Divide the thickness of the plate, in inches, by the square root of the pressure, in lbs. per square inch, and. multiply the quotient by 130, if the stayed surface is copper; by 164, if the stayed surface is wrought iron; by 212, if the stayed surface is steel.

Suppose the fire-box of a boiler is to be made of steel plates, 3/8 of an inch thick, and the pressure of steam is to be 100 lbs. per square inch.

Divide 0.375 by 10, and multiply the quotient, 0.0375, by 212; which gives 7.95, say 8 inches, as the proper distance between stays. B.

Note.-The rules for stayed surfaces and flat boiler-heads are adapted from methods explained by Dr. Grashof in "Die Festigkeitslehre, " Berlin, 1866.