By the aid of the accompanying table, the effective horse-power (that available for useful work) of small engines can be approximately determined. The table is designed for non-condensing engines, with cylinders up to (i inches in diameter, and for piston-speeds up to 400 feet a minute; the connection of the engine with the boiler being sup-posed to be tolerably direct, the ports and pipes being of sufficient sizes, and the Steam-valve closing when the piston has made three quarters of the stroke. As the table is designed for average conditions, it is evident that it will give results that are too large in some cases, and too small in others.

I.- To find the horse- power of an engine corresponding to a given diameter of cylinder, length of stroke, number of revolutions per minute, and pressure of steam in the boiler. (1) Multiply the Length of stroke in inches by the number of revolutions per minute, and divide the product by 6. The result is the piston-speed in feet per minute. (2) Find the number in the table the Dearest to the given steam pressure and Calculated piston speed, and multiply it by 0. 7854 times the square of the diameter of the piston in inches. Example: An engine has a cylinder 2 inches in diameter, and a length of stroke of 2 inches. It makes loo revolutions a minute, and the boiler pressure is 50 pounds per square inch. Ans.: Twice 400 is 800. 800 divided by 6 is 133-1/3, the piston-speed in feet per minute. (3) The nearest piston-speed in table Effective Horse-Power of am Engine with a Piston One Square Inch in Area, for different Steam-Pressures and is 130 feet, and the number in table corresponding to speed of 100 and pressure of 50, is 0.074 ; the number for speed of 30 and same pressure is 0.022 ; required number is sum of 0.074 and 0.022, or 0.096, corresponding to speed of 130 and pressure of 50. The product of 4 and 0.7854 is 3.1416, and the product of 0.096 and 3.1416, or the required horse-power, is 0.3+.