In a locomotive engine there are two such cylinders, working against opposite faces of the same brass block containing the ports. The cranks are also two, on the shaft of the driving-wheels, and are at right angles to each other; so that when one piston is at the middle of its stroke, the other is nearly or quite at the end of it. Thus, between the two there is always some force being exerted by the steam; and the dead points of one crank agree with the greatest leverage of the other. In locomotives, too, the cylinders generally are made as in the present drawing, viz., to oscillate on a point at the middle of their length; but it is just as easy to have the two ports meet at the bottom instead, so that the point of oscillation may be low down, like the single-acting cylinders of the last sketch, and this is generally done when the cylinder is to stand upright.
There is no occasion for me to draw an engine with double-acting oscillating cylinders, because in appearance it would be like the single-acting one; but whereas the latter is of absolutely no use, seeing that the greater part of its motion depends on the impetus of the fly-wheel, the former can be made to do real work, and is the form to be used for marine and locomotive engines. For the former, oscillating cylinders with slide-valves are used in practice; but for real locomotives fixed cylinders are always used. Of course either will answer in models, and it will be good practice to try both.
I have now given sufficient explanation of how engines work, and how they may be made, to enable my young mechanic to try his hand at such work. The double-action oscillating engines especially are well worthy of his attention, as he may with these fit up working models of steam-boats and railway trains, which are far more difficult to construct with fixed cylinders and slide-valves. I shall therefore close this part of my work with a description of one or two useful appliances to help him in the manipulative portion of his labour,—for here, as in most other matters, head and hand and heart must work together. The heart desires, the head plans, the hands execute. I think, indeed, I might without irreverence bring forward a quotation, written a very long time ago by a very clever and scientific man, in a very Holy Book: “Whatsoever thy hand findeth to do, do it with all thy might.” Depend upon it, success in life depends mainly upon carrying into practice this excellent advice. If you take up one piece of work, and carelessly and listlessly play at doing it, and then lay it down to begin with equal indifference something else, you will never become either a good mechanic or a useful man. If you read of those who have been great men—lights in their generation—you will find generally that they became such simply by their observance of that ancient precept of the wise man. They were not so marvellously clever—they seldom had any unusual worldly advantages; but they worked “with all their might,” and success crowned their efforts, as it will crown yours if you do the same.
Chapter XV.
HARDENING AND TEMPERING TOOLS.
I promised in a previous page to describe a little stove for heating soldering-irons, and doing other light work. It is made as follows, and will be found very useful.