same, whatever may be the velocity communicated to it, and to the mass which it carries with it, at any period of the stroke.

It is true that to put the piston, and the mass carried along with it, at first in motion, a pressure greater than the resistance is required, and therefore greater than the mean pressure necessary to complete the stroke: a pressure equal to the resistance would only bring it into the state of rest bordering upon motion; to cause it to pass from this state of rest to a state of motion, more pressure is required; and the more as the velocity to be acquired, whilst it moves through a given space, is greater-or in other words, in order to communicate any given velocity to a body whilst it moves through any space, there must be an excess of the work done by the driving pressure through that space, over that expended upon the resistance through that space; but all this excess is accumulated, and unless the steam pressure be afterwards made less than the resistance, or unless the steam be afterwards expanded through a distance dependent on the amount of this accumulated work, so that it may expend itself in overcoming the surplus resistance through that space, then the piston will strike upon the cylinder bottom.

:

This principle may be illustrated by an example suppose that the load upon the piston of an engine is 10 lbs. per square inch, and that the steam is admitted at a pressure of 15 lbs., it is evident that, by reason of the excess of 5 lbs. pressure of the steam above the load, the velocity of the piston will be made continually to increase until the steam is cut off, and afterwards, so long as the steam pressure exceeds the load, or until by its expansion the steam pressure is reduced to 10 lbs. per square inch. Up to this point the velocity of the piston and of the mass moving with it will continually have been increasing, a great momentum will therefore have been acquired by it, and this momentum will carry it on to the completion of the stroke; although, after this position is passed, the steam pressure will be less than the load, and would by itself be insufficient to move it.

In other words, the work done by the steam upon the piston will have continually exceeded that expended on the load up to this period of the stroke, and the surplus will have been accumulated in the moving mass, which surplus work will carry on the

*

piston to the end of the stroke, when a cylinder full of steam will be delivered of greatly less pressure than the load. If the steam had been worked at full pressure, it is evident that at every stroke a cylinder full of steam would have been discharged of the same pressure as the load. In this consists, therefore, the advantage of working expansively.

It is evident that the piston acquires its maximum velocity at the point where the steam pressure becomes equal to the load, and that the engineer by the manipulation of the steam valves produces that adjustment by which the velocity acquired by the piston at this point (or the work then accumulated in it) is caused to be just sufficient to carry on the piston to the end of the stroke, but without striking the cylinder bottom : it is moreever evident that the greater this maximum velocity can be made, the farther the piston will be carried beyond the point where the steam pressure is equal to the load, and the less will be the pressure of the cylinder full of steam discharged at the completion of every stroke, or the greater the economy of the steam power.

A second illustration of the same principle may be drawn from the effect produced by a pressure suddenly thrown upon a spring. Suppose a spring which would rest deflected through an inch under a pressure of one pound. If when this spring is in an undeflected state this pressure of one pound be suddenly thrown upon it, it is certain that the spring will, at first, deflect considerably beyond that distance of 1 inch in which its deflection will eventually, after many oscillations, terminate. In fact, if it is thrown on with mathematical suddenness, the first deflection will be 2 inches. To explain this, let the pound weight be supposed to be applied gradually to the spring by dropping grain after grain of sand slowly on it. The spring will 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 1 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 1 inch. Now

let all the grains be placed at once upon the spring. When it has deflected an inch, each grain will then 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. Wicksteed 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 England, the term "work was probably the most obvious translation of " travail;" that it moreover appeared to him the simplest, and the most intelligible; and that on these grounds he had adopted it.

In answer to the observation made by Mr. Parkes, suggesting the construction 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

Professor Moseley stated that such an instrument would undoubtedly be very valuable, especially if it could be made to register correctly the work transmitted by 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 registration 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 engines. No registration of the work done at the working points of the machine 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.

He 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 esti

mate those very 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 any 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 work (not effective power) 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 imperfectly 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 the determination of that duty that the indicator had been constructed, and the alterations which Mr. Parkes had suggested would have subjected its registration 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 were 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 observation, by 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 accurate 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 should be carried to a continuous account, to obtain a grand sum total representing all the force that had been exerted, during both halves of every 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 similar 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 the measured mile in the river Thames, along the shore of Dartford Marshes, it is usual to take an indicator card from each engine at every such run; and by summing up each card, some difference 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 cognizance of every stroke that is made by the engine during the whole time of observation; and in cases (such as in the Great Western steamer) where a considerable variation of force in succeeding strokes 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 respecting the engines in Cornwall, but not exactly the same as is there called "duty," because the new instrument would show the aggregate of the unbalanced 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 instrument ought 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 augmented by producing motion. Professor Moseley had just stated the true theory on that head, which theory was demonstrable mathematically, and admitted of no ques

tion.

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 machine

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 steamengine, that is the case at the termination of every half stroke.

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 occasioned 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 cylinder, 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 compensates in part for the waste 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 United Mines; one card was taken soon after it was first set to work, with an extravagant counterweight, and another card was taken immediately after several tons of balance had been added, without alteration of the load of water in the pumps: balance in Cornwall is contrary to counterweight, so that adding balance effects a reduction of counterweight. Now, if an attempt had been made to ascertain the friction of that engine by trying 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 4 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 1 lb. or 14 lb. per square inch, would be continually made, if dependance were to be placed on that mode of trial of engines working with so much counterweight as they may happen to have.

The friction of modern engines in Cornwall, including that of their pit-work and pumps, 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 flexure, and therefore the rods rub less against their guides; the plungers are set truer, and, being of large diameter, have less rubbing surface in proportion to their contents, the lifts being higher, and short lifts being avoided: these, and many other improvements, tend to reduce the friction in proportion to the force exerted.

The small quantity of steam expended, and consequently of water injected into the condensers, as well as better joints to prevent leakage of air into the exhausted parts, reduces the power required to work the airpump to a smaller proportion of the power exerted by the engine than formerly. And, in particular, the valves and water-ways through the pumps are made more open than formerly, so as to diminish the loss of force that is occasioned by resistance of the water; that loss of force by resistance increases as the square of the velocity of the motion, when loss of force by mere friction does not increase by increase of that velocity. He believed few large engines in Cornwall, which are making what is now thought tolerably good performance, lose more than at the rate of 3 lbs. per square inch of the piston, by friction of their moving parts, and by resistance of the water, and by working their air-pumps, and the best and newest engines probably still less. It would, of course, be understood that he meant, by 3 lbs., what is commonly called 1 lb., for

moving the engine each way, or through each half stroke; but that is not a correct way of stating it: 1 lb. friction in coming in-doors, and 14 lb. friction and resistance of water, in going out-of-doors, would be more likely to be correct.

LIST OF PATENTS GRANTED FOR SCOTLAND FROM 23RD JUNE TO JULY 18, 1842. John Cox, of Gorgie Mills, Edinburgh, tanner and glue manufacturer, for certain improved processes of tanning. Sealed, June 23.

John Bould, of Ovenden, in the parish of Halifax, York, cotton spinner, for an improvement or improvements in condensing steam engines. June 23.

John Americus Fanshawe, of Hatfield street, in the parish of Christ Church, Surrey, gentleman, for an improved manufacture of water-proof material applicable to the purposes of covering and protecting surfaces, bodies, buildings, and goods exposed to water and damp. June 30.

James Boydell, jun., of the Oak Farm Works, near Dudley, Stafford, iron master, for improvements in the manufacture of keel plates for vessels, iron gates, gate posts, fencings and gratings, June 30.

Michael Coupland, of Pond-yard, Park-street, Southwark, millwright and engineer, for improvements in furnaces. June 30.

Thomas Banks, of Manchester, Lancaster, engineer, for certain improvements in the construction of wheels to be employed on railways. July 6.

John Tresahar Jeffree, of Blackwall, Middlesex, engineer, for certain improvements in lifting and forcing water and other fluids, parts of which improvements are applicable to steam-engines. July 6.

James Nasmyth, of Patricroft, near Manchester, Lancaster, engineer, for certain improvements in machinery or apparatus for forging, stamping, and cutting iron and other substances. July 7.

Charles Augustus Preller, of East Cheap, London, merchant, for improvements in machinery for preparing, combing and drawing wool and goats' hair. (Being a communication from abroad.) July 13.

William Revell Vigers, of Russell-square, Middlesex, Esq., for a mode of keeping the air in confined places in a pure or respirable state to enable persons to remain or work under water, and in other places, without a constant supply of fresh atmospheric air. (Being a communication from abroad.) July 13.

Gottlieb Boccius, of the New Road, Shepherd's Bush, Middlesex, gent., for certain improvements in gas, and on the methods in use, or burners for the combustion of gas. July 14.

John Hall, of Breezes Hill, Rateliff Highway, Middlesex, sugar refiner, for improvements in the construction of boilers for generating steam. July

18.

John Elliott Fox, of Finsbury Circus, London, gent., for improvements in steam engines. (Being a communication from abroad.) July 18.

LIST OF PATENTS GRANTED FOR IRELAND IN JUNE, 1842.

M. M. Laroche Barre, for an improvement in the manufacture of a fabric applicable to sails and other purposes.

H. B. Rodway, for improvements in the manufacture of horse-shoes.

Erratum in List of English Patents given in our last No.

In the title of Lady Vavasour's Patent, for "improvements in obtaining images, &c." read "improvements in machinery for tilling land."

NOTES AND NOTICES.

The Great Northern (launched last week at Belfast,) is the largest vessel ever built in Ireland. Her dimensions are 220 feet in length, 37 feet beam, and 26 feet deep in the hold; burden, 1,750 tons, B.M.; she is to be fully rigged as a 50 gun frigate, the length of mainmast to be 90 feet, and 36 inches diameter, mainyard 79 feet, and 22 inches diameter in the slings, foremast 83 feet, and mizenmast 76 feet; she will be able to spread 6,400 yards of canvass. There are three decks, the upper one to be left entirely clear for action, and to be pierced for 44 guns; the windlass and capstan gear will be placed between decks. She is to be propelled by Smith's Archimedean screw, which will be 12 feet diameter, and 14 feet pitch, but the length will be only 7 feet; it is to make 88 revolutions per minute; the gearing consists of a cog-wheel 20 feet diameter, working into a smaller wheel, of 5 feet diameter, upon whose axis is the shaft of the screw. The engine power consists of two cylinders, 68 inches in diameter, 4 feet 6 inches stroke, and to make 22 strokes per minute; nominal power about 370 horses; there are to be 4 air-pumps, 19 inches diameter, and 4 feet 6 inches stroke, and cylindrical boilers. The engines are to be placed close abaft the vessel, leaving the midships clear for passengers. Derry Standard.

The Great Britain (late Mammoth) is not now expected to be finished before the spring of next year. The Montezuma Steam Frigate-A very successful trial was made, last week, of a new steam-frigate, which has been built for the Mexican Government, and appropriately named the Montezuma. She was constructed at the yard of Messrs. Wigram and Green, and her engines, which are of 300 horses power, and on a similar principle to those on board Her Majesty's steam frigates Gorgon, Driver, Styx, &c., were supplied and titted by the firm of Messrs. Seaward and Capel. Her burden is 1,100 tons, but she draws no more than nine feet water when fully equipped, and is built to carry two swivel guns, 68pounders, on the upper deck, besides the usual number of small guns. Although constructed rather for fighting purposes than for speed, she steamed at the rate of 10 miles an hour, against tide both ways, the engines making 21 strokes per minute. A new disconnecting apparatus, for releasing either paddlewheel, which was tried, was found to answer admirably.

High-pressure Boiler Explosion.- The last arrivals from Canada bring an account of an explosion on board the steamer Shamrock, attended with a most frightful destruction of human life. The list of sufferers, " of the English portion" alone, includes 43 killed, and 20 wounded. The Shamrock was a new boat, and built at Niagara; and her engines, which were of 32 horses power, were on the high-pressure principle. The engineer of the vessel stated, at the coroner's inquest, that, "according to the directions of the builders of the engine, he was allowed to carry 85 lbs. of steam, but that at the period of the accident there were not more than 70 lbs. of steam." [Exactly the pressure at which the Locomotive, now working on the Thames, is said to be worked.)

Steam Pile Driver.-Among the many improvements in machinery which are daily taking place, we notice with pleasure the introduction recently, at the harbour works, of a self-acting machine for driving piles. The moving power is taken from a cylinder connected with the engine erected for pumping out the water in the dock, which does its work in a most admirable manner. There are two other pile-driving machines, wrought by manual labour, in operation alongside of it, requiring nine men to each; and this self-acting machine, attended by one man, gives seven strokes for every one that

the others give, so that it does the work of sixtythree men. It can be extended in the same proportion to any power. It is the invention of Mr. James Milne, engineer at the dock.-Montrose Review.

The Thames Tunnel was opened on Monday last for the first time on the Wapping side of the river, and upwards of 500 visitors, of all nations, passed through the tunnel as far as the shaft on the Rotherhithe shore. The Wapping shaft is about 90 feet in height, and is surmounted with a handsome dome, which is glazed, and light and air admitted. There are two staircases, one terminating close to the western arch, and the other leading to the eastern arch. The western arch only is opened for visitors; but the eastern one appears likely to be appropriated to the same purpose in a few weeks, and a great number of workmen are now actively employed in preparing it for the reception of the public. The erection of the circular staircases in the shaft on the Surrey side, now closed to the public, will be commenced forthwith by the contractors, Messrs. Peto and Grissell, who have completed the staircase on the Middlesex shore. The time allowed for the performance of the contract is three months, when the tunnel will be opened as a thoroughfare for foot passengers; the toll to be charged is, we understand, to be 1d. each person. Some time, however, must elapse before the circular staircases and inclined planes for horses, cattle, and vehicles can be formed; but the plans are already framed, and the works will be conducted with all possible expedition. The engine and pumps are constantly at work in the Rotherhithe shaft, to clear the tunnel of the accumulation of water caused by the land springs. There is a culvert under the Western arch, into which the waters are collected and pumped out, which keeps that side of the tunnel always dry, and as a current of air now passes through the excavation, the place is rendered comfortable, and by the aid of the gas lights, which are always burning, the temperature of the atmosphere is nearly the same as it is on shore.-Times.

Progress of Steam Power in France.-We find by a recent statistical return, that at the end of last year there were in France 179 establishments having steam power, containing 5,600 boilers, of which 1,889 were for the purposes of heating, and 3,511 for giving motion to machinery. There were, besides, 2,637 engines, the aggregate of which was equal to 39,779-horses power. At the same period there were 260 steam-boats, being 128 more than in 1838, without comprising those belonging to the state. The number of engines was 400, of a force equalling together 45,000-horses power. The number of passengers conveyed by these vessels was 2,500,000, being 800,000 more than in the preceding year. The increase of merchandise sent by them on freight was equally remarkable, having exceeded by more than 60,000 tons the quantity thus conveyed in 1840. The locomotives employed on the rail-roads in the departments of the Seine, Rhoute, Herault, and Loire, were in number 118, and in force upwards of 300-horses power. Of these, about 35 were of French manufacture.

Erratum.-Mr. Jubber requests us to state, that his patent being dated 4th June, 1842, his specification could not have been enrolled, (as stated by mistake in our last,) on the 1st December, 1841.

Intending PATENTEES may be supplied gratis with Instructions, by application (postpaid) to Messrs. J. C. Robertson and Co., 166, Fleet-street, by whom is kept the only COMPLETE REGISTRY OF PATENTS EXTANT from 1617 to the present time).