Not the least interesting particular of this engine is the thorough way in which the lubrication is carried out. Four of the bolts which attach the caps of the main bearings are prolonged through the bottom of the crank case, and serve to carry a detachable oil sump which holds sufficient oil for a run of six hours. As already mentioned, the oil pump is driven at twice the engine speed, and maintains a pressure of something like 110 pounds per square inch. It delivers directly into a straight steel tube placed along the bottom of the crank case, and from this tube a vertical tubular connection is taken to each of the caps of the main bearings. The crankshaft and crank pins are hollow, and, as in the previous engine, in the hollow portions tubes of a slightly smaller diameter are placed, the tubes being expanded over at the ends, so that closed annular spaces are formed which are used as lubrication leads. The lubricating oil passes through the main bearings into these annular spaces in the shafts, from them to the annular spaces in the crank pins, and so to the big-end bearings. From the big-end bearings it travels up the connecting rods to the gudgeon pins. It is interesting to note at this point that the connecting rods work in slots in the crank case which just allow sufficient clearance for their travel, in order to prevent the flooding of oil into the cylinders. A steel-lined oil lead is taken up to the saddle which supports the tubular camshaft casing at the propeller end of the crank case. The bearings carrying the camshaft are cut away at their lower edges clear of the tube so that the oil can flow along the full length of the casing, the level being sufficient to allow the cams to dip. Precautions are taken to keep oil from flowing out of the bearings, and the casing over the gears is specially arranged to prevent the oil from flooding below. (48) Mesta Gas Engines. The Mesta four stroke cycle, double acting gas engine, built by the Mesta Machine Co., Pittsburgh, is an excellent example of American big engine practice. Mesta engines are built in sizes from 400 horse-power up to the largest used, and is built either in tandem or twin tandem units. While the engine does not differ widely in either principle or construction from engines of the same size it has several features worthy of note that are not found on other engines.