22,528 44 1831 Mercury Mars Phoenix Sun Sum 182,675 380 26,053 22,651 20,464 52 17,739 17.082 16,885 16,535 15,603 Victory Sun Fury Sum Average per week Ajax Leeds Saturn Venus Etna 23,134 52 503 220,117 8,542 12 8,526 12 Leeds 538 Among those engines, the Liver had worked for 107 weeks, had travelled 52,865 miles, or, on an average 494 miles a week during all that time; the Firefly had worked 57 weeks, had travelled a distance 33,421 miles, or 586 miles per week, and neither of these engines at the period in question, had yet required a fundamental repair.* MARBLE CEMENT. An important improvement, which has been for several years in progress, is about being introduced to the more general notice of the public, and we believe into extensive use for building purposes. It is a composition or cement, of which the principal ingredient is marble or lime stone, which, when applied to the inner or outer walls of buildings, presents the appearance of polished marble, of the various hues and qualities which distinguish the beautiful material imitated. What would be thought of a magician who possessed the power of changing the sombre brick and stone walls of the buildings of a city, in one week, into substances resembling the most beautiful Grecian, Italian, Egyptian, or Verd Antique marble, or porphyry, like the rock of Gibraltar! Yet all this may be done by this invention of a humble citizen, of Orange county, in this State. This cement has been sufficiently tested by experiments on buildings, to satisfy practical men of its decided superiority over any other cement, stucco, or other hard finish for walls, hitherto known. In our next Number we expect to be able to furnish the public with some interesting particulars on this subject; and in the mean time we can state, that a Company has been formed in this city to carry on the operations connected with the manufacture of this new cement, and its application to buildings.-New York Railroad Journal. The first column in the above table is the same as given in the Memoirs of the Astronomical Society, vol. ii. p. 516, and in the Edinburgh Journal, No. XI. The next, or middle, column is the 1th part of that preceding. The last column is from Professor Struve's new results, as stated in the above Journal, which are nothing more than a reduction of his first observations, as theth part of the first column is the precise difference between the first and the second observations of Professor Struve, with the exception of the fourth satellite only of Jupiter, which, it appears, the professor forgot to correct! Now, had the professor's micrometer, in the first instance, given the diameters too large, why not state that a reduction was necessary, and that the latter measures were the results of such reduction, instead of assuming that they were obtained from a more nu merous set of observations than in the first instance? As it is millions of times more probable, that if fifteen dice were thrown out of a box that they should all of them come up aces, than that the above results should obtain from observation only!! Now, Dr. Herschel was in possession of a telescope of a magnifying power ten times superior to that of Fraunhoffer's; it is therefore very unlikely that Dr. Herschel should have been in error oneseventh part of the whole, if observations can be made in England with any thing like the precision attained to by Professor Struve, as there is a difference resulting from the measurements of the two observers in the exterior diameter of Saturn's ring of 28,500 miles. I am, Sir, yours, &c., J. UTTING, C.E. Lynn Regis, July 22, 1836. SIDERIAL TIME. Sir,-Your scientific correspondent, Mr. T. G. Waldron, thinks (see No. 674) that the longitude of a ship at sea might be correctly found by means of a chronometer made to keep siderial time, and adjusted to some port whose longitude is exactly known; of course, Greenwich is the place best suited for that purpose, as all the articles in the Nautical Almanac are computed for Greenwich time. Mr. Waldron states, that by observing the exact time that any fixed star passes the meridian, by a siderial chronometer set for Greenwich time, the longitude of the ship may be determined. This is no doubt all true, provided you know that your chronometer is right for Greenwich time, or that the quantity of its daily gain or loss of time has been previously established; and also that you can determine by an observation, or a set of observations, the exact time by your chronometer (or within a small fraction of a minute) when the star transits the meridian. Before proceeding further I would remark, is there any thing particular in a siderial chronometer that gives it a preference over that of a chronometer that keeps mean solar time (the principle upon which all marine chronometers are constructed)? I certainly answer none whatever, or rather the advantage for the navigator would be in favour of a chro H. M. S. Regulus passes the meridian of Greenwich, 9 59 39 siderial time. March 31, 1836, at................. By the chronometer Difference of meridian in time..... 1 hour siderial time... reenwich,} Hence (1 10 29′5) × 15=17° 37′ 15′′ W. longitude. Now, a chronometer which indicates on March 31, 1836, 11h. 10m. 20s. of Greenwich siderial time, would be expressed by a mean solar chronometer at the same instant, and also set per Greenwich time by. Difference of meridian in mean solar time.. The difference of the meridians by both methods being exactly the sameand, of course, the longitude the same. But I am afraid that the longitude de termined by the above method could not be altogether depended upon. The only method (as far as I am aware of) of determining the time at sea when any of the heavenly bodies pass the meridian, is by taking a number of altitudes before and after the star passes the meridian, carefully noting the corresponding times indicated by the chronometer; then the time opposite to the greater altitude will be that of the star's passing the meridian. But every one knows who has considered the subject, that for a small portion of time before and after any of the heavenly bodies come to the meri dian, there is hardly any perceptible change in their altitudes; and that an error of 1 minute of time produces an error of 15 minutes of longitude; or if 4 minutes, the error would be a whole degree of longitude. Or if equal altitudes of the star were taken when a considerable way to the eastward and westward of the meridian, the middle time (if the ship was lying to, or making little or no way during the time of taking the altitudes) would indicate (as there is no change of declination) the time the star passed the • The difference between apparent siderial time and mean siderial time amounts only to 25 seconds in 19 years. SYMINGTON'S CONDENSATION BY INJECTION. meridian. But if the ship was sailing during the interval, still, although in this case, certain corrections might be made, errors of one, two, or perhaps three mi nutes might occur. In short, Mr. Waldron's method, I am afraid, if put to the test, would be found not to answer; and more so, when so many methods are now known for determining the longitude at sea to a degree of accuracy nearly equal to that of finding the latitude. I am, Sir, Your most obedient servant, A COUNTRY TEACHER. SYMINGTON'S CONDENSATION BY INJECTION. (Communicated by the Inventor.) The encrustation of the boilers of marine-engines has been long acknowledged one of the greatest drawbacks to the ap plication of steam to navigation; and the many evils arising from it-particularly in sea-going vessels are too familiar to every practical engineer to require explanation. The great loss of power from blowing out the boilers; the great waste in fuel to supply the place of so much hot water; the valuable space occupied by a larger quantity of coals than would otherwise be required; together with the rapid wear of the boilers themselves, even under the most careful management;are among the disadvantages with which steam-ships engaged in the coasting trade, or destined for foreign stations, have to contend. Economy of space and fuel, and the durability of the boilers, are objects of the first importance; and what ever will, in a simple and effectual manner, come in aid of these requisites (with out introducing other disadvantages), must be considered an important advance towards perfecting steam navigation. I am encouraged to think that I have devised a remedy for these evils, simple and cheap in its application, taking up no room, adding nothing to the tonnage of the vessel, and perfectly efficient in its operation. It appeared to me not a little singular, that so many attempts should be made to condense inside the vessel by means of unwieldy tanks, which, at the best, must be but imperfect coolers, when there is so simple and perfect a condenser outside as the open sea or river. I con 295 ceived that by cooling down the water in the hot well to the temperature of the external water, by means of a pipe, so placed outside the vessel as to receive the direct action of the water, in order that condensation might be effected by inject ing, again and again, a portion of the same water, while the remainder is returned to the boiler, it would succeed→→ more especially as such a plan would involve no alteration in principle-in producing a most simple and perfect mode of preventing encrustation, applicable with the greatest facility to any vessel in a few days, and without making any alteration in the engine itself. By this method, the injection-water, after condensing the steam, is conveyed in the usual manner by the air-pump into the hot well, from whence a portion of it en ters the refrigerating-pipe at about 960; and by the rapidity with which the pipe is brought into contact with the constant ly changing particles of water by the motion of the ship, every portion of warmth is speedily given out; and long before the water completes its passage, it will become of the same temperature as the external water, and thus be ready for injection again. The remaining portion of the water escapes to the boiler by means of a float in the hot well, which moves on friction-rollers, in front of the orifice lead. ing to the feed-pump, and rises and falls freely with the rise and fall of the water in the hot well. It is evident that by this means the circulation of the water in the refrigerating-pipes will be kept up with the utmost regularity, as only the precise quantity that has been previously used for injection will again flow into the refrigerating-pipe, to supply the vacancy thus momentarily occasioned, for the purpose of again being injected; whilst the remaining portion of the condensed steam, which will be the exact quantity that has been evaporated, will elevate the float in the hot well until it has escaped to the feed-pump. Thus the same water will be used over and over again in the boiler, and encrustation effectually pre vented; while, at the same time, the supply will be in exact proportion to the quantity evaporated, and, on account of the simplicity of the contrivances, with out any risk of derangement in either case. The steam from the safety-valve will be condensed by leading it into the condenser or external pipe; and by ap 296 SYMINGTON'S CONDENSATION BY INJECTION. plying a small cock to the pipe, near its entrance to the condenser, the engineer can at all times ascertain the temperature of the injection-water, and, by its circulation and purity, that the pipes are free from injury. These will be made of the best stout copper, so as to be abundantly durable, and will, in fact, require repair much less frequently than the copper sheathing of the vessel. It will be seen by the position of the pipes, that they are so embayed as to render it almost impossible for them to receive an injury, unless it be of such a nature as would be equally injurious to the vessel; but in the event of any unforeseen accident occurring, as the old injection-passage and discharge-pipe from the hot well will be left free to act, the engineer has merely to turn on the injection-water, and the same process will go on as if they had not been attached. Thus it is that the simplicity of the means employed; its durability, and consequent cheapness, as well in its first cost as afterwards; the little liability to derangement; and, should an accident happen, the momentary readiness with which the old plan can be resorted to; together with the principle remaining unaltered in the application-render such a mode of preventing encrustation particularly deserving the consideration of all who are interested in steam navigation. Many attempts have been made to prevent encrustation, by condensing without the usual jet, and although the plans hitherto adopted have been eminently successful-so far as the prevention of the encrustation is concerned-yet the best of them has been by means so expensive, so complicated, so liable to derangement from the numerous joints, occupying so much valuable space, and adding so much to the tonnage of the vessel, as to render even encrustation preferable, in most cases, to such a remedy. The mere circumstance of a good vacuum being produced, can be no test of the effective power of the engine, unless the means employed to produce it be also taken into account. Dr. Lardner, in his recent work on the Steam-Engine, has, with his usual discrimination, detected this fallacy. There is no difficulty in creating a perfect vacuum when a much larger airpump than is used in injecting engines is employed; but it follows, that as this is necessary for non-injecting engines, as well as an extra and powerful force-pump to keep up a stream of cold water in the cisterns, they must be burdened with additional duty to perform, from which injecting-engines are free, consequently that the quantity of power uselessly expended in producing the vacuum and doing this extra duty deducts just so much from the effective power of the engine. Nor is it possible to effect condensation with an air-pump of the same capacity, in so instantaneous and effectual a manner, without the usual condensingjet, whatever may be the means employed, or how great soever the extent of metallic surface exposed. The opinions of all scientific and practical engineers have long been decided upon this point, for it is impossible for steam to be brought so immediately in contact with a cold surface, however minute may be the divisions to receive it, as it will be by meeting with a stream of cold water dashed amongst it, every separate particle of the water taking hold of a portion of the steam and blending intimately with it. Condensing without the jet was long tried by Mr. Watt, but was at length abandoned on account of its inferiority, and it has not since his time been revived, until of late years. In a letter from Mr. Watt to Mr. Smeaton, dated the 24th of April, 1776, he thus speaks of the discovery of condensation by injection, and of its vast superiority :-" I have made considerable alterations in our engine lately, particularly in the condenser, for which we have substituted one which works by an injection. pursuing this idea I have tried several kinds, and have at last come to one which I am not inclined to alter, which operates beyond my ideas in point of quickness and perfection." And the vast superiority of this mode, verified by time and experience, have amply borne testimony to the usual sound judgment of Mr. Watt. In It is scarcely necessary to observe, that the disadvantage attached by some-now first discovered after an experience of more than sixty years-to injectingengines, from the supposed liability of the condenser and air-pump becoming choked with injection-water, however feasible it may appear in theory, can scarcely ever occur in practice. Independently of there being a very accurate index to marine-engines, by which the supply of injection-water can be regu |