alastio force, is the segment of a sphere, having conical ends, the points of the cones being towards the centre of the sphere; which arrangement forms an annular chamber. This channel is intersected by a segmental piston, or steam stop, which is fitted to the two cones, and also to the spherical part of the chamber, revolving steam-tight against the ball. A passage is formed through the lower cone, on one side of this piston, for the admission of steam, and a similar passage is formed on the other side for its escape; the communication between which is effected by a vertical shaft. If, therefore, no further means were provided, the steam would pass at once from the inlet passage, through the circular channel, and escape by the outlet passage, without yielding any mechanical force. The extent to which power can be obtained, is in proportion to the prevention of the escape of steam from the inlet to the outlet passage, except in consequence of the action of the engine, which action takes place after the steam has exerted its full force in impelling the piston. The prevention of this free passage of steam through the annular chamber, is effected by a circular disc or plate, which surrounds the ball, and extends to the periphery of the spherical chamber, to which it is made steam light by metallic packing. This disc is so placed, that a radial line on its upper side is in contact with the upper cone of the chamber, and a radial line on its lower side is in equal contact with the lower one. The disc is mounted on a shaft, which, being supported at one end by a bearing placed at a suitable angle to the central vertical line of chamber, provides for the two sides being at the same time in contact with the upper and lower cones. As each revolution of the steam chamber and the disc must be effected in the same time, and as their axes are placed at an angle to each other, different radial lines of the disc and cones will be brought into contact with each other during these revolutions; and any given point of the disc will be continually travelling from the upper to the lower cone, during one half of the revolution; and from the lower to upper during the other half. The consequence of this traversing motion is, that smaller chambers are continually forming, from the intersection of the main chamber by the disc and piston. These chambers serve for the reception of actuating steam from the boiler, the steam being prevented from communicating with the outlet passage, in one direction by the piston, which divides the annular chamber, and in the

other by the close contact of the disc with the upper and lower cones. One of these chambers increases in capacity in direct proportion to the revolution of the engine, until one half of each revolution is performed, when, by the change in the relative position of the disc and cones, the steam received is discharged; and, at the same moment that this change takes place,, the formation of a new chamber for the reception of the steam commences. The chambers formed on the upper and lower sides of the disc are always in communication with each other, through the slit in the disc; and, therefore, the whole area of the piston on the one side, is in constant communication with the actualing steam, whilst this area on the other side, is also in communication with the outlet passage; and, consequently, the power obtained is uniformly alike. As the construction provides that the revolution of the disc and cones, in contact with each other, should effect the necessary alternate communication of the actuating chambers with the inlet and outlet passages, it will be apparent that the valves which are required for effecting these changes in the reciprocating engines are dispensed with; and the whole power obtained being communicated to the rotating shaft, to which the steam chamber is attached, it may be applied at once. Thus, the moving parts necessary, merely consist of a spherical chamber, with its two cones aii'l a shaft, a piston, and a disc with its ball and shaft, the two nozzles and stuffing boxes for the passage of steam, the bearings for the two shafts, and the framework. The perfect action of these rotary engines depends upon the precision with which the fitting of the two sides of the disc against the upper and lower cones can be accomplished, and the continuance of this precision when the engine is working. As a matter of workmanship, it has been found that this precision is attainable with engines in which the steam chamber revolves on its own axis, and the two shafts revolt e in fixed bearings. There are, however, circumstances connected with the action of the steam, which tend to effect a separation between the disc and cones, and thereby to admit of the passage of some steam without producing an equivalent mechanical force. During one half of the revolution, the area of the lower side of the disc, which is exposed to the full pressure of the steam, is greater than that of the upper side, which is similarly exposed. During this period, the pressure of the steam has a tendency to raise the disc from absolute con.

tact with the lower one; and during the other half of the revolution, a similar effect is produced on the upper side of the disc. The extentto which this effect can be produced must be extremely minute; as, to admit of its recurring at all, it is necessary that an actual compression of the metals, or a bending of the disc, must take place, as it is seen that the disc should be prevented leaving the lower cone by its contact with the upper one; and the reverse. Notwithstanding this, it is found that one half of each side of the disc, and one half of the surface of each cone, have constantly a polished surface, from their bearing against each other; whilst the other halves have no indication of being in absolute contact—thus proving that the effect before described does take place. One of the inventors of the new engine (Mr. Davies) was led, by the consideration of this action, to devise means by which leakage between the cones and disc might be prevented; and the further advantage secured, of rendering unnecessary that mathematical precision of adjustment, which was before required for obtaining the contact of the cones and disc. The principle consists in the adaptation of teeth, or cogs, to the disc and cones; these teeth being so arranged as to work into each other with great accuracy, in the same manner as the teeth of bevelled wheels. With this arrangement, instead of having a single radial line of contact between each side of the disc and the upper and lower cones, a number of teeth on the disc are in gear with an equal number of teeth on the cones ; and as the suitable angle for the two axes is obtuse, this number may be extended to as many as seven teeth in gear at once. Thus, there are provided seven lines of contact in place of one; and as this contact of the teeth with each other is lateral, instead of being the contact of a flat plate against a round surface, any movement occasioned by the unequal pressure of the steam on the two sides of the disc, will only affect the depth to which the teeth are in gear, without disturbing the perfect fitting secured by their contact. For the sake of illustration, the disc and cones may be considered as bevelled wheels: it will be found that the diameter of the disc is considerably greater than that of the cone; yet these, if acting as wheels, must have an equal number of teeth, to secure their performing a revolution in the same time. According to the ordinary construction of the teeth of wheels, it would have been impracticable to effect this object; and it was, therefore,

necessary to devise a mode of construction suitable for this purpose. On considering the manner in which the best constructed wheels work together, the inventor perceived that the form considered the best might be made available; the only modification requisite being the adoption of one portion, or the point of the ordinary tooth, for the larger wheel,—and the other portion, or its root, for the smaller. This modification being followed, the steam entering the chamber on the actuating side of the piston, will have a tendency to cause the disc to revolve on its own axis, in the direction contrary to that in which it should be impelled by the action of the engine; the amount of this tendency being dependent on the sectional area of the disc, multiplied by the pressure of the steam. The tendency of the disc to revolve on its own axis, is overcome by its teeth being in gear with the teeth of the cones; the power necessary being communicated through the teeth, which are retained in contact with each other, whilst the amount of resistance is not sufficient to occasion any material wear. The modification in the construction provides for an engine having only one moving part, viz., the disc; and this part moves in such a position, with regard to those with which it comes in contact, as scarcely to admit the possibility of any derangement occurring. Although this description applies to noncondensing engines, the same principle is equally applicable to those in which the steam is condensed. For this purpose, it is only necessary to provide a smaller machine of the same construction; which, being connected with the condenser, and actuated by the engine, performs the duties of the air-pump, with the advantage of its action being constant, instead of alternating, as in the reciprocating engine. The advantages derived from this application consistin the simplicity of the engine, which renders it much less liable to derangement than ordinary, and in the reduction in weight and bulk, as compared with the engines now in use.

MODES OF WATERING HORSES. When the horse is at home, he is watered either in the stable from a pail, or in the yard from a trough, which, in racing establishments, is provided with a stout lockfast cover as security against poisoning. In general, the horse seems to care little how he gets the water; but some will drink only from the trough, except when very thirsty. I know of no objection to the trough, provided it be kept clean, and that the horse does not tremble after d ri nkiog from it. The water, however, is often very cold, and the man is often so very lazy, that he is unwilling to bring the horse to the door, and he makes two services stand for three. When the horse happens to be in the yard, he may get his water before going in; but at other times it is as well to make it a rule that the water be carried to the stable. Coming from a warm stable to the open air, and drinking cold water, the horse is apt to take a shivering fit. Each stable should be provided with water-pails always full, and standing in the stable.

In watering with a pail, the bucket is either placed on the ground, or raised manger-high to the horse's head. Old short-necked horses drink from the ground with difficulty, yet they always manage it. When the throat is sore, and when the horse is stiff after a day of severe exertion, his water should be held up to him. Some horses rarely drink well, and the less they drink the less they eat. They often require a little coaxing, and always a little patience. It is not enough to offer water and run away with it immediately. Hold the pail manger-high, and keep it before the horse for a little; after washing his mouth and muzzle he may take sufficient to create an appetite.

Post-horses are often watered on the road. They usually receive a little at the end of the stage, and also in the middle of it, if exceeding nine or ten miles. On the way home, the post-boy permits the horse to drink once or twice at watering troughs by the road-side. He does, or should endeavour to have, his horses fully watered, and cool by the time they arrive at stables. They are then ready for dressing and feeding without delay.

Horses are often taken to water at a pond or river some distance from the stables. If they need exercise or are passing the water, there is no objection to this practice. But it is not proper to send working horses out of the stable for the mere purpose of watering them. The weather, the state of the ground, and the laziness of stiblemen, render this mode of watering extremely irregular. Boys, too, are often employed in this service, and they are never out of mischief.

With many grooms it is a common custom to give the horse some exercise after drinking. Some give him a gallop, while others are content with a trot or canter for a few hundred yards. Exercise after a copious draught of cold water is very useful. It does not warm the water in the

horse's belly, as the groom says; but it prevents the evil effects which I have adverted to, in connexion with the temperature of water. Motion generates heat, and that which unites with the cold water can be better spared than if the horse were motionless. But the exercise need not be work. It is sufficient if it produce the least perceptible increase of warmth on the skin in eight or ten minutes. The man sometimes starts from the water at a gallop, but no good groom is guilty of this folly. Let the horse walk away for a few yards; from a walk he may proceed to a trot, and from that to a canter. In warm weather a walk is sufficient, and the pace need very seldom exceed a slow trot. The object is, not to heat the horse, but to keep him warm, to prevent shivering.

Water is not often given more than three times a-day. But in hot weather, when the horse sweats much, he often needs more water than it is safe to give at only three services. He should have it four or five times, and the oftener he gets it, the less he will take at once. Under ordinary circumstances, two rules will guide the groom. The first is, never to let the horse get very thirsty; the second, to give him water so often, and in such quantity, that he will not care to take any within an hour of going to fast-work. 'Water should always be given before, rather than after corn.

Broken-winded horses are usually much restricted in their water. I know that in stage-coaching they are not the worse for having as much as they please at night, provided it be given at twice or thrice, and not too cold Stewart" s St'ible Economy.

REVIEWS.

A TALE ABOUT A GIANT AND A DWARF.

Extracted from a clever little Work, entitled "Chemistry no Mystery;" or, a Lecturer's Request." By John Scoflln. London: Harvey and Darton.

[we shall give some further account of this amusing and instructive volume next week.]

Of all the merry-makings which it has been my lot to see, none has ever pleased me so much as B village fair. The Lord Mayor of London's show, the King's visit to Parliament, and all other fine sights

put together, never afforded me half the gratification that I have felt from being present at a country fair. But my recollections of all country fairs are not pleasant, as will appear in the course of the tale which I shall presently relate; although I am convinced that the chastisement which I then suffered for an act of wanton mischief, taught me a useful lesson for my guidance in after life. It taught me in a practical manner something which I had heard theoretically advanced many times before: that knowledge is power, either for good or for evil, and is only conducive to happiness when enlisted on the side of virtue.

In the early part of June, some sixty years ago, I was present at the annual fair of my village. I was then about ten years old. The approach of the fair-day was a subject of pleasurable anticipation for every one within a dozen miles of the place : the village cottages were whitewashed; the rose-trees were pruned; the garden walks were nicely weeded, and brushed clean from leaves; the cottagedoors were painted; and, in short, everything was done that could make our homes more comfortable or more neat; for the fair-day was one of hospitality to all strangers; and to have received them in negligenco or untidinesss, would have seemed to us the height of ill-breeding. It was a pleasing sight for us boys, when perched upon the cottage roofs, or seated on the bough of some tall tree, to watch the busy preparations which were making for the approaching festivities. Some were employed in partitioning off the villagegreen into square divisions for the cattle: some were erecting booths for sweetmeats and toys, and some were fixing swings and round-abouts; while in another part of the green the village authorities were in earnest conversation with mountebanks, showmen, conjurers, and fruitsellers, respecting the price which each should pay for a certain space of ground. No statesmen, settling a treaty between nations—no warriors, inspecting the field of an approaching battle, could look more serious and sedate than these: if their very lives had depended on the termination of the conference, they could not have looked more grave. The heads of some were moving from side to side: the heads of others were moving up and down; some grasped their pockets convulsively, and turned on their heels; some curled their lips and counted their fingers: in short, a careful observer, placed far enough away to be out of hearing, but still within sight, might have seen depicted in their ever

changing gestures, all those varieties of

feeling which are manifested in the course of mercantile transactions of the most extensive kind.

Far beyond this busy scene the horizon was clouded with rising dust, caused by the approaching cattle and caravans. In a short time they were distinctly visible, and in the space of a few minutes more, we saw them descend the hill immediately opposite to their place of destination. The cattle galloped and frolicked as if they too enjoyed the approaching festivities; and so perhaps they did, for none of them were tired from long travelling, having merely come from adjoining farmst and if they could be pleased with their own fine appearance, and experience a little of human vanity in being gazed on and admired, they must have felt pleasure indeed: be this so or not, they did appear pleased ; why I cannot tell. Now came donkieB, with gingerbread, fruits, and toys j carts, with mountebank-stages, balancing poles, swings, and round-abouts; then followed caravans with wild beasts, penny-peeps, giants, and dwarfs; next the more humble punchinellos, dog-cart men, and blind fiddlers; who, having allowed the aristocracy of the craft to advance before, now followed in the rear. The bells all the time continued ringing merrily, and thus passed away the evening.

Now I must suppose the night spent; not in sleep, at least, by me, for I was too anxious; however it was spent, and the fair-day had arrived, which brings me to the subject of my tale. I am sorry to own, that when young I employed my little stock of scientific knowledge chiefly in playing practical jokes, and this propensity did not entirely leave me until the fair-day, which I am now about to describe. Scarcely waiting to finish my breakfast, I sallied out with some of my young friends in search of adventures, and passing along a row of show-caravans, I was struck with the appearance of a picture, representing a giant and a dwarf, who were to be seen inside, together with a boa-constrictor and an alligator, all for the sum of one penny. Attracted by the harmony of a kettle drum and a cracked trumpet, a larger crowd of spectators surrounded this caravan than any other; and the managers were enjoying in consequence an undue monopoly. The wildbeasts' men in vain bawled forth the names and nations of their wonderful animals. Punchinello jabbered to the empty air, and the mountebanks danced and grimaced in vain; the giant, dwarf, alligator, and boa-constrictor were all the rage; and

the trumpet and kettle-drum drew won dering crowds into the caravan. "I have sartinly seed many a bigger fellow than he," said a countryman, stepping out. "If I beaut mistaken," continued another, ** the feller is on stilts, and if a body could make un come out upon the ground and show his inches fair and undeceitfully, he would look a wonderful different man." I do not know how it was, but this conversation aroused in me the most pleasurable sensations: I reasoned myself into a belief, that if there was any deceit in the matter, I should act properly in exposing it, by exhibiting the giant in his full proportions. When the mind is bent upon the performance of some mischievous trick, we first quiet conscience by endeavouring to clothe our evil propensities in a garb of virtue ;—so was it with me; I fancied, that by drawing the giant out I should exhibit any deceit that there might be; aad if there should be no deceit, then the giant might walk in again. But my conscience was not quite satisfied upon this point, inasmuch as the dwarf too must certainly experience some inconvenience if my proposed measure should be carried into execution:—perhaps also the alligator and snake might suffer. However, I had determined that the giant should come out, and conscience in vain whispered—no.

Returning home, I selected a basin— provided myself with ingredients for making this disgusting sulphuretted hydrogen, and filling the basin with nuts, the better to disguise my schemes, I crept stealthily under the giant's caravan, where, having set on the preparation of my gas, I retreated as fast as I could, allowing the noxious stench to ascend through the cracked and separated flooring of the caravan. standing at a little distance on a hillock, I watched the result. "Walk in, ladies and gentlemen," bawled the conductor; squeak" went the trumpet, * bang" went the kettle-drum ; but all in vain, the ladies and gentlemen kept walking out instead of walking in; their faces e<ntorted and their noses compressed. Presently the musicians too left their posts, for the stench was intolerable. Another moment, and the ground was cleared for the space of many yards around the caravan; that is to say, all had left it but myself, who, standing on the little hillock, was enjoying a sight of the mischief which I had created. Whilst I was one of the crowd, my ecstacies, for aught I know, might have remained unnoticed; but standing alone they must necessarily have been remarked, and, indeed, so they Presently the dwarf gave a convul

sive shriek—the giant roared aloud, and bursting from the caravan with the dwarf clinging tightly round his neck, he jumped from the platform to the ground, where heaving his great chest, and staring wildly around, he looked like an infuriated being from another world. Whether irritated by my laughter, or guided by an instinctive sense to the person of his tormentor, I know not, but leaping towards the hillock on which I stood, he snatched me in an instant from the ground.

I now repented of my joke, for he clawed and shook me about as a cat does a mouse;—a sound drubbing I would not have cared so much about, but the monster almost strangled me;—his great hands squeezed me so, that I thought every bone in my body was broken. Cry I could not, for he closed my mouth by main force, in order that I might be tortured with greater effect. He did not strike! me, it is true; if he had, I think I must have died; and in this forbearance he was generous, well knowing his own immense strength; but having clawed me for a minute or two, he very coolly held me under one arm, my head towards the ground, and my feet kicking aloft; while the dwarf on his shoulder was busily en. gaged in belabouring my back and sides with a cudgel; a task which he executed with great perseverance and effect, exerting at every blow his utmost strength: he not being at all afraid of breaking my bones. Even this treatment was a relief to me, because I could cry. The people were panic-struck, and what with the horrible smell, and what with fear of the giant, no one came to my assistance; indeed I did not deserve that they should. How the rest of the day passed, I know only from hearsay: feverish and delirious I found myself two days afterwards in bed, surrounded by two doctors and a nurse. Six weeks passed, and I was yet unable to walk from the effects of my squeezes and bruises: however, I suffered no lasting injury, and I have many times since then been thankful that my fondness for practical joking experienced such a timely and salutary check.

From what I have been told, the giant really looked as large outside the caravan as he did inside it, and he did not require the aid of stilts to increase his height. As to his strength, I can offer personal testimony. But the sun has set, and I have reached my abode, therefore good night to you all."