d2 v

---- = horse's power ; d representing diam. of cylinder in inches, and 8000 v the velocity of the piston in fret per minute.

This is alike to the rule of the British Admiralty, substituting 3000 for 6000, and it is based upon a uniform steam pressure of 10 bs. per square inch (steam gauge, or above the pressure of the atmosphere), cut off at one-half the stroke, deducting one-fifth* for friction and losses, with a mean Telocity of piston of 260 feet per minute for an engine of long stroke, and of 200 feet for one of short stroke.

* The friction and losses in a marine engine may be taken at 1'5 to 2 lbs. per squire inch for working the engine, and 6 to 7½ per cent, upon the remainder for the friction of the load.

The rule of the British Admiralty is based upon a uniform and effective pressure of 7 lbs. per square inch at full stroke, and a mean velocity of piston of 205 feet per minute: vis., 170 feet for a stroke of 2-5 feet, and 240 feet for a stroke of 8 feet.