Our readers may like to know the outlines of the process of making daguerreotypes and photographs, as just furnished us by Mr. Whipple, one of the most successful operators in this country.  We omit many of those details which are everything to the practical artist, but nothing to the general reader.  We must premise, that certain substances undergo chemical alterations, when exposed to the light, which produce a change of color.  Some of the compounds of silver possess this faculty to a remarkable degree,—­as the common indelible marking-ink, (a solution of nitrate of silver,) which soon darkens in the light, shows us every day.  This is only one of the innumerable illustrations of the varied effects of light on color.  A living plant owes its brilliant hues to the sunshine; but a dead one, or the tints extracted from it, will fade in the same rays which clothe the tulip in crimson and gold,—­as our lady-readers who have rich curtains in their drawing-rooms know full well.  The sun, then, is a master of chiaroscuro, and, if he has a living petal for his pallet, is the first of colorists.—­Let us walk into his studio, and examine some of his painting machinery.

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1.  THE DAGUERREOTYPE.—­A silver-plated sheet of copper is resilvered by electro-plating, and perfectly polished.  It is then exposed in a glass box to the vapor of iodine until its surface turns to a golden yellow.  Then it is exposed in another box to the fumes of the bromide of lime until it becomes of a blood-red tint.  Then it is exposed once more, for a few seconds, to the vapor of iodine.  The plate is now sensitive to light, and is of course kept from it, until, having been placed in the darkened camera, the screen is withdrawn and the camera-picture falls upon it.  In strong light, and with the best instruments, three seconds’ exposure is enough,—­but the time varies with circumstances.  The plate is now withdrawn and exposed to the vapor of mercury at 212 deg..  Where the daylight was strongest, the sensitive coating of the plate has undergone such a chemical change, that the mercury penetrates readily to the silver, producing a minute white granular deposit upon it, like a very thin fall of snow, drifted by the wind.  The strong lights are little heaps of these granules, the middle lights thinner sheets of them; the shades are formed by the dark silver itself, thinly sprinkled only, as the earth shows with a few scattered snow-flakes on its surface.  The precise chemical nature of these granules we care less for than their palpable presence, which may be perfectly made out by a microscope magnifying fifty diameters or even less.

The picture thus formed would soon fade under the action of light, in consequence of further changes in the chemical elements of the film of which it consists.  Some of these elements are therefore removed by washing it with a solution of hyposulphite of soda, after which it is rinsed with pure water.  It is now permanent in the light, but a touch wipes off the picture as it does the bloom from a plum.  To fix it, a solution of hyposulphite of soda containing chloride of gold is poured on the plate while this is held over a spirit-lamp.  It is then again rinsed with pure water, and is ready for its frame.