, together with the quantity of the coals consumed by each, it is evident that a competition amongst the engineers would be the immediate result, and a consequent economy to the company in the use of the fuel. A competition which would probably lead to that scientific adjustment of the amount of the load to the evaporating power of the engine and the speed of transit, which adjustment is the true and the great secret of the economical working of a line of railway. Passing over the use which the resident engineer of such a line of railway might make of an indicator like this, to determine the condition of the rails, and the general working state of any portion of the line, by throwing the indicator of a trial engine into gear at any such portion of the line, and thus registering the 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 economical working 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 apparent; enough, however, has been said to justify the Association in appointing a committee to inquire into the possibility of effecting such a registration, and placing at their disposal a grant of 100l. 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 correct 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 pressures sustained; the paper which receives the trace of the pencil receiving meanwhile a lateral motion, constantly proportional to the motion of the piston 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 'Mécanique Industrielle,' and in the work of M. Morin, 'Déscription 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 gistering the work done by a team of horses dragging a loaded carriage at any given velocity over any length of road. IGNO and EHK in the figure represent two separate pieces, which may be made to move upon one another in the directions H K and G I. Two springs shackled together at their extremities, and represented in a subsequent figure, are severally inserted in the apertures G and H, and fixed there by their middle points. The separation of the two in the direction G I and H K, supposes therefore a deflection of these springs. The piece G I is connected with the carriage to be moved by means of the bolt I, and to the piece EH K the horses are attached by means of the shank K. Thus the pressure of traction is transmitted from the horses to the carriage through the system of springs, and by the well-known property of elastic bodies a separation is thus produced in these springs, which (so long as it does not exceed a certain limit) is always directly proportioned to the amount of this pressure. BD represents a flat circular disc, and A L a pulley or sheave, both fixed upon the same vertical axis F C. The sheave A L receives its motion by means of a band from a sheave revolving with the wheel of the carriage, so that the motion of the circumference of A L bears always a constant ratio to the space traversed by the carriage. To the piece EH K is attached (by means of a joint or hinge) the box M, containing certain mechanism intended to register the number of revolutions made by a certain wheel. This wheel is represented at F; it rests by its edge upon the disc, its plane is at right angles to the line of traction; and its position on the box is such, that when the carriage sustains no traction, and the springs suffer therefore no deflection, it rests over the centre of the revolving disc B D. In this position of the wheel F it would evidently receive no motion from the revolution of the disc B D, however fast that disc might revolve, whilst in any other position between F and D, the wheel F would receive a motion from the revolution of the disc, which motion (if the revolution of the disc were uniform) would be directly proportioned to the distance of the wheel F from the centre of the disc, that is, directly proportioned to the separation of the springs, or to the force of the traction. Since then, if the revolutions of the disc were uniform, that is, if the motion of the carriage were uniform during any exceedingly small time, the motion of the wheel F would vary as the force of traction, and that evidently, if the force of traction were constant, the motion of the wheel F would vary directly as the motion of the carriage during the same time, it follows (by a well-known principle of variation), that if both the force of traction and the motion of the carriage were variable, the motion of the wheel F would vary as their product; and this being true of every exceedingly small period of the motion, it follows that the whole motion of the wheel F during any finite time, however long, is proportional to the sum of the products obtained by multiplying each elementary space described by the carriage, by the particular force of traction under which that elementary space is described, or, in other words, that the whole space moved over by the circumference of the wheel F is directly proportional to the whole work, or dynamical effect expended in moving the carriage, however varied the traction or the velocity may have been. It was to an application to the steam indicator of that admirable and fruitful principle of M. Poncelet, which combines the motions of the wheel F and the disc B D, and which, in fact, performs the complex operation known in analysis as integration-integrating the traction, considered as a function of the space-that the attention of the Committee was specially directed by the Association, and that their labours have particularly been devoted. The indicator which they have now the honour to present to the Association has nothing in common with the instrument which has just been described, except the principle of M. Poncelet and the springs of M. Morin ; these have been constructed according to the formulæ given by that gentleman in his work already quoted (Appareil Dynamometrique, &c.), and have been found admirably adapted to their use. The original design or project of the machine was given by Professor Moseley, and he being the only member of the Committee resident in London, the execution of it was placed under his direction. PROFESSOR MOSELEY'S INDICATOR. The accompanying engraving (Plate VI.) represents the indicator constructed by the Committee. C and D are cylinders, each four inches in length, communicating by the steam-pipes A and B with the top and bottom of the cylinder of the engine to which the indicator is applied, and well clothed with felt to prevent radiation. In these cylinders work two solid pistons, each four square inches in area, fixed upon the extremities of the same piston-rod E F, which piston-rod (when the steam passages A and B are open and the indicator is in action) sustains in the direction of its length a pressure equal to the difference between the pressures upon the two pistons fixed upon its extremities, or (since these sustain the same pressure with equal portions of the opposite sides of the piston of the engine) equal to the effective pressure of the steam on four square inches of the piston of the engine. This pressure upon the piston-rod is made to bear, by means of a shoulder Z, upon the steel |