juice of flower-petals, on protiodide of iron, and on what is called in plants solanine (the white pigment which appears in the shoots grown in dark cellars), changing its nature and forming from it chlorophyll, the green coloring-matter of plants. Indeed, many celebrated chemists have doubted whether all organic and most inorganic substances were not acted on when exposed to the direct rays of the sun. The actinic principle is independent of light, and in the portion of the spectrum where the light is strongest, these rays are weakest. They also converge at a focus slightly different from the visual focus, and in the infancy of the art this was a source of great difficulty, on account of which perfect pictures were very seldom obtained. Now, however, the actinic focus can be easily calculated from the visual focus, so that these rays always perform their work correctly. These rays do not traverse transparent objects colored red, orange, or yellow, though they will those of a blue so dark as to be almost opaque. The rays from the red extremity of the spectrum also exercise a protecting agency on sensitive plates, so that if they be thrown upon one so delicate that the light of a dip candle would blacken it, and from some other source the full meridian sunbeam be reflected upon it, a narrow sensitive stripe will be left where these rays fell, while an Egyptian blackness covers the rest of the plate. Yet the yellow and red rays possess a power of developing pictures, not exceeded even by the mercurial vapor. At first, solar light was supposed to be necessary to the production of photographic effect, but it has since been discovered that electric light, the Drummond light, the flames of camphene, coal-gas, nay, even of a common candle, each in proportion to its intensity, act upon substances more than ordinarily sensitive. The time required to produce perceptible results is almost inappreciable, but M. Claudet has discovered that one one-thousandth of a second amply suffices to produce a very sensible blackening of a sensitive paper. Kilburn obtained distinct impressions of stationary objects in ten minutes, using only a small gas-burner or solar oil-lamp. Four fleet horses rushing with a carriage at full speed past the window of a Daguerreotypist did not move with sufficient velocity to prevent his obtaining a picture in which the letters on the panels, the buckles of the harness, and the features of the passengers, were plainly perceptible. Having thus briefly sketched the origin, progress, and capabilities of Photography, it may be proper to describe the instrument of the greatest importance to the artist. This is an accurately constructed camera obscura, with an achromatic lens at one extremity, and a sliding frame at the other. This frame is filled at first with a piece of ground glass, on which are received the rays collected in a focus by the lens. The focus is adjusted in such a manner that the projection upon the glass may have the greatest possible clearness. The glass is then withdrawn, and the prepared plate or paper substituted. In a few minutes a picture is obtained, in the Daguerreotype process, like the reflection of a convex mirror, in the paper process, as a negative, that is to say, with lights where the shades should be, and with shades in the place of the original lights. The picture is then submitted to a process called fixing. From the negative any number of positives may be procured, by placing the negative upon a sheet of prepared paper and pressing the two closely between two plates of glass, and then submitting them to the action of the sun's rays, transmitted through the negative to the sensitive paper. This positive of course must be fixed before exposure to diffused light. - The preparation of plates for the Daguerreotype process is one requiring considerable delicacy of manipulation, but is with that exception rather simple. A highly polished silver plate is exposed to the fumes of iodine and bromine for a few minutes. It is then placed in the camera. The light of the sun exerts upon it two contemporaneous actions, -one slow, the other violent. By the first the haloid of silver is decomposed, while by the second it acquires an affinity for the mercurial vapor. The plate is next placed over a mercurial trough, the temperature of which must be about 130° Fahrenheit. Part of the mercury amalgamates with the silver, and part unites with the halogens, and bromo-iodide of mercury is formed. The plate is now washed with distilled water, and gently heated to drive off the superfluous mercury. If now examined, the parts amalgamated will appear whitish, and the unamalgamated parts black, owing to the deposition of pure silver in a finely divided state. As a matter of artistic finish not absolutely necessary, the plate is frequently gilded to soften the harsh outlines and sharp lights and shades. The paper process differs from this very widely in detail, although the principle is the same. A paper saturated with a solution of albumen, or with wax, is coated with some salt of silver and exposed in the camera. The sensitiveness of the paper is destroyed and the picture fixed by the use of hyposulphite of soda, gallic acid, and distilled water, repeated baths of each. Another process, and one which has given much satisfaction from the beauty of the sepia. tints which result from its use, has a sensitive of nitrate of silver and chloride of ammonium, developed by a bath of dilute chlorohydric acid, and chloride of gold, and fixed by baths of ammonia and hyposulphite of soda. I have spoken of the albumen and wax paper processes of preparation. The first does not produce so delicate pictures; but its proofs do not require immediate development, as do those taken by the albumen process. Hence artists travelling to obtain subjects for paintings generally prefer the wax process, as this allows them to dispense with much cumbrous apparatus of saucers and chemicals. All attempts to make anything but shaded drawings by means of the camera have been unsuccessful, except the copies of the solar spectrum by Becquerel in 1848, and by Herschel some few years previous. The prismatic tints can be produced in chloride of silver when exposed to the sun's rays, by the powerful action of the galvanic battery, but all attempts to render these tints stable have signally failed. Yet we are sure that there is a joyful success reserved for some future investigator, and though now we can only use the sunbeam as a crayon, erelong it will serve us as an artist's brush. We never can perceive the full beauty of a photograph until it is examined with a powerful microscope. Here is one of the Capitol, not larger than a wedding card, and yet we plainly perceive every fluting of the pillars, every ornament, every niche in the stone, every leaf of the grass around, nay, the very stones may be counted and the lines between them clearly viewed, and lo! imbedded in the marble columns we see the fossils of an antediluvian epoch. This is Nature that we behold. The artist is not man, but chemistry. There is one thing, however, which is always noticeable in the paper photographs. This is the total absence of outline and the minute distinction in shade which is utterly inimitable in either painting or engraving. You never can thoroughly understand this till a comparison is made between an engraving and a photograph of the same scene. In the photograph there is a mysterious generalization, yet each part is separable. In the engraving there is either a blank solid shade or light, or a separation. Either unity or detail must be sacrificed. In giving examples I have always preferred to take them from paper photographs, yet the remarks made apply equally to those on metal. The reason for this is that the Talbotype always appears softer, and devoid of the metallic glare which necessarily accompanies the Daguerreotype, and which, in the case of portraits, gives a very stern, unnatural, harsh, and staring expression to the eyes, which is far from prepossessing. To be sure, an air of earnestness, nay, even of sternness, is almost unavoidable in photographic likenesses, both from the strong will which it is necessary for most people to exert to preserve a single posture while the picture is taken, and also from the effect produced by the spherical aberration of the lens at this time, and from the fact that the rays by which the picture is taken are not reflected from a point, or even a plane, but from a very irregular surface, so that it would be impossible to bring them all to an exact focus in a single plane. Several methods of engraving from photographs have been invented, but as none of them has proved of any practical importance thus far, and further, as they all bring in some process of manipulation not simply photographic, we omit them, and pass to photography on glass, in this country the most common way of multiplying miniatures. This process resembles almost exactly the Talbotype process. The glass is coated with a varnish of albumen or collodion, it is made sensitive in the usual way, and afterwards it is fixed. Copies are taken from this as from a negative photograph. In one thing only does the glass photograph differ from the paper. On careful examination we see a negative on the upper surface of the sensitive coating, while below it, on the under surface of this coating, by turning the plate and holding it over a black ground, we can see a positive picture. This, it will readily be seen, is an advantage, as it dispenses with the use of labels for crystallotype plates, for it is only necessary to place them in frames over a black ground, and the artist readily perceives what they represent. These also have the advantage of furnishing their own glazing. The uses to which Photography has been and may be applied are manifold. From forging bank-notes exact even to their private marks and signatures, thus serving the purpose of a felon, its sphere extends to assisting the schemes of a Czar, or lightening the burdens of a commercial traveller. Since the revival of the theory of binocular vision, and the invention of a portable form of stereoscope, photographs taken in two po sitions have been given by manufacturers of machinery to their agents; and these, being combined by the valuable optical instrument above mentioned, furnish to the purchaser of water-wheels and steam-engines quite as good an idea of the excellence of what is recommended to his notice as the cumbrous thing itself, lying on the ground, and not in motion, would do. Every invention that has ever been patented has bid fair to revolutionize some world or other, and every enthusiast places his profession"the foremost in all the world." I then, as an enthusiast in photography, beg leave to follow this same good custom, and to be confident that the time may come when photographs will supersede metaphors, when descriptions will give place to Talbotypes, and when medical reports will be illustrated by Crystallotypes of post-mortems, Calotypes of convalescents, and Heliotypes of ampu tations. L. THE JENKINS PAPERS. No. I.THANKSGIVING AT MY UNCLE JACOB'S. for THE wind was blowing. True, sir, as you say, it blows very often, sometimes when you want it, sometimes when you wish it was strapped down into its bag, tight as old olus can pull the strings. But I am not to be frowned out of my beginning. A big wind and a storm Thanksgiving must bring, if he means to pass anything but a counterfeit. Let him come with turkey and pudding in one pocket and a big gale and snow in the other, and we 'll smile him a welcome when his shadow flits over the threshold, and bid him God speed till next year, when he leaves the joy he brought behind him on the hearth-stone, and hurries off with the old year. But when he comes smiling, one wants to say: Rattle the dry old elms for us! powder my head and whistle us a tune! In short, old fellow, show your credentials! However it may have been with you, my dear reader, who are so anxious to compare your Thanksgiving experience with mine, the wind was blowing at Harnton. It was snowing fast too, so fast, I thought, as it was the first time since last March, it took more pleasure than usual in coming down in |