To find the horse-power which a shaft of a given diameter will transmit, multiply the cube of the diameter in inches by its revolutions per minute and divide by 92 for steel shafts and by 190 for wrought iron shafts. The quotient is the horse-power. To find the revolutions per minute necessary for a shaft to transmit a given horsepower, multiply the given horse-power by 92 for steel and 190 for wrought iron and divide the product by the cube of the diameter of the shaft expressed in inches. The quotient is the required revolutions of the shaft per minute.

Considerable power is lost by the use of shafting and the average loss would be about as follows. For each 100 H. P. generated, 10 H. P. is consumed by the friction of engine, 15 H. P. by the line-shafting, 15 H. P. by the belts and pulleys, 15 H. P. by non-productive machinery, and only 45 H. P. goes for productive work. Therefore every effort is made to reduce friction and waste to a minimum, and shafts are usually adjusted every ten or twelve hours.