LIBRARY OF USEFUL KNOWLEDGE.

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The introductory address "The Society for the Diffusion of Useful Knowledge," which we noticed in our last, has been followed by the publication of the first of their scientific treatises. The subject is "Hydrostatics," and occupies thirtytwo closely printed pages, illustrated with numerous wood cuts. Chap. 1, treats of the nature of fluids; chap. 2, of their equal pressure; chap. 3, of the hydrostatic paradox and levelling; chap. 4, of pressure on oblique surfaces, and the centre of pressure; chap. 5, of specific gravity, the hydrometer and areometer; chap. 6, of the various specific gravities of bodies, including a very complete table of results, collected from a great variety of sources, and

reduced to one common measure; chap. 7, of the syphon, and intermitting springs, and chap. 8, of capillary attraction.

In these eight chapters, the writer has addressed himself to the understandings of readers who are unac quainted with mathematics; but there is a 9th chapter added, which contains series of "Mathematical Illustrations," for the benefit of those who are familiar with Euclid.

It is almost praise enough of so comprehensive a treatise to say, that it costs but sixpence. But besides being extremely cheap, it is extremely well written. It exhibits little either of novelty or originality, and in some instances, is rather behind the knowledge of the age, particularly where it treats of the syphon and capillary attraction; but all that it does contain, and that is a great deal, is not only well worth knowing, but presented to the reader in a manner strongly calculated to fix and engage his attention.

It appears from the selection of topics, which the Society have made for their first essay, that it forms no part of their plan to produce their treatises in a strictly systematic order, beginning with the simpler elements. We fear, that though this may facilitate their labours, it will diminish their usefulness. The com

MECHANICS' INSTITUTION.

Sir, I am requested by the committee of this institution, in answer to a letter inserted in the last number of your excellent publication, signed " J. WILBY," to inform you and our other friends in general, that this committee do not nor have they ever contemplated any innovation of the principles of this institution, as complained of by your correspondent: that they all feel zealously and warmly determined to support the institution as originally constituted, and, that they are resolved strenuously to repel (should it be made) any attempt to alter its name and its objects. The friends of the common cause may be confidently assured that similar sentiments are entertained by nearly the whole of the members forming the institution. An early insertion of this will oblige,

Dear Sir,-Seeing in your 165th number, Senex's improvement in carriages, it reminded me of an improvement in chaises, which I have long thought of communicating to the public, to whom it may not only be very convenient but economical. I think it may save individuals a score or so of pounds, which in these days, when money is so scarce, is well worth saving, and it will be especially useful to inn-keepers and private families, &c.

I have prefixed a rough sketch of the improvement, which is so very

nation; if any at all.

The object of it is that one chaise may be drawn by horses of different sizes, from a pony* to a horse 16,

* In the second figure prefixed, the engraver has by mistake omitted to make the horse of the pony size. EDIT.

TUAL MOTION.

Since inserting from a contemporary journal the plan of perpetual motion, devised by Sir W. Congreve, we have received a small pamphlet on the subject, by the ingenious baronet himself, from which we extract the following additional illustrations.

"It is evident that a constant accumulation of weight on one side of such a wheel as here described, and not on the other, would cause it to roll forward spontaneously in the circular path thus marked out for it; and as this progres sive motion must necessarily occasion a considerable undulation in the water contained in the cistern, this undulation will raise the water in front of the wheel some inches above the level of the accumulation caused by the mere capillary attraction. If, therefore, this rise of the waves thus created be four inches above the water's level, the accumulation of water in the sponge on the descending side, including the one inch gained by the capillary attraction, would be five inches in height, and by this means the motive power of a wheel, the original power of which would be 30lbs. as calculated above, would thus be raised to 150lbs. which might probably be still further augmented by some mechanical means placed in front of the wheel to increase

the agitation of the water. Thus if a ripple so created rose about nine inches including the capillary ascent, and were repeated every second, the periphery of the wheel would move through a space of nine inches in that period, and revolve at the rate of fortyfive feet per minute, with a constant descending weight of rather more than 180lbs.; which would make the power of such a wheel rather above the power of one man; and if five such wheels were combined, so as to work round one centre, their united force would be equal to that of a one horse power steam engine,

"This mode of increasing the power of the revolving wheel in the preceding figure, by exciting an undulation in the water in which the wheel floats, leads to an application of a similar principle, by which the force of the waves of the sea may be applied with great effect as a moving power to ships and boats, which I shall here, therefore, explain:

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"The above figure [represents the bow of a boat having 'a wheel of suitable dimensions fixed in front of its stem by a strong frame work. This wheel is a hollow cylinder closed at the ends, but open all round, with its interior divided into compartments, similar to the Persian wheel, and so disposed that, on a wave rising to any height on the periphery of this circle, all that part of the wave which enters the interior of the wheel or cylinder, shall be retained in the fore-part thereof; while any part of this water, which shall find its way into the after-part of the wheel shall not be retained, but flow out again immediately; so that in case of a wave rising to the full height of the wheel, the whole of the front half of the cylinder shall be fully charged with water, while there would be no counterbalancing quantity in the after-part. The consequence of this, therefore, would be, that a constant revolving force would be kept up by a succession of waves; this force being in proportion to the breadth and diameter of the wheel, and to the height of the wave. Thus, if a wheel be six feet in diameter, and six feet broad, and the perpendicular rise of the waves be also six feet, the maximum charge or moving power of such a wheel would be about 1 ton, being the weight of water contained in the front half of the wheel, and this, supposing the ship to be in motion, would probably be renewed by succeeding waves, about 20 times per minute. On an average, however, the perpendicular rise of a wave at sea, in lakes, or large rivers, could not, perhaps, be taken at more than from four to five feet, but this would be somewhat increased by the pitching of the vessel; the revolving power, therefore, of such a wheel might on an average be estimated at one ton, acting by repeated impulses, similar to that of the common oar or paddle; and supposing the least wave that could be reckoned upon to be from one to two feet in height, so the least probable power, in calm weather, might be taken at 5cwt.

"The velocity with which the charge of water will descend in these different cases would of course vary. Thus in the first instance, where the wheel has its full charge, the centre of gravity of this water, will be found rather above the horizontal radius, so that every charge would fall through a space of about five feet before it would discharge itself; and supposing therefore, the succession of waves were about 20 in a minute,

the moving force of this wheel might be taken at 1 ton X5 feet X 20, that is to say, 1 ton moving through 100 feet in one minute; which will be found to be about equal to the power of a ten horse steam engine. In the second case, allowing for a proportionate falling off in the succession of waves, and in the velocity of the descent of the water-the power exerted may be considered as equivalent to the power of a six horse engine, and in the latter case, to that of a two horse power. A similar wheel also might be placed at the stern of the vessel with equal effect, and two or three such wheels might be applied without inconvenience either side, being mere external appendages, by which means the first power of an enormous propelling force might be attached to a vessel without any internal apparatus, labour, or fuel whatever.

on

"In larger vessels it is evident that a wheel of ten or twelve feet in diameter may be used instead of six feet, by which a proportionate increase of power would be gained. Thus the maximum power of a wheel twelve feet in diameter, and six feet wide, would be equal to that of an 80 horse power engine, supposing it to be charged by a repetition of waves at twenty feet per minute, and supposing the centre of gravity of each successive charge to pass through a space of 10 feet before it emptied itself. Two such wheels, therefore, would propel a very large vessel without the slightest loss of stowage or expense beyond the first cost. When moderate velocities only are required, the propelling power may be obtained direct from these wheels by furnishing them with paddles similar to the propelling wheels of a steam boat; but where greater velocities are required, these cylinders should not themselves be furnished with paddles, but should be used merely to drive propelling wheels connected with them by machinery, so as to move at double or treble the rate of these first movers themselves.

"It may be objected to this mode of propelling vessels, that the necessary undulation on the surface of rivers and seas is not always to be found. To this objection, however, it may be most conclusively answered, that in this respect the system of propelling by the rise and fall of waves, is even more general in its application than the present system of propelling ships by the wind; for whenever there is wind there

must be waves, and considerable waves are frequently to be met with, even in a dead calm, which is so far a gain in favour of this new system. But there is a still more important circumstance in favour of the new system, which is, that in the latter case, the force is alike applicable to all points of the compass, whereas the power of sails can only be applied in about twenty points out of thirty-two, in which respect it obtains all the superiority of steam navigation without its expense or inconvenience. To this also may be added, it is much less liable to accident and danger from bad weather, than the system of navigation by sails.

(To be Concluded in our next.)

SYLVESTER'S HEATING APPARATUS.

Sir,-In reply to P. M. (in No. 185) as to Sylvester's heating apparatus, I beg leave to inform him, that Leek Church, Staffordshire; Mr. Turner's Mansion, Rooks' Nest, near Dorking, Surrey; the Infirmary at Derby, and some part of the new buildings at Christ's Hospital, now the Blue-coat School, London, have all been warmed by it. Whether Mr. S. be, or be not, the original inventor, I cannot positively state, but I believe he is qualified to direct and execute the necessary works wherever it may be decided to adopt, this method. As he some few years since connected himself with a firm in the ironmongery trade, who had a house of business on the south side of Great Russell Street, between the Museum and Bloomsbury Square-perhaps this may be a sufficient reply to P. M. But as I have derived much pleasure from your Magazine, to which I have subscribed from its commencement, I will not merely answer the enquiry, but hope to add a little information on the subject, and I trust this will not prevent P. M. from inspecting the apparatus, or seeing Mr. Sylvester; and if these objections be now obviated, that your readers will be be nefitted by his communicating the method of doing so.

Mr. Sylvester professes to supply, by his apparatus, atmospheric air,

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at a high temperature, in a pure state. I am averse to contradicting any practical man on the subject of his own business, but as far as my observations, at the period of my inspection extended, I am sorry to state, I did not find the above assertion proved,-The chief causes of complaint were closeness in the apartments, and a sensation of dryness in their atmosphere.

It is almost unnecessary to remark that, without providing for due ventilation, every system of heating would be liable to the first objection, closeness, but that the latter, dryness, would depend upon the mode of generating or communicating caloric to the atmospheric air.-If, in the process, it be partially decomposed, or undergo any change in the arrangement of its constituent parts, it is so far unfit for the use to which the wise economy of Providence has assigned it.

If I remember rightly, Mr. S. affirms that atmospheric air passed over or through a hot iron cylinder or cockle which has become oxydized, will not be injured.-I am of opinion, that the hydrogen (if not the oxygen likewise) will be so acted on that the air thus heated produces an unnatural sensation of dryness and uncomfortableness on the human frame. It is well known that in some parts of the continent of Europe, where the Russian stoves are used, that a vessel filled with water is placed in the room, the gradual decomposition or evaporation of which obviates their bad effect on the air, which otherwise would become unwholesome for the purposes of the animal system. Mr. Sylvester's method was tested by using it to warm a large greenhouse; the plants sickened, and would probably have died, but it was abandoned, and they recovered; steam has since been adapted, and they continue to do well.

Whatever P. M. does, let him not be led away by the blame or praises of this or that system of warming and ventilating-let him examine each thoroughly and judge for himself.-From Dr. Hale's time (who wrote tolerably well) to the present,