172 ON THE REVOLUTION OF THE MOON ON ITS OWN AXIS. partially obscured at intervals by a cirro-stratus cloud of variable tenuity, which, contrary to the usual effect of this modification in its more advanced state of formation, proved rather advantageous than otherwise to the eye, by taking off the glaring light of the moon, without vitiating the observation in the least. On the near approach of the star to the moon, its motion seemed to become irregular, and a few seconds before its immersion appeared to attach itself to the illuminated limb of the moon, when, throwing out a scintillating ray, it instantly disappeared. At the emersion, the star burst into view in its full splendour from the dark part of the moon. The M. S. T. of immersion was at 9h. 12m. 53s., and that of emersion at 9h. 49m. 58s., making the duration 37m. 5s. Now, what is the radius of curvature at this place to produce the above result? It is evident that the absolute time of immersion at Epping was later than at Greenwich, and on the whole the duration at the former place must have been less than at the latter. The error of the clock was ascertained, as on a previous occasion, by correct altitudes of the sun taken with the reflecting circle. An achromatic telescope with an astronomical eye-piece, and power of 80, was used for observing the immersion and emersion. That in lunar occultations of this, and other stars wherein the red rays predominate, they appear to be projected on the light disc of the moon near the time of immersion, is evidently owing to the difference in the refrangibility of the rays of light; those of the white light of the moon being greater than the red light of Aldebaran and similar stars. As the light of Spica Virginis has nearly the same refrangibility as that of the moon, it would be curious to know what appearance this star makes in an occultation about the time of its immersion and emersion. In this case, would not the star disappear or reappear at the moment its direct visual ray became a tangent to the moon's I remain, Sir, yours, &c. Epping, Oct. 22, 1829. EXTRACTS FROM MY NOTE-BOOK. On the Revolution of the Moon on its (Continued from p. 314.) ALL astronomical writers inform us, that the earth in its annual revolution preserves the parallelism of its axis. But though I have attentively. searched several works on astronomy, I have not found that any of them, with the exception of the London En cyclopedia, art. Astronomy, say, that all the planetary bodies also preserve their parallelism. This is an omission much calculated to mislead the astronomical student. The fact that the moon constantly presents the same face to the earth has been considered a proof of its revolution its axis. Now, by fig. 1, it upon is evident that the same face is presented during the whole period of the orbicular revolution, although there is no revolution upon the axis. But in fig. 2, where the parallelism of the axis is preserved, we see that there must be a revolution upon the axis, and that in the same time as that in the orbit, in order that the same face may. be presented. A represents the earth, e e, the moon's orbit, s s s, the moon's axis. Fig. 1. IMPROVEMENT IN WHEEL-CARRIAGES. Fig. 2. On the absolute Zero. It is not my intention to examine the theorem of Irvine for ascertaining the point of absolute zero, or to inquire into the cause of the great différence which exists between the results obtained by those philosophers who have attempted to determine it by experiment, but to point out the fallacy of the reasons assigned by Dulong and Petit, and other modern philosophers, for placing it at 448° Fahr. It appears by the experiments of M. M. Gay Lussac and Dalton, that all gases and vapours, of whatever na ture, when not in contact with liquids, are affected equally in their volume by changes of temperature; the increase in volume for every additional degree of heat of Fahr. scale being Fig. 2. 173 To part of the volume at 32° Fahr." -Farraday's Manipulation, p. 376. Hence it has been argued that since a reduction of the temperature of a given volume of gas to 480° below 32° Fahr. would annihilate all bulk, the point of absolute zero cannot be lower than 448°. Those who have advanced this opinion seem to have forgotten that bodies by a reduction of temperature pass from the gaseous to the liquid state, and from the liquid to the solid. Therefore, steam which at certain temperatures obeys the gaseous law of expansion, becoming fluid below 212° Fahr. obeys an entirely different law; a farther reduction of temperature causes solidity, and another law is obeyed. The same holds true with regard to many other gaseous fluids, both those called vapours and those improperly called permanent gases. And though there are some gases which have not been liquefied, yet it would be a most gross and absurd violation of analogy to suppose that they preserve their peculiar, that is, gaseous form, up to the point of a pretended absolure zero. I shall perhaps in some future communication inquire into the possibility of an absolute zero, but my object here is only to show that we have no reason for placing it at 448° Fahr. (To be continued.) IMPROVEMENT IN WHEEL-CARRIAGES. Fig. 1. Sir,-While treating on the subject of wheel-carriages (in answer to an inquiry by a correspondent) at page 12, of your tenth volume, I stated, that "no one will, I believe, deny that a waggon or other carriage on four wheels of equal diameter, is of lighter draught than those in common use, having the fore pair of wheels of less diameter than the hind;" but, I add ed, "if the load be placed on the fore and hind-wheels, in the same. proportion that their diameters bear to oné another, nearly all the advantages of having wheels of equal diameter will be obtained." On pursuing this subject, it occurred to me, that this proportioning of the load could not at all times be effected in carriages of the ordinary description, even if wished; 174 IMPROVEMENT IN WHEEL-CARRIAGES. because the body of the vehicle must The accompanying rough sketch, fig. 1, will exhibit the manner in which I propose to obtain this desideratum. In this which is a side section of a light waggon or van, mounted on springs, the fore-wheels are of the usual size, that is, as large as will admit of their locking under the body of the carriage in turning. The hinder wheels are unusually large, and are so situated, as to carry four-fifths of the weight when the body is fully loaded; with less than a full load they may be made to carry the whole weight, by placing it over them. To admit of such large wheels being used, the axle is bent, as will be better seen by referring to fig. 2, which is a section of the hinder portion of the carriage; it will also be seen that this part of the carriage is supported by three springs, two only being used in the fore part. Simple as this arrangement may at first sight appear, it will be found to possess a great superiority over waggons of the usual construction. The ease with which great weights may be transported upon wheels of large dimensions, has been a long and well-established fact: but at the same time, it is one of which the builders of carriages have never so fully availed themselves as they should have done. In passing over a rough or unevenly paved road, (such as yet abound in many parts of our metropolis) a small wheel sinks into every little hollow, and the axle, if noticed, would be found to describe a line almost as curved and irregular as the surface of the road. A large wheel on the same road would partake but slightly of its inequalities, and the line described by the axle would be found to deviate but little from a straight line; indeed, with a wheel sufficiently large, the axle would describe a perfectly straight line; in the latter case the friction and consequently the draught would be little more than if the carriage ran upon a rail-road. The larger therefore we use the wheels, the nearer we approach this favourable point of effect. It has been advanced as an objection to the use of large wheels, that they add greatly to the weight of the vehicle; that they do so, I will not deny; but on the other hand, the advantages which large wheels have over small ones are so very great, as to much more than counterbalance the trifling increase of weight. Several other objections have been made; but these as well as the former have been almost wholly removed, by the introduction of the patent metal wheels of Messrs. Jones and Co. a full description of which will be found at p. 209, of your ninth volume. I have attempted to represent this form of wheel in the prefixed sketch, because I am very certain, that no person attempting to improve the construction of wheel-carriages would use any other; they are now very extensively used in vehicles of almost every description. I must beg leave to observe, that I lay no claim to originality in the use of the bent-axletree; be cause that arrangement has been long employed in gigs, fire-engines, &c., by which means, wheels of a considerable size have been used, without raising the body to an inconvenient height. This principle, however, is also one that has not been so extensively applied as its advantage merits. We find, for instance, that brewers' drays, stone trucks, and carriages for the removal of large iron-work, &c. &c., which carry most immense weights, are placed upon the very smallest wheels, for the convenience of loading and unloading. By the application of the bent-axle, large wheels, so highly necessary in these cases, might have been employed without raising the body of the carriage. I flatter myself that the removal of the greater portion of weight from the small fore to the large hind-wheels, will be found to answer in a perfect manner all the purposes of using large fore-wheels DR. LARDNER'S LECTURES ON MECHANICS. the object to which carriage-builders have hitherto directed their attention. In conclusion, permit me to say, that I perfectly coincide with the opinion of the writer of the article on the size of carriage-wheels (R. C. Jun.) in your 321st Number, that the solutions of the problem, at p. 439, vol. ii. are by no means so conclusive as the gentlemen who furnished them may have imagined. I may observe, that they both consider the traces as attached to the axle of the wheel, which is never done. By varying the point of attachment, therefore, the line of draught from the horse's collar may still be kept perpendicular to the line Co (vol. ii. p. 439) with wheels of either more or less than two feet radius. I am, Sir, Respectfully yours, WM. BADDELEY, Jun. If any number of given forces act on any number of given points in the same plane, it is required to determine what effect will be produced? (In the following propositions all the forces are supposed to act on an inflexible rod, the weight of which is not taken into account.) First.-Let there be two equal forces acting on different points of the same body and in parallel directions, it is required to determine what their mechanical effect will be, or in other words, what single force will produce the same effect? 175 Now a weight (F), double C or D acting on a point (E) equidistant from the two given weights, and in the same direction, will produce the same effects as the two forces C and D acting together from the points A and B. It is of no consequence how great be the distance between the given forces so long as the single force is exactly equidistant from both of them. Secondly.-Let the two forces be unequal, it is required what is the single force productive of the same effect? There are two things to be here determined; viz. the magnitude, and the place of the required force. With regard to its magnitude, it is evident that it must be equal to the sum of the two given forces. Let the line AB (fig. 2), represent the body to be acted upon by the unequal weights or forces, C and D, (viz. C 16 and D=12) hanging from the points A and B; consequently the required force will be (16+12=) 28. With regard to its place, the distance between each given weight and that required, must be proportional to the opposite weight. Thus supposing that the distance between A and B be 7 inches, then the point E, on which the required weight F acts, should be distant from A 3 inches, and from B 4 inches, because as C: EB::D: EA, or as 16:4:12:3, therefore a weight F= 28, hanging from a point E at these distances, will be equal in effect to the two (C and D) together. These distances can also be found by common arithmetic. The rule ismultiply the weights by their distances from any point in the place beyond those on which they act, the sum of which products, divided by the sum of the two weights, will give its distance from that point. Thus, as in the last figure, let the distance AH be equal to 18 inches, 176 COPE AND SHERWIN'S NEW PRINTING-PRESS. Sir,-In No. 320 of the "Mechanics' Magazine," I observe a communication from a Correspondent headed "Cope and Sherwin's New Printing Press." I do not consider it my duty to say any thing on the merits of the press; let the trade judge for themselves; but as particular mention is made of the mode of adjusting the pull, I beg to say the improvement is borrowed from me. I introduced it in the late lamented Mr. R. W. Cope's Albion, before Messrs. Cope and Sherwin's press was thought of; and if you agree with me, that it is only just for those who win laurels to wear them, you will insert this communication, and oblige, Sir, your most obedient servant, J. HOPKINSON. 14, New North Street, Finsbury, Oct. 9, 1829. MISCELLANEOUS. Volatile Oil.-At a time when locomotive engines are likely soon to be found traversing all the populous districts of the country, it becomes highly desirable that these moving furnaces should be so heated as not to annoy the inhabitants with a never-ending stream of smoke, and we have the pleasure to find that this desideratum can now be effectually attained. In the manufacture of resin and oil gas a large quantity of volatile oil is collected. This combustible liquid is now used instead of coal at the oil gas-works in Leeds to heat a bench of four retorts, which generate 500 feet of gas per hour; and the heat is kept up during the day without the slightest variation, with two gallons of the volatile oil per hour, giving out neither the least smoke nor smell. The advantages of this discovery for the use of locomotive engines it is scarcely possible to appreciate; and it is not amongst the least of them, that two gallons of the volatile oil, weighing only 16lbs., will produce as much heat as 112lbs. of coal or coke, thereby dituiuishing the weight of fuel to be carried seven pounds in every eight.-Leede Mercury. Naval Architecture.-From two draughts thất have been presented to Sir Robert Seppings by Admiral Greig, two frigates of 60 guns have been built in the Black Sea, with a view to ascertain, by actual experiment, the truth of the principle as laid down by Romnie, the great French author on ship-building, viz. that the resistance the body meets with depends chiefly on the area of the greatest transverse section. The frigates are each about 171 feet long, and 44 feet broad. Their submerged part is a mathematical figure formed from the parabela; and the midships, and other transverse sections, with waterlines, are parabolas of different exponents. Both bodies have the same area of flotation and displacement, with the centre of gravity of displacement, and other elements of construction in the same relative position, but one has a much larger area of midship section than the other.-Hampshire Telegraph. The main-mast of the Briton has been fitted with a tin pipe, for the conveyance of the voice in boisterous weather from the quarter-deck to the main-top. The pipe is about one inch in diameter. It is a proposition of Mr. Parsons, of this dock-yard.-Ibid. Woollen Manufacture.-A French paper (Le Constitutionnel) states, that the manufacturers of Elbeuf and Louviers have discovered and adopted a mode of preparing woollen cloths without oil, or any description of grease-thus rendering the manufacture more cleauly, wholesome, and economical. The Constitutionnel adds, that the cloth prepared according to the new process is as soft, and in every respect as good, as that made upon the old system.——— Literary Gazette. INTERIM NOTICES. In our next Number we shall give a drawing and description of a Safety Railway Carriage, designed by Mr. G. Wilson. We beg to refer such of our Readers as may think with B, that we are occupying too much of our pages with Railways and Railway Carriages, to the developements given in our present Number of the vast influence which they are likely to exercise on society. We trust, however, that B is singular in his opinion. The Liverpool Paper from which we made the extract in our last Number (p. 146), was not, as there inadvertently stated, the Mercury, but the Chronicle. If An Old Subscriber" will state the case in question a little more distinctly, he shall have |