But this advantage of saving room comes much more prominently forward in marine engines, especially in war ships, where every inch of room saved is valuable; and in the new type of triple-cylinder engines now coming so much into vogue in the mercantile marine, whether those engines be only the ordinary three-cylinder engines with double expansion, or the newer, triple expansion engine, expanding the steam consecutively through three cylinders—­the form of marine engine which promises to come into use wherever high-class work and economy are required.  On this system, by placing all the valve chests in front of the cylinders instead of between them, or in a line with them, sufficient room is saved to get the new-type three-cylinder engine into the space occupied by the old form of two-cylinder engine.

Besides these prominent advantages there are others which, though of minor importance, are still necessary to the practical and permanent success of any new mechanical arrangement, such as the accessibility of all the working parts while in motion, for examination and oiling; the ease with which any part or the whole can be stripped and cleaned, or pinned up out of the way in case of break down or accident, or got at and dismantled for ordinary repair; the ease with which the whole may be handled, started, reversed, or set at any point of expansion—­all these being recommendations to enlist the care and attention of the engineers in charge by lightening their duties and rendering the engines easy to work.

With those advantages it is perhaps not surprising that this valve gear has been very considerably adopted for many classes of steam engines, especially where a high result has been required, with economy of space, and a minimum of complication.

Having crucially tested the original engine on the London and North-Western Railway, Mr. Webb proceeded to build others similar, and on his bringing out his Compound Express Engine—­notably the most advanced step in locomotive design of the present day—­he adopted this valve gear throughout.  There are now a number of these engines running some of the fastest trains on the London and North-Western Railway, with the most satisfactory results.

Following these, others of the leading railways took up the system, and prominently among these Mr. Worsdell, of the Great Eastern Railway, built a number of large express engines for his fast and heavy traffic, and is now building a number of others similar as to the valve gear for his suburban traffic, which is specially heavy.  Also the Lancashire and Yorkshire and the Midland and others of the chief railways are employing the system specially for large express engines; the Midland engines having cylinders of 19 inches diameter by 26 inches stroke, and four coupled wheels of 7 feet diameter.  A number of the above-named engines have run large mileages, in many cases already exceeding 100,000 miles per engine.  For other countries also a number of locomotive engines have been built or contracted for—­both of inside and outside cylinder types—­making a total of nearly 800 locomotives built and building, many of them being of special design and large size, up to 20 inches and 21 inches diameter of cylinder.