306 BELL-CRANK BELL-CRANK STEAM ENGINE, ROYAL MINT. STEAM ENGINE AT THE ROYAL MINT. Sir,—The queries which have appeared in some of your later Numbers respecting the proportions of steam engines, has convinced me of that which had frequently occurred in my mind relating to the extensive utility of such information; and it is to be wondered that most publications which profess to give an account of the steam engine, are nearly all silent as to these details. The drawing I enclose, from actual measurement, is one, among some others, I shall take the liberty of sending, in order to shew the admeasurement of the various modifications of steam engines whose powers are different. This description of engine is what is termed Bell Crank, from the form of the oscillating portion A A. The engine in question is taken from one in the royal mint, of six horse power, which is used for turning the lathes in the die turning apartment. B is the cylinder; C is the end of the steam pipe, shewing at what part the steam is admitted into the jacket of the cylinder; D is the continuation of the steam pipe to the boiler, E the rod which operates upon the air pump and condenser, F the eccentric that works the slide valves; G the blow valve; H cold water pump and pipe; I, part of bevil gear, that gives motion to the rod and governor K K. The bell-crank motion has certainly great recommendations for a low pressure engine; that massy appendage, the balance beam, is not required, and the rods for working the pumps are of such small length that they are never in the way, and the parallel motion is effected in a very simple manner. The connecting rod to the piston L is fixed upon moveable joints M and N, so that when the bell-crank A A oscillates towards O, the joints acting in concert with it brings the connecting rod in the direction of the dotted line P, and consequently, according to the motion, raises or depresses the piston in a perpendicular line. Such is the action also of the eccentric upon the slide valves. This establishment (the Royal Mint) employs several engines, but all excepting this are beam engines of different powers, and on Bolton and Watt's principle. So true, however, is the workmanship, that scarcely any thing is heard but the rush of the water from the condenser; and the engines and their apartments are patterns of neatness and cleanliness highly gratifying to the spectator. This (the bell-crank) performs forty strokes per minute, consumes per hour one bushel of coals, and possesses a power equal to six horses. Diameter of steam pipe D The bell crank, as follows: Ft. In. 0 42 0 23 0 21 10 6 2 11 0 16 MR. VALANCE'S NEW MODE OF CONVEYANCE. Sir, I am sorry I have been so long prevented from answering Vindex's observations (See page 252, No. 190,) on my opinion of Mr. Vallance's Mode of Conveyance. (Page 194 of your 188th Number.) If I were inclined to shuffle away from the arguments of the case, and attempt to convince without proof, I might justly reply to Vindex by placing my bare assertion against his, and say, that Mr. V.'s mode of conveyance has no advantage, in point of time, over that in use at Newcastle (and perhaps your readers would believe me as readily as Vindex), there being no sort of proof on either side. one What I maintain is this-that Mr. Vallance cannot drive his carriage along at the rate of 100 miles per hour, with a less expense of - power, than would draw the Newcastle carriages at the same rate, being equally loaded; and this I hope to prove. But, in the first place, I must dare to differ from that learned major of engineers, Chevalier Couling, &c. &c., who (p. 33, No. 178,) considers it". of the peculiar advantages of Mr. V.'s method, that it admits of the wheels of the vehicles which move in the cylinder, being several times larger than the wheels of carriages which run on roads," &c. &c. Now, how large wheels can be more easily employed in a tunnel than out of one, is more than my narrow intellects can take in, and I feel lost in wonder and amazement at the acuteness of this Russian Chevalier. Supposing, then, that it is possible to have as good a rail-road, and as large wheels out of a tunnel as in one, I shall consider the carriages 307 similarly situated in that respect, only imagining the one to be drawn by a rope, the other in the tunnel to be pumped along. Let them then be equally loaded; for example, let the carriage and load = 9,000 lbs., then 1 if the traction be part of the 300 load, which I believe is about the thing, a power of 30lbs, would keep the carriage in motion. In the first case, acting at the end of a rope :Suppose the carriage to go at the rate of 10 miles per hour, it requires a power of 30 lbs. raised 10 miles in an hour 30 lbs. raised 880 feet = per minute 26,400lbs. raised one foot in a minute, which (reckoning 30,000 lbs. to equal a horse power) is 7 about of a horse. Now, for the carriage in the tunnel, a power of 30 lbs. is also required to move this; but this 30 lbs. is to be produced by the pressure of the atmosphere on the end of the carriage; if the tunnel be seven feet in diameter, this pressure must be 14 drams on the square inch; now this pressure is produced by an air-pump at the other end of the tunnel, and if the air-pump is of no greater diameter than the tunnel, it is clear the piston must travel at the same rate with the carriage to keep up the necessary rarefaction, which, in this instance, is 1·4 drams per square inch, and is therefore equal to a pressure of 30 lbs. on the piston of the air-pump; which 30 lbs. raised 10 miles per hour, equals as before 26,400 lbs. 1 foot per minute, which is the same power as the other plan required. Now, suppose it necessary to double the speed of the carriages, the draught of the carriages, it is well known, does not increase with the speed; I, therefore, only want to pull my rope with a force of 30lbs., but must pull twice as far in the same time, or 30 lbs. raised 20 miles per hour, requires a power of 52.800 lbs. raised one foot high per minute, or 1 horse power, being double the former estimate. But how is it with the tunnel? The same pressure per square inch on the end of the carriage is sufficient; but to maintain the vacuum before the carriage moving at this rate, the ་ piston of the air-pump must either move twice as fast as before, or the area of the pump be doubled, either of which alterations (as there would be the same pressure of 14 drams per square inch on the area of the piston) would plainly require double the former power to work them. I therefore ask again, what advantage has Mr. V.'s plan over that in use at Newcastle? Has it not, on the contrary, decided disadvantages, enormous expense in construction, loss of power by friction of pumps, leakage, and loss of air round the carriage, &c.? But supposing it carried into effect, I suspect but few of Vindex's four millions would so far prefer this mode of travelling, as to submit to be immured in a dismal vault, squeezed in a close carriage, excluded from the cheering light of the sun, and forced patiently to submit to the -loss of the beautiful scenery around them. I remain, Your's sincerely, J. F. E. SIMPLE LEVELS. Then water was put in to fill the tube, and nearly both phials, by which it will appear, without further explanation, that the surface of water in both phials was a perfect and natural level, useful for many agricultural, read, and domestic purposes. When carried, the corks were put in the phials to the necks of which they were appended, but care must be taken that when used, both must be unstopped, or the two surfaces will not be level. To use the above, it is only necessary to strike the staff firm in the ground, no matter if it is awry, a little out of the perpendicular; then lodge the tube in it, in the direction wanted; no matter. also if this is awry or not quite horizontal, so that the two phials are in a line with the object wanted, and uncork the phials. Only note the perpendicular from either of the surfaces of water in the phials, which is the distance of the eye from the ground. In the sketch, (fig. 3) both staff and tube are placed as if by chance, yet showing the true level, proving what I consider its chief utility. A A represents the true horizontal line, B the height of the eye from the ground. I thought the water had better been tinctured with some colouring matter, as a Mr. Editor,-Some time ago, being on the continent, I observed some surveyors on the public works, taking the level of the grounds; the instrument they used appearing to me the simplest possible, I herewith send you a description of it, as I think many of your readers, particuor larly those in the country, may be benefited by so useful and extremely simple an instrument, for various purposes too numerous to mention. The principle part was a tin tube, the thickness of the finger or somewhat larger, bent up at both ends at right angles, like an elbow in a stove pipe (fig. 1.) Next, two phials with their bottoms beaten out, or off, and inserted one in each elbow of this said bent tube, which to make water-tight, were wound round the bottoms with thread exactly as one part of a german flute is fitted to the other when it is somewhat loose. A staff pointed at the bottom, had a gap sawn out as a crutch at top, just large enough few drops of ink, &c; but being a foreigner, I thought best not to interfere so far as to tell them so, I beg leave to add, that I saw this with mine own eyes, that I may be brought into no dispute; as was the case about my description of a constant, or perpetual pump, described to you in No. 93, which, though it had been working many years and now is, I expect, continuing the same, yet some unpolite correspondents of your's (pardon me if I use too harsh a term) without trying the experiment, actually pronounced it impossible. In travelling I endeavour to make use of my eyes, and have never yet found myself misled by trusting to them. Simple as is the above-mentioned level, I will suggest another of my own contrivance of a different kind; but whether more or less convenient than that already described, I leave others to decide. Form a pointed staff, making three or four horizontal holes in a vertical line, about the height of the eye from the ground when fixed, as fig. 4, so that a pin (the smaller the better) can be fixed in either as required: then take a piece of flat thick metal, or sheet-copper nailed on a board; or even seasoned board itself, though inferior; deal would 5 the middle of the upper arm, as a b in fig. 5, and another perpendicular thereto in the middle of the other arm cd, which can be easily done with a pair of beam compasses. At the lowest part of the latter, make a little hole for a thread to pass through, to hang a weight as at d, and at the angle of meeting e another hole to let the before-mentioned pin into, working freely. The weight below will therefore always keep the upper line ab perfectly horizontal; this therefore, is the true level, which may be used with a pair of sights like a rifle gun, or if preferred, a pair of sliding crosswire sights may be added; or if more simple, no sights at all, but using the line of the upper arm instead thereof, at the option of the |