horizontal part of an order that is supported siderable alteration without the just proporby the column, and consists of the cornice, tions of the columns be altered, and, consefrieze, and architrave, which differ essentially quently, spoiled. He makes the entablatures in all the orders. The cornice forms the upper of the Tuscan and Doric to be to their columns division, and it has been well remarked that one to four; and the Ionic, Corinthian, and "there is as great a characteristic difference Composite, as one to five. The proportions of between cornices of the several orders, as the entablature in each order is explained as between the capitals of the columns; and in a follows:good style of art they never encroach upon each other." The Corinthian cornice is richest and loftiest in proportion-the fullest of members and enrichments of all the orders. It is known by its graceful proportions, its modillions, dentels, and sculptured members. The Ionic cornice is of graver proportions, has no modillions, and very seldom, in the best examples, dentals, which had better always be left to the rich and gay Corinthian. Harmony of proportion, beauty of profile, particularly in the cymatium; breadth of parts, especially in the corona, are the leading features which characterise this order. The Doric cornice is lower in its proportions than either of the others; has a greater comparative projection, and is known by the masculine character of its cymatium, which is always, in the purest examples, a beautiful echinus; by its mutules and drops, one of which is over every triglyph and metope of the frieze. The frieze forms the middle compartment or division of the entablature. The frieze is the best situation in an entablature for sculptures and inscriptions, and many of the finest of the ancient temples have had their friezes superbly decorated. The splendid metopes of the Elgin marbles were ornaments of the frieze of the Parthenon, and the Phigaleian marbles of the Temple of Apollo Epicureios, at Phiguleia. The frieze of the Temple of Jupiter Olympius, at Elis, bore sculptural representations of the chariot-race of Pelops and Oenomaüs. Bucklers of gold, which were part of the spoil after the battle of Marathon, were suspended, according to Pausanias, in the frieze of the Temple of Apollo, at Delphos, which gave rise to sculptural imitations of them in many metopes of the Doric frieze. Among the most celebrated friezes of modern times, that of the Royal Exchange at London deserves at least a passing notice. The architrave is the chief or principal beam in a building, lying horizontally on the summit of the column, and forming the sustaining portion of the entablature. The form and number of the mouldings, faces, and members of which an architrave is composed, varies according to the character of the order to which it is to be applied. In the Tuscan order it is a plain surface, surmounted by a fillet; in the Doric order it has sometimes two faces; in the Ionic and Corinthian it has sometimes two, and at others three faces; and in the Composite always three. Having set forth a rule for the proportions of columns, we must now state that the entablatures must bear a proportion to them in each order. On this point Palladio has given a rule which cannot be subjected to any con Tuscan.-One and three-fourths of the dia meter, which is one-fourth of seven diameters. Doric.-Two diameters, which is one-fourth of eight diameters. Ionic.-One and four-fifths of the diameter, which is one-fifth of nine diameters. fifth of ten diameters. Corinthian.-Two diameters, which is one Composite. The same as the preceding. Of Pedestals.-The pedestal is a solid body of a round or square form, serving to support the column, and is divided into three parts, namely, the base, the die, and the cornice. No particular proportions can be laid down for the pedestal, but it is usual to allow it onefourth or one-third of the height of the column, including the entablature; and this being divided into nine parts, two are for the base, one for the cornice, and six for the die, which latter is of similar dimensions with the plinth of the column. Pedestals vary both in their shape and ornaments, according to the order of architecture which surmounts them. 110851.242 cubic in. whose side is 1. = (To be continued.) 40 40 1600 solidity req. Photography on Paper.* SINCE the discovery of Daguerre, numerous attempts have been made, with greater or less success, to obtain on paper those images which Daguerre's process produces only on metallic plates. From its porous nature, paper thoroughly imbibes the chemical preparations used in the photographic process, and offers, accordingly, this great advantage over metallic plates, that, whilst the images formed on the latter are only superficial, and liable to be wiped or brushed off by contact with other bodies, those on paper are perfectly fixed, and admit of reproduction to any extent. Daguerre and others, have recommended various processes for photography on paper; but the results are either uncertain or the processes difficult of execution The object of M. Guillot Saguez's paper is to examine the chemical phenomena in which the real modifications of the process, as applied to paper, consist. M. Guillot Saguez's theoretical views are by no means merely speculative, but are the results of close and attentive observations made during the last three years. Before describing the mode of preparing the papers, it is necessary to mention certain conditions indispensable to ensure a successful result. In the first place, all the substances employed must be of the greatest purity. The gallic acid especially, which, on account of its scanty solubility in water, we are almost compelled to use at a lower degree of concentration than could be wished, must be perfectly free from admixture of tannic acid; the nitrate of silver, the hyposulphite of soda, and the iodide of potassium, must, in like manner, be free from admixture of foreign substances. The quality of the object-glass is also of considerable importance. Preparation of the Negative Paper.-Take very smooth and fine letter-paper, of perfectly equal textures throughout, and sufficiently AMIANTHUS CLOTH, OR INCOMBUSTIBLE strong to resist the action of a water-bath for CLOTH, is made as follows:-Expose amianthus twelve hours without tearing. The paper to steam, separate the fibres with the hand, must be perfectly white, and at all events spin and weave it along with one-third the rather inclined to yellow than to blue. Too quantity of flax, or cotton; and afterwards much stress cannot be laid upon the fineness of throw it into the fire to burn the cotton away. the paper, experience having shown that, The cloth will be found well formed, and unin- cæteris paribus, images are formed the more jured by the fire. It has been used as an en-speedily the finer the paper; other advantages veloping dress for those who have to enter of fine paper are, that it absorbs water more burning houses, or to inclose substances which readily and thoroughly, and becomes transare to be burnt, and yet the ashes of them to be parent in less time than the courser sorts. retained. No. 1.-Negative Paper Solution : ELECTRIC TELEGRAPH IN THE UNITED Iodide of potassium. .. 5 parts STATES.-The following is a table of the elecDistilled water........ 120 parts. tric wires finished, in progress, and contemplated, as far as is known :-Finished and Take a piece of paper about an inch longer working, 3,047; in progress, 2,812; contem-than the unpolished glass of the camera, dip plated, 2,000-7,859. As many of these have it for one minute into the above solution, and two wires, the length of wire may be safely suspend it subsequently for twelve hours in estimated as exceeding 11,000 miles.-New the air by fastening two of its corners to a line. York Herald. It will speedily acquire a rose tint, which will * See table to the problem for finding the area of a regular polygon, page 163, vol. i. From a paper lately read before the French Academy of Sciences, by M. Guillot Sagues, of Paris. deepen considerably in the course of a few days, and turn finally violet, when it may be considered ready for solution No. 2. The iodide of potassium with which the paper has been impregnated is here unquestionably decomposed by the action of the oxygen of the air, hydriodic acid being liberated. The process need not be conducted in a darkened 100m, and the paper may be prepared in any quantity long before required for use, provided always it be kept perfectly free from moisture. When it is wished to take a photographic mage, spread over the surface of a glass plate, kept especially for the purpose, a teaspoonful of the following preparation : And, seizing the iodised paper gently by two of the corners, lay it even on the glass, taking care to blow on the back of the paper to remove all the air bubbles between the paper and the glass. After a few seconds the paper acquires a marbled appearance with white pots, and after a short time the whole surface assumes a white tint. The surface of the paper in immediate contact with the solution has now become very sensible to the action of light, and can be placed in the camera obscura to receive the photographic impression. This operation is to be conducted in a room from which daylight has been most carefully excluded. Before proceeding further we will here first briefly examine the chemical changes suffered by the paper in the second process. The iodised paper, upon coming in contact with the solution of nitrate of silver (No. 2), receives a solid coating of white iodide of silver, excessively liable to decomposition by the action of light; in this operation a change of bases has taken place; the nitric acid has left the silver and united with the potassium, forming a nitrate of potass soluble in water, and which plays no part in the photographic process; and the iodine has combined with the silver, to form an iodide, or rather a sub-iodide, of silver. It is deemed preferable to call the compound formed a sub-iodide, since, though in all other respects identical with the common iodide, it yet comports itself differently to the light. heat upon addition of iodide of potassium in excess. sur Formation of the Negative Picture.-The paper is now to be placed between two sheets of white paper, well soaked in water, to ensure its perfect adhesion to the glass of the camera obscura, upon which it is then placed evenly and carefully, the air bubbles that might get between it and the surface of the glass being expelled by blowing on the surface of the paper. The time during which the paper should remain in the camera varies according to the time of day, the position of the model, the quality of the object-glass (whether short or long focus), &c., but, cæteris paribus, to take a picture in the shade requires an exposure of from 30 to 45 seconds' duration; practice, however, will here prove the best guide. The frame, closed again and covered with a piece of dark cloth, is then to be taken back into the room where the paper has been prepared. Spread about a teaspoonful of a mixture of equal parts of a saturated solution of gallic acid and a concentrated solution of nitrate of silver carefully and evenly over the face of a perfectly clean glass plate, kept for the purpose, and place the paper carefully on it, with the side that has been exposed to the light turned to the glass; a transparent picture will speedily make its appearance. The paper is then to be taken off the glass and kept suspended from a line until the blackened parts have acquired the requisite degree of intensity. If the operation has been properly performed, four or five minutes will suffice to give a perfect negative picture; the paper is then to be kept three or four hours in a basin of very clear water, which must be renewed at first four or five times per hour, and afterwards, at least, once an hour. All these operations should be conducted in a darkened room. The effect produced by the action of light on the surface of paper imbued with the sub-iodide of silver arises from the light separating the iodine from the silver, and liberating the oxide of silver, and that in particles of such minuteness that the finest gradations of tint can be obtained in the positive picture to be subsequently produced. It will now be readily conceived why, in acting with the nitrate of silver, the picture formed should be negative; the emission of the rays of light from the model, proceeding in the proportion of the refrangibility of the colours composing them, tends to separate the It is of the highest importance that the re- oxide of silver from the sub-iodide, which latspective proportions of the two substances em- ter substance is naturally black, and rendered ployed should be exactly as above prescribed; still more so by its combination with the gallic if they are used in equal proportions the com- acid. The acetic acid, which is present to pound formed will be insensible to the action some extent in the solution, has for its object of light. This fact of the difference between to make the saline solution penetrate more the respective photographic properties of the readily into the very substance of the paper, iodide and sub-iodide of silver has been ascer- and thus to aid and accelerate the photographic tained by a series of comparative experiments. process. In fact, experience has proved that, Another fact which will serve to corroborate cæteris paribus, the less the proportion of acetic our assertion that the operation will not suc-acid, the less rapid is the action of the light. ceed if the iodine be employed in too large a As the paper is not allowed to remain long proportion to the silver, is, that the precipitate enough in the camera to develop the picture, which forms upon the addition of a few drops the latter is subsequently made apparent by of solution of nitrate of silver to a solution of the contact of the gallic acid with the oxide of iodide of potassium will be redissolved by silver liberated, and which instantaneously |