"This world is a circle of wonders, it seems, Where reality surpasses th' most sanguine of dreams." LAST week we paid a visit to the Royal Surrey Zoological Gardens, in order to view the above novelty, and must confess that, despite all our preconceived notions of scientific progress, we were taken aback at beholding, thrown across a lake some eighty feet in width, a structure so light as to be shaken by a touch of the hand, yet capable of supporting a weight which the observer would suppose sufficient to crush it to atoms. The bridge is supported by two wooden buttresses, one on either side of the lake, standing seven feet out of the ground and five in; to these are securely fastened the ends of four stringers, made by glueing pieces of wood together in several places in order to obtain the required length. At the buttress readers to pay a visit to this novelty, at least so it is in this country, though we understand that is is in practical operation in America, of which country its ingenious inventor is a native, premising that they will be both gratified and instructed by the sight of what may truly be denominated one of the wonders of the nineteenth century.. Mensuration of Superfices. (Continued from page 163.) PROBLEM X. end these stringers are four inches square, but THE diameter of a circle being given, to find in the centre of the bridge, where the greatest the circumference; or, the circumference strain might be naturally expected, they taper given, to find the diameter. to one inch. This constitutes the bridge itself, the footway being merely laid on for the convenience of passengers, and formed by placing slips of deal across the longitudinal stringers. Forty men, each averaging eleven stone in weight, have marched across this structure; but Mr. Remington estimates that it will bear six tons with perfect safety. Bridges of this construction may be made of any breadth and of any length-in fact, the longer they are the stronger they become." The advantages and utility of such bridges are self-evident: by their means a communication may be made in a short time over rivers, ravines, and valleys; and at an expense of twenty pounds a structure of this description can be formed to cross a sheet of water, and, by keeping it well painted, will last twenty years, and even longer than that if the wood be submitted to the anti-rot process. In conclusion, we earnestly recommend our circumference. C circle is found, the one from the other, by one The diameter or the circumference of a of the following rules : 1. As 7 is to 22, so is the diameter to the As 22 is to 7, so is the circumference to the diameter. 2. As 113 is to 355, so is the diameter to the circumference. As 355 is to 113, so is the circumference to the diameter. 3. As 1 is to 3.14159, so is the diameter to the circumference. As 3.14159 is to 1, so is the circumference to the diameter. OBS. The exact ratio which the diameter of a circle bears to the circumference has never been determined. This celebrated problem, called squaring the circle, has for ages exercised the abilities of the greatest mathematicians. Many persons of eminence have, at various times, laid claim to the honour of having achieved the task, but their errors have been soon detected; and although the problem is apparently very simple, yet its solution defies all the arts of analysis, and is now generally considered an impossibility. But although the exact relation between the diameter and the circumference cannot be expressed in known possible quantities, an approximation to the truth may be made to any assigned degree of exactness. In this manner the problem was solved by Archimedes, who, about two thousand years ago, discovered that the diameter is to the circumference is 7:22; which affords our first Rule. The proportion of Vieta is that of 113: 355; which is more exact than that of 7: 22, and is true to six decimal places. It was derived from the pretended quadrature of a Mr. Van Eick. But the person who first ascertained the ratio to any great degree of exactness was Van Ceulen, a Dutchman, in his book "De Circula et Adscripsis." His proportion was true to thirtysix places of decimals. Abraham Sharp (amanuensis to Sir Isaac Newton), of Little Horton, near Bradford, Yorkshire, extended his calculation to upwards of seventy decimal places. Machin, who was Professor of Geometry in Gresham College, London, calculated the quadrature of the circle true to a hundred places of decimals. Mons. de Lagny has carried it to 127 places; and in an Oxford MS. it is carried to 152 places. Mr. Rutherford, of the Royal Military Academy, Woolwich, has lately computed the ratio of the diameter to the circumference to 208 places of decimals. If the exact ratio could be obtained, it would be a sort of mathematical triumph, rather than a real good; for any one of the ratios we have given is sufficiently accurate for all practical purposes. Example 1.-What will be the circumference of a circle, whose diameter A c is 20 ft.? 458410 314159 Varnishes. (Continued from page 163.) 61. Varnish for Oil-Paintings. TAKE the whites of as many eggs as you have paintings to be varnished, and also as many lumps of white sugar-candy, each the size of a hazel nut. Dissolve the last and mix with a teaspoonful of brandy, then beat the whites of the eggs to a froth, and, after it has settled, add the clear portion to the brandy and sugar, and varnish over your paintings. N.B. This is much better than any other varnish, as it is easily washed off when the paintings require cleaning. 62. Pumicing Varnish. Take of sandarach three hundred and fifty parts, mastic twenty-five parts, gelatine twenty-five parts, Venice turpentine thirty parts, Benjamin (benzoin) eight parts, and rectified alcohol five hundred parts; the whole to be dissolved and strained through a piece of linen. 63. Second Kind. viously added) is then to be poured upon the mixed mass. The brass objects to be varnished should be heated before immersing them in the liquid. e. Introduce into a glass mattras sandarach one hundred parts, mastic one hundred parts, Venetian turpentine fifteen parts, alcohol five hundred parts; close the aperture of the mattras with a perforated piece of bladder, and expose to the heat of a sand-bath until the mass is completely dissolved, taking care to shake the mixture from time to time. When complete solution has ensued the liquid is to be filtered through paper. This varnish has a great gloss, and may be pumiced and polished without peeling off. For pumicing, tripoly and a damp piece of cloth may be used. The articles pumiced should be wiped and rubbed with oil, then wiped again with a fine cloth, and the oil finally removed with starch. (To be continued.) PROJECTILE FORCE OF COMPOUNDS.-The words strong and strength are very fallacious, and therefore the notion which the public have of projectile compounds, is, among other things, very incorrect. An ounce of powder, fired loosely, scarce makes a noise-a little smoke, a little smell of sulphurous gas, and all a. Varnishes made equally with alcohol, but is over; yet, the same ounce of powder in a of less desiccative nature and less strongly musket would be a charge far more than pronounced odour than the preceding. San-necessary to urge with deadly effect a leaden darach ten parts, resin elemi one hundred and twenty parts, resin fifty parts, camphor fifteen parts, ground glass one hundred and twenty parts, and pure alcohol one thousand parts. This composition is used for carvings, toilet boxes, and small pieces of furniture. b. Sandarach one hundred and eighty parts, plate lac sixty parts, arcarson one hundred and fifty parts, white glass, in powder, one hundred and twenty parts, liquid turpentine one hundred and twenty parts, and pure alcohol one thousand parts. This varnish is used for wainscoting, furniture, gratings, &c. ball. An ounce of fulminating silver on the other hand may,-but who would dare to handle an ounce of such a substance?-say the ninety-sixth part of an ounce, or just five grains; well, five grains of fulminating silver are taken out of a paper with much fear and trembling, touched with no hard substance for fear of explosion, then gently laid on a piece of metal, say a penny-piece; then, suppose it ignited by means of a very long stick, with a match at one end, and, begging the operator's pardon, with a somewhat rash man at the other-what is the result? A terrible crash, which deafens the operator for some days, and the penny-piece is almost bent double! "How strong!" exclaims a nonchemical operator; "how well this will project a ball!" He tries a small charge in a musket, and what are the results? Why, the gun is burst, the iron literally rent into threads and fragments, the ball is perhaps projected, but to an inconsiderable distance-if of lead, flattened as if by a hammer; if of cast-iron, broken into fragments!-Now, which shall we say is the strongest substance, gunpowder or fulminating silver? The force of all explosive d. Lac, in grain, one hundred and eighty parts, bodies depends on the gases which are liberated melted amber sixty parts, gum six parts, aqueous during the explosion, and the peculiar effect of extract of red sandal one part, sandragon thirty- their explosion depends on two separate cirfive parts, saffron two parts, glass, in powder, cumstances,-the total quantity of gas elimione hundred and twenty parts, and pure al-nated, and the rapidity of elimination. Guncohol one thousand parts. c. Sandarach one hundred and twenty parts, lac, in grain, sixteen parts, mastic, thirty parts, Benjamin, in tears, thirty parts, pounded glass one hundred and twenty parts, Venetian turpentine sixty parts, and pure alcohol one thousand parts; it is coloured with a small quantity of saffron. This varnish, which is of a light colour, is used for violins and other chorded instruments, and also for furniture made of the wood of the plumtree, acajou, and rosewood. powder, perhaps, compared weight for weight This varnish is generally used for brass with fulminating silver, liberates more gas of articles, to which it imparts a golden tint. The the two, but not so rapidly: the liberation is amber, lac, gum, and sandragon are to be progressive, not instantaneous. Hence its porphyrised first, and subsequently mixed with immediate disintegrating effects are not so conthe powdered glass; the alcohol (to which the siderable as those of fulminating silver, but as saffron and extract of sandal have been pre-a projectile agent are more efficient. MECHANICS AMONG THE ANCIENTS.-The town of Pompeii was supplied with water by means of pipes of iron, lead, and baked clay. The museum of the dug-out city contains a bronze cock, of a large size, which has two communicating pipes. The splashing of water, which has been so long hermetically sealed, can now be heard in it. It is proved, both by the fountains and fresco paintings, that the Pompeiians were acquainted with that law of water, which causes the fluid flowing in a pipe to ascend to the level of its source. It has always been gravely asserted that this property was not known to them, or it is presumed they would not have carried their aqueducts over such stupendous arches of masonry. Perhaps in some of these cases, there may have been labour lost, but they must have known well the impossibility of making masonry to resist the hydrostatic pressure where there was a great head of water. GIGANTIC GASOMETER.-There is now in the course of construction, at the extensive ironfoundry of Messrs. Westwood and Wrights, Hope Works, Brierley-hill, a gasometer measuring 471 feet in circumference, the mean diameter being upwards of 150 feet. The depth from the centre of the crown to the bottom will be 45 feet, of which 38 feet is to be the available mean depth for containing gas, and it is calculated will hold 671,498 cubic feet. This stupendous piece of workmanship will contain upwards of 28,000 feet of riveting, and when completed will weigh upwards of 400 tons. It is being made to the order of the Phoenix Gas Company, Vauxhall, London, which is to be its destination, and will be the largest of the kind in the world. ARCHITECTURAL ASSOCIATION. - The first. conversazione of this new society was held on the evening of Friday last, the 8th instant, at Lyon's Inn Hall, Strand. NOTICE. With No. 26 the First Volume of the DECORATOR'S ASSISTANT will be completed, and with that Number will be issued a Title-page, Preface, Index, and A MAGNIFICENT FRONTISPIECE. ment advertisement duty of eighteenpence, and they will therefore perceive that it is entirely out of our power, without submitting to a pecuniary loss, to comply with their requests. NOTICE.-Any of our readers having matured inventions, which they are desirous of communicating to the public, are informed that we shall always be ready to introduce such in our pages. QUERIES. [In order to collect as much useful information as possible, we have determined on devoting a portion of our space to the insertion of Queries which may be interesting to many of our Readers; at the same time we must intimate that the replies should be as brief as possible, without incroaching on their completeness.-EDITOR DECORATOR'S ASSISTANT.] Required-The method of preparing glass for laying transparent colours upon, and also the method of preparing the colours.-C. Š. (Leeds). ANSWERS TO QUERIES. CALOTYPE.-Sir, I beg to offer the following directions on calotype in answer to "Le Pense Plus:"-Paper-Good writing paper is washed with a solution of the sulphate of copper, and partially dried; it is then washed with a solution of the bichromate of potassa, and dried at a short distance from the fire. Papers thus prepared may be kept for any length of time, and are always ready for use. They are not sufficiently sensitive for use in the camera obscura, but they are available for every other purpose. Method of obtaining the Picture-An engraving, botanical specimens, or the like, being placed upon the paper in a proper photographic copying frame, it is exposed to sunshine for a time, varying according to the intensity of light, from five to fifteen or twenty minutes. The result is generally a negative picture. This picture is now washed over with a solution of nitrate of silver, which immediately produces a very beautiful deep orange picture upon a light dun-coloured or sometimes perfectly white ground. This picture is quickly fixed by being washed in pure water and dried.-Your obedient servant, PTOLEMY.-Finsbury. MENSURATOR (Dublin).-The first stone of St. Paul's Cathedral was laid June 21, 1675, during the reign of Charles II., and the choir was opened for divine service on the day of thanksgiving for the peace of Ryswick, December 2, 1697. St. Peter's at Rome occupied 145 years in building, and twelve successive architects were required to complete it; St. Paul's was finished in 40 years, under the presidency of one Bishop of London, and the direction of one architect, and by one builder. The parliamentary grants for this purpose were increased by a tax levied on all coals imported into London, and still further enlarged by the contributions of private individuals. The whole expense of the building, according to the estimate in Sir Henry Ellis's edition of Dugdale's "St. Paul's," amounted to £736,752 28. 3дd. Z.-We are satisfied. As to the perpetual motion, we can only say that, as the thing is an utter impossibility, we ROBERT EDWARDS (Manchester).-We should prefer the must decline treating upon it. In order to meet the great additional expense thus neces-A. sarily incurred, the price of that Number will be raised to THREEPENCE. Early orders are respectfully requested, as no greater number will be printed than is warranted by the average sale. Notices to Correspondents. Part V. of the DECORATOR'S ASSISTANT, in a beautifully embellished Wrapper, is now ready, price Sevenpence. Parts I., II., III., and IV. still continue on sale. As the demand for the Back Numbers of this Work is very great, and as there is every probability of their soon becoming exceedingly scarce, new Subscribers are respectfully requested to complete their Sets without delay. Many correspondents having written to us to inquire the names and prices of particular books, we beg to state that a reply on our part would subject us to the Govern brass instruments to the German silver ones. C. SHILLAM (Leeds).—Thanks for the receipt. ERRATUM. In the paragraph headed "To obtain Heights which cannot be Measured," in page 123, ante, instead of 66 as the distance between the rods is to the height of the long rod over the short one, so is the distance of the long rod from the building to the height of the building," read "so is the distance of the short rod," &c. NOTICE TO THE TRADE.-Ornamental Designs made, and, if necessary, engraved, on the most reasonable terms, with punctuality and despatch. For particulars, &c., address (if by letter, post paid) to Mr. Wm. Gibbs, Ornamental Draughtsman and Engraver, at the DECORATOR'S ASSISTANT Office, 17, Holywell-street, Strand, London. London: Published at the Office of the SPORTING LIFE, 17, Holywell-street, Strand (where all communications to the Editor are to be addressed); and to be had of all Booksellers.-Saturday, October 16, 1847. Printed by W. COOLE, Lumley Court, Strand. An Illustrated Glossary of Technical Terms used in Architectural and Enterior Decoration. (Continued from page 170.) CAMEO (in gem sculpture), a precious stone carved in relievo. The term is also applied to stones of different coloured lamine or scales, which are left or removed with much art by the sculptor, for the head, beard, hair, and other colours of a bust. Some antique cameos have four layers. The finest specimens of cameo engraving that are known are those devoted to mythological subjects, and consequently are liable to the caprice or fancy of the artist, whose object is to portray the general character without the necessity of subscribing to the features, except so far as they are classically delineated. A young medallist of the name of Picourt has, however, struck out a new path, and has ventured upon taking likenesses upon cameos, which of course are imperishable, and his essays have been crowned with the greatest success, more particularly with_regard to those of her Majesty and Prince Albert. CARMINE, a red pigment prepared from cochineal. It is prepared by pouring four ounces of finely pulverised cochineal into four or six quarts of rain or distilled water, that has been previously boiled in a pewter kettle, and boiling it for the space of six minutes longer.* Eight scruples of Roman alum are then to be added in powder, and the whole to be kept upon the fire one minute longer. As soon as the gross powder has subsided to the bottom, and the decoction has become clear, the latter is to be carefully decanted into large cylindrical glasses covered over and kept undisturbed, until a fine powder is observed to have settled at the bottom. The superincumbent liquor is then to be poured off from this powder, and the powder gradually dried. From the decanted liquor, which is still much coloured, the rest of the colouring matter may be separated by means of the solution of tin, when it yields a carmine little inferior to the other. CASTOR, a description of wheel affixed to the * Some recommend the addition of two drachms of pulverised crystals of tartar during the boiling. No. 23.-VOL. I. dillions. Also, stones and timber similarly fixed in order to secure the floor or roof of a vault. The base of the Corinthian capital. A niche to receive a statue. (To be continued.) |