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from experiment.-- Mr. Fairbairn stated, that in hand-hammered rivets the heads frequently dropped off, and presented a crystallized appearance, while those compressed by machine were sound. He found that repeated percussions, from the rivetting, hammering plates, &c., induced magnetism in iron boats.- Mr. Vignoles could not, from his experience, subscribe to Mr. Nasmyth's theory of the oxydization of rails by single traffic, as the railway from Newton to Wigan had been single for a long time, and was as bright as the Manchester and Liverpool. The Blackwall railway was not an analogous case, as no locomotives were employed.Mr. Roberts disbelieved the deterioration of axles by work; he would rather trust an old axle than a new one. He believed cold swaging and hammering to be the chief causes of mischief. In fact, if axles were sent out sound and well manufactured, they would rather improve by working.–Athe
or electric changes in the molecular structure of the iron, caused by friction in the bearings and great velocities; and in his opinion it was probable that the continual strains and percussions to which the crank axle is subjected would account for the changes in the molecular constitution of the iron.
Mr. Hodgkinson was certain, from the results of his experiments, that a succession of strains, however slight, would produce a permanent deterioration of the elasticity of the iron.--Mr. Fairbairn had been told by the engineer on the Leeds line, that he considered all crank axles to be constantly deteriorating from percussions, strains, &c., and that they should be removed and replaced by new ones periodically, to avoid danger of fracture.- A discussion arose as to whether the crystallized appearance observed in fractured axles arose from defects in the manufacture, in the quality of the iron, or from the effects of working, either by percussions, strains, or magnetic action.—Mr. Grantham, although a manufacturer of cranked axles, admitted that straight axles were less liable to break. Cranked axles, from the way in which they were welded together and shaped, were rendered weak and liable to fracture. On other grounds, however, he believed that the cranked axles were preferable, as they produced a steadier motion, and much heat was saved.- Mr. Garnett believed that more straight axles had broken than cranked ones. - Professor Willis showed the effect of vi. bration in destroying molecular arrangement, by reference to the tongues in musical boxes, &c.--Mr. Nasmyth believed that the defects in arles, &c. arose in the manufacture, especially from cold swaging and hammering, and also from over-heating in welding, all of which causes injured the toughness of the iron. In small articles, he found great ad. vantage from annealing; and he believed that arles might be annealed very cheaply, and would be more serviceable. He disliked the fashion of referring all unaccounted phenomena to magnetism and electricity, although he was convinced that very singular electric phenomena accompanied the transit of locomotives and the rapid generation of steam. With this was connected the nonoxydization of rails, where the traffic was in one direction, and the rapid oxydization when the same rails were travelled over in both directions, as in the Blackwall railway. He had also observed that brasses, in some cases, had from friction entered into cold fusion, that is, at a heat not perceptible to the eye, a complete disintegration of the molecular structure had taken place, and he had seen the brass spread as if it had been butter or pitch. He had no doubt that this arose from electricity, but had not ascertained the fact
INSTITUTION OF CIVIL ENGINEERS.
MARCH 22, 1842. “ Results of a Trial of the Constant Indi.
cator upon the Cornish Engine at the East London Water-works." By Pro. fessor Moseley, F.R. S., &c.
The object of this communication is to exhibit and explain the results given by the author's indicator during a continuous registration from the 28th January to the 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 are recorded in a table 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 suc. cessive registrations of the indicator. These are followed by the mean registrations of the indicator at every stroke of the engine, being the quotients of the numbers in the lastnamed column divided by the corresponding numbers of the preceding column. The paper after thus stating the numbers registered daily by the indicator during the period 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 va. lues of the constants dependant upon this engine, is
U 161.4474 N 09051 L. In this expression, U represents the units
of work (in lbs. raised one foot high), done a spring thus formed, the deflection is distri. upon each square inch of the piston through buted more equally throughout, and being any given time, during which the number thus diminished for a given separation of the registered by the indicator is represented by springs at every point, the elastic limits are N, and the space in feet which the piston nowhere so soon exceeded. traverses by L. The second term of the By this connexion of the piston-rod with formula, which is very small as compared the springs, its position is made to vary with the first, is a correction for the influ. directly as the effective pressure upon four ence of the friction of the indicator on the square inches of the area of the piston of the number registered by it. The formula being steam-engine, so that every additional pound then reduced by the substitution in it of the in that pressure will cause the piston-rod to numerical values before alluded to, the whole alter its position by the same additional disnumber of units of work per square inch of tance in the direction of its length. the piston done between the 28th January A steel wheel (termed the integrating and the 25th February is shown to have wheel) having the edge milled, turns upon been 21 · 464 067•1727. From this is de. the piston-rod as its axis, traversing with it duced the work done during the same time also in the direction of its length. Through upon the whole area of the piston as well as the arms of this wheel pass three rods, conthe duty done upon the piston for each cwt. nected at their extremities by two pieces so of coals. These calculations are followed by as to form with them a rigid frame, which a comparison of the results given by the in turns, in fixed bearings, upon hollow axes dicator with those previously obtained from through which the piston-rod passes, so that actual experiment by Mr. Wicksteed; whence the integrating wheel is free to traverse lon. it appears, that with a necessary allowance gitudinally upon the frame, but cannot refor a difference in the lengths of stroke at volve without carrying the frame with it. the periods of the two experiments, the re The integrating wheel is made to revolve by sults of the two are almost coincident. The the rotation of a cone which is held in conwork per stroke upon every square inch of tact with it by a spiral spring, acting con. the piston, as obtained by experiment, is stantly against the extremity of the axis of 120.574, whilst as shown by the indicator it the cone. A system of bevil-wheels commuis 119.338 lbs.
nicates to this cone the rotation of a pulley,
which is driven by a cord carrying a weight Professor Moseley exhibited the indicator at one extremity and communicating by the and described its construction and action; it other with the piston-rod of the engine, or consists of two cylinders, each four inches with some point whose motion accords with long, communicating by pipes with the top it, but travelling through a less space. The and bottom of the cylinder of the steam-en circumference of the pulley moving precisely gine to which the instrument is applied. In as the piston, the angle described by the each of these cylinders there works a solid cone in any period of time, must be exactly piston four square inches in area; both being in proportion to the space described by the fixed upon the extremities of the same rod, piston in that time. The circumference of which (when the indicator is in action) sus the integrating wheel moving with that part tains in the direction of its length a pressure of the cone, with which it is in contact, the equal to the difference between the pressures portion of a revolution which it is made to upon the two indicator pistons, or equal to describe in a given time, is dependent, first, the effective pressure of the steam on four upon the angle which the cone describes square inches of the piston of the engine. about its axis, during that time; and seThis pressure is made to bear upon a steel condly, upon the distance of its point of spring, connected by a link at each end with contact from the apex of the cone at that a similar spring, supported at its centre upon time. If either of these two elements of vaa projection from the frame of the instru. riation remained always the same, then the ment. The pressure of the piston-rod upon portion of a revolution, made by the wheel, the lower spring, causes the two springs to would vary directly as the other, whence it separate from each other, and the separation follows, by a well-known principle of varia. produced is, by a well-known law of deflec tion, that when both these elements vary, it tion, directly proportional to the pressure varies as their product; or that the portion sustained, so long as the deflections are of a revolution, made by the integrating small. A peculiar form, first suggested (it wheel in a given time, varies directly as the is believed) by M. Morin, is given to these product of two factors, one of which is the springs; one surface of the spring is plane, angle described during that time by the cone, and the opposite surface is of a parabolic and the other the distance of the point of form, by which equal strength is given contact of the wheel and cone, from the apex throughout every portion of its length. In of the cone. The former of these factors
varies directly as the space described by the of the edge of the integrating wheel on the piston of the engine, and the latter as the surface from which it receives the impulse is effective pressure then exerted by the steam lessened in proportion. upon the piston : therefore the portion of a Thirdly ; in the separation of the registerrevolution made by the integrating wheel, ing apparatus from the integrating wheel; varies as the product of the space described by which separation, whilst the springs are by the piston of the engine during a given relieved from the effect of the momentum time, by the effective pressure of the steam and the friction due to the weight of the upon it during that time; that is, it varies
registering apparatus, the latter being in a as the work or dynamic effect of the steam state of quiescence, the registration is legible upon the piston during that time; whence it whilst the indicator is in action. follows, that the number of revolutions or Fourthly; in the variable appearance of parts of a revolution made by the integrating the links connecting the springs together, by wheel, during the stroke is proportional to which variation the same series of deflexions the whole work, or dynamical effect of the may be obtained under different ranges of steam upon the piston during the stroke.
pressure. By a number of toothed wheels the num In fact, that the indicator has nothing in ber of revolutions of the integrating wheel common with the “compteur" of M. Morin, is registered to five places of integers, except the principle of Mr. Poncelet, and and to one place of decimals. The number the springs under a modified form. registered is not diminished by the backward The amount of the friction of the pistons, motion of the cone during each return was then examined, and the peculiar constroke, because the integrating wheel ascends struction of their metallic packing explained : to the apex of the cone, and remains there it was shown also, that instead of great difduring each return stroke, so that no number ficulties arising from the friction of the inis registered during that interval.
tegrating wheel upon the cone, or its slipIn order effectually to guard, however, ping upon the surface, a very slight pressure against any error which might arise from
of the spring produced sufficient adhesion this reversed motion of the piston, a combi. to drive the registering apparatus.
The nation of wheels has been introduced, by Professor then explained the advantages rewhich the revolution of the cone can be ar sulting from a registration of the duty of rested during the return-stroke; and to steam-engines generally, not during the time adapt the instrument to register (if required) of a few isolated experiments, as with the every stroke, a fourway cock has been con common indicator, but extended over any structed, by which one of the indicator cy given period, and through every stroke of the linders may be made to communicate always engine, displaying all the changes which had with the steam end of the steam-engine cy occurred during that time :-with this view linder, and the other to be acted upon by it had been decided that the instrument the vacuum end : in this case the movement should be attached to the engines of the of the cone should be constantly forwards. Great Western steam vessel on her next voyThe Professor then gave the mathematical
age to America. formula by which the work is determined He then expressed his obligation to Mr. from the numbers registered by the indicator. Wicksteed for the facilities afforded him for He then described the difference between the the experiments at Old Ford, and paid a instrument, and that of M. Morin for ap well-merited compliment to Mr. Holtzapffel plying the principle of M. Poncelet, to con. for the excellent construction of the indisist,
cator. First, in all those mechanical combinations In reply to a question from Mr. Vignoles, which are peculiar to the instrument in its he stated that the instrument was not under application to the steam-engine. M. Morin's its present form adapted to locomotive eninstrument having been applied to measure gines, but that a grant of 1001. had been made the traction of horses.
by the British Association for the construcSecondly; in the surface of a cone being tion of such an instrument. substituted for the plane surface of a circular Mr. Cowper, in compliance with the redisc; by which arrangement the rapidity of quest of Professor Moseley, illustrated his the changes of velocity due to corresponding description by setting the instrument in changes in the position of the integrating motion, showing that the registration dewheel is diminished in the same proportion pended upon the revolutions of the integrat. in which the sine of one-half the angle of ing wheel; he demonstrated the cases of the cone is less than unity ; and the force motion without pressure, and pressure withnecessary to drive the integrating wheel being out motion ; in the former case, the intediminished in the same proportion, the grating wheel being stationary at the apex chance of an error arising from the slipping of the cone while revolving, does not receive
any impulse from the contact with it, and Cornwall the performance is reckoned actherefore does not register ; in the latter cording to some reputed length of stroke, case, the surface of the cone upon which the which had been fixed upon for each engine, integrating wheel traverses, being at rest, when it was first reported, and it is afterdoes not communicate any rotative motion wards assumed that no departure from that to it, and consequently no registration can reputed length has taken place, when in fact take place; but when motion and pressure such departure does often occur. are combined, the cone revolving, and the It would be very desirable to have a morintegrating wheel travelling from the apex ing card applied to the new instrument, in some distance towards its base, the exact order to indicate the impelling force of the product of the motion of the cone and the steam in the cylinder, by tracing curves on steam's pressure upon the piston would be paper like those by the ordinary indicators. registered by the amount of the revolution This, it appeared, might be done with the ad. of the integrating wheel.
vantage of causing the paper on which the Mr. Wicksteed observed, that every facility curve is drawn to travel onwards, and bring had been afforded to Professor Moseley for fresh paper into its place, so as to obtain a applying his new indicator, for the purpose series of distinct curves for as many succeedof ascertaining the duty performed by the ing strokes. Cornish engine at Old Ford, but that he The form of the springs of Professor had not at all interfered with the experi Moseley's instrument would be a decided ments, being desirous of ascertaining whe improvement if substituted for the spiral ther the results would correspond with his spring of ordinary indicators ; Mr. Farey trials. That after the work of the engine had applied to an ordinary indicator, a mode had been registered while it was making of exhibiting at a glance, whether the engine about 179,000 strokes, the mean result, as was exerting more or less force than its orstated by Professor Moseley was so nearly dinary appointed task; the plan answered that arrived at by Mr. Wicksteed, that he that purpose; but as it required the indicator had no doubt of the accuracy of the machine to be always in action the spring of the inas a good indicator of the real duty performed dicator broke after working more than two by the engine; the difference in the result of days, he therefore abandoned it. The springs the mean pressure of the steam, deducting the in the new instrument were proved by the vacuum, or 0.731b., was 0.121b., namely, trial at Old Ford to be capable of enduring according to Mr. Wicksteed's experiments continual exertion without breaking. 12.94-0.73=12.21lbs., and according to The Professor had stated that the scale of Professor Moseley 12.091bs. ; this difference flexure of the new springs was found to be might arise from a variation in the mean exactly, according to theory, equal divisions length of stroke during the two sets of ex with equal forces; this might be expected, periments—from a slight variation in the because the flexure of the springs was small, point at which the steam had been cut off and the bending force acted in a direction from a variation in the level of the water in nearly at right angles to the length of the the pump well, or other practical causes-the springs. In ordinary indicators the scale difference, however was so insignificant, that should not always be equal divisions, because he would rely on the accuracy of Professor the wire of the spring being wound spirally Moseley's indicator, and allow the possibility into a screw of small diameter, the spiral of a slight error in his own experiments. obliquity of the thread of such screw be
Mr. Farey observed, that Professor Mose comes more obliqne to the direction of the ley's instrument must be influenced by vari bending force, as the spring is stretched, and ations in the length of stroke, for whenever less oblique as the spring is compressed, and the piston makes a long stroke, the cone and hence the scale of pounds per square inch, the train of registering wheels must be by which the curve should be measured for turned farther round, and would register a summing up the results, ought to be a scale higher number than they would do in case of unequal divisions. of a shorter stroke, supposing the impelling The indicators originally used by Boulton force exerted by the steam to be always the and Watt were of a large size, with a long
If the instrument could be really and powerful spring curled into a cylindric made to give its results according to the form, as large in diameter as could be inactual length of all the varying strokes made cluded in the cylinder of the indicator, and during the time of observation, by truly ag the motion allowed to the piston by the gregating these varying lengths into one sum, spring was very short ; such indicators were the results would be free from the usual judiciously proportioned, and they do not uncertainty respecting an average length of show any sensible inequality of divisions in stroke.
their scale. But recently, indicators have In the monthly reports of engines in been frequently made without the knowledge
of their true principle, and the rules of proportion are not observed, so that it will sometimes be found, on actual trial of such instruments with weights, that their scale of pounds per square inch is not in equal divi. sions, although it is usual to employ a scale of equal divisions for summing up the curves traced by them.
In Boulton and Watt's indicators the scale of pounds per square inch was formed from actual trial with weights ; but such trials were made when the indicator was cold, and dismounted from its place upon the steam-engine.
A much better mode is to apply the weights on the upper end of the piston-rod when the indicator is placed on the cylinder of the engine, while it is hot, its piston being supplied with the same quantity of oil, and the spring being in the same state as when it is in use. The depression of the piston by the weights is recorded by drawing a line with the pencil of the instrument on the card itself in the same manner as the usual atmospheric line is drawn thereon.
A series of lines thus drawn with given weights, become so many original stages for subdividing between them, to form a true scale for summing up the curve described under the same circumstances and nearly at the same time.
Professor Moseley's instrument had two cylinders and pistons operating in concert on the same piston-rod, and springs of peculiar construction to indicate the unba. lanced pressure exerted by the steam to impel the piston of the engine. The elastic force wherewith the steam acts above the piston (called the positive pressure or plenum) is shown by a common indicator, but the elastic force wherewith the uncondensed steam is at the same time reacting beneath the piston (called the negative pressure, or imperfect exhaustion or vacuum) is not shown; hence the observations are limited to two odd halves of the stroke made by the piston ; those halves being commonly the plenum during the descent, and the exhaustion during the ascent of the piston; it is taken for granted that the other two odd halves are the same as those which are ob. served, although such assumed parity is not always the true state of the case.
In the new instrument the indication that it would make by drawing on a card, would be that of the difference subsisting between the plenum above, and the exhaustion beneath, the piston of the engine during its descent and ascent, wherefore it would indi. cate on one card as much as two ordinary indicators can do on two cards, if they are applied one to the top and the other to the bottom of the cylinder of the steam-engine;
in that case each indicator shows on its own card what the elastic force of the steam is during the plenum, and what it is during the exhaustion, but the required result (which is the difference between the two) must be ob. tained by combining together in the computation those distinct curved lines which are drawn on two separate cards. Professor Moseley's combined indicator pistons, act. ing on the same springs, would at once indi. cate such difference, by the curve which it would trace on the one card.
In answer to a question from Mr. Parkes as to whether the new instrument had been put to any other test than its apparent agreement with Mr. Wicksteed's estimate of the resistance overcome, and whether the common indicator had been applied to the engine at the same time, Professor Moseley said, that he had not compared the instru. ment with any other, but had subjected Mr. Wicksteed's calculations to a rigid investigation, and felt quite satisfied that they approximated closely to the truth. He relied upon them as corroborations of the accuracy of the instrument.
Mr. Parkes observed that it would have been more satisfactory to engineers to have been assured that every means had been taken to demonstrate the truth of the results recorded by an instrument which had such important functions in view. He wished to know in what manner the pressures denoted had been ascertained, -whether by weights or by comparing them with a mercurial co. lumn. He had found the latter mode more exact than weights, in verifying the scale of the common indicator, as the instrument being heated was then in precisely the same state as when it was in use. He had found that a certain amount of correction was frequently necessary, as both the spring and the amount of piston friction were affected by heat.
Professor Moseley replied that the instrument had not been compared with the mercurial column, but that the resistance of the springs, and the friction of the piston and instrument generally, had been ascertained by very accurate experiments, so that he had full confidence in the results.
Mr. Parkes said that notwithstanding the respect and deference he felt for Professor Moseley's attainments and ingenuity, his past experience would not permit him to place entire confidence in the results afforded by the instrument: indeed he considered them to be altogether fallacious as representing the force acting on the piston of the Old Ford engine. He could not admit that the apparent near identity between Mr. Wicksteed's computations of resistance, and the constant indicator's registration of force