268 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[August, 



Professor Moseley's Constant Indicator. 



" Jiesul/s of a Trial of the Constant Indicator upon the Cornish Engine at 

 the East London ITater-troris." By Professor Moselc-y, F.R.S., c&c. 



The oliject of tliis communication is to exliibit ami explain the results 

 given by the author's Indicator during a continuous registration from the 

 28th January to tlie 25th February, 1842, the engine during that time making 

 232,617 strokes. The numbers registered by the counter of the engine and 

 the Indicator were noted each morning and evening, and .ire recorded in a 

 fable appended to the paper. The differences between each two consecutive 

 numbers registered by the counter, giving the number of strokes made 

 between each two observations, are contained in one column of the table, and 

 in another column are the differences between the successive registrations of 

 the Indicator. These arc followed by the mean registrations of the Indicator 

 at every stroke of the engine, being the quotients of the numbers in the 

 last-named column divided Ijy tl-.e corresponding numbers of the preceding 

 column. The paper, after thus stating tlie numbers registered daily by the 

 Indicator during the ]>eriod of trial, proceeds to explain the formula to which 

 they are to be applied, in order to determine the work done daily by the 

 engine. The formula, when reduced from the general one by the introduction 

 of the numerical values of the constant dependant upon this engine, is 



U-16I-.1474 N--090J1 L. 

 in this expression, U represents the units of work (in lb. raised one foot 

 high.) done ujmn each square inch of the piston through any given time, 

 during which the number registered by the Indicator is represented by N, 

 and the space in feet which the piston traverses, by L. The second term of 

 the formula, which is very small as compared with the first, is a correction 

 for the influence of the friction of the Indicator on the number registered 

 by it. The formula being then reduced by tlie substitution in it of the nu- 

 merical values before alluded to, the whole number of units of work per 

 square inch of the piston done between the 2Sth January and the 25th 

 February is shown to have been 2I,464,067"1727. From this is deduced the 

 work done during the same time upon the whole area of the piston as well 

 as the duty done upon the piston for each cwt. of coals. These calculations 

 are followed by a comparison of the results given by the Indicator with those 

 previously obtained from actual experiment by Mr. Wicksteed ; whence it 

 appears, that with a necessary allowance for a difference in the lengths of 

 stroke at the periods of the two experiments the results of the two are 

 almost coincident. The work per stroke upon every square inch of the 

 piston as obtained by experiment is 120'574, whilst as shown by the 

 Indicator it is 110-338'lb. 



Professor Moseley exhibited the Indicator, and described its construction 

 and action ;* the accompanying engraving (Plate XI.) represents the Indi- 

 cator constructed by the committee. C and D are cylinders, each four inches 

 in length, communicating Ky the steam 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 cyhnders 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 i>assages A 

 and B are oi)en and the Indicator is in action) sustains in the direction of its 

 ]ength 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 tlie 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 spring S T, which spring is connecteil by means 

 of links at its extremities with a second similar and equal spring Q R. sup- 

 ported at its centre upon a solid projection P, from the cast-iron frame of the 

 instrument. The pressure of the piston-rod upon the lower spring borne at 

 ■the extremities of the upper spring, whose centre is fixed, is thus made to 

 separate the two springs from one another, and the separation produced is, 

 by a well-known law of dcllection, directly proportional to the pressure sus- 

 tained, so long as the deflections are small. The limits within whicli this 

 !aw of deflection obtains, are greatly extended by the pecuhar form given to 

 these springs, first suggested (it is believed) by M. Morin. One surface if 

 each spring is plane, and the opposite surface of that well-known parabolic 

 form by which an equal strength is given to every portion of the length of 

 the spring. The spring being thus tapered from its centre to its extremities 

 wittiout impairing its strength, its deflection is distributed more uniformly 

 throughout its length, and being thus made less (for a given separation of 

 the springs) at every point, the elastic limits arc nowhere so soon passed. 



By this connection of tlie piston-rod with the springs, its position is made 

 to vary directly as the effective pressure upon its extremities, or as the 

 effective pressure upon four square inches of the piston of the engine, so 

 that every additional pound in that pressure will cause the piston-rod to alter 

 Its position by the same additional distance in the direction of its length. 



The pulley or wheel I K (which, from the peculiar functions assigned to it 

 Sn this machine, we propose to call the integrating wheel,) turns upon the 

 piston-rod as its axis, and traverses with it at the same time in the direction 

 of its length, being prevented from moving on it in that direction by means 

 of two shoulders fixed by adjustment screws. 



* The Editor is indebted for the annexed engraving of the apparatus and 

 description to a report of a eommittee appoinlcd at the tenth mei'ting of the 

 British -\ssociaiion. Memljers of the committee, the Rev. Professor Moseley, 

 M.A., F.RS., Eaton Hodgkinson, Esq., F.R.3., J. Enys, Esq. 



The arras of this wheel are pierced by apertures, through which pass three 

 rods united at their extremities (as shown in the figure,) so as to form the 

 rigid frame G II, which frame turns also upon the piston-rod as lis axis, but 

 does not traverse with it in the direction of its length ; so tliat the wheel I K 

 is made by its motion with the piston-rod to traverse the rods of the frame 

 longitudinally, whilst it is made to sweep the frame round with it by any 

 motion of rotation which may at the same time be communicated to it about 

 its axis. It receives such a motion of rotation from the cone K L, which is 

 so placed that its side may be accurately parallel to the piston-rod, and which 

 is kept continually pressed against the wheel at K by means of a spiral spring 

 inclosed in a tube at II, and acting continually against the extremity of the 

 spindle on which the cone turns. 



A system of bevel wheels U, Y, X, communicates to this siiindlc, and with 

 it to the cone, the rotation of the pidley N, which pulley is driven by a cord 

 carrying a weight at one extremity, and passing by the other extremity (over 

 directing pulleys) to the piston of the engine, or to some point which moves 

 preciselg as tlie piston of tfie engine does, but through a less space. The circum- 

 ference of the pidley N being thus made to move precisely as the piston of 

 the engine, the angle described by the cone, during any exceedingly small 

 period of time, is made to be exactly proportional to the space described 

 during that time by the piston of the engine. Now let it be observed, that 

 the circumference of the integrating wheel I K partaking of the motion of 

 that portion of the surface of the cone with which it is at any instant ia 

 contact, the number of revolutions, or rather parts of a revolution, which it 

 is made to describe during any exceedingly small period of time, beginning 

 from that instant, is dependent upon two causes ; first, upon the dimensions 

 of the particular circle of the cone which is at that instant <hiving it, and, 

 secondly, upon the particular angle through which it is driven by that circle, 

 that is, it depends, first, upon the distance of its point of contact K with the 

 cone from the apex of the cone at that time, and, secondly, upon the angle 

 which the cone describes about its axis during that small period of time. 

 Jloreover, that if either of these two elements of variation remained always 

 the same, then the number of revolutions, or parts of a revolution, made by 

 the wheel, would vary directly as the other, whence it follows by a well- 

 known principle of variation, that when (as in the present case) both these 

 elements vary, it varies as their product ; or that the number of revolutions, 

 or parts of a revolution, made by the integrating wheel during any exceed- 

 ingly small period of time, varies directly as the product of two factors, of 

 which one is the angle described during that time by the cone, and the other 

 the distance of the point of contact K of the cone and wheel from the apex 

 of the cone. 



Now the former of these factors has been shown to vary directly as the 

 space described during that small period of time by the piston of the engine, 

 and the latter to vary directly as the effective pressure which the steam is 

 then exerting upon the piston of the engine.* 



Thus, then, it appears that the number of revolutions, or parts of a revo- 

 lution, made during any exceedingly small period of time by the integrating 

 wheel, varies as the product of the space described by the piston of the engine 

 during that time, by the effective pressure of the steam upon it during that 

 time, that is, it varies as the work or dynamical effect of the steam upon the 

 piston during that time. And this being true in respect to every small period 

 of the time during which the stroke of the engine is in progress, is true of 

 the whole stroke ; whence it follows, that the number of revolutions, and 

 parts of a revolutiou, made by the integrating wdieel during the stroke is pro- 

 portional to the w hole work, or dynamical efl'ect of the steam upon the piston 

 during the stroke. 



The integrating wheel carries round with it the frame G H, on the hollow- 

 axis of which frame is fixed a pinion running into a wheel, whose axis turns 

 upon bearings fixed to the frame of the instrument, and the number of whose 

 teeth is to that of the teeth in the pinion as ten to one. This wheel carries 

 also a pinion running into a second wheel, their numbers of teeth being in 

 the same proportion, and so through a train of five wheels and pinions. The 

 circumference of each of the four last wheels is divided into ten equal parts 

 and numbered, and the circumference of the first into 100. The number of 

 revolutions of the integrating wheel is thus registered to five places of inte- 

 gers, and to one place of decimals. 



Now this number of revolutions has been shown to he proportioMal, in re- 

 spect to each stroke, to the work done by the steam upon the piston during 

 that stroke ; if, therefore, the .iction of the Indicator continued the same 

 during successive strokes, or if the direction of the pressure of the steam 

 upon the piston, and that of the motion of the piston, were not reversed at 

 every stroke, then would the number registered during any number of strokes 

 of tlie engine be directly proportional to the work done by the steam upon 

 its piston whilst that number was registered. At the return-stroke of the 

 piston of the engine, the pulley N, however, revolves backwards, and sup- 

 posing it to carry with it the spindle of the cone, the cone also revolves 



" The position of the integrating wheel upon the piston-rod is so adjusted, 

 that Ijefore the steam is admitted the integrating wheel may be brought, by 

 the elasticity of the springs, exactly to the apex of the cone. In order to 

 prevent it from being stoppetl by the ajicx of the cone, if accidentally it 

 should be made to pass it, a S'jlid piece projects frum the frame of tlie instru- 

 ment, having its surfaces adjusted so as to receive the edge of the wlu'el when 

 it IS lorced bBvonil the apex of the cone, and to serve as a stop to the motion 

 of the cone in iho direction of itsspindle when the resistance of the wheel is 

 thus removed from it. 



