WATER-CRESS GROUND, AT SPRINGHEAD.

SPRINGHEAD, a pleasantly-situated spot, about a mile and a half from Northfleet, in Kent, close to the small and retired village of Swanscombe, is celebrated for the cultivation of Water-cresses for the supply of the London markets. The quantity of this wholesome vegetable grown expressly for the consumption of the metropolis, is much more extensive than would readily be believed. From Springhead alone two van loads of hampers, containing water-cress, are despatched every day during the Summer, and every other day in the Winter

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The principle on which the pungent taste of the water-cress depends, is extremely volatile, and almost entirely escapes as the leaves dry.

Water-cresses have obtained a place among medical herbs on account of their antiscorbutic qualities, and are considered great purifiers of the blood: in this respect they rank with the celebrated Scurvygrass of navigators, (Cochlearia officinalis) and are recommended by medical authors to be eaten with it as a salad, with the addition of Seville oranges. They are supposed to be always most efficacious when eaten with an acid, such as vinegar. The French are in the habit of expressing the juice of the watercress, and using it in the preparation of a salad.

The

ON PHOTOGENIC* DRAWING. AT the commencement of the present year, considerable surprise was manifested by the public at the announcement of the startling discovery of a mode, by which natural objects were made to delineate themselves, without the aid of the artist's pencil. beautiful miniature landscape, which the camera obscura produces, was made to paint itself upon paper; and that with a fidelity and minuteness so extraordinary, that a microscopic examination was necessary to bring out all its details. A distant building represented in one of these landscapes was depicted even to the number of bricks in the façade, and a pane of one of its windows being broken and mended with paper, was faithfully represented and detected by the microscope.

It is worthy of remark, that we find those productions of nature which are most essential to the This discovery was first announced a few months support of man, or most conducive to his health, scattered with the greatest abundance in all parts of ago by M. Arago, as communicated to him by M. the globe, their species varied according to climate Daguerre, the dioramic painter, which latter gentleman doubtless thought the discovery to be new, and and soil. We find, in all quarters of the globe, grain from which bread can be made, but not in every to pertain to himself; but it appears that Henry Fox Talbot Esq., F. R. S., a gentleman who has long been country the same species. In the case of the cresses, the species are very numerous, and yet naturally distinguished for his mathematical and optical discoconfined to limited districts. The water-cress seems veries, is the original inventor of the process; although not peculiar to Great Britain: some species are found M. Daguerre has the advantage of priority of publion the sea-shore, others on barren heaths, while cation of his results, but has concealed the processes many will only succeed in water. The American | by which they are attained. Mr. Talbot has published land-cress answers well in a garden, and is worth both, and from his account of the invention we procultivation, as a substitute for the water-cress. There ceed to inform our readers of the details of this reis one species, (Sisymbrium trio,) the London Wildmarkable and valuable invention. which belief once existed Rocket, respecting that it was produced by the great fire of London in 1666. It is not confined to the neighbourhood of London, although it grows there in great abundance, but is common in cultivated ground throughout Europe.

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&c., 75,000,000.

The military strength employed is, 56,000 European regulars; 156,000 Colonial (coloured) regulars; and 250,000 Colonial militia (whites).

The Colonial revenues amount to 23,000,0007. sterling. The civil and convict expenses defrayed by Great Britain, to 225,000.; the military expenses, to 1,800,000.; and the total expenditure of the Colonies is therefore 25,000,0007. sterling per annum. The taxation averages 4s. 6d. per head. The metallic money circulating in the Colonies is about 5,000,0007., and the paper money about 3,000,0007. sterling. Maritime commerce of the Colonies: exports, 30,000,000l.; imports, 25,000,000l. To Great Britain: exports, 15,000,000l.; imports, from 10,000,000l. Total shipping annually, in and out of Colonial ports, 8,000,000 tons, of which there are to and from Great Britain, 3,000,000 tons. Vessels built in the Colonies, from 1814 to 1837,

8,975; tonnage, 1,022,937.

The property annually created in the Colonies is estimated at 400,000,0007., and the value of the property moveable and immoveable in the transmarine possessions of the empire in land, houses, stock, &c., at 2,500,000,000l. sterling.-MARTIN.

THE Consciousness of doing that which we are reasonably persuaded we ought to do, is always a gratifying sensation to the considerate mind: it is a sensation by God's will inherent in our nature; and is, as it were, the voice of God Himself, intimating his approval of our conduct, and by his commendation encouraging us to proceed.-BISHOP MANT

There is a class of salts known to the chemist by the term salts of silver, some of which undergo decomposition by exposure to the solar rays, and become variously coloured. Silver, dissolved in nitric acid, forms a nitrate of the oxide of silver, which is soluble in water. If a sheet of paper be washed with this solution and then set in the sunbeams, it becomes blackened: but if some object be placed before it, which casts a well-defined shadow, the light acting on the rest of the paper would blacken it, while the parts within the shadow would retain their white

ness.

Thus a kind of image or picture is formed, But resembling the object from which it is derived. such images must be preserved in the dark, and viewed only by artificial light; because, if viewed by daylight, the same natural processes which formed the images would destroy them by blackening the rest of the paper.

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So far this process had long been known. Humphrey Davy and Mr. Wedgwood had investigated the subject, but abandoned it, because the paper, on which the images were depicted, soon became entirely dark, and nothing tried by them would prevent it; but Mr. Talbot was so fortunate as to devise a method of fixing the image in such a manner that it is no more liable to injury from the action of light.

The images obtained by Mr. Talbot's process are themselves white, but the ground upon which they display themselves, is variously and pleasingly sently, is capable of producing much variety, by coloured. The process, which we shall describe premerely varying the proportions of the materials employed, and any of the following colours are readily attainable: sky-blue, yellow, rese-colour, various shades of brown, and black. Green alone is absent from the list, with the exception of a dark shade of it, approaching to black. The blue coloured variety has a very pleasing effect, somewhat like that produced by the Wedgwood ware, which has white figures on a blue ground.

The first kind of objects which Mr. Talbot attempted to copy by this process, were flowers and From two Greek words, signifying produced by light.

leaves. "It is so natural," says he, "to associate the idea of labour with great complexity and elaborate | detail of execution, that one is more struck at seeing the thousand florets of an agrostis, depicted with all its capillary branchlets (and so accurately, that none of all this multitude shall want its little bivalve calyx, requiring to be examined through a lens), than one is by the picture of the large and simple leaf of an oak or a chestnut. But in truth the difficulty is in both cases the same. The one of these takes no more time to execute than the other; for the object which would take the most skilful artist days or weeks of labour to trace or to copy, is effected by the boundless powers of natural chemistry in the space of a few seconds."

"To give an idea," continues he," "of the degree of accuracy with which some objects can be imitated, by this process, I need only mention one instance. Upon one occasion, having made an image of a piece of lace, of an elaborate pattern, I showed it to some persons at the distance of a few feet, with the inquiry whether it was a good representation; when the reply was that they were not so easily to be deceived, for that it was evidently no picture, but the piece of lace itself."

The reader may probably have heard of one of the legends of that intellectual and extraordinary people, the Germans; where Peter Schlemil sells his shadow, the purchaser of which kneels down in the broad sunshine, detaches the shadow from its owner's heels, folds it up, and puts it in his pocket. By the spells of our scientific enchanter, Mr. Talbot, this most transitory of things, the proverbial emblem of all that is fleeting and momentary, may be permanently fixed in the position which it seemed only destined for a single instant to occupy. Such is the fact, that we may receive on paper the fleeting shadow, arrest it there, and in the space of a single minute, fix it there so firmly as to be no more capable of change, even if thrown back into the sunbeam, from which it derived its origin.

Let us now consider the method of preparing what Mr. Talbot calls photogenic paper, and the means of fixing the design.

A sheet of superfine writing-paper is dipped into a weak solution of common salt, and wiped dry, by which the salt is uniformly distributed throughout its substance. A solution of nitrate of silver is spread over the paper on one surface only, and dried at the fire. The solution should not be saturated, but six or eight times diluted with water. When dry, the paper is fit for use.

There is a certain proportion between the quantity of salt, and that of the solution of silver, which answers best, and gives the maximum effect. If the strength of the salt be increased beyond this point, the effect diminishes, and in certain cases becomes exceedingly small.

"This paper," says Mr. Talbot, "if properly made, is very useful for all ordinary photogenic purposes. For example, nothing can be more perfect than the images it gives of leaves and flowers, especially with a summer sun: the light passing through the leaves delineates every ramification of their nerves.'

If a sheet of paper, thus prepared, be washed with a saturated solution of salt, and dried, and again washed with a liberal quantity of the solution of silver, it becomes more sensible to the action of light than it was at first. In this way, by alternately washing the paper with salt and silver, and drying it between times, Mr. Talbot prepares what he calls sensitive paper, well adapted to the reception of images formed by the camera-obscura.

The photogenic picture being formed, requires fixing; for, if left to the light, the whole surface of the paper which bears it will become of one hue, and the design will of course be obliterated. Two methods of fixing are named by Mr. Talbot; the one is to wash the picture over with a solution of iodide of potassium, whereby an iodide of silver is formed, which is absolutely unalterable by the solar light: the other method is to immerse the picture in a strong solution of common salt, to wipe off the superfluous moisture, and then dry it. Pictures preserved by iodine are of a pale primrose yellow, which possesses the remarkable property of turning to a full gaudy yellow, when exposed to the heat of a fire, and recovering its former colour when it is cold.

The writer of this article has formed several photogenic pietures, with ease and complete success. He will shortly resume the subject, and offer the reader a few directions on the precautions necessary to their formation, and sum up the great advantages which are likely to be derived from this beautiful discovery.

ANCIENT AND MODERN WORKS. THE London and Birmingham Railway is unquestionably the greatest public work ever executed, either in ancient or modern times. If we estimate its importance by the labour alone which has been expended on it, perhaps the Great Chinese Wall might compete with it; but when we consider the immense outlay of capital which it has required, the great and varied talents which have been in a constant state of requisition during the whole of its progress,together with the unprecedented engineering difficulties, which we are happy to say are now overcome, the gigantic work of the Chinese sinks totally into the shade.

It may be amusing to some readers, who are unacquainted with the magnitude of such an undertaking as the London and Birmingham Railway, if we give one or two illustrations of the above assertion. The great Pyramid of Egypt, that stupendous monument which seems likely to exist to the end of all time, will afford a comparison.

After making the necessary allowances for the foundations, galleries, &c., and reducing the whole to one uniform denomination, it will be found that the labour expended on the great Pyramid was equivalent to lifting fifteen thousand seven hundred and thirty-three million cubic feet of stone one foot high. This labour was performed, according to Diodorus Siculus by three hundred thousand, to Herodotus by one hundred thousand men, and it required for its execution twenty years.

If we reduce in the same manner the labour expended in constructing the London and Birmingham Railway, to one common denomination, the result is twenty-five thousand million cubic feet of material (reduced to the same weight as that used in constructing the Pyramid) lifted one foot high, or nine thousand two hundred and sixty seven million cubic feet more than was lifted one foot high in the construction of the Pyramid; yet this immense undertaking has been performed by about twenty thousand men in less than five years.

From the above calculation have been omitted all the tunnelling, culverts, drains, ballasting, and fencing, and all the heavy work at the various stations, and also the labour expended on engines, carriages, wagons, &c. These are set off against the labour of drawing the materials of the Pyrainid from the quarries to the spot where they were to be used-a much larger allowance than is necessary.

As another means of comparison, let us take the cost of the Railway, and turn it into pence, and allowing each penny to be one inch and thirty-four hundredths wide, it will be found that these pence laid together, so that they all touch, would more than form a continuous band round the earth at the equator.

As a third mode of viewing the magnitude of this work, let us take the circumference of the earth in round numbers at one hundred and thirty million feet. Then, as there are

about four hundred million cubit feet of earth to be moved in the Railway, we see that this quantity of material alone, without looking to any thing else, would, if spread in a band one foot high and one foot broad, more than three times encompass the earth at the equator.-LECOUNT.

the back part of the roof of the mouth, near where | channel,-having once or twice disappeared amongst the under and upper jaws articulate.