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PHOTOGRAPHY. Two centuries ago, a philosopher of Naples, Giovanni Battista Porta, discovered that if a very small hole be pierced in the window-shutter of a room completely darkened in other respects: or better still, if the aperture be perforated in a thin metallic plate applied to the shutter; all the exterior objects from which rays can enter through this opening will be represented on the opposite wall; in dimensions enlarged or diminished according to the distance. He found also that even with this imperfect apparatus, throughout a large extent of the picture, objects were painted in their natural colors, and with considerable truth of linear perspective. A short time afterwards Porta found that it was not necessary to have the opening very small, thus limiting the view, but that if the perforation were covered with a lens or convex glass, it might be of any dimension. He remarked also the great improvement thus produced in the delineation. The images passing through the simple medium of the hole were without distinctness of position, intensity of color, or neatness of outline. On the contrary, with the lens the mimic forms rivalled the vivacity and strength of nature herself, the focal distances being properly adjusted. It is well known that all these discoveries of Porta have become truly astonishing in precision of detail and strength of coloring since the art of constructing achromatic glasses has been brought to its present perfection. Formerly a simple lens composed of one kind of glass only, and consequently acting with as many separate focuses as there are colors in the undecomposed white ray, transmitted a comparatively indistinct image of objects. Now that we employ achromatic glasses which combine all the incident rays in one focus, and that a periscopic construction of the apparatus likewise has been adopted, great perfection has been given of its effects.
Porta constructed also a portable dark chamber, or camera obscura. These chambers were usually formed like a box with a tube furnished with the proper lenses at one end; and at the other a screen of white paper, or some prepared substance, occupied the focus, upon which the images of external objects were recejyps). The Neapolitan philosopher proposed his simple arrangement for the benefit of those who had not been taught drams According to him, nothing else was required in order to
er to o
El the most perfect transcripts of nature than merely to trace Ve carefully the outline of the focal image. by These anticipations of Porta have not been completely realized.
Painters and draughtsmen, those particularly who execute large views for panoramas, dioramas, and theatres, have indeed still recourse to the camera. They, however, employ it merely to
group objects or to trace their outline and arrangements. FREE Long ago, the chemists had succeeded in forming a solution of 47 silver in muriatic acid. This compound, which assumes the
appearance of a white salt, they called lunar or caustic silver. This salt possessed the remarkable property of becoming black by light, and of blackening more or less rapidly in proportion to the intensity of the incident rays. Cover a sheet of paper with a wash of lunar caustic, or, as we say at present, with a wash of chloride of silver ; form upon this, by means of a lens the image of an object; the shaded parts of the image, or those upon which no light falls, will remain white; the portions, on the other hand, strongly illuminated, will become completely black; the demi-tints will be represented by grays more or less dark. This monochrome, in short, will be the reverse of the real object as respects the lights and shadows.
Again, if any engraving be placed on a sheet of paper moistened with a solution of chloride of silver, and both be exposed to the solar light, the engraving being uppermost, the dark lines of the latter will intercept the rays, and the corresponding portions of the paper below will retain their original color. In those parts, on the contrary, which lie immediately under the lights in the engraving, the solar rays, acting through the imperfect transparency of the print, will blacken the chloride wash. The · necessary consequence of this operation will be a copy of the engraving, correct in its outlines, but reversed in its effects, the lights being reproduced in shadows, and the shadows in lights.
These applications of this curious property of the chloride of silver, one would think, might have readily occurred to the first discoverers of the substance, or to their early successors, who devoted more attention to practical results. Not so, however, was the case. We must descend to the first years of the present century before we detect even the beginnings of the photographic art.
About this time a Frenchman, named Charles, in his lectures, made use of a prepared paper to produce silhouettes, or black profiles, by the action of light. Charles died without describing the preparation which he employed. As the historian of science, under the pain of falling into inextricable confusion, is not authorised to proceed, except upon printed and authentic docu. ments, it is no more than justice to assign to Wedgewood, the celebrated porcelain manufacturer and inventor of the pyrometer for high temperatures, the first application of this new art.
The memoir of Wedgewood appeared in 1802 in the number for June of the Journal of the Royal Institution of Great Britain. The author there proposes by means of skins, or with paper steeped or washed in chloride or nitrate of silver, to copy paintings on glass as in the windows of churches, and also engravings. "The images formed by means of the camera obscura,” we quote faithfully a passage from the article, “have been found to be too faint to produce, in any moderate time, an effect upon the nitrate of silver.”
The commentator upon Wedgewood's experiments, the illustrious Sir Humphry Davy, does not contradict the assertion relative to the images of the camera. He merely adds, as to his own experiments, that he has accomplished the copying of very small objects by the solar microscope, but only at a short distance from the lens.
Finally, neither Wedgewood nor Sir H. Davy discovered how, the operation once finished, we were to give it permanence, or, prevent the pictures from becoming black by the action of light. It thence resulted that the copies which they had obtained could not be examined by day-light, for in a very short time they became uniformly black, and all lineaments of the previous objects disappeared. What was this in reality but to produce imagery so evanescent, that only a furtive glance could be cast upon the work, and that by the light of a lamp? The whole would have vanished in a few seconds if these delineations had been examined in day-light.
We now arrive at the researches of Messrs. Niepce and Daguerre. The late M. Niepce was a country gentleman, who lived on his property near Châlons, on the Saône. The P.hotographic researches of M. Niepce appear to have been begun só
early as the year 1814. His first connexion with M. Daguerre dates from the month of January, 1826.
In the following year M. Niepce repaired to England. In the month of December, 1827, he presented a paper on his Photographic experiments, to the Royal Society of London. This memoir was accompanied with several sketches on metal produced by methods then already discovered by him. On an attempt having been made to establish a priority of invention, these sketches, still in a state of good preservation, were immediately and honourably produced from the collections of certain English philosophers. They prove beyond dispute, as respects both the photographic copies of engravings, and the formation,
for the use of artists, of plates in the state of advanced etchtenyings, that M. Niepce in 1827 was acquainted with a method of nye making the shadows correspond to shadows, the demi-tints to me the demi-tints, the lights to the lights. These early essays farther
prove that he had discovered how to render his copies, once - formed, impervious to the erasing and blackening effects of the solar rays. In other words, the ingenious experimentalist of Chalons, by the composition of his grounds, had so early as 1827 resolved a problem, which had defied the lofty sagacity of a Wedgewood and a Davy.
The deed of co-partnery between Messrs. Niepce and Daguerre, for mutually investigating and following out the subject of photography, bears date Dec. 16, 1829. Later deeds entered into by M. Isidore Niepce, as his father's heir, and M. Daguerre, distinctly mention, in the first place, the improvements made upon the earlier methods of the philosopher of Chalons, by the Parisian artist : in the second instance, they also particularize processes entirely new, invented by M. Daguerre, and possessing the advantage (in terms of the deed) “ of producing images with sixty or eighty times greater rapidity than the earlier applications of the photographic principle."
The studies of M. Niepce referred chiefly to the photographic copy of engravings. It was only, in truth, after a multitude of fruitless attempts, that M. Niepce himself had almost renounced
the idea of ever being able to fix the image in the camera. The The preparations which he at first employed as the ground of the
ure design, did not yield with sufficient rapidity to the action
of the solar rays, so that ten or twelve hours proved hardly sufficient for producing a single design. During an interval so protracted, the shadows cast upon the various points of view were very much altered, indeed, entirely changed in place, form, and extent: they had passed, in fact, from the left to the right of objects, and this traverse, wherever it operated, gave birth to flat and uniform tints, without life or distinctness. But by the method discovered by M. Daguerre, after an immense number of minute, difficult, and expensive experiments, the feeblest rays impress the substance of the Daguerreotype, and the effect is produced before the shadows have had time to change in any appreciable degree. The results are certain, by the operator's acting according to a few very simple directions. Finally, the images being once produced, the solar rays continued for years, affect neither their purity, brightness, nor harmony.
COVENANT AND DISPENSATION.
(From Allon's Lecture on Deut. xviii. 15.*) A Covenant is a mutual agreement between two contracting parties : in religion, between God and man, whereby God promises certain spiritual blessings on the fulfilment by man of certain stipulated conditions. Of such covenants there have been only two, both with the first and parent man-one before the fall, and the other immediately after it.
The covenant made with Adam before the Fall is called the Covenant of Works, inasmuch as spiritual blessings for himself and for his posterity were promised on the condition of personal and literal obedience. This covenant Adam did not keep; he transgressed by eating of the forbidden fruit, and thereby the
• This beautiful and lucid address, the full title of which is “The Religion of Moses, and the Religion of Jesus, essentially the same," has been published for the British Society for the Propagation of the Gospel among the Jews, by Aylott and Jones, and is well worthy the earnest perusal of every Bible student, and particularly of all who feel an interest in the praiseworthy movement now making on behalf of God's ancient people. Without pleading directly for this noble cause, it is nevertheless one of the most cogent and persuasive appeals we ever remember to have read, shewing as it does in a striking manner, the exact relation of Jew and Christian not only to each other, but to the common salvation by grace through faith-the covenant confirmed of God in Christ to Abraham four hundred and thirty years before the Law.