_To find diameter of a circle_ multiply circumference by .31831.
_To find circumference of a circle_, multiply diameter by 3.1416.
_To find area of a circle_, multiply square of diameter by .7854.
_To find surface of a ball_, multiply square of diameter by 3.1416.
_To find side of an equal square_, multiply diameter by .8862.
_To find cubic inches in a ball_, multiply cube of diameter by .5236.
_Doubling the diameter of a pipe_, increases its capacity four times.
_One cubic foot of anthracite coal_ weighs about 53 lbs.
_One cubic foot of bituminous coal_ weighs from 47 to 50 pounds.
_A gallon of water_ (U. S. standard) weighs 8-1/3 pounds and contains 231 cubic inches.
_A cubic foot of water_ contains 7-1/2 gallons, 1728 cubic inches and weighs 62-1/2 pounds.
_To find the number of pounds of water a cylindrical_ tank contains, square the diameter, multiply by .785 and then by the height in feet. This gives the number of cubic feet which multiplied by 62-1/2 gives the capacity in pounds of water. Divide by 7-1/2 and this gives the capacity in gallons.
_A horse-power_ is equivalent to raising 33,000 pounds 1 foot per minute, or 550 pounds 1 foot per second.
_The friction of water in pipes_ is as the square of velocity. The capacity of pipes is as the square of their diameters; thus, doubling the diameter of a pipe increases its capacity four times.
_To find the diameter of a pump cylinder_ to move a given quantity of water per minute (100 feet of piston being the standard of speed), divide the number of gallons by 4, then extract the square root, and the product will be the diameter in inches of the pump cylinder.
_To find the horse-power necessary to elevate water_ to a given height, multiply the weight of the water elevated per minute in pounds by the height in feet, and divide the product by 33,000 (an allowance should be added for water friction, and a further allowance for loss in steam cylinder, say from 20 to 30 per cent).
_To compute the capacity of pumping engines_, multiply the area of water piston, in inches, by the distance it travels, in inches, in a given time. Deduct 3 per cent for slip and rod displacement. The product divided by 231 gives the number of gallons in time named.