272 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[August, 



explain this, let tlie pound ■n-eight be supposed to be applied gradually to the 

 spring liv dropping grain after grain of sand slowly upon it. The spring -nill 

 then evidently be brought to its deflection without ever passing it. Now let 

 it be observed that on this supposition the first grain of sand only will have 

 descended through one inch, the next descending through less than an inch, 

 the next through yet less, and so on. Thus the work done upon the spring 

 by each succeeding grain will be less than that done by the preceding. Yet 

 the aggregate work done by these successive small pressures, each working 

 through a different space, is' sufficient to deflect the spring one inch. Non- 

 let all the grains be placed at once upon the S])ring. When it has deflected 

 an inch, each grain will tlien have worked through an inch, and a great deal 

 more work will, on the whole, have been done on the spring than before, 

 indeed twice as much ; but the work done before was enough to deflect the 

 spring an inch ; more than enough to deflect it has now therefore been done, 

 that is, more has been done than has been expended. The remainder is 

 accumulated in the moving mass of the sand and the spring, and carries on 

 the deflection greatly beyond the position of equilibrium. 



The Indicator was placed upon the engine of the East London Water- 

 works, in the belief that by the experiments of Mr. Wieksteed, the work 

 actually performed by that engine was better known than that of any other. 

 All the calculations and inquiries which have since been made have fully 

 confirmed that opinion. And he had full confidence in that verification of 

 the registration of the Indicator which is supplied by its agreement with Mr. 

 Wicksteed's estimate of the work of his engine. 



In reference to the use of the term " work," Professor Moseley stated, that 

 the various terms used by foreign engineers to convey the idea attached to 

 that term, appeared at length to have resolved themselves into the single 

 term " travail ; " and that of the variety of corresponding terms used in Eng- 

 land, the term " work " was probably the most obvious translation of " tra- 

 vail; " that it moreover appeared to him the simplest and the most intelli- 

 gible ; and that on these grounds he had adopted it. 



In answer to the obseriation made by Mr. Parkes suggesting the con- 

 struction of an indicator which would register the work of the machine at 

 the point where it is applied, instead of at the cylinder of the engine, Pro- 

 fessor Moseley stated that such an instrument would undoubtedly be very 

 valuable, especially if it could be made to register correctly the work trans- 

 mitted bv a rotating shaft ; but that for the purpose contemplated by him it 

 would be entirely useless— this object was to effect, in respect to ordinary 

 engines working' under constantly variable pressures, that constant registra- 

 tion of the duty, the introduction and publication of which had led to so 

 remarkable an economy of steam power in the working of the Cornish en- 

 gines. No registration of the work done at the working points of the ma- 

 chine driven by the engine, would supply a fair estimate of the duty done by 

 the engine ; a' greater or less portion of the work done by the engine being 

 lost by reason of friction in its transfer through the machine, from its driving 

 to its'working points, according as there was a greater or less complication 

 of moving parts and rubbing surfaces intervening, lie repeated that his 

 object had been to determine the working qualities of the engine itself; and 

 that he had for this reason specially sought to eliminate from his estimate 

 those verv influences of the friction of the machine driven by the engine 

 which Mr. Parkes thought it so important to include in it. It would have 

 been a fault of his Indicator (for the purpose contemplated by it) if it had 

 taken anv notice of the effect of that change made in the machinery of Mr. 

 Lucy's mill, which Mr. Parkes had spoken of. He had used the term effective 

 wori; (not effective pow er) of the engine, to signify that excess of the work 

 of the steam on one side of the piston, over that opposed to it by the im- 

 perfectly condensed steam on the other, which it was necessary to know in 

 order to estimate the real duty of the engine. It was solely for tlie deter- 

 mination of that duly that the Indicator had been constructed, and the 

 alterations which Mr. Parkes had suggested would have subjected its regis- 

 tration to influences which, in reference to that purpose, he had specially 

 sought to eliminate. 



Mr. Farey remarked, that it would lead to an incorrect appreciation of the 

 merit of the new indicating instrument, if it were to be considered merely as 

 a substitute for the ordinary indicator, when in fact they are two instruments, 

 adapted to and equally useful for different purposes. The new instrument 

 does not preserve any record of the minute details of any one stroke, like 

 the ordinary indicator, but it records a true aggregate of all the details of 

 any number of succeeding strokes ; it gives the same results as would be 

 obtained if it were possible to have two ordinary indicator cards correctly 

 taken, at each succeeding stroke of the engine, during the whole time of ob- 

 servation, bv means of two indicators, one of them applied to the upper, and 

 the other to the lower end of the cylinder ; and also provided, that an accu- 

 rate admeasurement of every one of all those cards was afterwards made, at 

 ten places in the length of the card, by the scale of pounds per square inch, 

 in the usual manner, and the amount of the ten measurements added into 

 one sum, and then (without averaging each card) that such sum of each card 

 shoidd be carried to a continuous account to obtain a grand sum total repre- 

 senting all the force that had been exerted, during both halves of each stroke 

 made throughout the experiment, reckoned at ten stages or portions of the 

 length of stroke. Such a grand total of all the cards would be a number 

 representing the same fact, as is represented by the number shown by the 

 new instrument ; and would therefore be dealt with, in each case, in a simi- 

 ,ar manner, as one of the data (viz. that representing force) for calculating 

 (by aid of other data representing motion or space) the whole power exerted 

 during the time of observation. 



In trying the performance of a steam vessel, alternately up and down a 

 measured mile in the river Thames, it is usual to take an indicator card from 

 each engine, at every such run ; and by summing up each card, some diffe- 

 rence will be found between them, wherefore an average of the results of 

 several cards will give more authentic information respecting the force 

 exerted by the engines during the whole trial, than could be obtained if one 

 such card alone had been depended upon. The new instrument takes cogni- 

 zance of every stroke that is made by the engine during the whole time of 

 observation; and in cases (such as in the Great iVestern steamer) v\here a 

 considerable variation of force in succeeding strokfs occurs frequently during 

 such time, it is a desideratum to obtain the results which this instrument is 

 intended to give, and which, as far as it has been tried, it seems likely to give 

 with fidelity. 



The instrument when applied as it had been at Old Ford, becomes another 

 mode of ascertaining performance, similar to what is reported monthly re- 

 specting the engines in Cornwall, but not exactly the same as is there called 

 " duty," because the new instrument would show the aggregate of the un- 

 balanced force, that had been exerted (during a given time) by the steam, to 

 impel the piston ; whilst the monthly reports show (by load in pounds, 

 length of stroke in pumps, and number of strokes made) the aggregate of 

 force exerted in the same time, in overcoming the resistance that the mere 

 hydrostatic weight of the columns of water in the pumps, opposes to the 

 motion of the engine. 



The instriimpnt (.usht always to show more force than the reports do, and 

 the difference between the two, would be the aggregate of all the force that 

 had been lost during the time, by friction of the moving parts of the engine, 

 pumps. &c. Respecting that loss of force, there is no more of it than arises 

 from such friction, from working the air-pumps, &c., and from resistance of 

 the water, but it is wholly a mistake to .suppose that any such loss is aug- 

 mented by producing motion. Professor Moseley had just stated the true 

 theory on that head, which theory was demonstrable mathematically, and 

 admitted of no ijuestion. It would be needless to go further into what had 

 been so well explained, except to observe that the theory applies without the 

 least abatement, or modification by incidental causes, to the case of any ma- 

 chine which, like a steam engine, regains the same state, as to rest, (or as to 

 motion) at the end of the time of observation upon it, as the state in which 

 it was at the commencement of that time ; and the theory shows that in such 

 a machine, no part of the force exerted upon it (or exerted by it) can have 

 been expended, or lost, in producing motion, whatever may be the number or 

 the extent of changes or variations in velocity of motion, that the machine 

 had undergone during the time of observation ; for although force must be 

 exerted to produce motion from a state of rest, yet all force that is so exerted 

 will be rendered back again when the motion which was produced has ceased, 

 and the state of rest regained ; in the steam engine that is the case at the 

 termination of every h.tlt-struke. Respecting trials by means of the smallest 

 force of steam, which will just press the piston of a pumping engine slowly 

 down in the cylinder, or cause the engine to come creeping in-doors: they 

 are not much to be depended upon as evidence of the force that is actually 

 lost in overcoming friction ; first because no steadiness of exhaustion can be 

 kept up beneath the piston, nor steadiness of steam above the piston, whilst 

 the engine is so treated, and also because the counterweight of engines in 

 Cornwall is not apportioned with any great nicety. In general they are 

 worked with more counterweight than is requisite, and but little loss is occa- 

 sioned by so doing ; for if the counterweight is unnecessarily great, so as to 

 carry the engine quick out of doors (that is, to cause the pump-rod to 

 descend briskly) then the equilibrium valve is closed sooner, and therefore 

 retains more steam between the top of the piston and the cover of the cyl n- 

 der. in what has been called the steam cushion, which stops the descending 

 motion of the pump-rod ; and in consequence of more steam being reserved 

 in such cushion to go towards the supply for the succeeding stroke, that 

 increase in the reserved steam compensffles in part for the v\aste of force 

 occasioned by the redundancy of counterweight, which caused the quick 

 motion. 



Mr. Farey had received from Mr. John Taylor indicator cards of Taylor's 

 engine at the Uniled Mines ; one card was taken socm after it was first set 

 to work, with an cxtravagaut counterweight, and another card was taken 

 imiuediately after several tons of balance had been added without alteration 

 of the load of water m the pumps ; balance in Cornwall is contrary to coun- 

 terweight, so that adding balance eflTects a reduction of counterweight. Now 

 if an attempt had been made to ascertain the friction of that engine by try- 

 ing what strength of steam would cause the engine to creep in-doors, the 

 day before the balance was added, the friction would have appeared (by that 

 mode) to have been 3 lbs. or 1 lbs. per square inch greater than it would 

 have appeared to be after the balance had been added : although that was an 

 extreme case not likely to occur often, yet errors in the imputed amount of 

 friction, to the extent of I lb. or l^lb. per square inch would be continually 

 made, if dependence were to be placed on that mode of trial of engines w nrk- 

 ing with so much counterweight as they may happen to have. The friction 

 of modern engines in Cornwall, including that of their pit-work and pump, 

 and the resistance of the water, he believed would not be found materially, 

 if any, greater, than was the case in Mr. 'Watt's old engines, when the depth 

 of the mines was not half as great, and the weight of moving parts not one- 

 third as great; for the improvement in pit-work and pumps, and engine- 

 work, had kept pace with that increase of depth and weight.^ The pump- 

 rods are hung more truly perpendicular, and the lengths of timber for the 

 rods are better jointed so as to cause them to hang straighter in the pit 

 whilst working, and avoid lateral vibratory fle.xure, and therefore the rods 

 rub less against their guides ; the plungers are set truer, and being of larfje 

 diameter, have less rubbing surface in proportion to their contents, the lifts 

 being higher, and short lifts being avoided ; these and many other improve- 

 ments tend to reduce the friction in proportion to the force exerted. 



The small quantity of steam expended, .and consequently of water injrcied 

 into the condensers, as well as better joints to prevent leak:ige of air into the 



