The Practical Astronomer / Comprising illustrations of light and colours--practical descriptions of all kinds of telescopes--the use of the equatorial-transit--circular, and other astronomical instruments, a particular account of the Earl of Rosse's large telescopes, and other topics connected with astronomy

by Thomas Dick

CHAPTER II.

OF THE CAMERA OBSCURA.

Before proceeding to a particular description of the different kinds of telescopes, I shall first give a brief description of the Camera Obscura, as the phenomena exhibited by this instrument tend to illustrate the principle of a refracting telescope.

The term Camera Obscura literally signifies a darkened vault or roof; and hence it came to denote a chamber, or box, or any other place made dark for the purpose of optical experiments. The camera obscura, though a simple, is yet a very curious and noble contrivance; as it naturally and clearly explains the manner in which vision is performed, and the principle of the telescope, and entertains the spectator with a most exquisite picture of surrounding objects, painted in the most accurate proportions and colours by the hand of nature. The manner of exhibiting the pictures of objects in a dark room is as follows:—In one of the window-shutters of a room which commands a good prospect of objects not very distant, a circular hole should be cut of four or five inches diameter. In this hole an instrument should be placed, called a Scioptric ball, which has three parts, a frame, a ball, and a lens. The ball has a circular hole cut through the middle, in which the lens is fixed, and its use is, to turn every way so as to take in a view of objects on every side. The chamber should be made perfectly dark; and a white screen, or a large sheet of elephant paper, should be placed opposite to the lens, and in its focus, to receive the image. If then, the objects without be strongly enlightened by the sun, there will be a beautiful living picture of the scene delineated on the white screen, where every object is beheld in its proportions, and with its colours even more vivid than life; green objects appear in the picture more intensely green, and yellow, blue, red or white flowers appear much more beautiful in the picture than in nature; if the lens be a good one, and the room perfectly dark, the perspective is seen in perfection. The lights and shadows are not only perfectly just, but also greatly heightened; and, what is peculiar to this delineation, and which no other picture or painting can exhibit—the motions of all the objects are exactly expressed in the picture; the boughs of the trees wave, the leaves quiver, the smoke ascends in a waving form, the people walk, the children at their sports leap and run, the horse and cart move along, the ships sail, the clouds soar and shift their aspects, and all as natural as in the real objects; the motions being somewhat quicker, as they are performed in a more contracted scene.

These are the inimitable perfections of a picture, drawn by the rays of light as the only pencil in nature’s hand, and which are finished in a moment; for no sensible interval elapses before the painting is completed, when the ground on which it is painted is prepared and adjusted. In comparison of such a picture, the finest productions of the most celebrated artists, the proportions of Raphael, the natural tints and colouring of Titian, and the shadowing of the Venetians, are but coarse and sorry daubings, when set in competition with what nature can exhibit by the rays of light passing through a single lens. The Camera obscura is at the same time the painter’s assistant, and the painter’s reproach. From the picture it forms he receives his best instructions, and is shown what he should endeavour to attain; and hence, too, he learns the imperfections of his art, and what it is impossible for him to imitate. As a proof of this, the picture formed in the dark chamber will bear to be magnified to a great extent, without defacing its beauty, or injuring the fineness of its parts; but the finest painted landscape, if viewed through a high magnifier will appear only as a coarse daubing.

The following scheme will illustrate what has been now stated respecting the dark chamber. EF represents a darkened room, in the side of which, IK, is made the circular hole V, in which, on the inside, is fixed the scioptric ball. At some considerable distance from this hole is exhibited a landscape of houses, trees, and other objects, ABCD, which are opposite to the window. The rays which flow from the different objects which compose this landscape, to the lens at V, and which pass through it, are converged to their respective foci, on the opposite wall of the chamber HG or on a white moveable screen placed in the focus of the lens, where they all combine to paint a lively and beautiful picture of the range of objects directly opposite, and on each side, so far as the lens can take in.

Though I have said, that a scioptric ball and socket are expedient to be used in the above experiment, yet where such an instrument is not at hand, the lens may be placed in a short tube made of pasteboard or any other material, and fixed in the hole made in the window shutter. The only imperfection attending this method is, that the lens can exhibit those objects only which lie directly opposite the window.

figure 37.

Some may be disposed to consider it as an imperfection in this picture, that all the objects appear in an inverted position; as they must necessarily do, according to what we formerly stated respecting the properties of convex lenses, (p. 72). There are, however, different modes of viewing the picture as if it were erect. For, if we stand before the picture, and hold a common mirror against our breast at an acute angle with the picture, and look down upon it, we shall see all the images of the objects as if restored to their erect position; and by the reflection of the mirror, the picture will receive such a lustre as will make it still more delightful. Or, if a large concave mirror were placed before the picture at such a distance, that its image may appear before the mirror, it will then appear erect and pendulous in the air in the front of the mirror. Or, if the image be received on a frame of paper, we may stand behind the frame, with our face towards the window, and look down upon the objects, when they will appear as if erect.

The experiment of the Camera Obscura may serve to explain and illustrate the nature of a common refracting telescope. Let us suppose, that the lens in the window-shutter represents the object-glass of a refracting telescope. This glass forms an image in its focus, which is in every respect an exact picture or representation of the objects before it; and consequently the same idea is formed in the mind, of the nature, form, magnitude, and colour of the object—whether the eye at the centre of the glass views the object itself, or the image formed in its focus. For, as formerly stated, the object and its image are both seen under the same angles by the eye placed at the centre of the lens. Without such an image as is formed in the camera obscura—depicted either in the tube of a telescope or in the eye itself—no telescope could possibly be formed. If we now suppose that, behind the image formed in the dark chamber, we apply a convex lens of a short focal distance to view that image, then the image will be seen distinctly, in the same manner as we view common objects, such as a leaf or a flower, with a magnifying glass; consequently, the object itself will be seen distinct and magnified. And, as the same image is nearer to one lens than the other, it will subtend a larger angle at the nearest lens, and of course, will appear larger than through the other, and consequently the object will be seen magnified in proportion. For example, let us suppose the lens in the camera obscura, or the object lens of a telescope, to be five feet, or sixty inches focal distance, at this distance from the glass, an image of the distant objects opposite to it will be formed. If now, we place a small lens two inches focal distance beyond this point, or five feet two inches from the object-glass, the objects, when viewed through the small lens, will appear considerably magnified, and apparently much nearer than to the naked eye. The degree of magnifying power is in proportion to the focal distances of the two glasses; that is, in the present case, in the proportion of two inches, the focus of the small lens, to sixty inches, the focus of the object lens. Divide sixty by two, the quotient is thirty, which gives the magnifying power of such a telescope, that is, it represents objects thirty times nearer, or under an angle thirty times larger than to the naked eye. If the eye-glass, instead of being two inches, were only one and a half inch focus, the magnifying power would be in the proportion of one and a half to sixty, or forty times. If the eye-glass were three inches focus, the magnifying power would be twenty times; and so on, with regard to other proportions. In all cases, where a telescope is composed of only two convex lenses, the magnifying power is determined, by dividing the focal distance of the object-glass, by the focal distance of the eye-glass, and the quotient expresses the number of times the object is magnified, in length and breadth. This and various other particulars, will be more fully illustrated in the sequel.

In performing experiments with the camera obscura in a darkened chamber, it is requisite that the following particulars be attended to:—1. That the lens be well figured, and free from any veins or blemishes that might distort the picture. 2. That it be placed directly against the object whose image we wish to see distinctly delineated. 3. The lens should be of a proper size both as to its breadth and focal distance. It should not be less than three or four feet focal distance, otherwise the picture will be too small, and the parts of objects too minute to be distinctly perceived; nor should it exceed fifteen or eighteen feet, as in this case the picture will be faint, and of course not so pleasing. The best medium as to focal distance, is from five to eight or ten feet. The aperture, too, or breadth of the glass, should not be too small, otherwise the image will be obscure, and the minute parts of it invisible for want of a sufficient quantity of light. A lens of six feet focal distance, for example, will require an aperture of at least two inches. Lenses of a shorter focal distance require less apertures, and those of a longer focal distance larger. But if the aperture be too large, the image will be confused, and indistinct, by the admission of too much light. 4. We should never attempt to exhibit the images of objects, unless when the sun is shining and strongly illuminating the objects, except in the case of very near objects placed in a good light. As one of the greatest beauties, in the phenomena of the dark chamber, consists in the exquisite appearance and contrast of light and shadows, nothing of this kind can be perceived but from objects directly illuminated by the sun. 5. A south window should never be used in the forenoon, as the sun cannot then enlighten the north side of an object; and besides, his rays would be apt to shine upon the lens, which would make the picture appear with a confused lustre. An east window is best in the afternoon, and a western in the morning; but a north window is in most cases to be preferred, especially in the forenoon, when the sun is shining with his greatest strength and splendour. In general, that window ought to be used which looks to the quarter opposite to that in which the sun is shining.

The picture should be received upon a very white surface, as the finest and whitest paper, or a painted cloth, bordered with black; as white bodies reflect most copiously the incident rays, while black surfaces absorb them. If the screen could be bent into the concave segment of a sphere, of which the focal distance of the double convex lens which is used, is the radius, the parts of the picture adjacent to the extremities would appear most distinct. Sir D. Brewster informs us that, having tried a number of white substances of different degrees of smoothness, and several metallic surfaces, on which to receive the image, he happened to receive the picture on the silvered back of a looking-glass, and was surprised at the brilliancy and distinctness with which external objects were represented. To remove the spherical protuberances of the tin foil, he ground the surface very carefully with a bed of hones which he had used for working the plane specula of Newtonian telescopes. By this operation, which may be performed without injuring the other side of the mirror, he obtained a surface finely adapted for the reception of images. The minute parts of the landscape were formed with so much precision, and the brilliancy of colouring was so uncommonly fine, as to equal, if not exceed the images that are formed in the air by means of concave specula.

The following additional circumstances may be stated respecting the phenomena exhibited in the dark chamber. A more critical idea may be formed of any movement in the picture here presented than from observing the motion of the object itself. For instance, a man walking in a picture appears to have an undulating motion, or to rise up and down every step he takes, and the hands seem to move almost exactly like a pendulum; whereas scarcely any thing of this kind is observed in the man himself, as viewed by the naked eye. Again, if an object be placed just twice the focal distance from the lens without the room, the image will be formed at the same distance from the lens within the room, and consequently will be equal in magnitude to the object itself. The recognition of this principle may be of use to those concerned in drawing, and who may wish, at any time, to form a picture of the exact size of the object. If the object be placed further from the lens than twice its focal length, the image will be less than the object. If it be placed nearer, the image will be greater than the life. In regard to immoveable objects, such as houses, gardens, trees, &c., we may form the images of so many different sizes, by means of different lenses, the shorter focus making the lesser picture, and the longer focal distance the largest.

The experiments with the camera obscura, may likewise serve to illustrate the nature of vision, and the functions of the human eye. The frame or socket of the scioptric ball may represent the orbit of the natural eye. The ball, which turns every way, resembles the globe of the eye, moveable in its orbit. The hole in the ball may represent the pupil of the eye; the convex lens corresponds to the crystalline humour, which is shaped like a lens, and contributes to form the images of objects on the inner part of the eye. The dark chamber itself, is somewhat similar to the internal part of the eye, which is lined all around, and under the retina, with a membrane, over which is spread a mucous of a very black colour. The white wall or frame of white paper to receive the picture of objects, is a fair representation of the retina of the eye, on which all the images of external objects are depicted. Such are some of the general points of resemblance between the apparatus connected with the dark chamber, and the organ of vision; but the human eye is an organ of such exquisite construction, and composed of such a number and variety of delicate parts, that it cannot be adequately represented by any artificial contrivance.

The darkened chamber is frequently exhibited in a manner somewhat different from what we have above described, as in the following scheme, (fig. 38) which is termed the revolving camera obscura. In this construction, KH represents a plane mirror or metallic reflector, placed at half a right angle to the convex lens HI, by which, rays proceeding from objects situated in the direction O are reflected to the lens, which forms an image of the objects on a round white table at T, around which several spectators may stand, and view the picture, as delineated on a horizontal plane. The reflector, along with its case, is capable of being turned round, by means of a simple apparatus connected with it, so as to take in, in succession, all the objects which compose the surrounding scene. But as the image here is received on a flat surface, the rays fm, en, will have to diverge farther than the central rays dc; and hence the representation of the object, near the sides, will be somewhat distorted; to remedy which, the image should be received on a concave surface, as ab or PS. This is the general plan of those Camera Obscuras, fitted up in large wooden tents, which are frequently exhibited in our large cities, and removed occasionally from one town to another. Were an instrument of this kind fitted up on a small scale, a hole might be made in one of the sides, as at E, where the eye could be applied to view the picture. The focal distances of the lenses used in large instruments of this kind, are generally from eight to twelve feet, in which case they produce a telescopic effect upon distant objects, so as to make them appear nearer than when viewed with the naked eye.

figure 38.

figure 39.

The camera obscura is frequently constructed in a portable form, so as to be carried about for the purpose of delineating landscapes. The following is a brief description of the instrument in this form. AC is a convex lens placed near the end of a tube or drawer, which is moveable in the side of a square box, within which is a plane mirror DE, reclining backward in an angle of forty-five degrees from the perpendicular pn. The pencils of rays flowing from the object OB, and passing through the convex lens—instead of proceeding forward and forming the image HI, are reflected upward by the mirror, and meet in points as FG, at the same distance at which they would have met at H and I, if they had not been intercepted by the mirror. At FG, the image of the object OB is received either on a piece of oiled paper, or more frequently on a plane unpolished glass, placed in the horizontal situation FG, which receives the images of all objects, opposite to the lens, and on which, or on an oiled paper placed upon it, their outlines may be traced by a pencil. The moveable tube on which the lens is fixed, serves to adjust the focus for near and distant objects, till their images appear distinctly painted on the horizontal glass at FG. Above is shown the most common form of the box of this kind of Camera Obscura. A is the position of the lens, BC, the position of the mirror, D, the plane unpolished glass on which the images are depicted, GH a moveable top or screen to prevent the light from injuring the picture, and EF, the moveable tube.

figure 40.

The Daguerreotype.—An important, and somewhat surprising discovery has lately been made, in relation to the picture formed by the Camera Obscura. It is found, that the images formed by this instrument are capable of being indelibly fixed on certain surfaces previously prepared for the purpose, so that the picture is rendered permanent. When a Camera is presented to any object or landscape strongly illuminated by the sun, and the prepared ground for receiving the image is adjusted, and a certain time allowed to elapse till the rays of light produce their due effect, in a few minutes or even seconds, a picture of the objects opposite to the lens is indelibly impressed upon the prepared plate, in all the accurate proportions and perspective, which distinguish the images formed in a dark chamber—which representations may be hung up in apartments, along with other paintings and engravings; and will likely retain their beauty and lustre for many years. These are pictures of nature’s own workmanship finished in an extremely short space of time, and with the most exquisite delicacy and accuracy. The effect is evidently owing to certain chemical properties in the rays of light; and opens a new field for experiment and investigation to the philosopher. The only defect in the picture is, that it is not coloured; but, in the progress of experiments on this subject, it is not unlikely that even this object may be accomplished, in which case, we should be able to obtain the most accurate landscapes and representations of all objects, which can possibly be formed. This art or discovery goes by the name of the Daguerreotype from M. Daguerre, a Frenchman, who is supposed to have been the first discoverer, and who received a large premium from the French government for disclosing the process, and making the discovery public. Several improvements and modifications, in reference to the preparation of the plates, have been made since the discovery was first announced, about the beginning of 1839; and the pictures formed on this principle, are frequently distinguished by the name of Photogenic drawings; and are now exhibited at most of our public scientific institutions.

This new science or art, has been distinguished by different names. It was first called Photography, from two Greek words, signifying writing by light: it was afterwards called the art of Photogenic Drawing, or drawing produced by light. M. Daguerre gave it the name of Heliography, or writing by the sun, all which appellatives are derived from the Greek, and are expressive, in some degree, of the nature of the process. We shall, however, make use of the term Daguerreotype, derived from the name of the inventor.

As it does not fall within our plan to give any minute descriptions of the Daguerreotype process, we shall just give a few general hints in reference to it, referring those who wish for particular details, to the separate treatises which have been published respecting it. The first thing necessary to be attended to in this art is, the preparation of the plate on which the drawing is to be made. The plate consists of a thin leaf of copper, plated with silver; both metals together, not being thicker than a card. The object of the copper is simply to support the silver, which must be the purest that can be procured. But though the copper should be no thicker than to serve the purpose of support, it is necessary that it should be so thick as to prevent the plate from being warped, which would produce a distortion of the images traced upon it. This plate must be polished;—and for this purpose, the following articles are required—a phial of olive oil—some very fine cotton—pumice-powder, ground till it is almost impalpable, and tied up in a piece of fine muslin, thin enough to let the powder pass through without touching the plate when the bag is shaken. A little nitric acid diluted with sixteen times, by measure, its own quantity of water—a frame of wire on which to place the plate, when being heated—a spirit lamp to make the plate hot—a small box with inclined sides within, and having a lid to shut it up close—and a square board large enough to hold the drawing, and having catches at the side to keep it steady.

To the above prerequisites, a good Camera Obscura is, of course, essentially necessary. This instrument should be large enough to admit the plate of the largest drawing intended to be taken. The lens which forms the image of the object, should, if possible, be achromatic, and of a considerable diameter. In an excellent instrument of this description, now before me, the lens is an achromatic, about 3 inches diameter, but capable of being contracted to a smaller aperture. Its focal distance is about 17 inches; and the box, exclusive of the tube which contains the lens, is 15 inches long, 13½ inches broad, and 11 inches deep. It forms a beautiful and well-defined picture of every well-enlightened object to which it is directed.

Before the plate is placed in the camera, there are certain operations to be performed. 1. The surface of the plate should be made perfectly smooth, or highly polished. For this purpose, it must be laid flat, with the silver side upwards, upon several folds of paper for a bedding; and having been well polished in the usual way, the surface must be powdered equally and carefully with fine pumice enclosed in the muslin bag. Then taking a little cotton wool, dipped in olive oil, it must be rubbed over the plate with rounding strokes, and then crossing them by others which commence at right angles with the first. This process must be repeated frequently, changing the cotton, and renewing the pumice powder every time. A small portion of cotton must now be moistened with the diluted nitric acid, and applied equally to the whole surface. The next thing to be done is to make the plate thoroughly and equally hot, by holding the plate with a pair of pincers, by the corner, over a charcoal fire, and when the plate is sufficiently hot, a white coating will be observed on the silver, which indicates that that part of the operation is finished. An even cold surface is next wanted, such as a metallic plate cooled almost to the freezing point by muriate of soda, and to this the heated plate must be suddenly transferred.

2. The next operation is to give the plate a coating of Iodine. This is accomplished by fixing the plate upon a board, and then putting it into a box containing a little dish with iodine divided into small pieces, with its face downward, and supported with small brackets at the corners. In this position, the plate must remain till it assume a full gold colour, through the condensation of the iodine on its surface—which process should be conducted in a darkened apartment. The requisite time for the condensation of the iodine varies from five minutes to half an hour. When this process is satisfactorily accomplished, the plate should be immediately fixed in a frame with catches and bands, and placed in the Camera; and the transference from one receptacle to another should be made as quickly as possible, and with only so much light as will enable the operator to see what he is doing.

3. The next operation is to obtain the drawing. Having placed the Camera in front of the scene to be represented, and the lens being adjusted to the proper focus, the ground-glass of the Camera is withdrawn, and the prepared plate is substituted for it; and the whole is left till the natural images are drawn by the natural light from the object. The time necessary to leave the plate for a complete delineation of the objects, depends upon the intensity of the light. Objects in the shade will require more time for their delineation than those in the broad light. The full clear light of the south of Europe, Spain, Italy, and particularly, the more glowing brilliancy of tropical countries, will effect the object much more speedily than the duller luminosity of a northern clime. Some hours of the day are likewise more favourable than others. Daguerre states, that ‘the most favourable, is from 7 A.M. to 3 o’clock P.M., and that a drawing could be effected in Paris in 3 or 4 minutes, in June and July, which would require 5 or 6, in May and August, and 7 or 8 in April and September.’ In the progress of this art, at the present time, portraits and other objects are frequently delineated in the course of a few seconds.

4. Immediately after removing the plate from the Camera, it is next placed over the vapour of mercury, which is placed in a cup at the bottom of a box, and a spirit lamp applied to its bottom, till the temperature rise to 140 of Fahrenheit. This process is intended to bring out the image, which is not visible when withdrawn from the Camera; but in the course of a few minutes a faint tracery will begin to appear, and in a very short time the figure will be clearly developed.

5. The next operation is to fix the impression. In order to this, the coating on which the design was impressed must be removed, to preserve it from being decomposed by the rays of light. For this purpose, the plate is placed in a trough containing common water, plunging, and withdrawing it immediately, and then plunging it into a solution of salt and water, till the yellow coating has disappeared.

Such is a very brief sketch of the photogenic processes of Daguerre. Other substances, however, more easily prepared, have been recommended by Mr. Talbot, F.R.S., who appears, about the same time, to have invented a process somewhat similar to that of Daguerre. The following are his directions for the preparation of Photogenic Paper.

The paper is to be dipped into a solution of salt in water, in the proportion of half an ounce of salt to half a pint of water. Let the superfluous moisture drain off, and then, laying the paper upon a clean cloth, dab it gently with a napkin, so as to prevent the salt collecting in one spot more than another. The paper is then to be pinned down by two of its corners on a drawing board, by means of common pins, and one side washed or wetted with the Photogenic fluid, using the brush prepared for that purpose, and taking care to distribute it equally. Next dry the paper as rapidly as you can at the fire, and it will be fit for use for most purposes. If, when the paper is exposed to the sun’s rays, it should assume an irregular tint, a very thin extra wash of the fluid will render the colour uniform, and at the same time somewhat darker. Should it be required to make a more sensitive description of paper, after the first application of the fluid, the solution of salt should be applied, and the paper dried at the fire. Apply a second wash of the fluid, and dry it at the fire again: employ the salt a third time, dry it,—and one application more of the fluid will, when dried, have made the paper extremely sensitive. When slips of such papers, differently prepared, are exposed to the action of day light, those which are soonest affected by the light, by becoming dark, are the best prepared.

When photogenic drawings are finished in a perfect way, the designs then taken on the plate or paper are exceedingly beautiful and correct, and will bear to be inspected with a considerable magnifying power, so that the most minute portions of the objects delineated may be distinctly perceived. We have seen portraits, finished in this way by a London artist, with an accuracy which the best miniature painter could never attempt—every feature being so distinct, as to bear being viewed with a deep magnifier. And in landscapes and buildings, such is the delicacy and accuracy of such representations, that the marks of the chisel and the crevices in the stones may frequently be seen by applying a magnifying lens to the picture; so that we may justly exclaim, in the words of the Poet: ‘Who can paint like nature!.’ That LIGHT—which is the first-born of Deity, which pervades all space, and illuminates all worlds—in the twinkling of an eye, and with an accuracy which no art can imitate, depicts every object in its exact form and proportions, superior to every thing that human genius can produce.

The Photogenic art, in its progress, will doubtless be productive of many highly interesting and beneficial effects. It affords us the power of representing, by an accurate and rapid process, all the grand and beautiful objects connected with our globe—the landscapes peculiar to every country—the lofty ranges of mountains which distinguish Alpine regions—the noble edifices which art has reared—the monumental remains of antiquity—and every other object which it would be interesting for human beings to contemplate; so that in the course of time, the general scenery of our world, in its prominent parts, might be exhibited to almost every eye. The commission of the French Chambers, when referring to this art, has the following remark, ‘To copy the millions upon millions of hieroglyphics which cover even the exterior of the great monuments of Thebes and Memphis, of Carnac, &c., would require scores of years and legions of designers. By the assistance of the Daguerreotype, a single man could finish that immense work.’—This instrument lays down objects, which the visual organs of man would overlook, or might be unable to perceive, with the same minuteness and nicety, that it delineates the most prominent features of a landscape. The time-stained excrescences on a tree, the blades of grass, the leaf of a rose, the neglected weed, the moss on the summit of a lofty tower, and similar objects, are traced with the same accuracy as the larger objects in the surrounding scene.

It is not improbable, likewise, that this art (still in its infancy) when it approximates to perfection, may enable us to take representations of the sublime objects in the heavens. The sun affords sufficient light for this purpose; and there appears no insurmountable obstacle in taking, in this way, a highly magnified picture of that luminary, which shall be capable of being again magnified by a powerful microscope. It is by no means improbable, from experiments that have hitherto been made, that we may obtain an accurate delineation of the lunar world from the moon herself. The plated disks prepared by Daguerre receive impressions from the action of the lunar rays to such an extent as permits the hope that photographic charts of the moon may soon be obtained; and, if so, they will excel in accuracy all the delineations of this orb that have hitherto been obtained; and if they should bear a microscopic power, objects may be perceived on the lunar surface which have hitherto been invisible. Nor is it impossible that the planets Venus, Mars, Jupiter and Saturn, may be delineated in this way, and objects discovered which cannot be descried by means of the telescope. It might perhaps be considered as beyond the bounds of probability to expect that even distant Nebulæ, might thus be fixed, and a delineation of their objects produced which shall be capable of being magnified by microscopes. But we ought to consider that the art is yet only in its infancy—that plates of a more delicate nature than those hitherto used, may yet be prepared, and that other properties of light may yet be discovered, which shall facilitate such designs. For, we ought now to set no boundaries to the discoveries of science, and to the practical applications of scientific discovery which genius and art may accomplish.

In short, this invention leads to the conclusion, that we have not yet discovered all the wonderful properties of that Luminous Agent which pervades the universe, and which unveils to us its beauties and sublimities—and that thousands of admirable objects and agencies may yet be disclosed to our view through the medium of light, as philosophical investigators advance in their researches and discoveries. In the present instance, as well as in many others, it evidently appears, that the Creator intends, in the course of his providence, by means of scientific researches, gradually to open to the view of the inhabitants of our world the wonders, the beauties and the sublimities of his vast creation, to manifest his infinite wisdom, and his superabundant goodness, and to raise our souls to the contemplation and the love of Him who is the original source of all that is glorious and beneficent in the scene of nature.