EFFECT OF IRON MASTS AND CHIMNEYS ON THE COMPASS. 1 press; but his advocate, W. T., one may almost be led to suspect, is hostile to these liberal sentiments. In respect to the illiberality with which I am indirectly charged by W. T., I must observe, that having read Mr. C.'s overdrawn statements of the many excellent qualities of this stove, I was induced to inspect it, and must own that I was greatly disappointed, on being shown so filthy, clumsy an article, as the highly-praised American stove in question. Now, as respects myself, or such persons who have an opportunity to see and judge for themselves, the consequence is but trifling; but to such of your readers who live at a distance in the country, and who have no other means of forming an opinion, except what may be gathered from the Political Register, the case is very different, and it was principally to guard these from disappointment, by trusting to such statements, that the article in your 80th Number was intended; and I have to remark, that W. T.'s assertion that Mr. Cobbett has given his readers and the public an engraved representation of the stove represented by him, is not correct. It is true, that an engraving has been given in one of Mr. C.'s subsequent numbers, but it appears that this engraving was furnished by the person who makes the stove, and is very unlike that recommended by Mr. C.; in fact, he disowns it. It is so altered (like Peter's coat in the Tale of a Tub), that it is quite different from the original. "The enclosed body," says Mr. C. (I have not his Register at hand to refer to his exact words, but I "know that I am right in substance), " is not mine; neither the ornament nor the burning martyrs," as he terms the figures-"I want none of them; two bricks being all that I use to keep the fire together." An elegant mode truly, and which must look admirably in a gentleman's drawing-room. Still the body, as introduced in the engraving, is an improvement, and is what I recommended in my former statement, inserted in your 80th Number; but, upon the whole, my opinion of its merits remains unaltered; for unless the projecting sides and hearth-plate 27 can be done away with, it will never I am, Sir, Professor Barlow having been requested to give his opinion as to the probable effect which the projected hollow iron masts (see M. M. p. 432, vol. III.) in men of war might have on the compass, he returned for answer, that he " thought it probable so great a surface carried above the deck would have a counteracting effect on the usual iron of the vessel, by bringing the common centre of attraction of all the iron nearly into a horizontal plane with the compass, and therefore, in these latitudes, nearly into the plane of no attraction, so as to leave it doubtful whether the actual effect would be the same as, or the reverse of, what happens in the usual cases. If the power of the mast prevailed over the other iron, the effect would be reversed; but if, on the other hand, it did not amount to so much, then the effect would remain the same in quality, but would be diminished in quantity." Mr. Barlow has since made a series of experiments to determine the local attraction of steam-vessels, which present nearly a similar arrangement of materials to a vessel with an iron mast; the iron chimney standing in place of the mast, and the boiler and engine in lieu of the usual iron tanks, ballast, and guns. The result of these experiments fully confirms the theoretical opinion advanced by the learned Professor. The counteracting power of the chimney was rendered very obvious, the local attraction having been found very inconsiderable, and just such as might have 28 FRAUNHOFER'S REFRACTING TELESCOPE. been predicted from the circumstance of elevating the common centre of attraction, as in the case of the iron mast above-mentioned. It appeared from another set of observations which the Professor made with two compasses, one in the fore and the other in the aft line of the vessel (Comet steam-packet), that, with the ship's head to the east, the north end was repelled to the west, and with the head to the west, the north end passed to the east of its true bearing, which shows that the result was either due to the superior action of the chimney, or to some iron abaft the wheel, being directly the reverse of what generally takes place in the usual order of vessels in these latitudes "Whether this," says the Professor, "is the case in all steam-vessels with iron chimneys, may be worth the inquiry of those engaged in the navigation of them, particularly in those intended for voyages." FRAUNHOFER'S REFRACTING TELESCOPE. A Refracting Telescope, of extraordinary power, manufactured by the celebrated Fraunhofer, has just been erected at the Observatory of Dorpat. When in a perpendicular position, the height of the object-glass is 16 feet 4 inches (Paris measure) from the floor, 13 feet 7 inches of which belong to the telescope itself, so that the eye-glass stands 2 feet 7 inches from the floor. The diameter of the object-glass is 9 Paris inches (about 9 inches English). The weight of the whole instrument is about 3000 Russian pounds. It is so constructed that it may be used as an equatorial. The upper part of the instrument consists of the tube, with its axis of motion, two graduated circles, and a variety of levers and counterpoises, producing the most perfect equilibrium in every direction, and providing against all friction. The declination circle is directed from 10' to 10', but, by means of the vermice, may be read off to 5". The instrument may be turned in declination with the finger, and round the polar axes with still less force. The most perfect motion round the polar axes is produced by means of clock-work, which is the principal feature of this instrument, and the greatest triumph for the artist, the mechanism being as simple as it is ingenious. A weight, attached to a projection connected with an endless screw, overcomes the friction of the machine. The clock, vibrating in a circle, regulates the motion by moving an endless screw, connected with a second wheel in the above projection. The weight of the clock, as well as that of the friction, may be wound up without the motion being interrupted. When the telescope is thus kept in motion, the star will remain quietly in the centre, even when magnified 700 times; at the same time, there is not the least shake or wavering of the tube, and it seems as if we were observing an immovable sky. But the artist has done still more; he has introduced a hand on a graduated dial of the clock, by which the motion of the latter can be instantly altered; so that a star may be brought to any point of the field of vision to which it may suit the observer to carry it, according as it is required to make the course of the instrument go faster or slower than the motion of the heavens; and if once placed, it may be kept in that position by returning the hand to its original position. The same mechanism is also used to make the motion of the instrument coincide with that of the sun and moon. This instrument has four eyeglasses, the least of which magnifies 175 times, and the largest 700 times. Professor Struve has com-. pared the power of this telescope with Shroëter's 25 feet reflector, by means of which that astronomer saw the constellation of Orion twelve or thirteen fold; whereas Struve clearly ascertained the existence of sixteen distinct stars. This instrument is furnished with four annular micrometers of Fraunhofer's construction, and an excellent net micrometer of the same artist. By means of these, it appears that the probable error in the measurement of some minute distances, of 7′′ and WATER-CLOCK-UNSINEWING TURKEY S➡ATMOSPHERIC PRESSURE. 29 under, did not exceed the 18th part of a second. The expense of this instrument was about 9501. sterling. PLAN OF A WATER-CLOCK. SIR-Your Correspondent C.D.Y. (p. 339, vol. III.) proposes a plan for a Clock without Wheels; it is ingenious, but I think, while he retains the cylinders, he will have gone but little way towards the accomplishment of his design; for though they may not be wheels by name, still their principle being the same, there are many who will call them so in effect; and a clock, to be properly without wheels, ought to have no part of it moving in a circular direction. Believing it to be possible to construct such a clock, I will, with your permission, lay the means before you. 12 the upper part of the wire moves: the wire has a small flanch on the top. To be filled with water, when a, being set the clock going, the vessel, b, must empty, will, of course, be lifted into the position shown in the sketch. The diameter of this vessel may be regulated so as to allow a fall of nine or ten inches in the 24 hours: the fall (if the idea I have formed be correct) will become more rapid as it descends; but if it can be regulated so as to fall about 3-8ths of an inch in an hour, a nonius or vernier may be applied on the top of the wire, and may be divided to show the time to a single minute, whereas, unless the scale be very long, it will not do it to less than ten or eleven minutes, without crowding the scale. I am, Sir, February 23rd, 1825. MACHINE FOR UNSINEWING SIR, I beg to offer to the public, through the medium of your valuable publication, the Plan of a Machine I have lately made, by which the cook can, with ease, extract the Sinews from the Legs of Turkeys. The following is a rough sketch of it. 1 b Description of the Drawing. b is a vessel, open at the top, containing water; a is another vessel similar to b, but smaller in diameter, and of sufficient weight to sink; this vessel has, in the bottom, a small hole that will but just allow the water to pass; c is a wire fixed in the centre of a, as shown by the dotted line; d is a scale divided into hours, and numbered twice 12; e is a glass tube, let half-way into the scale, about half an inch in diameter, in which 1111 is a trunk,fifteen inches long, three inches wide, and two inches deep; 2, a small winch, to which is attached the cord, 3, which, having a noose at the end, is fastened to the leg of the turkey, which, having been previously broken is laid in the hole, 4; by turning the winch the sinews will be drawn out. I am, Sir, Your humble servant, G. F.. REMOVING ATMOSPHERIC PRESSURE. A Correspondent in our 74th Number, page 275, vol. III., mentioned that he had raised water to the height of eight inches, in a funnel, by the blast of a pair of bellows directed 30 STATE OF SCIENCE IN OUR DOCKYARDS. over the mouth of it. A writer in Dr. Brewster's Journal of Science (No. IV., for April, page 243), states that, profiting by what he had thus read in the Mechanics' Magazine, he has "since found the principle of much service in the use of a syphon, for, by directing a blast from the mouth, through a tube rather larger than the syphon, in a direction nearly parallel with the leg, the liquid is raised over the bend, and thus begins to flow without the inconvenient process of filling it, as is usual.” STATE OF SCIENCE IN OUR DOCKYARDS. [We have already given insertion (page 427, vol. 11.) to one able answer to the presumptuous article in the Quarterly Journal on this subject; and though the writer of the following paper offers little that is decidedly new in the way of argument, he advocates the claims of our operative shipwrights with sufficient intelligence and zeal to entitle him to a hearing. He will perceive that we have omitted two or three passages of his MS.; we thought they were somewhat irrelevant to the main question. EDIT.] SIR,-On perusing the "Journal of Science," Article 12, No. 36, on Naval Architecture, and on the State of Science in our Dockyards, I felt surprise that a Journal of such high character should be the vehicle of a series of observations evidently designed to accomplish a partícular object at the expense of persons who, in the execution of their professional duties, have been of the greatest service to the state. Such an article, I think, demands some remarks, and I shall feel myself obliged by your allowing the following a place in your Journal Alpha begins the article by referring to the experiments which are now making by the vessels constructed by Sir Robert Seppings, Professor Inman, and Captain Hayes, severally, and proceeds to express his wonder that the art of shipbuilding has been hitherto so "singularly neglected." "By far the major part," he says, "of our present knowledge of Naval Architecture has been derived from an imperfect experience, the principles and maxims of theory having but little to do with its improvement." Whatever, Sir, may be the claims of Alpha to knowledge of this subject, and by what means he has acquired that knowledge, I am unacquainted; I am inclined, however, to think that he will ever find that experience is the best teacher. Unhappily for society, the taste of the present day inclines too much to speculation and theory-experience is treated as a thing out of fashion, and the maxims founded on experience are deemed worthy only of contempt and ridicule. Experience, Sir, is the effect which facts or experiments make on the understanding, or it is knowledge gained by practice. We have no more knowledge than we have expeperience. Alpha rightly assumes a suitable name, for he is certainly the first who, to perfect experience, would lead us to the study of theory. I would beg to recommend the contrary, and prove a theory to be correct by the test of experiment. Unfortunately for Alpha, he contrasts civil with naval architecture, and thinks the contrast remarkable. I think it is remarkable, but quite in the contrary direction. It is remarkable that civil architecture has not made any advancements. No doubt the ancients very far surpassed the moderns on this subject, if we may judge by their mighty operations at Athens, Palmyra, &c. Who, in modern times, has written on this subject any thing new? And where is the edifice which can claim even equality with the famous buildings of old? St. Paul's Cathedral, by Sir C. Wren, is all composed of ancient science; the beautiful buildings of Greenwich Hospital are all ancient science: I am confident modern churches and other public building's do not favour Alpha's assertion, unless we select, for beauty, the steeple of Langham-place Church, in Regentstreet; and for stability, the noble edi fice of the Custom-House. The reverse is the case with naval architecture. Let any one examine STATE OF SCIENCE IN OUR DOCKYARDS. the construction of our ships of war; who, of the ancients, produced such pieces of mechanism ? Begin with the reign of Henry the Eighth, travel century after century, and that mind must be dull in the extreme that cannot perceive the progress made in naval architecture, combining "those branches of knowledge on which ship-building so essentially depends." Alpha asserts that "there is scarcely an element in which the naval engineer can predict with certainty what will be its effects when actually applied." Such an assertion is all theory-it is not even imperfect experience; it is rather (I say not ignorance) unacquaintance with the subject altogether. Alpha means to insinuate that such has been heretofore the ignorance of our naval engineers, that they could not predict the depth to which the vessel would be immersed when launched, nor its relative stability compared with other vessels when at sea, nor the comparative resistance it would meet from the water, nor if she will possess with certainty any properties, as weatherly, &c. I much fear Alpha has taken too much for granted, because of the unassuming habits of a class of persons whose engagements necessarily limit the sphere of their acquaintance, and whose situation precludes them from mixing with the scientific world. I suspect Alpha apprehends that the persons on whom it has devolved to construct our ships of war, were deficient in science and imperfect in experience, because they have not become authors, and intruded themselves on the public notice by works of elementary philosophy. It is proper he should be informed, that though they do not boast of their science, yet, if a fair opportunity offered, they would not be found deficient in that measure of knowledge which would perpetuate their names in the estimation of good judges. Hence a Bately, a Sir Ï'. Slade, names which probably Alpha never heard of, and probably the country has forgotten, but whose ships were the result of pure science, and not imperfect experience. 31 Let Alpha look to the operations in our dockyards, especially during a war of twenty-five years, and witness the activity, energy, and zeal of those who had the conducting of the business of them, and he will find that their attention was too much engaged, and their time too fully occupied, to allow of their figuring also in the field of letters. But are they to be deemed ignorant on that account? If there be scarcely "a single element in which the naval engineer can predict with certainty what will be its effects when actually applied," I ask, how came it to pass that, during a long and arduous war, not one catastrophe or failure happened from the defective construction of our ships of war? Which of them sunk or overset ? And is it not a fact beyond dispute, that they brought most of the enemies' ships into our ports, especially those of the French-a people whom, probably, Alpha will refer us to as purely scientific. I will readily and cheerfully admit, that much of the credit is due to our noble sailors, for bringing into our ports the ships of the enemy; yet, however skilful they may have been in naval tactics, or heroic in their military operations, unless the ships had possessed a superabundance of good qualities, they could not have answered to the helm " so uniformly as they did. Let it be always remembered, that the construction of our navy, and their equipment, all devolved, or was principally conducted and managed by two practical gentlemen, namely, the two Surveyors of the Navy. I call on Alpha to inform me, in what respects our ships of war, either in their formation or construction, were inferior to the French in efficiency? What did they do, which our ships did not out-do? I was not aware, when I took up my pen, that the subject would have afforded so much material; I could adduce a variety of facts to substan tiate my position, but as they would bear on a subject to which Alpha alludes in his last page, I fear it would be considered invidious; I shall,' |