miles an hour, will, on an average, raise about 150 lbs. by a cord hanging over a pulley; which is equivalent to 33,000 lbs. one foot high in a minute. Boulton and Watt estimate this at 32,000. Tredgold, still lower, at 27,500. Taking the first measure, however, as a basis of comparison; putting d for the diameter of the piston in inches, p for the pressure of the steam "pon each square inch (diminished usually by about for friction and inertia), 7 for the length of the stroke of the piston in feet, n for the number of strokes in a minute: then the power of the engine in "Horse-powers" (H P), is

(HP) = '0000238 d2 n p l, if it be a single stroke

HP =

0000476 d n p l, if it be a double stroke engine. Example. Suppose d= 20 inches, l = 3 feet, n = 36, p = 50, and the engine one of double stroke.

Then

0000476 x 20 x 36 x 50 × 3 = 102 816, or nearly 103 horse-powers, the measure of the energy of the engine.

Mr. Boulton states that 1 bushel of Newcastle coals, containing 84 pounds, will raise 30 million pounds 1 foot high; that it will grind and dress 11 bushels of wheat; that it will slit and draw into nails 5 cwt. of iron; that it will drive 1000 cotton spindles, with all the preparation machinery, with the proper velocity; and that these effects are equivalent to the work of 10 horses.

18. The rule usually given to adjust the weight of the flywheel is this:

Multiply the number of Horse-powers in the machine by 2000; divide the product by the square of the velocity in feet, per second, of the fly's circumference; the quotient will give its weight in hundred-weights.

Thus, suppose the fly-wheel of a 20 horse-power engine to be 18 feet diameter, and to revolve 22 times in a minute ; what should be its weight?

CHAPTER XIV.

USEFUL TABLES AND REMARKS ON STEAM-ENGINES, RAIL-ROADS, CANALS, AND TURNPIKE-ROADS.

TABLE I.-Quantity of Coals equivalent to the horse power of 33,000 lbs. raised one foot per minute in high pressure, steam-engines, when the greatest possible effect is obtained.

TABLE II.-Quantity of Coals equivalent to the horse power of 33,000 lbs. raised one foot per minute in condensing steam-engines, when the greatest possible effect is obtained.

• The curious tables here given, marked I. II. III., were extracted, with the author's permission, from Mr. Tredgold's work on Rail-roads.

Remarks on Tables I, and II.-The columns showing the pounds an engine ought to raise one foot high, by the heat of one bushel of coals, are added chiefly for the purpose of com parison with actual practice. Now, it is stated, that after the most impartial examination for several years in succession, it i found that Woolf's engine at Wheal Abraham Mine, raised 44 millions of pounds of water, one foot high, with a bushel of coals. And," the burning of one bushel of good Newcastle or Swansea coals, in Mr. Watt's reciprocating engines, working more or less expansively, was found, by the accounts kept at the Cornish mines, to raise from 24 to 32 millions of pounds of water one foot high; the greater or less effect depending upon the state of the engine, its size, and rate of working, and the quality of the coal."

We shall further add the results of half a year's reports taken, without selection, from Lean's Monthly Reports on the work performed by the steam-engines in Cornwall, with each bushel of coals. The numbers show the pounds of water raised one foot high with each bushel, from January to June, 1818.

22 to 25 Common En-
gines average
Wheal Vor (Woolf's
Engine)

Wheal Abraham (ditto)
Ditto

January. February. March. April. May.

June.

lbs. raised lbs. raised lbs. raised lbs. raised lbs. raised lbs. raised

one foot. one foot. one foot. one foot. one foot. one foot.

22,188,000 22,424,000 21,898,000 22,982,000 23,608,000 23,836,000

30,834,000 26,158,000 29,511,000 26,064,000 29,032,000 30,336,000 41,847,000 35,364,000 30,445,000 32,723,000 31,520,000 34,352,000 (ditto) 27,942,000 28,000,000 26,978,000 23,626,000 29,702,000 34,846,000 Wheal Unity (ditto) 31,900,000 32,306,000 Dalcouth Engine

Wheal Abraham Engine
United Mines Engine
Treskirby Egnine
Wheal Chance Engine

42,622,000 41,354,000 40,499,000 41,888,000 38,233,000 38,143,000 32,239,000 36,180,000 35,715,000 33,934,000 33,714,000 34.291,000 36,396,000 31,830,000 31,427,000 33,564,000 33,967,000 30,105,000 38,733,000 39,375,000 41,867,000 41,823,000 40,615,000 42.098,000 28,49€,000 32,319,000 33,594,000 33,932,000 |

35.797.000

These numbers are less than the immediate power of the engines, by the friction and loss of effect in working the pumps; hence in comparing them with Mr. Tredgold's table, it may be inferred that he made his calculations from such data as can be realized in practice. It is known from experience, that a cubic foot of water can be converted into steam equal in force to the atmosphere, with 7 lbs. of Newcastle coals; but we also know the attention necessary to produce that effect, and therefore have assumed that 8 lbs. will be required for that

purpose.

According to Mr. Lean's Monthly Report, for January, 1833, the following engines raise more than 50 millions of pounds, one foot high, by consuming a bushel of coals:

Of the above, the engine of greatest operation, the first at Wheal Vor, raises the water 190 fathoms, at 7 lifts, drawing perpendicularly 160 fathoms, and the remainder diagonally. Main beam over the cylinder; stroke in the cylinder 10 feet; one balance-bob at the surface, and three underground.

TABLE III.-Showing the effects of a force of traction of 100 lbs. at different velocities, on canals, rail-roads, and turnpike-roads.* (From Tredgold.)

This table is intended to exhibit the work that may be performed by the same mechanical power, at different velocities, on canals, rail-roads, and turnpike-roads. Ascending and descending by locks or canals, may be considered equivalent to the ascent and descent of inclinations on rail-roads and turnpikeroads. The load carried, added to the weight of the vessel or carriage which contains it, forms the total mass moved; and the useful effect is the load. To find the effect on canals at different velocities, the effect of the given power at one velocity being known, it will be as 32: 2.52 :: 55,500: 38,542. The mass moved being very nearly inversely as the square of the velocity at least, within certain limits.

This table shows, that when the velocity is 5 miles per hour, it requires less power to obtain the same effect on a railway than on a canal; and the lower range of figures is added to show the velocity at which the effect on a canal is only equal to that on a turnpike-road. By comparing the power and tonnage of steam-vessels, it will be found that the rate of decrease of power by increase of velocity, is not very distant from the

* Though the force of traction on a canal varies as the square of the velocity; the mechanical power necessary to move the boat is usually reckoned to increase as the cube of the velocity. On a rail-road or turnpike the force of traction is constant; but the mechanical power necessary to move the carriage increases as the velocity.