The cross-head which I designed at this time has always interested me, not only on account of its success, but also for the important lesson which it teaches. I abolished all means of adjustment. The cross-head was a solid block, running on the lower guide-bars if the engine were running forward, as was almost always the case, and these guide-bars were formed on the bed. The pin was of steel, with the surface hardened and ground truly cylindrical, set in the middle of the cross-head, and formed with square ends larger than the cylindrical portion. These were mortised parallel into the cross-head, and a central pin was forced through the whole. The flats on the pin I afterwards copied from a print. These prevent the formation of shoulders at the ends of the vibration of the boxes. I would like to know to whom we are indebted for this valuable feature. Every surface was scraped to absolute truth. The lubrication was internal, as shown. There are many of these cross-heads which have been running at rapid speeds in clean engine-rooms from twenty to thirty years, where the scraping marks on the lower bars are still to be seen. The lesson is a most important one for the future of steam engineering. It is this. Two flat cast-iron surfaces, perfectly true and incapable of deflection, with the pressure equally distributed over a sufficient area, protected from dirt and properly lubricated, will never have the clean film of oil between them broken or even varied in thickness, and will run together without wear perpetually and at any speed whatever. The conclusion is also abundantly warranted that a tendency to heat need not exist anywhere in even the least degree, in engines running at the greatest speeds. This can always be prevented by truth of design and construction, and the selection of suitable material. This fact is abundantly established by varied experience with cylindrical as well as with flat surfaces, and for other materials, though not for all, as well as for cast iron.