To Compute the mean Pressure of Steam upon a Piston by Hyperbolic Logarithms..

Rule

Divide the length of the stroke of a piston, added to the clearance in the cylinder at one end, by the length of the stroke at which the steam is cut off, added to the clearance at that end, and the quotient will express the relative expansion of the steam or number.

Find in the table the logarithm of the number nearest to that of the quotient, to which add 1. The sum is the ratio of the gain.

Multiply the ratio thus obtained by the pressure of the steam (including the atmosphere) at it enters the cylinder, divide the product by the relative expansion, and the quotient will give the mean pressure required.