All About Engines

The Locomotive 261 necessarily full of detail, the accompanying index to parts will render it intelligible. The aim of the designer is, of course, to produce the largest quantity of steam at the required pressure in the smallest time. He is limited, however, by the gauge. The Great Western alone of the pioneer lines had the rails 7 feet apart. Stephenson chose 4 feet 8J inches, and as all other railway builders in this country, except Brunel, followed his plan, the necessity for interchanging traffic forced the G.W.R. ultimately to alter their gauge. Thus, while the driving wheels are only 4 ft. 8J in. apart, the boiler must be less than that. Moreover, tunnels and bridges in Great Britain had all been built to accom- modate the pioneer engines of sixty years ago. The modern locomotive must therefore be built to pass through holes of limited size. It must not be more than a certain breadth, nor more than a certain height, and its rigid wheel-base must not be more than a certain length or it would not go round curves. It is like a giant in chains, always struggling to grow larger in order to draw heavier burdens, and always prevented. When the limit in size has been reached, more power can only be obtained by producing steam more quickly. To produce a greater quantity of steam in a given time two methods may be used. One is to improve the circulation, and the other is to increase the grate area. A large improvement in the circula- tion could only be obtained by altering the type of boiler, and using water tubes instead of, or as well as,