Mechanics' Magazine, MUSEUM, REGISTER, JOURNAL, AND GAZETTE. No. 576. SATURDAY, AUGUST 23, 1834. Price 3d. 338 SECURE METHOD OF TUNNELING. SECURE METHOD OF TUNNELING. Sir, It is currently reported, that, owing to the soft and crumbling nature of the earth through which the tunnel of the Birmingham railway is to pass, at the foot of Primrose-hill, accidents will probably occur, and even lives be endangered. many With a view to obviate this evil, I would beg a small space in your valuable columns, to describe a plan which, if practicable in itself, would probably render the progress of an excavation of a like nature perfectly free from risk. Let there be a series of cast-iron sections or shields (pointed and sharpened at one end to facilitate their penetrating the clay), of about 12 or fourteen feet long, 12 to 15 inches broad, and of moderate thickness, each section being arched or circular, as shown in fig. 2. Between the sides of the sectious let there be grooves for their edges to slide in, by which means the whole may be kept compact, and the horizontal movement preserved. These detached sections and grooves may be alternately driven forward into the clay, until they are in a line with each other; for this purpose a projecting plate is made on each, to enable them to be driven by a small lever, or jack winch (the latter I should prefer). When this is done the excavators may proceed with perfect security until they come to within two feet of the end, when the shields may be driven forwards as before. The other end of the shields are supported by the brickwork upon which they rest, in conjunction with the earth at the other end (as seen in fig. 1), where they have just been driven forwards into the clay. By using the above method several advantages seem to me to present themselves. One will be that of safety to the workmen, who feeling themselves more secure will be enabled to proceed more rapidly; another will be, that the earth will be cut level, and the settlement upon the brickwork be gradual and regular, so that if the arch be well built in the first instance, which the shields will enable them to accomplish without risk, there will be no sinking of the arch, as is the case in the tunnel of the Regent's Canal. Another will be that, from the earth not being shaken during the process of excavation, or the air admitted to act upon its surface, and also the circular figure of the incision, there will be far less pressure upon the shields (and consequently the brickwork) than were the contrary the case, and the excavation to proceed in the usual way, when the earth falls in. One difficulty will occur, but which may be removed-this is when a large stone comes in contact with one of the sections, in which case that section may be for a time left, and the others forwarded as usual, when the workmen may excavate under the one that is stopped first, without removing the earth from the others until the obstacle is removed. Fig. 1 is merely a sectional view of a tunnel; a the sections and grooves as they may be used; b the brickwork; e the body of clay through which the tunnel is to pass; d the pointed ends of the shields, as they pass into the earth, but shown here for the sake of illustration. Fig. 2, a the shields, e the grooves. Trusting that I have not infringed upon your patience, I remain, Sir, Yours respectfully, JAS. WOODHouse. Kilburn, August 9, 1834. THE UNDULATING RAILWAY. Sir,-As the communication from Mr. Badnall, touching the railway experiments, did not reach me till late on Monday evening, it was of course too late to take advantage of his offer; but by your note in No. 575, I perceive the experiments are postponed, and therefore I take the opportunity of saying a few words on the subject, though much occupation will not allow of sufficient time for any well-digested proposition. After all that has been said and written, pro and con, my opinion remains the same, i. e. that the undulating system is inferior to the horizontal line. Perhaps there may not be available means to produce what I am about to propose, and if so, let it rest for quantum valeat. If there be a correct means of ascertaining the exact amount of duty put ON THE CONSTRUCTION OF A ZODIACAL MAP. forth by a locomotive engine in running a given distance, on a perfect level, so as to run (say) a mile after attaining a maximum speed, let it be tried, and suppose the whole to be exactly a mile and a quarter. Then let the same engine be placed at the lowest part of an undulation which descends from and ascends to the same horizontal level. Let the steam power be then set on to work the engine up to that level, and as much more of it be used in conjunction with the power of gravity, as will enable it to descend the undulation, and place it in the level on the opposite side; the total distance run on a horizontal line, without taking the undulation into account, being exactly a mile and a quarter, as in the former case. Let the total amount of duty expended be then ascertained, and if all the circumstances in the two experiments be alike, and the amount of duty expended in the undulation be less than that on the level, then the verdict must be decidedly in favour of undulation. Mr. Badnall will perhaps object to this, that I propose to do more distance on the undulating than on the horizontal line. This is true; but his power of gravity can only be obtained through the means of extra force applied to place the engine in an unnatural position for rolling bodies, i. e. on a summit level. I will suggest another experiment:Get an engine up to its maximum speed on a horizontal line, and then measure the amount of duty required to progress it a mile. Place the same engine on the summit level above an undulation, urge it downwards by gravity alone, and when gravity ceases to operate, measure the amount of duty required to overcome the ascent, and place the engine on the same level it descended from. The total distance on the horizontal line to be an exact mile, as before. Did not want of leisure prevent me from acceding to Mr. Badnall's request of personal attendance, other impediments would intervene; but I doubt not that, if the experiments I propose are capable of trial, they will be tried with perfect fairness. I remain, Sir, yours, &c. August 16, 1834. JUNIUS REDIVIVUS. 339 ON THE CONSTRUCTION OF A ZODIACAL MAP. (For the Mechanics' Magazine.) The angular positions of the heavenly bodies are expressed by co-ordinates referred to the plane, either of the ecliptic or of the equator. Ancient astronomers adopted the former, modern ones the latter. The change began about the time of Flamstead, whose catalogue of fixed stars was the first that exhibited the R. A. and Decl. from direct observation, and the Long. and Lat. by calculation. For the last half century, notwithstanding the more complex expression of the effect of precession, aberration, and nutation, when referred to the equator, astronomers have decidedly adopted it as the basis of their determinations, and within that period all the original catalogues of stars have been expressed in R. A. and Decl. only. But down to a much more recent period, the national Ephemerides gave the planetary places in Long., Lat. and Decl. only, and when the R. A. was first inserted it was merely approximative. It being obviously proper that Ephemerides and Catalogues should be consistent, it was ordered, upon the remodelling of the "Nautical Almanac," that the geocentric places of the planets should be exhibited with the utmost accuracy in Right Ascension and Declination only.t The construction of zodiacal maps by R. A. and Decl., necessarily follows from the present state of things. I propose to point out a simple method of doing this. The labour of previous calculation may be saved by using the printed tables, entitled "Reduction of the Ecliptic to the Equator-Declination of the EclipticAngles of the Ecliptic with the Meridian."+ In these tables, as usually given, longitude is the argument; but they can be transformed into others having Right Ascension for argument. * The globe-makers have been slow in adopting the modern form. With the exception of Addison's 36-inch sphere, all the celestial globes now on sale are delineated by longitude and latitude. + I trust that the editor of "White's Ephemeris" will contrive to give the planetary R. A. to tenths of a minute of time at least. Mayer, Tabulæ Solis; Tables de Berlin; Philosophical Magazine, vol. lvii.; Pearson's Practical Astronomy, vol. i. 340 DYNAMOMETRICAL EXPERIMENTS. Having then drawn a right line, 90o long by scale, to represent the first quadrant of the ecliptic, and parallels to it 10° north and south, divide the line into forty-five parts, according to the second column of the table, beginning at the right hand. 2. Through the points so ascertained draw meridian lines, making with perpendiculars to the ecliptic the several angles denoted in the third column. 3. Mark off on those meridians the degrees of declination, in such manner that the intersections with the ecliptic may agree with the values indicated in the fourth column. Lastly, through the graduated meri 4. dians, draw curved parallels of declinaPof tion, which, at the equinoctial end the projection, will approximate to rights lines. The meridians at the odd degrees of R. A. may be inserted by bisection. The projection thus made for the first three signs will serve, by reversion and inversion, for the other nine signs. I have recently lithographed a projection of one-third of the sphere, aos cording to the principles described in the last volume (No. 539). The dia meter is 17 inches, the central scale 0.105 inch, being that of a 12-inch globe, and the meridians and parallels exhibited for every two degrees. At tlie foot of this is a projection of a quadrant of the zodiac, on a scale of 02 inch to a degree, the lines of R. A. and Decl. drawn for every degree. These projections I shall probably publish for the use of students. An impression of them has been forwarded to the editor.* J. W. WOOLLGAR. Lewes, August 18, 1834. DYNAMOMETRICAL EXPERIMENTS. Sir,-About six weeks ago I had a dynamometer made, and I now send you an account of some experiments I have made with it: 1st. A waggon and its load 3 tons was moved by one horse, exerting a force of 6 cwt. 2d. The same horse exerting all its force at a dead weight=12 cwt.; weight of horse 131 cwt. 3d. Waggon and its load1 ton, 17 cwt., was moved by one horse exerting a force of traction=4 cwt. 4th. Experiments with boats on the Grand Junction Canal. STEAM COMMUNICATION WITH INDIA. STEAM COMMUNICATION WITH INDIA. Sir, While it may be freely admitted that the Messrs. Seaward have advanced some strong reasons in favour of attempting a regular communication by steam with India, by the Cape of Good Hope, it is by no means so clear that they have established the superiority of the old route over the proposed "south-east passage," as a line for the rapid transmission of intelligence. It is quite a mistake to suppose that either the Steam Committees in India, or the Committee of the House of Commons, propose to "drive commerce back into its ancient channels." The convenience of the Cape route for mercantile purposes is fully admitted, and the chief, and almost only, purpose of the new arrangement, is to provide a conveyance of greater and more certain rapidity for letters and despatches. That this is a great desideratum, is evident from the fact, that our Indian governors, as well as merchants, have sometimes had to wait not less than two months over the time of the expected arrival of a vessel,-a period sufficient for the accomplishment of the whole distance by the proposed "south-east passage." The article in the Mechanics' Magazine of August 2, calls the new route "from 4 to 5,000 miles shorter than that by the Cape of Good Hope." This is quite an understating of the amount saved. Messrs. Seaward tells us that the usual passage is about 14,000 miles; and I believe it will be found that the south-east passage, whether by the Red Sea or the Persian Gulf, is under 5,000, so that nearly double the distance specified will be actually saved. No speed, surely, in steaming, by the old route, will make up for so great a difference as this. Besides, if it is so very practicable to steam away at ten miles an hour throughout the whole of the longer passage, what is to prevent the same being done with the shorter ? True, there is the land carriage in the way, and this is, of course, the grand obstacle to the new plan. I do not see, however, that it necessitates the division of the passage into four stages. By the Persian Gulf, for example:-one steamer would proceed from England to Scanderoon, the port on the Mediterranean,from thence the letters and passengers 341 would be conveyed overland to the nearest port on the Euphrates, where a second steamer would be in waiting to complete the passage down the Euphrates and the Persian Gulf to Calcutta and Bombay. Where is the necessity of a vessel exclusively for the river? Such a necessity has never, I believe, been contemplated by any but the Messrs. Seaward, and they, perhaps, would not have discovered it, had they not been hard pushed for objections to the southeast passage. It should not be overlooked that the European half of the proposed line of steam navigation is already established. All that would be necessary to complete the chain, were the proper measures taken on the Asiatic side, would be, for our Government to order one of the Malta mail-packets to proceed on to Alexandria or Scanderoon, as the case might be. The arrangements for steaming by the old passage, of thrice the length, would have to be wholly made throughout the whole extent. No slight task, if we recollect that the only officer who has a knowledge of steam navigation by the Cape, from experience (Lieut. Johnson, commander of the Enterprise), considers that no less than twenty depôts of coals ought to be provided at different places on the route! True, Messrs. Seaward do not think so; but then Messrs. Seaward have had as little experience in steaming to India, as their friend the Dutch engineer had in making steam-engines. He was sanguine enough of success; and Messrs. Seaward are sanguine enough of being able to reach India in about half the time the Enterprise consumed in effecting the passage. But the Dutchman found his inexperience had deceived him. Verbum sat. Allowing that Messrs. Seaward's plans would be perfectly successful, it appears that the old passage would take twenty days' more time than the new. Even if this were all the saving, it would surely still be worth while to establish the new route, if only for the conveyance of letters. It is not by any means clear, however, that the south-east passage would take up so many as fifty-two days. In In the article referred to, the Euphrates is spoken of as if it communicated with the Mediterranean, if it did, there would be no need of an overland journey. |