1842.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



269 



backwards, so that if the integrating wheel remain in contact with the cone 

 at any other point than its apex, it too will be made to revolve backwards, 

 and the number registered iu the preceding stroke will thus l)e diminished by 

 the number of revolutions made by the integrating wlieel during this stroke: 

 but let it be observed, that before the motion of the piston of the engine is 

 reversed, the direction of the pressure of the steam upon it, and therefore the 

 direction of the pressure upon the piston-rod of the Indicator is reversed, 

 by which altered direction of the pressure, as well as by the elasticity of the 

 springs, the integrating wheel is made to ascend to the apex of the cone, and 

 to remain there during the return-stroke, so that no number wliatever is 

 registered during that stroke. 



Thus, then, the remaining number registered during any time by the instru- 

 ment when applied to the double acting engine, is proportional to the work 

 done upon the piston by the steam at the alternate strokes during that time. 

 The mathematical formula by which the work is determined from this 

 number, and allowance made for the friction of the Indicator, is given in a 

 subsequent part of this report. 



In order etTectually to guard against any error which might accidentally 

 result from the reversed motion of the piston, a contrivance has been intro- 

 duced in the combination of wlieels Y, X, U, by which the revolution of tlie 

 cone may be arrested whilst that reversed motion takes place. To adapt the 

 instrument to register (if required) the work done at every stroke of the 

 piston, a four-way cock has been constructed, which may be made, by the 

 action of the engine, to control the direction of the steam passages of the 

 Indicator, in such a way that the upper cylinder C shall always communicate 

 with that portion of the cylinder of the engine which is tilled with steam, 

 whilst the lower cylinder D is made always to communicate with the vacuum. 

 When the Indicator is thus used, the cone is made, by a simple adjustment 

 of the mechanical combination U X Y, to revolve constantlyyb/'icffn/s, whilst 

 the motion of the piston of the engine, and therefore of the pulley N, alter- 

 nates. It remains now only to speak of the application of the Indicator to 

 the single acting engine, or Cornish engine. 



The registration during the down or in-doors stroke of that engine is 

 already explained. During the first portion of the nji or out-of-doors stroke 

 the equilibrium valve is opened, and the pressure upon both the pistons of 

 the Indicator thus becoming the same, the integrating wheel is brought by 

 the elasticity of the springs to its initial position at the apex of the cone, 

 and thus, although the cone turns backwards, the wheel remains at rest and 

 nothing is registered. When the equilibrium valve closes, the pressure of 

 the steam in the upper portion of the cylinder of the engine, and therefore 

 in the upper cylinder C of the Indicator, preponderates ; the integrating 

 wheel descends from the apex of the cone and tlie register revolves bac.;- 

 wards, deducting from, or diminishing, the number before registered by pre- 

 cisely the number of units of work w-hicli is done by the steam (jammed 

 back into the upper portion of tlie cylinder) ayainst the returning piston. 

 Now this is precisely the deduction which the theory of the steam engine 

 shows ouglit in this case to be made, and the registration of each double 

 stroke of the single acting or Cornish engine is, by this backward movement 

 of the integrating wheel, perfected. Let it be here observed, that the Indi- 

 cator in the r/owH-stroke performs the definite integration of a loyarithmic 

 function, viz. that which represents the pressure of the steam as a function 

 of space, described by the piston during the expansion of the steam, that it 

 then calculates the numerical amount of the integral it has thus completed, 

 and registers that amount ; that it performs a similar operation in tlie up- 

 stroke, and deducts the corresponding amount as a correction from the first. 



The above must be received as an attempt to place the theory of the 

 instrument under a general and popular form. .\ mathematical discussion 

 of it accompanies this Report, in which the corrections due to friction and 

 other causes are fully considered. 



formul.e for detekmixixg the work of .\n exgine by mean's of the 

 Indicator. 



The following are the values of the constants which enter into the general 

 equation in its application to the Indicator constructed by the Committee. 



Radius of the integrating wheel. ... =p ='J'99 in. 



Radius of the piston of the indicator = ;-* = l'125 in. 



Radius of the pvdiey measuring to the centre of the cord = R = 3 in. 



.■\ngle at apex of cone =2 i = 90^ 



Friction of piston, of integrating wheel on cone, Sic, mean value = F= 

 1-2074 lb. 



-Additional deflection of springs due to each additional pouud of pressure 

 on piston of Indicator = \ Spring No. l = -028. 



Substituting the above values of p, r, R, i in equations (2) and (3), we obtain 

 for double acting engines, 



If in these equations we substitute the values of A for the different systems 

 of springs, and also the mean value of F, which is l-2a lb., we shall obtain 

 for spriny \o. 1, A = '028 in. 



U = 59G614 »jX--3018 



L (common engine). 



U = l-67052(^')N--i-F(,-=)L (4. 



for single acting Cornish engines, 



U = l-670o2 (^)X_.(,« ;-l)f.l (5. 



' The radius of the piston is so taken that its area may e jual exactly 

 four square inches. 



(-1) 



(2 1\ 

 1 + -1 L (Cornish engme). 

 P »/ 



The values of U, obtiiined from the above formula?, being mnltipled by the 

 number of square inches in the surface of the piston of the engine, will give 

 the whole number of units of work yielded by it during the time of the 

 experiment. 



It will be observed, that no account is taken in these formulse of the 

 weight (3 lb. Oi oz. ) of the pistons, the integrating wheel, and the rod to 

 which these are attached. The influence of this weight is, in fact, allowed 

 for when, the springs being placed in the Indicator, and therefore loaded 

 with it, and sustaining no other pressure, the iutegrating wheel is moved to 

 such a position upon the rod as tliat its circumference may coincide with the 

 apex of the cone. The springs are then just so much deflected as by their 

 elasticity to sustain this weight, and that initial deflection remaining super- 

 added to any additional deflection to which they may be subjected by the 

 additional strain thrown upon them, the weight of the pistons, &c. will in 

 every position be accurately balanced by it, and the additional strain thrown 

 upon the springs will produce precisely the same deflections as though no 

 such weight existed. 



Mr. Xloseley then described the difference between the instrument and 

 that of M. Morin for applying the principle of M. Poncelet, to consist — First, 

 in all those mechanical combinations which are peculiar to the instrument in 

 its application to the steam-engine, M. Morin's instrument having been 

 applied to measure the traction of horse. — Secondly, in the surface of a 

 cone being substituted for the plane surface of a circular disc ; by which 

 arangement the rapidity of the changes of velocity due to corresponding 

 changes in the position of the integrating wheel, is diminished in the same 

 proportion in which the sine of one-half the angle of the cone is less than 

 unity ; and the force necessary to drive the integrating wheel being di- 

 minished in the same proportion, the chance of an error arising from the 

 slipping of the edge of the integrating wheel on the surface from which it 

 receives the impulse is lessened in proportion. — Thirdly ; in the separation 

 of the registering apparatus from the integrating wheel ; by which separation, 

 whilst the springs are relieved from the ertect of the momentum and the 

 friction due to the weight of the registering apparatus, the latter being in a 

 state of quiescence, the registration is legible whilst the Indicator is in 

 action. — Fourthly; in the variable position of the links connecting the 

 springs together, by which variation the same series of deflexions may be 

 obtained under diti'erent ranges of pressure. In fact, that the Indicator has 

 nothing in common with the " compteur" of XI. Morin except the principle 

 of M. Poncelet and the springs under a modified form. 



The amount of the friction of the pistons, was then examined and the 

 peculiar construction of their metallic packing explained; it was shown also 

 that instead of great difficulties arising from the friction of the integrating 

 wheel upon the cone, or its slipping upon the surface, a very slight pressure 

 of the spring produced sufficient adhesion to drive the registering apparatus. 

 Tlie professor then explained the advantages resulting from a registration of 

 the duty of steam-engines generally, not during the time of a few isolated 

 experiments, as with the common Indicator, but extended over any given 

 period and through every stroke of the engine, displaying all the changes 

 which had occurred during that time : — with this view it had been decided 

 that the instrument should be attached to the engines of the Great Western 

 steam-vessel on her next voyage to .\merica. 



He then expressed his obligation to Mr. Wicksteed for the facilities afforded 

 him for the experiments at Old Ford, and paid a well-merited compliment to 

 Jlr. Iloltzapffel for the excellent construction of the Indicator. 



Hemarks. — In reply to a question from Jlr. Yignoles, Mr. Xloseley stated 

 that the instrument was not under its present form adapted to locomotive 

 engines, but that a grant of £100 had been made by the British Association 

 for the construction of such an instrument. 



Mr. Cowper, in compliance with the request of Professor Moseley, illus- 

 trated his description by setting the instrument in motion, showing that the 

 registration depended iipon the revolutions of the integrating wheel : he 

 demonstrated the cases of motion without pressure, and pressure without 

 motion ; in tlie former case the integrating wheel being stationary at the 

 apex of the cone while revolving, does not receive any impulse from the con- 

 tact with it, and therefore does not register ; in the latter case, the surface 

 of the cone upon which the integrating wheel traverses, being at rest, does 

 not communicate anv rotative motion to it, and consequently no registration 

 can take place; but when motion and pressure are combined, the cone 

 revolving and the integrating wheel travelling from the apex some distance 

 towards its base, the exact product of the motion of the cone and the steam's 

 pressure upon the piston would be registered by the amount of the revolution 

 of the integrating wheel. 



Mr. Wicksteed observeil that every facility had been afforded to Professor 

 Moseley for applying his new Indicator for the purpose of ascertaining the 

 duty performed by the Cornish engine at Old Ford, but that he had not at 

 all interfered with the experiments, being desirous of ascertaining whether 

 the results would correspond with his trials. That after the work of the 



2 P 



