12 inches stroke, which are placed about a foot before the hind axle. The two beams, about three feet long, extend backward across the hind axle, and they move on a joint or fixed point at the back end, so that the lifting rod which passes down to a crank on the axle will make a stroke of about nine inches. The cylinders, beams, and other working gear, are all above the level of the axle, and will exactly occupy a boot of the carriage, which, in this case, will be merely a cover for this part of the machinery. The boiler, the cistern, and steam-cylinders, are so placed as to balance one another on the opposite sides of the axle of the hind or large wheel, which will thus very properly sustain two-thirds of the weight. The carriage for the passengers is placed between the hind and fore wheels, but somewhat nearer the latter than is usual. Over the axle of the fore-wheels, but rather in a lower position than the driver usually occupies, sits the director or steerer, who, by means of a teethed circular rack aud a pinion, turns the axle of the fore-wheels to the right or left, and thus guides the motion of the vehicle. The machine is nearly completed, and will be brought to trial in a few days. "Those who have followed us will now have a tolerably accurate idea of this Steam Carriage. It is a stage-coach, with the machinery of a small double steam-engine stowed behind and below it-the water cistern being under the body of the coach, the cylinders and beams in the boot, and the boiler suspended behind the axle. A working rod passing down from the beam to a crank on the axle turns the hind wheels, which, in consequence of the great weight upon them, take a firm hold of the ground, and roll the machine forward. The fore-wheels, which are small, as in the common coach, roll without any application of steam power. Thinking, however, that in steep acclivities, the friction of both fore and hind wheels might be wanted, Mr. Burstall has contrived machinery for transmitting the motion of the hind wheels to the fore ones, which can be applied at any time, and plays idly when not needed. Our conviction is, that this part of the machinery will be found unnecessary, and, as it adds to the expense, friction, and weight, would have been better wanted. "The commou stage-coach weighs about a ton. The machinery in this vehicle, with the charge of water and coals (for a run of twenty miles) will, in the opinion of the engineer, add about a ton and a half; so that the Steam Coach, if loaded with twenty persons and luggage, would not weigh more than three tons and a half; every twenty miles the supply of water and coals will be required to be renewed, but this can be easily done in two or three minutes. "The engine, as in all the English locomotive machines,is on the high pressure principle. Its power is, of course, variable; but, with a free pressure of 15 lbs. it would be of three computed horses power, which would be equal to the efficient for one of seven or eight horses, running at eight miles an hour. This will, probably, be sufficient to give the Steam Coach the usual velocity of stage-coaches. But where the supply of fuel and water constitutes so considerable a part of the burden of the vehicle, economy in the use of these articles is of the first importance. Accordingly, it forms part of the engineer's plan to let more or less water into the boiler, as a greater or less force may be required. In going down a declivity, for instance, the steam will be entirely saved, and in going up an extra quantity will be used. The large wheels, we think, are about four feet and a half in diameter, or fourteen in circumference. Supposing the engine to make fifty double strokes per minute, this would give the machine a velocity of eight miles an hour. If the experiment succeed, the expense of fuel and attendance for an engine like this will be such a mere trifle,compared with the keep of sixteen horses, that the cost of travelling per coach to Glasgow, which is now about fourpence per mile, may certainly be reduced two-thirds. "Manydifficulties arise from the nature of the vehicle that have no existence in the steam-boat, and for which the artist has provided very ingeniously. As the wheels, for instance, move unequally in turning, and may sometimes be required to move backward, they are connected with the axle by a sort of bush with ratchet-work. Some of the pipes are twisted into a spiral, to give them the elasticity necessary to withstand the shocks occasioned by the jolting motion of the wheels on rough roads. He observed, however, that as to steam-carriages moving on common roads, we have nothing but theory to guide us, and that experience will discover defects which no skill can anticipate. The observation is just, and we were well pleased to find that a scheme so difficult was in the hands of SIR,-Some years ago, I joined two small Watch-Glasses, of the same diameter, in a bason of water, by pressing their edges together with my finger and thumb, so as to fill them completely. When taken out, I was then in possession of a single microscope, whose focal length being 3-16ths of the distance of distinct vision, magnified the surface of an object 25 times. It then occurred to me, that two such glasses cemented together, leaving a small aperture to fill them up with pure spirit, and cased in a small frame similar to the drawing, would form an instrument simple in construction, and excellent as a pocket companion, for the examination of minute objects, such as plants, insects, &c. For the purpose of holding objects to be examined, I place a brass pin, turning on a hinge, in the manner represented, on one side of the frame, and a forceps, with screw, on the other, both of such a length as to set exactly to the focus of the lens. There is a groove on each side of the frame to receive the pin and forceps when not used. One principal object ought to be, to make the frame sufficiently thick to protect the convexity of the glass-a small shagreen case would secure the whole. ( 394 ) WORK OF STEAM-ENGINES IN CORNWALL. From a Return of the Work performed by Fifty-nine Steam-Engines employed in the Cornish Mines, for July, 1825, it appears that six of them accomplished as follows: ADVANTAGE OF THE DOUBLE CYLINDER STEAM-ENGINE. [We have already inserted, p. 295, Vol. IV., an answer to the inquiry on this subject; we select from several other answers the two following, which furnish some useful explanations.-EDIT.] SIR,-Having observed a letter in a late Number of your Publication, requiring information relative to the advantage of applying Steam on Woolf's principle, and calling on any of "the first engineers" for assistance, allow me, through the same medium, to attempt a reply. Al though I by no means lay claim to the above rank, "mine being the last of all the families of Benjamin, and I the youngest in my father's house," I contemplate little difficulty in convincing our friend F. J-k-n, that an absolute advantage is derived by such application, which may be clearly demonstrated by practice or theory, mechanics or mathematics. with Let us proceed, and suppose, out entering into minute detail, that we have a single (or double) engine capacities of the cylinders being as on Woolf's principle, the relative 1 to 5 (which cylinders we will designate by a and b); we raise the steam in the boiler to the pressure of 50lb. per square inch; let us blow through, and then apply it to the top of a, whilst, at the same time, the valves at the bottom of a, and top of b, are opened; the steam which was below the piston of a rushes into the space above the piston of b, and expanding itself into five times the space it previously occupied, is, of course, reduced to 101b. per square inch, which acts with equal force on the top of b and bottom of a; therefore the effective force of the steam on the pistons may be stated at 50101b = 40lb. on a, and 10lb. on b, by which it is very evident, that a great addition of power is derived from raising steam to a high temperature in the boiler, and employing it in that state before reducing it to a common pressure. NEW IMPERIAL MEASURE. Whatever may be said of the principle, facts are stubborn things; by facts it may be, and is, clearly demonstrated in almost every case in which this plan has been adopted, and I feel assured this engine only requires to be fully known for its more general adoption; reflecting, as it does, infinite credit on the inventor, who, with mighty strides, has trod the paths of science, admirably improved this invaluable assistant, and given to the world the efforts of his genius. SIR,-In your instructive Magazine, Number 100, a Correspondent requests information relative to Woolf and Edwards's Steam Engines. The writer asks how the steam, after leaving the high pressure cylinder, gains its power to act on the low pressure one? "and further," Will not the steam serving the high pressure cylinder have as much power to resist the return of the high pressure piston, as it will to give action to the low pressure piston? I answer, if the two cylinders were of the same diameter, the fact 395 piston, on account of its having 90 square inches more to act upon. I believe these engines work with steam, first, upon the high pressure piston, at a pressure of about 50lbs. upon the square inch; and the first action of the steam upon the low pressure piston will be nearly of the same impetus-I say, the first action, because the pressure will vary as room is made for it to expand, by the ascent or descent of the low pressure piston. When it has expanded into the whole length of the large cylinder, it is by that means brought down to an ordinary pressure, say five or six pounds, upon the square inch (a proper temperature for condensation), which next takes place, and a vacuum produced, on the same principle as in a Watt's engine, by which a further gain of 10lbs. upon every square inch of the low pressure piston is effected, by working the steam over again. If you think the above will have any tendency to settle the controversy between your Westminsterbridge-road Correspondent and his fellow-workmen, your giving it a place in your useful miscellany will oblige, Your obedient servant, EDMUND FEARNLEY. would undoubtedly be as it has al- Shipley, near Bradford, Yorkshire. ways appeared to your Correspondent. But this is not the case. In these engines there are advantages, in having the low pressure cylinder eight or ten times the area of the high pressure one. When the steam leaves the high pressure cylinder, it acts with equal force upon the low pressure piston; but there will be a gain of power upon the latter, on account of its additional area. Let us, for example, suppose two cylinders; the high pressure one 10 inches area, and the low pressure one 100 inches area; the steam leaving the high pressure cylinder of 10 inches, is made to act upon the low pressure piston of 100 inches; and though there is the same resistance against the former as there is action upon the latter, yet it is evident, on well-known principles, there will be again of power upon the low pressure NEW IMPERIAL MEASURE. C B A SIR, I beg to offer a shorter solution of T. H.'s problem than your Cor respondent, Mr. Lake. Let s solid required, Rr, the greater and less radii of frustrum, FEh, GF = a, and DGE = 0. Now y ==Xx tan. is equation to generating line GD; but, by Differential Calculus, any solid of revolution = Respected Friend,--I have been much gratified by the perusal of your useful publication, but have received greater pleasure from no circumstance connected with it, than from that noble disinterestedness with which men of the same profession communicate their knowledge to each other. No sooner does a mechanic make known his ignorance of any particular subject, and express his desire to be informed, than generally there are several of his brother mechanics willing, and often eager, to give him the information which he requests. I should question if another instance could be found of men so ready to possess their goods in common, losing sight of all emolument and fame, and influenced by the pure motive of benefitting those who are but too often considered and treated as rivals in trade. In my youth I took great delight in mechanical and mathematical studies; and although I have, for many years, ceased to be a mechanic by profession, I well remember the pleasure with which I imparted whatever I had met with in books, acquired by study, or struck out by my own invention, to all who showed themselves desirous of being made partakers of what I considered a treasure. In those days I contrived many simple and easy rules," either for my own convenience or that of my friends, by which the labour of calculations, often recurring, was greatly abridged, or the operation put within the reach of such as were but little accustomed to apply mathematical investigations to mechanical principles. Some of these, which I have often found useful, and which at present recur to my remembrance, I shall subjoin, that, if you think them of sufficient importance to deserve a place in your Magazine, they may, through that medium, be transmitted to your very numerous class of readers. 1st. To find an equivalent for the power of a steam-engine, expressed in horse power. Let a horse power be equal to 200 pounds, raised at the rate of 25 miles per hour, as laid down by writers on that subject. Let a low-pressure engine, with a load of 10 pounds to the inch, work at the rate of 11 strokes per minute, 8 feet stroke. Then multiply the dia. meter of the piston by its circumference, and cut off two figures from the right hand of the product, we have the number of horses' power exactly. Example. Let the diameter of the cylinder be 28 inches, then will the circumference be 88 inches nearly, and 28 × 88 = 2464; whence the engine equals 24 horses' power. If the engine be supposed to move with the load of 10 pounds to the inch, at the rate of 200 feet per minute, find the power, as before, and increase it by 1-7th part of itself; thus, 24.64 + 24.64 28.16, equal 28 horses' power. 7 = If the engine work at the rate of 220 feet per minute with the same load, find the power as at first, and increase 24.64 it by part; thus, 24.64 + 30.7, equal 304 horses' power nearly. 2nd. To find the load, on the square inch, of an engine employed in pumping water. Divide 5 times the diameter of the cylinder; square the quotient, and pump by 4 times the diameter of the multiply by 5, and divide by 3 (or the pounds avoirdupois on each square annex a cipher, and divide by 6), gives inch of the piston for every fathom deep, exactly. Example.-Let a 40-inch cylinder draw a 10-inch bucket 50 fathoms deep. |