Mensuration of Superfices. (Continued from page 182.) PROBLEM XIII. THE area of a circle being given, to find the diameter. Divide the area of the circle by .7854, and take the square root of the quotient, which will be the diameter. Example.-What is the diameter of a circle, the area being 176.715 square feet? .7854) 176.715 (225. 15708 Example 1.-What will be the area of the less segment a CB A, the radius D A being 20 inches, the chord a c 22.42 inches, the length 225 (15 diam. of the arc A B C 24.43 inches, and the perpen[required. dicular D G 16.56 inches? 1 19635 15708 25) 125 125 39270 39270 = 24.43 2) 488.60 244.3 sq. in. area of the sector A B C D A. To find the area of the segment of a circle. Find the area of the sector A D C B A, or that of ADCEFA, by the preceding problem, according as the area of the less or greater segment is required. Find the area of the triangle A c D, formed by the chord A c of the segments, and the radii DA, D C, of the sectors. Then, the sum or difference of these areas, according as the segment is greater or less than a semicircle, will be the area. 22.42 16.56 2) 371.2752 185.6376 sq. in. = area of triangle A D C. 1012.3 185.6376 1197.9376 sq. in. = area required. (To be continued.) Bricks. to be not only sufficient for general purposes, but even of a ringing hardness; respecting those in Greece, we are uncertain whether they were burnt or merely dried, but the presumption, on considering the nature of its relations, ON reference to the sacred records, we find that the use of brick has arisen in very prime-is in favour of the former. val times; the city of Babel, the earliest in our The Babylonian bricks are objects of ancient history, having been built of it. If, curiosity and interest, on account of the Chalhowever, we set aside the testimony offered by dean characters which are inscribed on them; these writings, the pyramid of unburnt brick, those of the burned description are of good which modern travellers describe as still exist-quality, varying in form, size, and colour, some ing at Sakhara, and occupying an area of being of long proportions, about a foot in upwards of 30,000 square feet, affords a suffi- length, and three to four inches thick, others cient mass of evidence in support of its high about a foot and a half square and of similar antiquity. Turning to the favoured cities of thickness: their hues are similar to the red and Athens and Rome, we trace that even in the yellow, so familiar here; they are usually built Pentelican temples of the former, the applica- with coarse lime or with bitumen, but sometion of this homely material to interior work times only with clay, and the work is bonded towas not rejected; while among the proud re-gether by layers of reeds, which in Babylon are mains of the latter, external and even carved frequently found introduced to every course, works still present themselves; as is also the but in other parts to about every sixth or case to a much greater extent at Pompeii, eighth; according to Herodotius, the Grecian where the facilities for building in stone were historian, they were placed to every thirtieth of an inferior order. course. The Persian sun-dried bricks of modern times are described as being made of tempered earth and finely-chopped straw, in moulds about eight inches by six by two and a half; those of the furnace-baked sort, of two parts earth and one of cinders, well incorporated, and cast in moulds somewhat larger than the above, to provide for about seventy hours' baking. The similarity between these ornamental works at Rome, and the fine old Italian specimens of moulded brickwork which are extant in England, naturally suggests the idea that it is to Italy we are indebted for the degree of excellence which it attained in this country; and probably the inference is fair and correct; and it is curious that when we seek the origin of the use of brick, in its more ordinary form, in our island, we are carried back to a period The Grecian bricks, as descriped by Vitruat which no other conclusion seems tenable, vius, were of three sorts, called pentadoron, than that we owed its first introduction to the tetradoron, and didoron; the two first were same source; for it is in the scattered remains square, and as their names imply, measured, of the Roman boundary walls that our earliest the former five, and the latter four palms on examples are found; and although there is a the side; the didoron were oblong, being two shade of probability that the inhabitants had, palms in breadth and four in length, that is, a prior to the inroads of that people, something foot by half a foot; to each of these they of a rude description bearing an analogy to made half bricks, which gave them the choice brickwork, yet its utter absence among the well- of a greater variety of thicknesses for their walls scanned remnants of past ages must discoun- than they should otherwise have had. The tenance any hypothesis that would confer on it same writer states that the Greeks used the aught of a higher character than mere perish-pentadoron for public and the tetradoron for able clod-work; such as that in which the peasant of Ireland and mountaineer of Scotland construct their huts and hovels in the present day. private works: but on the use to which they A NEW STEERING WHEEL has been in Although so much of the rudiments of art has been transmitted to us from the ancient Egyptians, it is generally thought that there is not evidence to justify the assumption that their knowledge in this branch extended to the important operation of burning; and the circumstances of those magnificent yet mournful memorials which now tell the tale of their once vented by Mr. Wm. Peoples, of New Orleans. wondrous greatness, being almost all of granite The novelty consists in the mode of attaching or other stone, sufficiently accounts for their not excelling in a manufacture for which they the wheel to the tiller, the vibrations being had not extreme occasion. If they ever did obtained by a screw, working in a sliding nut possess that art, however, certain it is that now there is no vestige of it visible, either in the mighty monuments of the past or the mean and short-lived fabrics of the present. -The ancient Babylonian and Persian, as well as Roman remains, exhibit both sun-baked and kiln-burnt bricks, the former being in the east where rain is unfrequent, and they undergo the action of a very powerful solar heat, found upon the tiller. Sufficient play is allowed by the connection to prevent any bad effect from lurching, the helmsmen being of course safe in all weathers. GYMNASIUM AT PRIMROSE-HILL.-The commissioners of Woods and Forests have erected a gymnasium on the ground at the foot of Primrose-hill, which is to be opened to the use of the public under certain regulations. Casting Figures, &c. THIS useful art supplies the painter and sculptor with exact representations from nature of limbs, bodies, heads of men and inferior animals, anatomical subjects, draperies, and plants; it multiplies models of all descriptions, and is now practised in such perfection that casts of the antique statues are made so precisely like the original that no difference whatever is discernible, excepting in the colour and material. The following is the process employed:-Plaster of Paris is mixed with water in a basin or pan, and stirred with a spatula until its consistence is like that of batter for pancakes; it it then poured on the figure of which the impression is to be made, and which figure has been previously greased or oiled in the slightest possible manner, to prevent the adhesion of the plaster; after a few minutes the plaster acquires the hardness of soft stone, and may be removed from the object on which it has been placed, when it will be found to contain an exact impression of every part, even the minutest pores of the skin. This impression, which is the reverse or hollow of the original subject-like a seal in comparison with its impression-is called the mould. The mould being removed from the figure and slightly greased, may have plaster mixed with water, as before, poured into it, and this being allowed to remain until it has become hard, and then removed from the mould, is an exact image of the original figure. If the figure be flat, having no deep hollows or high projections, it may be moulded in one piece. If its surface be varied with great hollows and projections, it must be moulded in many pieces fitted together, and held in one or more outside containing pieces. 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. H 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 Government 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. 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 easiest method of producing a good polish on new furniture; likewise the best method of imitating ground glass.-T. G. JOHANNES (Carrickfergus).-The idea of employing guncotton as a motive power was not entirely a new one, as you will see from the following passage extracted from the Caledonian Mercury of Jan. 6th, 1838 :-" Gunpowder Engine-After years of labour and many disappointments, sustained only by patience and perseverance rarely equalled, Mr. J. Smith, of Dysart, has completed a machine, which he terms a gunpowder engine, and which moves with great ease against a weight of 2,600 weight on the square inch of the piston, equal to a column of water a mile and a quarter high; and yet, with this enormous power, the machine is so perfect, that not a particle of leakage proceeds from any part of it. Nor is it possible to increase this power by any effort of the person to whose care the machine may be intrusted-a circumstance which renders it perfectly safe. Mr. Smith calculates the saving in the use of his machine, as compared with steam, to be fully 80 per cent., whilst the space it occupies is not one-twentieth of that taken up by the steam-engine." We do not, however, think that the application of either gun-cotton or gunpowder can ever VITRUVIUS.-Moulds for lead are sometimes cut out of have a successful result. hearthstones. J. F. BRUIN (Bristol).-No. 3 of the DECORATOR'S ASSISTANT is in print, and always has been so, ever since it was published; those who state to the contrary state that which is not true, to say the least of it. You would oblige us by forwarding the names of the booksellers who have stated that number to be out of print. If you remit 24d. to our office it shall be sent to your residence postage free. BLUCHER (Oxford).-Your communications all reach us, but T. W. (Liverpool). A good material for diluting ink that T. FRY (Taunton).-We are much obliged for your good opinion of our work; but we are sorry to say that your suggestion is not practicable. We shall always be glad to receive any hints with which you may be disposed to favour us. A SUBSCRIBER TO THE DECORATOR'S ASSISTANT.-We cannot exactly understand your query regarding the method of measuring round, oval, and square French shades, but if you will be more explicit we will endeavour to answer you. To insert the price would amount to an advertisement, and we should have to pay the Government duty accordingly. A LOYAL SUBSCRIBER (Glasgow).-You directed your letter H. B.-Any good black colour, velvet black; or, if you London: Published at the Office of 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 30, 1847. Printed by W.COOLE, Lumley Court, Strand. |