ox, set 3 inches in advance of the centre of the
shaft, and in the same horizontal line. This pin is encircled by a cast
iron collar, to which rods are attached 1-3/8 inch diameter in the centre,
proceeding to the levers, 7 inches long, fixed on the back of the floats in
the line of the outer arms. One of these rods, however, is formed of nearly
the same dimensions as one of the arms of the wheel, and is called the
driving arm, as it causes the cast iron collar to turn round with the
revolution of the wheel, and this collar, by means of its attachments to
the floats, accomplishes the feathering action. The eccentricity in this
wheel is not sufficient to keep the floats in the vertical position, but in
the position between the vertical and the radial. The diameter of the pins
upon which the floats turn is 1-3/8 inch, and between the pins and paddle
ring two stud rods are set between each of the projecting ends of the arms,
so as to prevent the two sets of arms from being forced nearer or further
apart; and thus prevent the ends of the arms from hindering the action of
the floats, by being accidentally jammed upon the sides of the joints.
Stays, crossing one another, proceed from the inner flange of the centre to
the outer ring of the wheel, and from the outer flange of the centre to the
inner ring of the wheel, with the view of obtaining greater stiffness. The
floats are formed of plate iron, and the whole of the joints and joint pins
are steeled, or formed of steel. For sea-going vessels the most approved
practice is to make the joint pins of brass, and also to bush the eyes of
the joints with brass; and the surface should be large to diminish wear.

634. _Q._--Can you give the dimensions of any other oscillating engines?

_A._--In Messrs. Penn's 50 horse power oscillating engine, the diameter of
the cylinder is 3 feet 4 inches, and the length of the stroke 3 feet. The
thickness of the metal of the cylinder is 1 inch, and the thickness of the
cylinder bottom is 1-3/4 inch, crossed with feathers, to give it additional
stiffness. The diameter of the trunnion bearings is 1 foot 2 inches, and
the breadth of the trunnion bearings 5-1/2 inches. Messrs. Penn, in their
larger engines, generally make the area of the steam trunnion less than
that of the eduction trunnion, in the proportion of 32 to 37; and the
diameter of the eduction trunnion is regulated by the internal diameter of
the eduction pipe, which is about 1/5th of the d