the teeth of an arched head of the ong lever, called the working beam: but the most efficacious of all contrivances of this kind, is that of Watt, commonly called the parallel motion This contrivance is founded on geometrical principles, which it would be inconsistent with the plan of this work to consider; we shall therefore simply describe the contrivance of this illustrious mechanic. The working beam has an alternating circular motion ound its centre A, and it is clear that the points B and G ill have a circular motion round the common centre A. et the point B be exactly in the middle, between the centre and end of the beam. Let there be a bar or rod CD, of the same length as AB, capable of moving round the centre C, by means of a pivot. The other end of this rod is attached by means of a pivot, to the rod DB. Now, by the alternate rising and falling of the beam, the points D A B and D will move in circular arches, but the middle point P of the connecting rod BD, will move upwards and downwards in a vertical straight line, or at least so very nearly so, as the difference cannot be perceived. Now, to this point P, there is attached the end of the pump rod, which will, of course, follow the direction of the impelling point, and move in a straight line. For the purpose of communicating a similar motion to the other piston rod, conceive another rod CP' introduced, of the same length as BD, and its extremities moving likewise on pivots. The piston rod of the cylinder is attached to the point P', and this point moves quite in the same way as the point P. The only difference in the motion of these two points will be, that the point P' will move twice as fast as the point P, o will, in the same time, move twice as far. = The length of the links are made 4 to 5, the length of the stroke being 1, according to circumstances, the longer link being preferred when practicable. From the length of the links must be determined the position of the radius bar, for the vertical distance between the centres of motion of the working beam and the radius bar must be equal to the length of a link. When the parallel bar is not more than one-half of the working beam's radius, then, length of stroke, length of radius bar; we have B-2 PX (S)° B−√(B2 — [S]2) × 2 P +1= R. Suppose the length of the beam from the centre = 12 feet, the length of stroke 6, and of parallel bar 5 feet, that is, 6, and P = 5, then, = B = 12, S = 12 10 × (6)9 = 18 = the dividend; then, B — √(Bo — [S]o) × 2 P = 12 √(12o — [6]3) × 10 = 12 3.8 the divisor, wherefore, x 10 - 11.62 x 10 = 0.38 the length in feet of the radius bar. When the parallel bar is more than half the length of the radius of the beam, the rule is, by which rule it will be found that when the length of stroke and radius bar are each 6, and the radius of beam 10 feet, the length of radius bar will be 2.75 feet. Many rules have been given for the quantity of fuel necessary for the production of steam, but they cannot be depended on, so many circumstances must be taken under consideration-the quality of material used for fuel and the mode of constructing the fireplace. It has been found that 3 cwt. of Newcastle coals are equivalent to 4 cwt. of Glasgow coals, or 9 cwt. of wood, or 7 cwt. of culm. A chaldron of coals in London contains 36 bushels, and weighs 3136 lbs., or nearly 1 ton. 8 cw. It would appear, that in the common low-pressure steam engines, the consumpt of coal per hour for 1 horse power, is about 16 lbs., of wood 56 lbs., and of culm 35 lbs. These statements are given somewhat large, and by proper regulation much less fuel might serve. In the boiler there are certain proportions generally observed. The width, depth, and length, are as the numbers 1, 1∙1, 2.5. So that if the width be 5 feet, then the depth will be 1.1 x 5 12 ft. 6 in.; 5 feet 6 inches; and the length 5 × 2·5 = and the whole content of the boiler will be, 5 X 5.5 x 12.5 343 75 cubic feet. = Now Boulton and Watt allow 25 cubic feet of space in the boiler for each horse power; and according to this estimate, 13 and a fraction, the number of horses' power 343.75 25 = of this engine for which this boiler would be fitted. Some, instead of computing the size of boiler in this way, allow 5 square feet of surface of water for each horse's power; but in all cases, it is common to make the boiler of a size fitted for an engine of at least 2 horses' power more than that to which it is applied. There are two ways of loading the safety valve of a boiler; the one by placing a weight on the top of it, and the other by causing the weight to act on the valve by a lever. When the weight is placed upon the valve; area of valve pressure per square inch whole weight, and also whole weight area of valve = pressure per square inch. Thus, if a weight of 50 lbs. be placed upon a valve whose area is 10 inches, then the pressure per square inch is 50 10 = 5 lbs. pressure per square inch. When the weight acts by a lever, it is placed at one end the fulcrum being at the other, and the valve connected with the lever somewhere between them; this, then, is a simple case of the lever. Hence, if the length of the lever be 24 inches, the diameter of the valve 3 inches, (its area will be 7,) the distance between the fulcrum and the valve 3 inches, then to give 60 lbs. pressure per square inch on the valve 60 × 7 420 lbs. the whole pressure on the valve, and = 420 × 3 24- 3 60 lbs. will be the weight hung at the end of the lever to give the required pressure. To find the action of the weight of the lever divide its whole length by the distance of the valve from the fulcrum, and multiply the quotient by half the weight of the lever. The following rules for calculations connected with the steam engine are extracted from a useful little compendium lately published by Mr. Templeton, of Liverpool. These rules we have inserted here, not so much for their superior accuracy, as from a desire to present our readers with methods by which they may approximate to the true results. by means of the sliding rule. It is to be observed that the term gauge point is used to denote the number to be taken on the line stated in the rule. RULE.-Set the gauge point upon C to 1 upon D, and against the number of horses' power upon C, is the diameter in inches upon D; or, against the diameter in inches upon D, is the number of horses' power upon C. Ex. 1.-What diameter must a cylinder be with a 4 feet stroke, to be equal to 20 horses' power? Set 343 upon C to 1 upon D; and against 20 upon C is 24.2 inches diameter upon D.. Ex. 2. What number of horses' power will an engine be equal to, when the cylinder's diameter is 19 inches and stroke 3 feet? 192 × 7854 × 7.25 × 192 11.96 or 12 horses' power nearly. 394672-7328 33000 The proportion of parts of a high-pressure steam engine. The length of the stroke should, if possible, be twice its diameter. The velocity in feet per minute should be 103 times the square root of the length of the stroke in feet. And, as 4800 is to the velocity thus found, so is the area of the cylinder to the area of the steam passages. The proportions of the parts of an atmospheric engine. The length of the cylinder should be twice the diameter. The velocity in feet per minute should be ninetyeight times the square root of the length of the stroke in feet. The area of the steam passages will be as 4800 is to the velocity in feet per minute, so is the area of the cylinder to the area of the steam passage. If the area of the cylinder in feet be multiplied by half the velocity in feet, and that product by 1.23 added to 14 divided by the diameter in feet, the result divided by 1480 will give the cubic feet of water required for steam per minute. If the number of times the quantity of water required for injection must be greater than that required for steam, in general it will be about twelve times the quantity, but it had better be a little in defect than excess. The aperture for the injection must be such that the above quantity of water will be injected during the time of the stroke. In order that the injection be sufficiently powerful at first, the head should be about three times the height of the cylinder; and making the jet apertures square, the area should be the 850th part of the area of the cylinder. The conducting pipe should be about four times the diameter of the jet. The proportions of the parts of a single-acting lowpressure engine.-The length of the cylinder should be twice its diameter. The velocity of the piston in feet per minute should be ninety-eight times the square root of the length of the stroke. The area of the steam passages should be equal to the area of the cylinder, multiplied by the velocity of the piston in feet per minute, and divided by 4800.. The air pump should be one-eighth of the capacity of the cylinder, or half the diameter and half the length of the stroke of the cylinder, and the condenser should be of the same capacity. The quantity of steam will be found by multiplying the area of the cylinder in feet by half the velocity in feet; with an addition of one-tenth for cooling and waste, and this divided by the volume of the steam corresponding to its force in the boiler, gives the quantity |