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iron press, placed about a foot above the cistern, which is fitted with doors (omitted, for clearness' sake, in the drawing) perfectly air-tight; i a pipe, which forms a communication between A and B, having a stop-cock f to regulate that communication at pleasure; a a a a a a six copper cases for holding the paper to be wetted, which are open in front, and perforated with small holes (about a dozen to the inch) on the top, bottom, and sides; C an air-pump; D a mercurial barometer; and E a float-gauge, with a glass covering.

The paper to be wetted being placed in the cases a a (which should only be about three fourths filled, that the paper may have room to expand freely), the cocks g and ƒ are opened; and while the cistern A is filling with water, the operator employs himself in pumping the air out of the press B B. As soon as A is filled, the water rushes up the pipe i into the partially exhausted chamber B B, until that also becomes filled as high as the float E (which will be indicated by the rise of that float in its glass cover), and the paper-cases are completely immersed in water. The cock ƒ is now closed, and the air-pump again worked, till such a vacuum is produced over the water in B B, as drives the mercury in the barometer D to the top; by which time the paper has yielded up all, or nearly all, the particles of air confined within its pores (the great obstacle to wetting by the ordinary process), and is in a state fit for the most perfect saturation; to effect which object, a process somewhat the reverse of the preceding is adopted. The vent-cock * is opened, and the air, rushing into the empty space of the press BB, forces the water, in its turn, between every leaf, and into every pore of the paper.

To make the saturation more complete, this alternate process of exhaustion and injection may be performed twice or thrice; but I

Omitted, by mistake, in the engraving. It may be placed anywhere at the top of the press B B.-EDIT,

have found doing it once generally sufficient for my own purposes.

The vent-cock k, and the cock f of the pipe i, are now left open until the water which has not been imbibed by the paper drains back into the cistern A; from which it may be afterwards discharged by the pipe h. The paper is then taken out, and placed in a common screw press, to have the superfluous water pressed out of it; after which it is in a state fit for printing. I am, Sir, Yours, &c.

London, Jan. 25, 1829.

C.

ON THE CAUSES OF VARIATION IN CHURCH CLOCKS.

(Continued from p. 446, Vol. X.)

Sir,—Having, in my last paper, made a comparison between the principles dictated by Mr. Harrison, and those which I practised in my Boston church clock, as relates to the watch part, it remains for me to say a little respecting the striking part. Mr. H. has been saying a great deal about the hammers he has applied; but he is so extremely cautious on this head, that he does not describe a single principle they possess, to convince your readers of their excellence. However, the very circumstance of his finding it necessary to effect some improvement in this part of the machinery ought rather to make us agree than dispute. Indeed, a man must be passing obstinate, who would for a moment attempt to argue against the necessity of making some improvements in the hammers and cranks of clocks, as they have been heretofore made by our wholesale clock manufacturers. The result of the experiment alluded to in the first paper of this series (No. 282, p. 366) will convince your readers of this; for although I do not attempt to say that every hammer experiences so great a resistance to its fall as the one which was the object of that experiment, yet all are bad enough, and some are even worse than that. As Mr. H. has kept us so much in

the dark in respect of his mode of striking the bell, he has, of course, the advantage over me (being well acquainted with the principles of my method-both from his son's report, and from his having seen the elaborate description and engravings of that method, in the Society of Arts' Transactions); but although I would not attempt to give an opinion relative to the merits of his performance, yet I will deny the possibility of bis making a hammer that shall be so far superior to mine, as to produce equal force with two thirds or three fourths the maintaining power. Your readers will, I trust, give me credit for this assertion, when I assure them that the whole of the friction of the machinery of my improved hammer does amount to anything like one per cent. of the weight of the ball,every means being made to reduce it, by the application of fountains to the pivots, on the principle of the airtight carriage axles; and joints being applied to the levers, instead of fixing the wires through rusty holes, &c. &c. If the friction, therefore, be so small as I describe, it cannot be possible for Mr. H. to create an equal force with two thirds or three fourths of the power, as compared with mine, unless he has some pretensions to perpetual motion.

not

I have taken a great deal of pains with the cranks and wires in the Boston clock, and have introduced some novelties in them. The cranks have good brass sockets substantially fixed in their centres, well fitted to turned pins; and a pivoted joint is run in the end of each arm, which admits of the wire passing through them, and fastening with nuts and screws, which adjust the length of the wires, and place the arms of all the cranks in their true positions, with the greatest facility,—an object which cannot be accomplished without some such means; for even supposing them to be originally well placed, they are not likely long to remain so. With this mode of adjustment it is easy at all times to bring the cranks most accurately to their position; which causes the force to be conveyed through all the

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wires without any loss whatever, and brings up the hammer with the greatest solidity, however distant its connexion may be from the clock. In fact, there is but little less than ninety feet of wire in each pull of that clock, and yet there is no more elasticity in the draught of the hammer than if it were fixed within a few feet of the clock. The application of the pivoted joints is also of great advantage; for there is as much friction in the axes, and in each lever of the cranks, and in the hammer tail and bammer detent lever, as there is in the pin-wheel pivots, or those of the hammer itself, there being, as nearly as may be, the same pressure and the same angular motion in all these axes of motion; and as there is seldom less than eight of these axes to each hammer, the aggregate prevention of friction by these cranks is very considerable. The arms of the crauks are made as light as is consistent, and are strengthened with braces. They are balanced so that the weight of their arms is not a drag upon the hammer, to reduce the force of its fall.

Mr. H. says, he raises his hammer detent by rollers, to reduce the friction. I say that that is a labour not worth practising; for he must make the pin-wheel pins too small and weak, and his rollers must be of so large a size as to occupy too much of the circumference of the wheel, and thus cause a waste of mechanical power, to be able to reduce the friction one half, as compared with the wholesale plan; whereas, by the application of the toothed sector, which is in the Boston clock, the friction is reduced to one fiftieth.

Although Mr. H. bas ventured to make many comparisons between his mode of work, from the mere report of an inspection of this clock, without being acquainted with any of the actual powers there applied, yet I assure you, I would not attempt to do the same with bis, having never had the means to measure the powers or resistances of any that he has made; but having had opportunities to ascertain the

the medium of the crank fixed on a moveable axis, or whether it be acting on the wheel itself, in the same direction, the wheel moving on a fixed axis.

I am now arrived at a point which embraces a favourite idea I have for some time entertained, which is this:-If a machine or carriage could be moved by a force acting from within it, the forces employed acting in the most favourable directions,-it would be moved by much less power than would be required by a force acting from without. If it be admitted that the moving power, communicated either to the crank, the circumference of the wheel, or to any point in its radius, converts the wheel into a revolving lever, or, more properly, a series of revolving levers, what are the consequences? In the case of a single lever, in which the fulcrum is a fixed point, a great resistance may be overcome or moved by a small weight or power; but then,-as is well known, what is gained in power is lost in time, or the resistance overcome, or body moved, is with a velocity in an inverse ratio to its weight, compared with the power. Will this be the case in our supposed series of revolving levers ?—that is, admitting them to be effective in moving the machine;—and if they are not, what becomes of the steamcoach speculation?

Let us imagine the machine on a horizontal plane, and impelled forward by the machinery terminating in a series of levers acting on the road, as a fulcrum, or fixed object, without the system; does not the circumference of the wheels describe the same line of distance as that through which the centre, or point of resistance, travels in the same time? and if so, are not their velocities equal? (My brains must certainly be woolgathering, as they frequently are, if this is not a poser for the moment!) That no power can be gained without a corresponding loss of time, is a maxim hitherto considered as one of the fundamental laws of nature. Now, though I am an advocate for another maxim, that there is no general rule without an exception, I

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shall endeavour to rescue the firstmentioned maxim, or favourite dogma, from contradiction, though all I expect to do is to show (to use a phrase of Sir William Congreve's), that ours is one of those particular cases that does not come within the sphere of its applicability. To explain the seeming contradiction, that a greater resistance will be overcome by a smaller power, and at the same time the body, or resistance, be moving with equal velocity through the same space as the power; and this by means of a lever; I will observe, that it is the circumstance of its being a series of levers, that makes the distinction. In the case of the common wheel being effective on an horizontal plane,-from the circumstance of the friction being sufficiently great, and the wheels sinking in the road to form a fulcrum to the levers-the series, in this case, may be considered indefinitely numerous, and succeeding one another on a new fulcrum, with a rapidity equal to the velocity of the moving force; and thus remove the seeming incongruity. In the kind of wheel I have hinted at, the series are less numerous, each lever presenting its arm to a new fulcrum some distance in advance,—something like a number of men turning over timber, each one taking a fresh purchase (as it is called), before the others have expended their strength on their respective levers. I hope I shall be excused for my prolixity on this point, as it is certainly a very curious one; and I should be happy to see the opinion of some of your correspondents, whether I am borne out in my notion, that by employing the power from within the machine, a less power is required than when the power is applied from without it. Whether, in this case, power is gained without loss of time, I leave to others to determine: it is a matter of indifference to me: I am no dogmatist.

I shall now state my objections to the crank placed so near the point of resistance. With respect to the power of a crank,' compared with the arm of a lever of the same radius, and acted on by a force whose di