train if all thrown
upon the end of the pin will be equal to the elastic force; but in ordinary
working, the strain will only be equal to 1/3d of the elastic force.

365. _Q._--What are the dimensions of the cross head?

_A._--If the length of the cross head be taken at 1.4 times the diameter of
the cylinder, the dimensions of the cross head will be as follows:--the
exterior diameter of the eye in the cross head for the reception of the
piston rod, will be equal to the diameter of the hole, plus 0.02827 times
the cube root of the pressure on the piston in lbs. per square inch,
multiplied by the diameter of the cylinder in inches; and the depth of the
eye will be 0.0979 times the cube root of the pressure on the piston in
lbs. per square inch, multiplied by the diameter of the cylinder in inches.
The diameter of each cross head journal will be 0.01716 times the square
root of the pressure on the piston in lbs. per square inch, multiplied by
the diameter of the cylinder in inches--the length of the journal being
9/8ths its diameter. The thickness of the web at centre will be 0.0245
times the cube root of the pressure on the piston in lbs. per square inch,
multiplied by the diameter of the cylinder in inches; and the depth of web
at centre will be 0.09178 times the cube root of the pressure on the piston
in lbs. per square inch, multiplied by the diameter of the cylinder in
inches. The thickness of the web at journal will be 0.0122 times the square
root of the pressure on the piston in lbs. per square inch, multiplied by
the diameter of the cylinder in inches; and the depth of the web at journal
will be 0.0203 times the square root of the pressure upon the piston in
lbs. per square inch, multiplied by the diameter of the cylinder in inches.
In these rules for the cross head, the strain upon the web is 1/2.225 times
the elastic force; the strain upon the journal in ordinary working is
1/2.33 times the elastic force; and if the outer ends of the journals are
the only bearing points, the strain is 1/1.165 times the elastic force,
which is very little in excess of the elastic force.

366. _Q._--How do you find the diameter of the main centre when
proportioned according to this rule?

_A._--The diameter of the main centre may be found by multiplying 0.0367
times the square root of the pressure upon the piston in lbs. per square
inch, by the diameter of the cylinder in inches, which will give the
diameter of the main centre jo