exquisite polish. If a tool requires grinding, fine emery powder must first be used, to be followed by oil-stone powder, finishing off with crocus.

No one but those who have had experience can form any idea of the difference in appearance between work when finished with a blunt tool and with a sharp one; and the time and labour spent in getting up a brilliant polish on the tool is compensated for tenfold by the beauty and lustre of the work it produces.

B

A

This (Fig. 19) will be founa to be a most useful instrument when perfect truth in the boring the inside of a cylinder, &c., is required.

A is a steel shaft, fitting into the slide which carries the eccentric cutting-frame, &c., in the sliderest, with a slot cut through its head exactly at right angles, to admit of the tool B being inserted, which is kept firmly in its place by two binding-screws, as shown in the engraving. C is a movable cutter, having a sharp bevilled edge on its end and side. By the aid of the slide-rest it moves in an exact straight line, and therefore cuts the inside of a tube, cylinder, &c., with perfect accuracy.

FIG. 19.

THE AMATEUR ENGINEER.

HOW TO MAKE A HORIZONTAL STEAM-ENGINE.

In these advanced days of science and civilization I doubt whether any boy could possibly be ignorant of the fact that steam is simply water in a state of vapour, produced at a temperature of 212°, and upwards, "Fahrenheit." In these pages it is not my intention to enter into a detailed account of the discovery, or rather the invention, of the steam-engine (on which subject volumes have been and still might easily be filled), which may be traced as far back as B.C. 130 years, when Hiero of Alexandria invented a species of engine, which has been so extensively modified and altered that it is now almost a difficulty to ascertain which was the precise form devised by the inventor. Small glass and metal constructions, which are frequently called "Hiero's engines," may be purchased at many opticians', and are used for diffusing perfumes. Neither do I intend writing a long dry essay on the properties and quality of steam. I shall only write sufficient to enable the reader to become somewhat acquainted with the properties and power of this great motive agent, and to understand what he is about before attempting the construction of a model engine. I shall only attempt to supply, in generally intelligible language, an explanation of the facts and principles on which the structure of the steam-engine depends.

The first thing necessary for the production of steam is a Boiler," i.e., a vessel sufficiently strong to be capable of resisting a certain pressure, and furnished with a valve (called a safety-valve) for relieving the boiler of the superabundant pressure, which valve is regulated by a weight placed on a lever, or else by means of a strong spiral spring.

Boilers are now usually made in the style known as Cornish," that is, longitudinal, with one or more tubes or flues running through them, containing the fire; or else vertical or upright, with a number of tubes inside, conveying the heat from the furnace below to the chimney on the top of the boiler.

A most striking peculiarity of steam is that it increases most enormously in bulk compared with the water from which it is generated. One cubic inch of water will produce one cubic foot of steam, and as a cubic foot contains 1,728 cubic inches, it follows that the space occupied by the steam would be over 1,700 times greater than that required for the water.

I fancy I can hear some of my readers say, "If that is the case, what an immense boiler would be required!" Very true, but the difficulty is solved thus: steam is remarkably elastic and compressible, so much so that hundreds of cubic feet can be packed into the space originally occupied by one foot, provided that the vessel containing it is sufficiently strong to resist the great increase of pressure. This is called "high pressure." For instance, a boiler capable of containing only three cubic feet of steam, the pressure of which is 20 lbs. to the square inch, has another three feet of the same pressure added, then the pressure on the boiler would be doubled, or, as a "pressure gauge" would show, would equal 40 lbs. to a square inch, and so on till the boiler is burst by undue pressure. This clearly shows that it is absolutely necessary to provide ample means of escape for the steam generated in boilers, as most frightful accidents are constantly taking place from the neglect of this condition. We will now proceed to the machanism required for developing the force of steam, so as to render it available for any purpose to which we may feel inclined to apply it.

There are several different classes of engines, viz. : locomotives, marine, screw, paddle, and trunk; vertical, horizontal, oscillating, beam, and Cornish. These different styles are mostly modifications of the arrangements of the horizontal and vertical engines. Locomotives and the ordinary arrangements of horizontal and vertical engines are what are termed "high pressure," whilst marine engines are "low pressure condensing," and the beam and Cornish engines frequently high and low pressure condensing combined.

Before going further, I think it advisable to describe as shortly as practicable what is meant by "condensing." The exhausted steam which has done its duty in the cylinder is conducted into a vessel in which a quantity of cold water is continuously injected in the form of a jet; this has the effect of turning the steam again into water, which is afterwards partly made use of for feeding the boiler, and, as the water is warm, there is necessarily a saving of fuel.* This

*This vessel is immersed in a tank of cold water and is supplemented with a pump, by means of which the water supplied by the injection and the condensed steam are constantly being pumped out. This is called the air-pump.

The water surrounding the condenser, unless it were changed, would in time become warm, and fail to effect the condensation. This is remedied by the application of a pump and waste-pipe to the cold cistern in which the condenser is submerged; the pump continually supplies cold water, which, by its comparative weight, has a tendency to sink to the bottom, and the waste-pipe, placed near the surface, lets the warm water escape, which, by its comparative lightness, ascends. Thus, by these arrangements, the method of condensation becomes complete.-Dr. Lardner on the Steam-Engine.

class of engine is not always available, on account of the large quantity of water required for condensing the steam.

I shall direct your attention in the following pages to the Horizontal and Oscillating engines. For the benefit of such of my readers as may not be acquainted with the names of the various parts of the steam-engine, I will enumerate them and explain their various uses.

The engine first claiming attention is that known as the "Horizontal." This is one of the simplest forms of engine, and is most generally used. Figs. I and 2 show an elevation and plan of horizontal engine, drawn to 3-in. scale, or a quarter the size which it is intended to be built. The various parts are distinguished by letters corresponding with the following list:

A. Bed-plate. This is a frame or plate, made of cast iron, to which the cylinder, plummer-blocks, guide, &c., are firmly bolted. (In our model I should advise it being made of brass, as it is more easily worked.)

B. Cylinder. A description of this important part of an engine will be given hereafter.

c. Cylinder-covers. These are discs of cast metal, bolted to flanges cast on the ends of the cylinder; one is made with a projection, called a stuffing. box, through which the piston-rod works. The stuffing-box is a recess turned on a boss cast on the cover for the purpose of receiving some "packing," such as hemp, or tow, or gasket, well soaked in tallow, which is pressed tightly against the piston-rod by means of the

D. Gland, which is usually made of brass or gun-metal, although in many large engines it is made of cast iron, "bushed," or lined with brass. It is tightened down to the packing by means of screws or studs and nuts.

E. Steam-jacket. A cast iron case or box bolted to, and sometimes cast on, the cylinder face, in which the slide-valve works, and into which the steam is admitted before it enters the cylinder.

F. Piston (see Figs. 14 and 15). A solid disc or plug, fitting the interior of the cylinder with sufficient accuracy to prevent the steam from passing from one side to the other.

G. Piston-rod. A round rod, usually made of steel, firmly screwed or keyed in the centre of the piston, and passing through the stuffing-box and gland, through which it must move so closely as not to allow any steam to escape. H. Cross-head. A species of boss or crossbar, fixed on the piston-rod, to which the connecting-rod is jointed.

1. Fork Connecting-rod. A rod somewhat similar in shape to a tuning-fork, forged out of wrought iron, connected at one end with the cross-head, and at the other end with the crank disc-pin. The ends of the connecting-rods that are used for practical purposes are fitted with gun-metal bearings, termed brasses, to prevent undue friction.

J. Guide. This is a block or bracket to keep the piston-rod in a straight line with the centre of the shaft, and to prevent it from getting buckled or bent. K. Disc. A circular metal plate fixed to the end of the shaft, and carrying a pin to which the connecting-rod is attached. The disc is usually cast heavier on the side opposite to the crank-pin, to carry the connecting-rod over the "centres."

L. Fly-wheel Shaft. This is a stout wrought iron shaft, to which the disc is keyed. It carries the disc, eccentric, fly-wheel, and pulley (M) for transmitting motion to whatever machinery the engine is intended to work. (In the engraving the fly-wheel is omitted for want of space. Its use is that, by

means of its impetus, it carries the crank over the points.)

66 centres" or dead

N. Pedestals or Plummer-blocks. Cast iron blocks fitted with brasses, on which the shaft revolves. These blocks are provided with caps, and bolts and nuts, for tightening down the brasses as they may be worn away. This is called "taking up the wear."

0. Eccentric. A circular plate of metal keyed on the shaft at a point at some certain distance from its true centre, giving by this means a reciprocating motion, similar to that of the crank or disc itself.

P. Eccentric Straps. Rings of metal, usually made in halves and bolted together, in which the eccentric revolves. A groove is generally turned in the rim of the eccentric sheave, to keep the straps in their places.

Q. Eccentric-rod. An iron rod fixed to the eccentric straps at one end, and connected with the valve-spindle at the other end.

R. Slide-valve. (Figs. 14 and 16.) An iron or brass block, working over the "ports" of the cylinder-face, to regulate the admission of steam. The centre is hollowed out to allow the exit of the exhaust steam. must be "faced" to ensure a perfect fit against the cylinder-face.

The valve

s. The Valve-spindle is a short steel red, working through a stuffing-box and gland on the steam-jacket, connecting the eccentric-rod with the slidevalve.

T. Holding-down Bolts are used for bolting the bed-plate down to its proper foundation.

Having now described the various component parts of the engine, I shall go on to show how any boy possessed of a moderate amount of intelligence

and perseverance may, with the aid of a few tools and a few shillings, construct for himself a working model of a horizontal steam-engine.

For the benefit of my readers who do not possess the necessary tools, I will commence by giving a list of those required, with the approximate prices, and information as to their various uses. If, however, they can be borrowed, so much the better.

The first and foremost among tools is the lathe (Fig. 3). This is a machine for turning metal or wood by causing the material to revolve on centres," and to be cut by a tool, either held by the hand of the operator or else fixed in a "slide-rest." In the ordinary form of foot-lathe shown in the engraving, the tool is held in the hand. The spindle, A, is called the mandril, and is caused to revolve by means of speed pulleys, S S, which are connected by a stout cord or gut. c is the bed to which the fast headstock, D, the loose headstock, or poppet-head, E, and rest, F, are secured by means of bolts. GG are the standards or gantries, to which the bed, C, is firmly bolted. The speed pulleys, SS, which act also as a fly-wheel, are made to revolve by the crank, H, on pressure being applied to the treadle, I. The work to be turned is fixed between the points or "centres," K K, and is made to revolve with the mandril by means of a stud or pin fixed in the face-plate, L, which forces round a clamp or carrier fastened on to the work. The price of a lathe varies according to size. They may be bought from £2 to £100. The amateur who does not possess one, or who cannot afford to purchase one, can always get his turning done by a turner for a very moderate sum.

A 3-in. bench-vice (Fig. 4) will be found quite large enough. It is used for holding or gripping any piece of work that is to be fitted, chipped, or filed. Fig. 4 a shows a vice and portable vice-bench. A vice similar to Fig. 4 a, without bench, new, is 15s.; secondhand, about 9s.

Files: one each 8-in, bastard, smooth half-round, smooth flat, taper square, and one 6-in. round smooth, will be found ample. These will cost about 35. The rough or bastard are used for reducing work to a proper form, when it is finished and polished with the smooth files.