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dredge earth, and blow furnaces. The subject, however, is so important that I shall here recapitulate other cases for the most part derived from experiments made with the dynamometer in France by General Morin,* whose researches on this subject have been highly interesting, and have been conducted with much care and ability.

Comparative efficiency of different machines for raising water. -Of the different pumps experimented upon by General Morin, the result of eight experiments made with pumps draining mines showed that the effect utilised was 66 per cent. of the power expended. But in these cases there was considerable loss from leakage from the pipes. At the salt works of Dreuze the useful effect was 52.3 per cent. of the power expended. In fire-engine pumps employed to deliver the water pumped at a height of from 12 to 20 feet, the proportion of the water delivered to the capacity of the pump was, in the pumps of the following makers -Merryweather, Tylor, Perry, Carl-Metz, Letestu, Flaud, and Perrin, respectively, as follows:-920, ·887, 910, 974, ·910, 920, and ·900; while the percentage of useful effect relatively with the power expended was 39.7, 39′1, 30·2, 28·7, 27·1, 19′4, and 15.5, respectively. With a higher pressure, the efficiency of the whole of the pumps increased; and when employed in throwing water with a spout-pipe the delivery of water relatively with the effective capacity, or space described by the piston, was, when the names are arranged, as follows:-Carl-Metz, Merryweather, Tylor, Letestu, Perry, Flaud, Perrin, and Lamoine, respectively, ·950, 810, 565, 870, 910, 912, 950, and 900; while the proportion of useful effect, or percentage of work done relatively with the power expended, was 80, 57′3, 54.5, 45·2, 37·8, 33·4, 28.8, and 17.5, in the respective cases. In the membrane pump of M. Brûle the efficacy was found to be 40 to 45 per cent. of the power expended. In the water-works pumps of Ivry, constructed by Cavé, the efficiency was found to be 53 per cent. of the power expended; and in the water-works of St. Ouen, by the same maker, 76 per cent. It is desirable that the buckets of the pumps of water-works should move slowly, otherwise the Aide Mémoire by General Morin, 5th edition, 1864.

water will go off with considerable velocity, involving a corre sponding loss of power. The area through the valves should be half the area of the pump, and the area of the suction and forcing pipes ought to be equal to three-fourths of the area of the body of the pump. Waste spaces should be avoided. The loss of water through the valves before they shut is, in good pumps, about 10 per cent.

In a chain-pump the efficiency was found to be 38 per cent., but in many chain-pumps the efficiency is much more than this. The efficiency of the Persian wheel was found to increase very much with the height to which the water was raised. For heights of 1 yard it was 48 per cent., for 2 yards 57, for 3 yards 63, for 4 yards 66, and for 6 yards and upwards 70 per cent. of the power consumed. For a wheel of pots the efficiency is 60 per cent.; Archimedes screw, 65 per cent.; scoop wheel with flat boards moving in a circular channel, 70 per cent.; improved bucket wheel, 82 per cent., and tympan-wheel, or, as it is sometimes called, Wirtz's Zurich machine, 88 per cent. This machine should dip at least a foot into the water to give the best results. In the belt-pump the efficiency was found to be 43 per cent.; in Appold's centrifugal pump, 65 per cent.; in the centrifugal pump, with inclined vanes, 42 per cent., and with radial vanes, 24 per cent. In Gwynn's pump the efficiency was 30 per cent.

In the Archimedes screw the diameter is usually one-twelfth of the length, and the diameter of the newel or central drum should be one-third of the diameter of the screw. It ought to have at least three convolutions, and the line traced by the screw on the enveloping cylinder should have an angle of 67° to 70° with the axis. The axis itself should make an angle of from 30° to 45° with the horizon. There is a sensible advantage obtained from working hand-pumps by a crank instead of a lever.

Old French Flour Mill at Senelle.-Diameter of millstones, 70 inches; number of revolutions per minute, 70; quantity of corn ground and sifted per hour, 260-7 lbs. ; power consumed, 3.34 horses. The power is in all cases the power actually exert d, as ascertained by the dynamometer.

English Flour Mill near Metz.—Diameter of millstones, 51 18

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inches; number of revolutions per minute, 110; weight of millstones, 1 ton; corn ground per hour by each pair, 220 lbs.; with two pairs of millstones acting, one bolting machine and one winnowing machine, the power consumed was 8 horse-power.

English Flour Mill near Verdun.-Diameter of millstones, 51.18 inches; number of revolutions per minute, 110; quantity of corn ground per hour by each pair, or by each revolving millstone, 220 lbs. ; with two stones revolving the power consumed was 5.64 horses. The power consumed by one winnowing machine and two bolting machines, with brushes sifting 1,650 lbs. of flour per hour, was 6 horses. In another mill the number of turns of the millstone was 486 per minute, the quantity of corn ground by each horse-power was 120 lbs., and the quantity of corn ground per hour was 110 lbs. of which 72.7 per cent. was flour, 7.8 per cent. was meal, and 19.5 per cent. was bran. In a portable flour-mill, with machinery for cleaning and sifting, the total weight was 1,000 lbs.

Barley Mill.-Number of revolutions of the millstone per minute, 246; barley ground per hour, 143.68 lbs. ; motive force in horses, 3.11; barley ground per hour by each horse-power, 48.2 lbs. The products were, of first and second quality of barley flour, 60.12 per cent., of meal and bran, 30-25 per cent., and of bran and waste, 9.63 per cent.

Rye Mill.-Number of revolutions of the millstone per minute, 448; rye ground per hour, 92-114 lbs.; power expended, 2.86 horses; temperature of flour, 60.8° Fahr.; products 64.9 per cent. of flour, 9.1 per cent. of meal, and 26 per cent. of bran. In another rye mill the revolutions of the millstones per minute were 232; rye ground per hour, 180 lbs. by 2.19 horse-power, and the rye ground per hour by each horse-power was 82.21 lbs. The products were 72.5 per cent. of flour; 17.5 per cent. of meal and fine bran, and 10 per cent. of bran and waste.

Maize Mill.-Number of revolutions of the millstone per minute, 246; maize ground per hour, 73.96 lbs.; motive force in horses, 2.69; maize ground per hour by each horse-power, 27.5 lbs. Products: first and second quality of flour, 61.1 per cent.; meal and fine bran, 30.2 per cent.; bran and waste, 4-7 per cent.

Vermicelli Manufactory.-External diameter of edge runners, 66.93 inches; internal diameter of edge runners, 62.99 inches; number of revolutions of the arbour of the mill per minute, 4; pounds of paste prepared per hour, 77 lbs. ; power expended, 2.95 horse-power.

Bean Mill.-Number of revolutions of the millstone per minute, 496; power expended per hour, 1·76 horse.

Oil Mill.-Weight of edge runners, 6,600 lbs.; number of turns of the vertical spindle per minute, 6; weight of seed introduced every ten minutes, 55 lbs.; weight of seed crushed daily, 3,300 lbs.; product in oil in 12 hours, 1,320 lbs. ; power expended, 2.72 horses.

Saw Mill--Weight of the saw frame, 842-6 lbs. When cutting dry oak 8.73 inches thick, with 1 blade in operation, the reciprocations or strokes of the saw were, 88 per minute, the surface cut, 525 square foot, and the power expended 3.3 horses. When cutting the same wood with 4 blades in operation, the number of strokes of the saw per minute was 79; the surface cut by each per minute ·433 square foot, or 1·73 square foot per minute for the 4; and the power expended was 3.70 horses, which is equivalent to 28 square feet cut per hour by 1 horse-power. When cutting four-year seasoned oak, 12-4 inches thick, with 4 blades, making 90 strokes per minute, the surface cut by each blade was 35 square foot, and the surface cut by the 4 blades, 1·41 square foot. When the saw was run along the middle of a cylindrical log of beech one-year cut, 23.6 inches diameter, the number of strokes of the saw per minute was 88; the surface cut per minute, •968 square foot; and the power expended, 3 horses. In these experiments the breadth of the saw cut was 157 inch, and the experiments show that it does not take more power to drive a frame with one saw than to drive a frame with four, the greatest part of the power indeed being consumed in giving motion to the frame. The common estimate in modern saw mills, when the frame is filled with saws, is, that to cut 45 superficial feet of pine, or 34 of oak per hour, requires 1 indicated horse-power. The crank, which moves the frame up and down, and which is usually placed in a pit under the machine, should have balance

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weights applied to it, the momentum of which weights, when the saw is in action, will be equal to that of the reciprocating frame. In some cases the weight of the saw frame is borne by a vacuum cylinder, and with a 20-inch stroke it makes 120 strokes per minute.

Circular Saw.-Diameter of saw, 27.5 inches; thickness of oak cut, 8.73 inches; number of revolutions per minute, 266; surface cut per minute, 1·93 square foot; power consumed 3·55 horses. When set to cut planks of dry fir, 10.62 inches broad, and one inch thick, the number of revolutions made by the saw per minute was 244; surface cut per minute, 7·67 square feet; and the power expended, 7.35 horses. These results show that in sawing the smaller class of timber one circular saw will do at least as much work as four reciprocating saws, with the same expenditure of power. The surface cut is, in all these cases, understood to be the height multiplied by the length, and not the sum of the two faces separated by the saw. The speed of the circular saw here given is not half as great as that now commonly employed. Circular saws now work with a velocity at the periphery of 6,000 to 7,000 feet per minute, and band saws with a velocity of 2,500 feet per minute, and it is generally reckoned that 75 superficial feet of pine, or 58 of oak, will be sawn per hour by a circular saw for each indicated horse-power expended. Planing machine cutters move with a velocity at the cutting edge of 4,000 to 6,000 feet per minute, and the planed surface travels forwardth of an inch for each cut.

Reciprocating Veneer Saw.-Length of stroke of saw, 47.24 inches; thickness of the blade, 01299 inch; breadth of saw cut, 02562 inch; length of teeth for mahogany and other valuable woods, 196 inch; pitch of the teeth, 3939 inch; distance advanced by the wood each stroke, 0196 to 03937 inch; number of strokes of the saw per minute, 180; surface cut per hour counting both faces, 107.64 square feet; power expended 0·66 horses.

Sawing Machine for Stones.-Soft sandstone: breadth of sawcut, inch; time employed to saw 10 square feet, 5 minutes 25 seconds; power expended 4.54 horses. Hard sandstone: breadth