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sheets in the manner suggested by Mr. Talbot, (page 12,) one of themis carefully fastened by the four corners to the inner box; and with thesensitive side towards the lens, is placed in the outer box, so that the mostdefined images fall on its surface. In this position, it is left undisturbeda sufficient length of time to receive the impression, which is, of course,formed by the strong light of the sky, and all brilliantly illuminatedobjects. These darken the paper to an extent corresponding with thequantity of light they radiate ; thus the darkest portion of the pictureis the sky, and the bright objects exhibit various gradations of darkness,while the shadows producing no action, leave the paper still white.
The length of time required to produce the best effect, is, of course,very variable, depending on the intensity of day light, and the sen-sibility of the paper. It may, however, be stated, as a general guide,that with highly sensitive paper, in the sunshine of a summer morning ,a good picture should bo produced within thirty minutes; even withpaper which is ordinarily sensitive, one hour is sufficient. I have pur-posely given the most simple method of procuring photographs with thecamera obscura, considering that many, by producing tolerable effectswith a very inexpensive apparatus, and with little trouble, may be in-duced to take the additional pains requisite, to furnish them with thegems of the art; who, if annoyed with tedious processes in the firstplace, might abandon the pursuit in displeasure.
A camera of a very simple kind may be constructed out of a cigarbox ; a hole being pierced in one end of it, and fitted with a lens, thephotographic paper may be pinned upon a stiff piece of card-board thesize of the box, and placed in the focus of the lens. It is necessary thatthe box be painted on the inside with a mixturo of lamp black and stiffsize, to prevent the reflection of the dispersed light. Fig. 9, gives thisarrangement.
Fig. 9.
Some of the most important results, relativo to the chemical actionof the different rays, have been arrived at with an apparatus of thiskind; and Dr. Draper, of New-York , the first who succeeded in takingportraits by the Daguerreotypo, used no other. Daguerre 's apparatusis sold at twenty guineas and upwards; here we find one of the mostdelicate of the photographic processes, accomplished with an instrument,the cost of which is only two or three shillings.
A description of a camera obscura of a superior kind, adapted forevery photographic purpose, and comparatively inexpensive, will be foundin another part of this treatise.