FOOTNOTES:

[24] If 22 square inches of piston surface be allowed to represent a horse-power, the power of an engine may always be computed by dividing the square of the diameter of the piston expressed in inches by 28. And, on the other hand, to find the diameter of piston which would correspond to any given power, multiply the number of horses' power by 28, and take the square root of the product. These rules, however, cannot be applied if the piston be supposed to move with any other velocity; since, in that case, the same amount of piston surface would cease to represent a horse-power, unless the effective pressure on the piston were at the same time changed.

WATT'S CHAPEL IN HANDSWORTH CHURCH.