Photography.

carefully and completely dried, as this is essential to its proper preparation. It must then be dipped into a solution of nitrate of silver (lunar caustic), and dried, without artiTHE first person who seems to have had any ficial heat, in a room from which every ray of notion of Photography was Mr. Wedgewood, light is carefully excluded. By this process it who, in the year 1802, recorded an experiment acquires a very remarkable facility in being in the Journal of the Royal Institution, to blackened on a very slight exposure to light, which his attention had been directed by even when the latter is by no means intense. observing that light blackened a solution of The paper, however, rapidly loses its extreme nitrate of silver. Assisted by Sir Humphrey sensitiveness to light, and finally becomes no Davy in his experiments, Mr. Wedgewood's more readily acted upon by the solar beams endeavours were, however, doomed to be un- than common nitrate paper. In the prepasuccessful, and it was not until the year 1814, ration of the paper there are two circumstances when M. Niepce, of Chalons, on the Soane, which require particular attention. In the first appears to have directed the attention to the place, it is necessary to mark it. It will be production of pictures by light, that any prac- seen that the nitrate of silver solution is applied tical method of fixing the drawings obtained to one side only. In order, therefore, to be by the process was arrived at. That gentle- able to know the sensitive side, it is necessary man having, in conjunction with M. Daguerre, to place a mark on its extreme edge. This pursued his researches, he presented a paper answers two purposes: in the first place it to the Royal Society of London in 1827, on his serves to inform the experimentalist of the method of taking pictures by means of light, sensitive surface; and secondly, it will be a naming his discovery "Heliography;" but as guide as to which portion of the paper has he kept his process a secret, it could not, been handled during the application of the. agreeably to one of their laws, be printed by solution, as the impress of the finger will prothem. The memoir was accompanied by bably come out upon the photograph. The several designs on glass, copper plated with second caution is that the application of the silver, and well planished tin plate. M. sensitive solution (nitrate of silver) and the Daguerre had at the same time produced some subsequent drying of the paper, must be specimens on paper saturated wth chloride of always conducted in a perfectly dark room, the silver, but the want of sensibility in the pre-light of a candle being alone used. paration had necessarily rendered them extremely confused.

In order to make the drawing, the simplest mode is to procure a flat board and a square of On the 31st of January, 1839, Mr. Fox Talbot plate glass, larger in size than the object incommunicated to the Royal Society his Photo- tended to be copied. On the board place the' graphic discoveries; and six months afterwards, photogenic paper with the prepared side upthe French philosophers published to the world wards, and upon it the object to be copied; their process, termed " Daguerreotype." Mr. over both lay the glass, and secure them so Talbot's most recent discovery was accidental. that they are in close connexion by means of He was trying some experiments on the relative binding screws or clamps. Should the object sensitiveness of several kinds of paper, by to be copied be at all in relief, such as a leaf, exposing them for very short periods in the grass, &c., it will be necessary to place on the camera; some papers which were taken from board, first, a soft cushion, which may be made the instrument, exhibiting no impressions, were of a piece of fine flannel and cotton-wool. By thrown aside as useless in a dark room; after this means the object is brought into closer some time they were again examined, and, contact with the paper, which is of great constrange to say, by a process of natural magic, sequence, and adds materially to the clearness pictures of the objects to which the camera had of the copy. The paper is now exposed to been pointed were found on them in the dark. diffused daylight, or, still better, to the direct Previously, however, to the secret discovered rays of the sun, when that part of the paper by MM. Daguerre and Niepce having been not covered with the object will become tinged, published, it was offered to the French with a violet colour, and if the paper be well government, who entered into an arrange-prepared, it will in a short time pass to a deepment with them, by which they undertook brown or bronze colour. It must then be to make public their discovery, on the receipt of an annuity of £250 to M. Daguerre, and £166 to M. Niepce. In the former case, this annuity has been increased to £446. From this time the progress of the Photographic art has been rapid, and the improvements in it manifold, owing to the continued exertions of Herschel, Talbot, and others.

Having thus briefly sketched the history of this important invention, we proceed to present our readers with the details of the process:The paper to be employed (satin post is recommended) must be immersed in hydrochloric (or, as it is more commonly called, muriatic) æther, which has been kept sufficiently long to have become acid; and then

removed, as no good will be obtained by keeping it longer exposed; on the contrary, the delicate parts yet uncoloured will become in some degree affected. The photogenic paper will now show a more or less white and distinct representation of the object.

The most certain material to be used for fixing the drawing is the hyposulphite of soda. One ounce of this salt should be dissolved in about a pint of distilled water. Having previously washed the photogenic drawing in a little lukewarm water, which of itself removes a large portion of the muriate of silver which is to be got rid of, it should be dipped once or twice in the hyposulphite solution. By this operation the muriate which lies upon the

three of them close to each other. This disposition of the two or three windows occasioning a dead space between their heads, a trefoil or quatrefoil was introduced between them. The effect of this simple ornament caused it to be introduced into the arches themselves, so that there is hardly an arch, or resemblance of an arch, of any kind, from the days of Edward the Second to those of Henry the Eighth, which is not ornamented in this manner.

lighter parts will become so altered in its nature The windows having been made very narrow as to be unalterable by light, while the rest at the first adoption of the pointed arch, it remains dark as before. It will be evident became necessary sometimes to place two or from the nature of the process that the colour of an object is reversed. That which is originally opaque will intercept the light, and consequently those parts of the photogenic paper will be least influenced by light, while any part of the object which is transparent, by admitting the light through it, will suffer the effect to be greater or less, in exact proportion to its degrees of transparency. The object wholly intercepting the light, will show a white impression, but in selecting such for example as a butterfly for an object, the animal being The trefoil by an easy addition became more or less transparent, leaves a proportionate cinquefoil, and being made use of in circles gradation of light and shade, the most opaque and squares, produced fans and Catherine' portion showing the whitest colours. It may wheels. To the large roses or circular winbe said therefore that the representation is not dows, which prevailed about the time of natural. This is admitted, and in order to Edward the First, it was necessary that obtain a just delineation, we must place our numerous divisions, or mullions, should be first acquired photograph upon a second piece added, which, as well as the ribs and transoms of photogenic paper. Before we do this, how-of the vaultery, began to ramify into a great ever, we must render our photographic picture transparent, otherwise the opacity of the paper itself will mar our efforts. To accomplish this object, then, the back of the paper containing the negative, or first acquired photograph, should be covered with white or virgin wax. This may be done by scraping wax upon the paper, and then, after placing it between two other portions of paper, passing a heated iron over it. The picture being thus rendered transparent should now be applied to a second piece of photogenic paper, and exposed in the manner before directed, either to diffused daylight or to the direct rays of the sun. The light will now penetrate the whiter parts, and the second photograph be the reverse of the former, or a true picture of the original.

Gothic Architecture.

variety of tracery, according to the architect's taste; all of them uniformly ornamented with the trefoil or cinquefoil head.

That magnificent object, a grove of tall trees, was very naturally and beautifully imitated in the aisles of the cathedrals of this light architecture: the ribs of the vaulting, springing from the tops of the tall pillars, and meeting in the pointed arch in the roof, produced a fine effect; and, pursuing this idea, the lightness of all the parts, and the rich variety of tracery, contributed to make the resemblance more perfect.

The cathedral at Durham, is, perhaps, the grandest specimen existing of the Saxon or early Norman style, before the invention of the pointed arch introduced that exquisite lightness to be seen in the west end of Westminster Abbey. The splendid vaulting of Henry the Seventh's Chapel in Westminster Abbey, enriched with clusters of pendant ornaments, like the natural roof of a beautfiul grotto, exceeds any other specimen of the kind. F. E.

Ir is not necessary to seek abroad for the origin of the pointed arch, the progress of which we can distinctly trace at home in the twelfth century-the great age of improvement and magnificence among a people versed in art and arms. REAL AND SPURIOUS GILDING.-It is someAbout this time many illustrious Norman times difficult to employ the usual test for prelates (chiefly in our own country), ex-gold, especially for distinguishing between hausted their talents and their wealth in real and spurious gold leaf, gilt paper, &c. M. carrying the magnificence of their churches Altmüller recommends the application of merand other buildings to the highest degree.cury, which rubbed in on true gilding immeHenry, Bishop of Winchester, probably contri-diately produces a white spot, while it has no buted most to the improvements which gra-action on spurious gold (consisting of alloys of dually changed the early Norman architecture into the style called "Gothic."

copper). On the other hand, an acid solution of mercury in nitric acid leaves untouched real gold, and produces a white spot on the spurious. The thinnest layers of gold, which it is frequently impossible to detect by means of aqua regia, are immediately recognised by this test. The coating of varnish must be removed previous to its application.

The Normans admired height no less than length, in the construction of their churches, and used to pile arches and pillars on each other. By way of ornament and variety they often imitated these arches and pillars on their walls, and they sometimes caused these plain round arches to intersect each other probably, the most ancient instance of this IRON-FRONTED EDIFICES.-A block of threeintersecting ornament to be met in the king-storied buildings is in course of erection at dom, is on the upper part of the south Cincinnati, the entire fronts of which are to be transept of Winchester Cathedral.

of cast-iron.

182

249.9696 sq. in. = area.

2) 18

―

9

Example 3.-How many square feet are there in a circle whose circumference is 20.1 yards?

20.1

20.1.

404.01
.07958

201

323208

4020

202005

363609

404.01

282807

32.1511158

9

289.3600422 (To be continued.)

sq. ft. area.

Review.

The Steam-Engine, from the earliest to the
present time; Atmospheric Railways; the
Electric Printing Telegraph; and the
Screw Propellor. By EDWARD PORTWINE.
Second Edition.-London: E. Appleyard,
Farringdon-street.

SECOND NOTICE.

interesting feature of the work, and contains The description of marine engines is an an immense quantity of useful matter, illustrated with several well-executed diagrams. Atmospheric railways also occupy a prominent position in its pages. The following is Mr. Portwine's description of the atmospheric principle:

fifteen inches diameter is laid between the "In the atmospheric railway, a pipe of about rails on which the carriages run, this pipe is exhausted at once by an air-pump; a travelling piston is forced along it by the pressure of the atmosphere. A rod connects the piston with the carriages, traverses a slit on the top of the pipe. The great difficulty to be overcome is to cover this slit with a substance which would render it air-tight, and yet permit the connecting rod to pass without offering obstruction. The opening at the top of the pipe is covered by a continuous valve, extending its whole length. It is formed of leather, riveted between steel plates. The upper plate is wider than the slit, and prevents the leather being pressed in by the pressure of the atmosphere; the lower plate just fits the slit, and is curved IMPROVEMENTS IN to the shape of the pipe; one edge of the THE MANUFACTURE OF leather is fastened to a longitutinal rib cast WHITE-LEAD. Two very important improve- along the opening, and forms a hinge as on a ments in the preparation of white-lead, by common pump valve. means of which the serious injury which often valve, when it covers the opening, forms with The other edge of the] results to the workmen engaged in its manu- a ridge cast on the pipe, a channel, or trough, facture is entirely obviated. The first is by a on its whole extent. This trough is filled with Frenchman-M. Gannai,-who_ rotates granu- a composition which adheres to the side valve lated lead in an octagonal revolving cylinder, to keep it air-tight. As the travelling piston with water, until it is reduced to impalpable is forced along the pipe, one side of the valve powder, when it is exposed to the air and is raised by four small wheels fixed behind the oxidates, after which carbonic acid is intro- piston, so as to admit the connecting rod to duced through a flexible tube, and converts pass. the oxide into carbonate, or white-lead, of air to act against the piston. The opening thus made also admits the dazzling whiteness, after two days washing. the composition ought to be sealed again before The rupture in The mass is lastly pressed on filters, divided the train passes. into pieces, and dried in stoves. The second a spring, is attached to the carriage, and A steel wheel, regulated by is that of Mr. R. C. Lotham, who submits lead presses down the valve immediately after the to the action of the acid vapours evolved in connecting arm has forced it open; and a the brewing process in air-tight chambers, copper heater, about five feet long, filled with heated by a furnace, until it is converted into burning charcoal, should pass over the comcarbonate; the workmen being thus protected position, and melt it; thus leaving the valve from the fumes evolved during the process. air-tight as before, and ready for the next plates of iron, about five feet long and hinged train. A protecting cover, formed of thin with leather, is placed over the valve to protect it from rain and dust. Each tube is about two and a half miles in length, with a stationary engine for each length of piping, to exhaust the air; and an arrangement is made, by means of which the piston, as it approaches

ANCIENT PAYMENT FOR LABOUR.-According to Sir N. H. Nicolas, the following were the wages paid to those employed in building the galley La Phelipe, at Lynn, in 1336:-master carpenter, 6d. per day; other carpenters, 5d.; clinkerers, 4d.; holders, 3d.; and servants or attendants on those workmen, 24d.