PRACTICAL GEOMETRY OF THE CHI

NESE.

The learned Mr. Barrow, secretary to the Admiralty, in his description of China, in the supplement to the Encyclopedia Britannica, observes, that though the Chinese are marvellously ignorant of the nations around them, they have, by the aid of "practical geometry," acquired a tolerable knowledge of their own country. "Pere Mailla," says Mr. B.," asserts, that on comparing the ancient chart of China, said to be copied out of the Shoo King, with the actual survey made by his brother Jesuits and himself, and which took them ten years to complete, they found the limits and the positions of the provinces, the courses of the rivers, and the direction of the mountains, pretty nearly to accord, but the proportions of the objects to each other, and to the whole, were not in the least observed. He (Pere Mailla) further observes, that they saw, and gazed

with astonishment and admiration at the chasms which the emperor Yu caused to be cut through solid mountains, to open new channels for the waters of the Yellow River. Some, however, will be apt to conclude, that it was the water itself, and not the emperor Yu, which opened these channels.-Query. Who but some of the sagacious folks concerned in ploughing down the Croker mountains would conclude any such thing

CELLAR DRAINING.

Sir, I would advise " Inquisitor," (page 405, vol. vi.) to have his well domed, to within three feet of the bottom, leaving an aperture at the top for a pipe, and to puddle the space between the dome and the level of the cellar, with pure yellow clay. I have no doubt of the spring being high enough for the water to be conveyed by a pipe, to a reservoir above the hall or passage. If the water do not rise to the height required, at first, he need not be disheartened. I know an instance where water was bored for, with the

expectation of its rising six feet above the ground, as it had risen to that height in the immediate neighbourhood; but the party was disappointed at an insignificant trickling scarcely above the level, and yet, in a few weeks, it came stronger; three feet of piping were added, and, in a few Additional days, it overflowed. lengths of piping were afterwards added, and, in a few months, the proPrietor of the brewery, where it was tried, was gratified in finding a constant, though not rapid flow, at a height above twenty feet from the ground. to cementing, the bricklayer is gamoning him. Should Inquisitor be inclined to adopt the suggestion, and find his purpose thereby answered, perhaps he will acquaint you with his success.

As

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IMROVEMENT IN THE WATER

WHEEL.

Sir, There have been various contrivances for evading the obstruction occasioned by tail water, but all that have hitherto been in use, seem to be quite inadequate to the purpose; at least, the time and trouble spent in making the necessary alterations, quite overbalance any advantage to be derived from them.

Now, as the best method must certainly be that which will accomplish the object with the greatest ease and facility, without obstructing the work, it is proposed that the water-wheel shall be elevated above the tail water, and that may be done even while the wheel is at work.

A similar movement is performed in the best constructed wind-mills, as often as the wind changes, which, in some situations, is exceedingly frequent.

By the plan now proposed, it is intended to have what may be termed three pit-wheels, instead of one, and two horizontal shafts instead of one, as represented attached to the waterwheel at fig. 2. The two new spur pit-wheels being also in view at fig. 1, it will soon be seen, that as the smallest is stationary, the largest may still keep working into it, while rising or falling with the water-wheel.

The water-wheel is elevated or depressed by means of two levers, the fulcrum of which must be first exactly in a direct line with the small stationary spur-wheel before described, and there is room on each side of the water-wheel for them to be so placed, as in fig. 2.

There is also a moveable curb or bed to confine the water in the wheel, the upper part of which is hung by two pins that go through the levers, and the bottom of the curb is suspended from the levers by means of two strong iron rods, which have pins through them at each end.

To raise or lower the water-wheel, a man turns the winch at fig. 4, and the worm working into the facewheel, turns the two pinions connected with the two racks at the ends of the levers; but should this be found too laborious, and take too much of

the miller's time, while the work is going on, a strap might be applied, and driven by a drum fixed on some convenient shaft already in the mill, and if expense be not too much considered, the addition of a governer will make the thing very complete, particularly where the tide is continually altering the height of the tail water; it may also regulate the quantity of water admitted to the wheel.

Though not much regard has been had to proportions in the sketch given, it will appear that by having a wheel low enough for the water to enter it near the top, the most will be made of the water, and if surrounded by close buckets, instead of open floats, the weight of the water will actually hang in the wheel down to the bottom, while in floats, the weight of the water slides down the bed or trough which the wheel runs in; the buckets will also leave the tail-water better by being in a curved instead of an angular form.

When a flood occurs, and brings down a large quantity of water, it is high at the mill tail, and the waterwheel should be very wide, with buckets as capacious as is consistent with keeping the water at a proper distance from the centre of the wheel, in order to compensate for the fall being reduced, by admitting so much more water when the wheel is raised.

If the new water-wheel is to revolve in the same direction as the old one, the moveable pit-wheel must be toothed inside, and the small spur wheel that it drives, work within it, as at fig. 3.

It may not be quite superfluous to remark, that the shafts, arms, and rim of the water wheel, as well as the ribs and frame of the new moveable bed, or curb, that confines the water in the wheel, should be of cast iron, and sheets of wrought iron are preferable for the buckets and surface of the curb.

By the application of the new principle, many advantages will be derived, a smaller water wheel is required, and, by its going slower, all the power possible will be gained.

When there is a flood, an additional vent may be formed for the

water, by raising the wheel without raising the curb, and letting it run all night, which will also have the effect of scouring and removing all impediments in the water-course at the mill tail.

Should any one of your readers, who may erect a wheel on this construction, transmit an account of his success, for insertion in the Mechanics Magazine, he will oblige your correspondent, and may render some assistance to those mills that are incommoded by tail-water. I am, respectfully,

SAMUEL RICHARDSON.

LONDON MECHANICS' INSTITUTION.

Sir, I am surprised that any one who professes to be a member of the London Mechanies' Institution, and who feels so much for its true prosperity as Aurum affects to do, should be so bold, in the face of great professions of hearty good wishes for its success, to put forth statements which must very greatly injure it in the estimation of those who may happen to read his letter, and who, living far from the scene of action, will be apt to take for granted what is advanced so speciously. Under the cloak of friendship, he conceals the dagger of an enemy; from such friends as these, may the society ever be delivered.

The last paragraph in Aurum's letter, contains a very serious charge against the committee of this institution. He asserts, that through ill management the members have of late been obliged to put up with very inferior lectures. Now, I do not appear as the representative of the committee, having no connexion in any way whatever with them. In speaking of them, therefore, I do so quite impartially, and my letter shall contain a plain, unvarnished statement of matters of fact. Nor do I doubt, but I shall be supported by the whole of the members who attend the lectures, when I state that they are far from being dissatisfied with what they have of late been attending to, in that department of their

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institution which consists of lectures. During the last quarter, Dr. Birkbeck, Mr. Hodgskin, Mr. Cooper, Mr. Hogg, Mr. Preston, and Mr. Green, have been the lecturers, and, with the exception of the latter gentleman's course, the lectures have been such as to do honour to those who delivered them, and afford amusement and INSTRUCTION to those who enjoyed the privilege of listening to them. Indeed, the names of the gentlemen are a sufficient guarantee for the kind of lectures which might be expected from men who stand so deservedly high in the scientific world; for it is not to be supposed that they would risk their reputations by sending forth that, of which they might be ashamed. It is also to be hoped, that there are among the 1500 members of the institution, a number possessed of acumen sufficient to discover any errors or deficiency in what may be advanced before them; and of independence also, which would prompt them to give intimation thereof to the person who would so impose upon them; that this is the case, is a fact too well known to be refuted. The insinuation of Aurum is highly injurious to the good sense of the members; that this inference might be drawn, he seems aware, for he says that the members have in consequence of the bad lecturing, decreased in their attendance; unfortunately for him, the reverse is the case. I have been in the habit of attending the lectures during the whole of the time, since the establishment of the institution, and I am prepared to state, without fear of contradiction, that during the last and the preceding, and indeed every quarter, the attendance has rather increased than diminished. I, of course, except Mr. Green's four lectures on architecture. How Aurum, in the very face of these facts, could so err, is to me a matter of much wonder, as he must be well aware that the menibers of the institution are in full possession of these truths, and he could also not but feel, that his very unfair statement could not pass unnoticed. I do not hesitate to tell him, that he has no excuse whatever his only

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way, will be to act the part of honour, and confess he was wrong. By doing otherwise, he will sacrifice his character (although an anonymous one,) for veracity; and it will appear, that his object was to calmly and deliberately do all that lay in his power to injure the institution for which he professes so great an attachment. I have now fully performed my task of clearing the committee from the charge of nismanagement, by proving that the lectures have not been, and are not inferior. I am sorry to be obliged to take up so much of your time, but the matter is one which calls for prompt interference, in order to prevent the contagion from spreading; I know well your anxiety to correct speedily any error or misstatement which may appear in your pages, and I think you will agree with me in the opinion, that this is one which calls for immediate correction. I therefore beg that you will not delay the insertion of this letter, as, in cases like the present, delay would be cruel.-I cannot help expressing my regret, that so able a correspondent as Aurum should thus so grossly err, as the object he has in view really appears to be that of calm calumniation, and will tend rather to weaken the cause he advocates. Trusting to your well-known candour and generosity in not delaying for a moment my communication, I am, Sir, &c.

VIATOR. We have three other communications of a similar purport from R. W. D.-D. Honor-and Veritas.

Question.

INDIAN RICE-MILL.

The inhabitants of Pegu have a mode of cleaning rice which is quite peculiar to them. Two large baskets, of a conical shape, are joined together at their apexes, which are grooved; the apex of the lower rises inside that of the upper, and around this a space remains, sufficient to allow the grain to pass, after it has been divested of the husk, by the revolution of the upper on the lower basket.

DR. SULLY'S METHOD Of feeding HORSES.

Sir, the public are much indebted to Dr. Sully, for relating so circumstantially his method of feeding horses.

I should be glad to know, from some of your correspondents, where cheap machines may be had for bruising oats, and cutting chaff. Having only one horse, it is a matter of importance to get these at a low price, and yet to be sufficient for my purpose.

I am, Sir,
Your obedient servant,
A CONSTANT READER.

ARITHMETICAL QUESTION.

Sir, I hope you will deem the following question worthy of insertion; it comprises simple addition, subtraction, and division. It is to be solved without the assistance of algebra, or the higher branches of arithmetic, and is chiefly intended for the amusement of beginners.

I remain, Sir, &c.

HERBERT D—.

THE BARNARDINE FIRE-STOVE.

Sir, I herewith send you a description of the Barnardine stove, for the benefit of those who may have the wisdom to estimate its qualities, and to put it into practical use. A few shillings laid out upon any stove in use, will prove what is herein said of it.

At the distance of 31 inches from the clear of the front bars, (inwards,)