in which the benefits of such economy are of less weighty import.  It needs nothing more than the establishment of an efficient system of registration in steam vessels, to insure a large and rapid economy in the consumption of fuel, as this quality would then become the test of an engineer’s proficiency, and would determine the measure of his fame.  In the case of the Cornish engines, a saving of more than half the fuel was speedily effected by the introduction of the simple expedient of registration.  In agricultural engines a like economy has speedily followed from a like arrangement; yet in both of these cases the benefits of a large saving are less eminent than they would be in the case of steam navigation; and it is to be hoped that this expedient of improvement will now be speedily adopted.

CHAPTER X.

EXAMPLES OF ENGINES.

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OSCILLATING PADDLE ENGINES.

618. Q.—­Will you describe the structure of an oscillating engine as made by Messrs. Penn?

A.—­To do this it will be expedient to take an engine of a given power, and then the sizes may be given as well as an account of the configuration of the parts:  we may take for an example a pair of engines of 21-1/2 inches diameter of cylinder, and 22 inches stroke, rated by Messrs. Penn at 12 horses power each.  The cylinders of this oscillating engine are placed beneath the cranks, and, as in all Messrs. Penn’s smaller engines, the piston rod is connected to the crank pin by means of a brass cap, provided with a socket, by means of which it is cuttered to the piston rod.  There is but one air pump, which is situated within the condenser between the cylinders, and it is wrought by means of a crank in the intermediate shaft—­this crank being cut out of a solid piece of metal as in the formation of the cranked axles of locomotive engines.  The steam enters the cylinder through the outer trunnions, or the trunnions adjacent to the ship’s sides, and enters the condenser through the two midship trunnions—­a short three ported valve being placed on the front of the cylinder to regulate the flow of steam to and from the cylinder in the proper manner.  The weight of this valve on one side of the cylinder is balanced by a weight hung upon the other side of the cylinder; but in the most recent engines this weight is discarded, and two valves are used, which balance one another.  The framing consists of an upper and lower frame of cast iron, bound together by eight malleable iron columns:  upon the lower frame the pillow blocks rest which carry the cylinder trunnions, and the condenser and the bottom frame are cast in the same piece.  The upper frame supports the paddle shaft pillow blocks; and pieces are bolted on in continuation of the upper frame to carry the paddle wheels, which are overhung from the journal.

619. Q.—­What are the dimensions and arrangement of the framing?