Imágenes de páginas


of land. By Arthur Young, Esq. Secretary to the Board of Agriculture. Accompanied by two Engravings. The econonical dwelling here recommendei to small proprietors of land, contains a drawing-room, study, dressing-rooms, butler’s-pantry, servant's hall, &c.; it could not be erected under an expence of several thousand pounds, and with the offices would occupy an area of 155 feet by 120. XXXII. Answers to queries respecting Gypsum, by Mr. Smith, of Tristall, Kent; comprehend little more than what is to be found in the pamphlets distributed to all purchasers of

We do not know that any thing would have persuaded us to take so much trouble in exposing the nature of this volume, except the hope that we should never have to reprobate such another. 'Art V. The Means of finding the Longitude at Sea, gradually developed,

discovered, and demonstrated, in four Astronomical, Geographical Nautical, Historical, Mathematical, and Mechanical Disertations. By Major-General Grant, Viscount de Vaux, &c. &c. 4to. pp. 194. four

plates. Price 11. 55. bds. Wyatt, 1808, GENERAL Grant presents himself before the public with

strong claims to candour and forbearance, and sometimes to commendation, if not to patronage. He is a Frenchman, descended from a respectable British family, who now writes in the English language with which he is not well acquainted ; though a military officer, he has for years devoted his time and talents to nautical improvements; and, though once high in rank under the old French Government, being then Maré.! chal des Camps et Armées de sa Majesté très-Chrétienne, he is now a foreigner in the land of his fathers, and in adversity.

Of the four dissertations contained in the volume before us, we wish, for the sake of the author, the first two had been onnitted. One of then relates to astronomy; but it contains nothing new, except an erroneous explication of the precession of the equinoxes, and a singular fancy about teaching astronomy at a sloping, pleasure ground in the Isle of Wight, near the bay of St. Helens, in a large pavilion, with soldier's marching to appropriate music, (the harmony of the spheres, of course) and carrying transparencies. The second relates to Geography, and proposes to bring the quarters of the world into their due proportion', and to construct maps upon principles different from what have been commonly used, naking them cylindrical, quadrangular, on a tuscan column, &c. The third dissertation comprises a concise history of navigation, divided into eight periods (whịch our author unfortunately calls epochs), and terminating with the seventeenth „century

There are a few inaccuracies in this part : but, on

[ocr errors]

the whole, it may be read with interest and advantange by those who have not opportunities of consulting larger and more elaborate histories.

The fourth and principal dissertation, both in magnitude and value, is on the inathematical, mechanical, and astronomical means for finding the Longitude at sea', and fills 67 pages. It is divided into an introduction and four chapters. The introduction explains briefly the various means used for finding the longitude at sea, from the time of Vitruvius to the present; and describes with perspicuity, though with brevity, twenty of the most approved methods ever proposed for ascertaining the velocity of a sailing ship, and thence obtaining what inariners call the dead reckoning. The most palpable, (and many of them, in truth, very weighty) objections against these different methods are then stated, after which the General proceeds to describe his own method. He has invented an instrument, by which he proposes to supersede the use of a log, or of any other instrument yet devised for measuring a ship's velocity; and on this instrument depends his method of determining the longitude, as by this he proposes to obtain a correct estimate of the dead reckoning. General Grant farther suggests an ingenious plan for preventing a ship being carried away by currents, or driving on a lee-shore, by opposing a resistance effected through the medium of buoys and elastic cables : but the longitude scheme is the most important, and to that we shall therefore confine our attention,

Our author's instrument, by which this grand business is to be accomplished, he calls, a Hydroscope. Though not very coniplex, it cannot easily be described without a plate: the following account, however, may perhaps give the reader a tolerably correct idea of its general structure.

The hydroscope consists of one or more globes of about 6 inches diameter, of greater specific gravity than the water, and fastened to the end of a cord, or rather to a round, smooth, and very flexible brass chain : the ball or balls to be plunged into the sea either at the centre of gravity of the ship, or at its stern, the chain to which they are appended being fastened at the other extremity to a spring steelyard posited horizontally, within the ship. The cominupication between the ball anđ the steelyard is preserved invariably, by means of a brass cylinder, exceeding the ball in diameter about an inch ; so that one or more balls may be readily passed through it either upwards or downwards: this hollow cylinder is so fixed that the lower end shall be level with the keel, and the upper end enter the cabin at a place above the level of the sea, so as to be free from all danger of giving admission to the water. The chain from the globe is to be directed through the cylinder by running over the grooves of two pulleys one at each end of the tube ; that at the upper end is graduated with equal divisions so as to indicate by means of a little hand the velocity of the vessel, as it is measured by the distance to which the resisting force draws out the spring steelyard. To save the trouble of constantly keeping an account, General Grant proposes that a reservoir containing sand, or powder of calcined tin, after the manner of an hour glass, shall be so posited that a rectangular aperture in its bottom will be opened more or less by a slider acted upon by the spring steelyard ; and thus allow the quantity of sand falling to furnish an adequaté measure of the rate of motion and distance sailed. We cannot enter into the minutiæ of this part of the

of the apparatus ; what we have said will suffice to convey a general notion. Let us now permit the inventor to state in his own language the advantages of his hydroscope.

1st, Instead of half a minute, this instrument has a continued operation. 2nd, Instead of a floating body, which can never answer on such an element as the sea, a diving one is issued, which will act with exactness in the proper mediunrof the ship. This body is one or several globes, the use of which is founded on the i rincipia of Newton, and its effects ascertained by experiments. It is not left at an uncertain place, or at so great a distance from the ship as the log, but is adapted to the ship herself, and follows immediately all her motions, acting accordingly.

3d, This diving body, or globe, cannot be affected by winds, waves, or currents : on the contrary, it will show continually all the effects, not only of the resistance of the water against that velocity, of the ship, but likewise all the first and second causes of the velocity ; for that velocity is occasioned, increased, or diminished by the winds, the currents, &c. and the different parts of the instrument will serve for estimating the direction and the strength of the currents, winds, &c.

4th, This instrument will show continually on a dial-plate the effect of the ship’s way upon the gl be ; for the impression received by the globe on the outside, and in the true medium of the ship, will be faithfully communicated to the machine in the inside ; hy a chain, a cord, or a wire, independently of the friction, which is accounted for by experiment also.

5th, This instrument will not only show, on a dial-plate, all the different degrees of the ship's velocity at every second of time, but will also keep an account of the space run over in every direction, either by means of the falling of sand, or of regular clock-work, as my experiments de. monstrate.

6th, By the means of the cylinder, I substitute to the globe, when I please, any other more active body or bodies, opening into a larger diameter, &c ; but it will be found, that one or several głobés, heavier or lighter, placed farther or nearer, will always act with a sufficient power, &c. &c. &c. pp. 60,61.

Such, in the estimation of the inventor, are the advantages of his apparatas, and these, to a certain extent, it must be al

[ocr errors]

lowed to possess : but the contrivance, though ingenious, is still far from perfect ; and we trust the following observations, should they fall under the author's notice, may be of some service to him. First, it seems to be assumed in the con. struction of this instrument, as described in the volume before us, hat the resistances of fluids to moving in them are simply as the velocities; whereas, they are nearly as the squares of the velocities. 2dly, Since fine sand in a reservoir is so circumstanced, that the upper particles act on the lower with something like a hydrostatic pressure, the quantity discharged through equal orifices will depend though probably not in any constant ratio) on the portion of matter ponderating above such orifices: hence, although sand may serve pretty well to measure equal portions of time by the discharge of equal quantities in similar circumstances, yet we cannot safely rely upon it when employed to measure unequal portions, rates, distances, &c. in the way General Grant proposes. 3dly. Supposing these objections removed, how will the General make bis standard experiment? If it be made by comparison with the log, many of the errors attending the use of the log must necessarily accompany the result of the experiment, and be proportionally incorporated with every other velocity. If it be made by means of a vessel in a river, where the velocity may be ascertained by measurement on its bank, still there will be a source of error ; because the specific gravities of river and sea water are different, and every one knows that the resistances will vary with the densities of the fluids. Lastly, if the waters in different seas have different densities, as is uniformly asserted with respect to the Atlantic and Mediterranean, that scale which indicates correct measures in one sea will be necessarily fallacious in the other. On these accounts the General's apparatus requires farther modification, and his ingenious plan a little more reflexion before it be brought to maturity. But we derive some hope from his fertility of invention ; and sincerely wish, as well for his own sake as the public's, that his labours may be followed by complete success.

We must briefly notice our author's charge of plagiarism against a Mr. J. W. Boswell

, whom he accuses of stealing part of his invention, and publishing it in No. 61 of the Repertory of Arts and Manufactures. Mr. Boswell has in the most. pointed and unequivocal manner denied the charge in No. 76 of that useful work, proving that his contrivance was made known to the public some months before he had heard of General Grant's apparatus, and nearly a year before the publication of the present volume. As persons who stand in a situation that enables us to judge impartially on this point,


we may say, that thie charge of plagiarism is too hastily brought; and farther, that there is no similarity in the two methods, except that in both of them spring steelyards are used as measures of resistance ; but they were employed for that purpose nearly a century ago, and therefore need furpish no ground of quarrel, between two gentlemen who have laboured so successfully in the improvement of nautical machinery as Mr. Boswell and General Grant. Art. VI. An Attempt to prove the Truth of Christianity, from the

Wisdom displayed in its original Establishment, and from the History of false and corrupted Systems of Religion ; in a Series of Discourses preached before the University of Oxford, in the Year 1808, at the Lecture founded by the late Rev. John Bampton, By John Penrose, M. A. of Christchurch College. Svo. pp. 375. Price 9s. bds. Oxford, Cooke ; Murray, 1803. THE versatility of error demands a corresponding variety

in the defence and illustration of truth. If the one adapts its appearances to the changing condition of the moral world, and insinuates its influence by every method which can elude detection or captivate assent, the other is no less capable of diversifying its aspects, and accommodating itself, without the degradation of its dignity, to all the modes of conveying instruction. The attacks, indeed, of infidelity have had the effect of calling forth the defenders of truth; and the malignity of enemies has served only to consolidate the union of friends around the standard of their common faith. The Jittle contrarieties objected against the evidence of Christianity, have been submitted to the most rigid investigation; and its collateral proofs have been greatly augmented by the discovery of those minute coincidences, which could have arised only from the consistency of absolute fact.

The volume before us, modestly intitled “ an attempt," is designed to elucidate one of those indirect arguments, which, assuming the truth of certain undisputed facts in the gospel history, endeavours to trace, in the religion founded upon them, that permanent adaptation to the interests of mankind, which is as opposite, as it is superior, to all the dictates of buman policy; and which is therefore to be attributed to the wisdoni of God. Omitting all inquiries into the nature and evidence of miracles, Mr. Penrose ascribes the continued existence of Christianity to the sublime purity of its doctrines and laws.

This characteristic sanctity he considers as having an uniform and invariable tendency to promote the welfare of men; as undebased by any accommodation to those immediate interests and passions which the designs of imposture might consult; and as hereby ensuring that ultimate success, which it

« AnteriorContinuar »