this balance piston two faults were committed.  The passage communicating between the condenser and the top of the balance piston was too small, and the pins at the ends of the link connecting the valve and balance piston were formed with an inadequate amount of bearing surface.  It followed from this misproportion that the balance piston, being adjusted to take off nearly the whole of the pressure, lifted the valve off the face at the beginning of each stroke.  For the escape of the steam into the eduction passage momentarily impaired the vacuum subsisting there, and owing to the smallness of the passage leading to the space above the balance piston, the vacuum subsisting in that space could not be impaired with equal rapidity.  The balance piston, therefore, rose by the upward pressure upon it momentarily predominating over the downward pressure on the valve; but this fault was corrected by enlarging the communicating passage between the top of the balance piston and the eduction pipe.  The smallness of the pins at the ends of the link connecting the valve and balance piston, caused the surfaces to cut into one another, and to wear very rapidly, and the pins and eyes in this situation should be large in diameter, and as long as they can be got, as they are not so easily lubricated as the other bearings about the engine, and are moreover kept at a high temperature by the steam.  The balance piston is packed in the same way as the main piston of the engine.  Its cylinder, which is only a few inches in length, is set on the top of the valve casing, and a trunk projects upwards from its centre to enable the connecting link to rise up in it to attain the necessary length.

[Illustration:  Fig 52.  CONNECTING ROD.  Messrs. Bourne & Co.]

647. Q.—­What is the diameter of the piston rods and connecting rod?

A.—­The piston rods, which are two in number, are 3 inches diameter, and 12 feet 10 inches long over all.  They were, however, found to be rather small, and have since been made half an inch thicker.  The connecting rod consists of two rods, which are prolongations of the bolts that connect the sides of the brass bushes which encircle the crank pin and cross head.  The connecting rod is shown in perspective in fig. 52.  The rods composing it are each 2-3/4 inches in diameter.

648. Q.—­Will you describe the configuration of the cross head.

A.—­The cross head, exhibited in fig. 53, is a round piece of iron like a short shaft, with two unequal arms keyed upon it, the longer of which b works the air pump, and the shorter c works the feed pump.  The piston rods enter these arms at a A. The cross head is 8 inches diameter where it is embraced by the connecting rod at e, and 7 inches diameter where the air pump and feed pump arms are fixed on.  The ends of the cross head d d, for a length of 12 inches, are reduced to 3 inches diameter where they fit into