HYDROSTATICS.-VIII.

AFUGAL PUMPS - MACHINES FOR PROPELLING VESSELS
-RIVERS-POWER STORED UP IN RAIN-TIDES-WAVES.

We have in our previous lessons described the construction and
mode of operation of those machines for raising water which
act mechanically, or by means of atmospheric pressure. These
embrace by far the greater portion, and we have now only to
look at those which act by centrifugal force.

It may, perhaps, be thought rather unnecessary to explain the construction of so many machines, all of which answer the same purpose; but they each have their special peculiarities, which render one or other of them the more advantageous, according to the special circumstances for which they are required; and as some of them are in use in almost every house and factory, it is surely well to understand their mode of action. It is a very good rule in everything to try and understand the reason, and not to be satisfied with the bare fact that the thing is so. The plumber who understands the principle on which any pump acts will be far more likely to succeed in his business than the one who merely works by routine. The latter is baffled by anything unusual or uncommon, while the other, since he understands the principle on which he is working, soon masters the difficulty. The same rule applies in all other matters.

We have, then, to consider now those pumps which act by centrifugal force. In our lessons on Mechanics we gave an explanation of the action of this force, and we saw then that it is merely a manifestation of the inertia of matter. instance, when whirled round by means of a string, tends at A stone, for every moment to fly off at a tangent, that is, to continue in the line in which it was moving at the instant, instead of being bent round in a curved path.

In the same way, if a tube be filled with water, and swung round rapidly, the water will be thrown out of it.

The apparatus usually employed to illustrate the application of this principle to pumps is represented in Fig. 40.

An upright spindle, c, is fixed so that it can be turned rapidly by means of a multiplying wheel. two tubes, A A, open at each end, but at the top bent outwards To this spindle are fixed and downwards, so that the water which issues from them is received in the ring-shaped trough, B. rotated with the axis, the water in the upper portion of them is As these tubes are rapidly thrown off, by centrifugal force, into the trough. This creates a vacuum in them, which is at once filled from the reservoir into which they open, and thus a continual stream is produced. The amount that could be raised by these pipes is, however, far too small to admit of the machine being practically employed in this form.

One of the simplest forms of a centrifugal pump consists of a circular disc fixed on a shaft. Attached to each side of this diso are a number of partitions radiating from the centre; these are made of the same height throughout, so that the whole may revolve between two fixed discs or cheeks which the partitions nearly touch. These cheeks form the ends of the cylinder into which the exitpipe opens, and are cut away at the centre so that the water may enter there; and as the wheel revolves it is thrown off against the rise in the exit-pipe to a considerable height. sides with such force that it will The size of the wheel is usually about a foot in diameter, that being quite sufficient when it is rotated rapidly, and it is found that when the partitions are made to curve to the right degree nearly three-quarters of the power of the engine may be utilised. If, however, the partitions are made straight, only about a third of the power can be obtained. The great advantages of this pump are the absence of valves, the small space in which it may be made to work, and also the fact that it supplies a continual stream.

Fig. 40.

Another mode in which the pump is constructed will be under

stood by reference to Fig. 41. The lower is the suction-pipe, and the upper that into which the water is forced. These open in it, in which are inserted the partitions c c. These partitions into the outer cylinder, which is fixed, and inside this there revolves another cylinder, A A, which has longitudinal slits made inner curved surface, except when they approach the division can slide in and out, but are kept fully out by means of the which separates the suction and exit-pipes, when the other pressed out again. curved piece forces them in. After passing this point they are

B

that as soon as one of these partitions has passed this point Now it will easily be seen, by reference to our illustration, leaves a vacuum behind it. This is speedily filled by water from the suction-pipe, which space BB by the next paris then carried round in the volves rapidly this water actition. quires a considerable degree As the cylinder reof centrifugal force, which tends to drive it up the exitpipe; the partitions also, as they move onwards, force the The machine, therefore, acts water in the same direction. pump, and has the advantage of maintaining a constant flow as a suction and a forcingof water.

B

Fig. 41.

water, having considered all the most important varieties. We must now turn to the last of the three classes into which we With this we conclude our description of machines for raising signed to propel vessels through the water. Locomotion by divided all hydraulic machines-namely, those which are dethe invention of the mariner's compass; but, till quite recently, water has always been more or less employed, especially since employed in rowing or sculling, or else by the force of the winds the only mode of propelling a vessel was either by human power, was found to be quite impracticable in the case of large vessels; acting upon sails properly set. The former of these two modes uncertainties of the wind, the ship being often detained, or sive, there are great disadvantages in its use, arising from the and though the latter is still very largely used, being inexpenobliged to tack about frequently when the wind is unfavourable.

an attempt was made to employ it in giving motion to vessels;
Accordingly, very soon after the invention of the steam-engine,
happens in the case of most useful inventions, the experiments
and though great ridicule was at first thrown on the idea, as
every river.
were successful, and now steamboats are to be seen on almost

little need be said here on the subject. There are two plans in
The mode in which they are propelled is so familiar that but
common use, the one being by means of paddle-wheels, the other
by a screw placed at the stern of the vessel.

of floats fixed round it, the axle turning on bearings fixed to the The ordinary paddle-wheel is simply a wheel with a number boat, and being set in motion by a steam-engine. The principle is exactly the same as that on which a rowing-boat is propelled, the water serving the purpose of a fulcrum; not that it remains absolutely at rest, but the reaction it produces on the surface of the paddles pressing against it is sufficient to propel the vessel with considerable speed. With a well-built vessel an average speed of upwards of twenty miles an hour is easily attained.

considerable loss of power, and that was that when the paddles There is one circumstance which was at first found to cause a were thus fixed to the wheel there was a great loss of power fact of their surfaces not being vertical, so that only a portion of their force was utilised. To remedy this defect, the floats of the when they entered the water, and when they left it, from the best paddle-wheels are now fixed on pivots, and by means of mersed their surfaces are always vertical, and thus a much larger portion of the power is rendered available. an eccentric are made to move in such a way that while imwheels are usually placed at the side; vessels have, however, been constructed with them at the stern, and these occupy rather The paddleless room, and are more available for river navigation.

For a river, or in perfectly smooth weather, a paddle-steamer

permitted to try again. Whatever the thickness of the bar, it is included within the height that is to be jumped.

In pole-leaping, each person is allowed, if he desire it, to use his own pole, and the rules just laid down for long and high jumping without the pole apply equally here. The paper already mentioned renders it unnecessary that we should say more upon this subject.

We now come to

THROWING OR PUTTING WEIGHTS.

This class of exercise or sport is usually practised under one or other of three forms, which, commencing with the easiest and most common, are as follows :-(1) Throwing the cricket-ball; (2) putting the weight; (3) throwing the hammer. In this order we shall treat on them; but first we must say something as to throwing exercises in general, and give a little counsel to those who think of engaging in them.

Throwing has always taken a high place among exercises conducive to muscular development. Throwing the "discus" was a favourite recreation with the ancient Greeks, by whom physical was held to be of quite as much importance as mental training. The discus was a spherical body, more or less heavy, according to the purpose of him who used it, whether for his own exercise merely, or as a trial of strength between himself and another. The nearest approach we have to the same exercise in the present day is perhaps the game of quoits, in which, as our readers are doubtless aware, the object is to throw an iron ring upon a peg placed in the ground some distance off. If only we imagine the quoit to be larger in form, and much heavier, we shall understand the difference between this modern amusement and the ancient one of throwing the discus.

Quoit-throwing is useful practice for any one who desires to enter into some at least of the athletic sports now before us. It brings out the muscles of the chest and the arm or arms; for, if taken simply as an exercise, there is no reason why it should not be practised with the left arm as well as the right, but rather the contrary, as this would tend to the equal development of the muscles on both sides of the body. But the ordinary form of the quoit, which is suited to what is merely a pastime, might for athletic practice

at cricket knows how to throw a ball. The style of throwing
may vary, just as some throw with the left hand while most
persons use the right, but this is a matter of no importance.
The object in athletic sports is simply to throw the ball to as
great a distance as possible, and whatever the manner of the
throw-under-hand, over-hand, or round-arm, with the right or
the left hand-is immaterial, so that a long distance is covered.
The distance is measured from the standing point of the
thrower at the moment when the ball leaves his hand, to the

place where the ball first reaches the ground. Each competitor
is generally allowed two or three throws, and the longest is
taken as his distance. Sometimes the test is for straightness
Then boundary marks are
as well as distance in the throw.
made at the side, and any ball that falls outside these is not

allowed to count.

2. PUTTING THE WEIGHT.

The weight used for this purpose is usually a common ball, but sometimes a round stone, of 16 lbs. or upwards. For practice a much lighter weight will suffice. Two lines are drawn, about seven feet apart, and the competitor is allowed to run from the one to the other of these, to gain an impetus, before making his attempt. He must not, however, overstep the second line before the weight leaves his hand, otherwise the attempt counts for a "put," although not towards the victory. The mode of delivery is usually as follows :-The shot is held

in the palm of the hand, and the hand is brought up to the shoulder, the knuckles resting upon the shoulder for a moment. The competitor then takes his spring, and on reaching the line he hurls the shot forward as far as possible, by the motion which is made in the act of pushing. He is allowed to use either hand for the purpose. The distance is measured from the foremost line to the spot where the shot falls, its rolling afterwards not being taken into account. A 16 lb. shot has been thrown to a distance of 37 feet.

3. THROWING THE HAMMER. The "hammer " used for this purpose is usually round-headed, with a handle from two to three feet long, and weighing altogether about 16 lbs. A hammer of half this

be so far changed that it would be a greater Fig. 3.-GRACEFUL ATTITUDE IN THROWING. weight will be heavy enough to commence task to hurl it; and then we should more nearly approach the perfection of a preli

minary exercise in throwing. It must be remembered that the ultimate object of all athletic exercises is to promote the health and strength of those who engage in them; and a true test of how far any particular exercise tends in this direction, is the apparent ease with which the task may be performed. In this view of the case, any feat that may be accomplished only by violent contortion of the body, and undue strain upon limbs or muscles, is not to be taken as the standard of imitation; but rather that kind of exercise in which we find a combination of grace and power.

We have said thus much because we observe, with the spread of athletic sports, a growing tendency to forget the primary principles of athletic training. It is almost to be regretted that a Professorship of Athletics is not established in one or other of our universities, to inculcate right principles upon the young members of those institutions who are such ardent followers of this class of pastime, and who set an example in the matter to the young athletes throughout the land.

As an example of what we mean by graceful movement in throwing, we give an illustration in Fig. 3. It will be sufficient to suggest to our readers the kind of motion in all parts of the frame which should accompany the act; but this general idea is susceptible of infinite variety, according to the character of the sport immediately in hand, and the method which the learner finds most convenient to himself.

After the foregoing remarks, we will now say a few words on the throwing exercises usually seen in the athletic arena, taking them in the order above given.

1. THROWING THE CRICKET-BALL.

with. The distance thrown is measured from the foremost footstep to the place where the

head of the hammer descends. A run of a few yards is allowed. The following is the method of throwing:-You stand with the left foot in advance, and the hammer swinging down by the right side. It is swung backward and forward until a good momentum is acquired, and at the moment of advancing to the throw, you swing it forward with all your power, taking care that it does not ascend high in the air, as this will proportionately reduce the length of the distance it will travel. A 16 lb. hammer has been thrown nearly 100 feet.

Hammer-throwing, although common as a trial of strength, is not suited to persons of comparatively weakly constitution; and we should recommend all such to devote their attention, in preference, to some other feature in athletic sports.

"Tossing the caber" must be ranked among this class of sports. Its practice is almost wholly confined to the Highlands of Scotland, and it will be sufficient if we mention it by a brief description, quoted from a Northern authority. A ponderous larch tree, some thirty feet long, is the implement used in the game. The competitor hoists it on to his shoulder perpendicularly, with the thick end up. Crouching down, and throwing into the effort every muscle, from the tendon Achilles to the vertebræ of the neck, he shoots the great tree upwards and forwards, his aim being that its heavy end shall smite the ground first, and the thin end which has left his grasp shall describe an exact somersault, so that the tree shall lie directly from him, with its thick end towards him. The nearer he attains to the describing of the exact semicircle, the better is his throw; should the tree fall sideways or slantingly, he has failed.

We have now gone the round of these amusements, and shall return, in our next Holiday paper, to the apparatus and the

This needs little explanation, as every one who has played exercises of the public gymnasium.

LESSONS IN ARCHITECTURE.-XV.

RAILWAY ARCHITECTURE.-I.

the most eminent engineers were divided in opinion as to what the gauge--or width between rail and rail of a single line-should be. Some contended for a broad, and others for a narrow

THE progress of railways has given rise to vast strides in prac-gauge, as most desirable; and the long discussion which took tical engineering, and been attended by the development of a place on this subject is known as the "battle of the gauges." kind of architecture entirely novel in its character. The won- At the head of the broad-gauge party was Isambard Brunel, derful bridges, the huge stations, and the many ingenious con- who contended for a width of 7 feet from the inside of one rail trivances of a less imposing but not less useful nature, which are connected with the modern railway system, will afford us a profitable subject of study in the next of our Lessons.

Let us first trace the process of construction of a railway line. Before the works can be commenced, the country has to be thoroughly surveyed, its principal features noted with minute accuracy, and the course of the line finally determined upon, with due regard, not only to readiness of transit from point to point, but also to the avoiding of physical obstacles where practicable, or overcoming them by engineering skill. A line is frequently taken many miles out of the straight course to avoid the necessity of the construction of lengthy tunnels through hills, of viaducts over precipitous valleys, or bridges over important streams. Where the country is comparatively level, the engineer's

to that of the other; and he constructed the Great Western Railway on this principle. In the front rank of his opponents was Robert Stephenson, who maintained the opinion of his father, George Stephenson the founder of our railway system-that 4 feet 8 inches was the most suitable width; and the Stephensons carried out their opinion in the series of railways now known as the London and North-Western. But the inconvenience of different gauges throughout the country threatened to become so serious as railway construction extended, that Parliament stepped in and enacted, in 1846, that the narrow-gauge of 4 feet 8 inches should thenceforth be adopted in all railways laid down in England and Scotland. By this means facility of communication, in the passage of the same carriages from one line to another, was secured; and the Great Western has since brought itself into communication with the narrow-gauge lines, by placing a third rail within the original two at those points where access to or from its own line is required, and continuing this third rail as far as it may be necessary to run the carriages of other lines on their system. The width of the gauge varies in different countries.

SECTION OF A RAILWAY TUNNEL.

task is easy, and he can go straight onwards; and where it departs but little from a certain general elevation, the minor obstacles it presents are readily surmounted, either by alteration of the gradient or incline of the line, or by cuttings or embankments, as the ground happens to be too high or too low.

The course having been determined on, it is marked through- | In Ireland it is 5 feet 3 inches; in India it has been fixed at 5 out at the width required either for a single or a double line of feet 6 inches. rails, and the removal of the surface earth commences, in readiness for the laying of the permanent way. The width of a line is now regulated in this country by the enforced adoption of a uniform gauge. When railway construction first commenced,

VOL. III.

The chief reasons for the final adoption of the narrow gauge were the greater economy in construction-less land being necessarily required-and the saving of wear and tear by the employment of smaller and more economical "rolling-stock," i.e.,

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