The ordinary effect of light upon white sensitive paper is to _blacken_ it. If therefore any object, as a leaf for instance, be laid upon the paper, this, by intercepting the action of the light, preserves the whiteness of the paper beneath it, and accordingly when it is removed there appears the form or shadow of the leaf marked out in white upon the blackened paper; and since shadows are usually dark, and this is the reverse, it is called in the language of photography a _negative_ image.
This is exemplified by the lace depicted in this plate; each copy of it being an original or negative image: that is to say, directly taken from the lace itself. Now, if instead of copying the lace we were to copy one of these negative images of it, the result would be a _positive_ image of the lace: that is to say, the lace would be represented _black_ upon a _white_ ground. But in this secondary or positive image the representation of the small delicate threads which compose the lace would not be quite so sharp and distinct, owing to its not being taken directly from the original. In taking views of buildings, statues, portraits, &c.
it is necessary to obtain a _positive_ image, because the negative images of such objects are hardly intelligible, subst.i.tuting light for shade, and _vice versa._
But in copying such things as lace or leaves of plants, a negative image is perfectly allowable, black lace being as familiar to the eye as white lace, and the object being only to exhibit the pattern with accuracy.
In the commencement of the photographic art, it was a matter of great difficulty to obtain good _positive_ images, because the original or negative pictures, when exposed to the sunshine, speedily grew opaque in their interior, and consequently would not yield any positive copies, or only a very few of them. But, happily, this difficulty has been long since surmounted, and the negative or original pictures now always remain transparent during the process of copying them.
[PLATE XXI. THE MARTYRS" MONUMENT]
PLATE XXI. THE MARTYRS" MONUMENT
PLATE XXI. THE MARTYRS" MONUMENT
Oxford has at length, after the lapse of three centuries, raised a worthy monument to her martyred bishops, who died for the Protestant cause in Queen Mary"s reign.
And we have endeavoured in this plate to represent it worthily. How far we have succeeded must be left to the judgment of the gentle Reader.
The statue seen in the picture is that of Bishop Latimer.
[PLATE XXII. WESTMINSTER ABBEY]
PLATE XXII. WESTMINSTER ABBEY
PLATE XXII. WESTMINSTER ABBEY
The stately edifices of the British Metropolis too frequently a.s.sume from the influence of our smoky atmosphere such a swarthy hue as wholly to obliterate the natural appearance of the stone of which they are constructed. This sooty covering destroys all harmony of colour, and leaves only the grandeur of form and proportions.
This picture of Westminster Abbey is an instance of it; the faqade of the building being strongly and somewhat capriciously darkened by the atmospheric influence.
[PLATE XXIII. HAGAR IN THE DESERT.]
PLATE XXIII. HAGAR IN THE DESERT.
PLATE XXIII. HAGAR IN THE DESERT.
This Plate is intended to show another important application of the photographic art. Fac-similes can be made from original sketches of the old masters, and thus they may be preserved from loss, and multiplied to any extent.
This sketch of Hagar, by Francesco Mola, has been selected as a specimen.
It is taken from a fac-simile executed at Munich.
The photographic copying process here offers no difficulty, being done of the natural size, by the method of superposition.
[PLATE XXIV. A FRUIT PIECE.]
PLATE XXIV. A FRUIT PIECE.
PLATE XXIV. A FRUIT PIECE.
The number of copies which can be taken from a single original photographic picture, appears to be almost unlimited, provided that every portion of iodine has been removed from the picture before the copies are made. For if any of it is left, the picture will not bear repeated copying, but gradually fades away. This arises from the chemical fact, that solar light and a minute portion of iodine, acting together (though neither of them separately), are able to decompose the oxide of silver, and to form a colourless iodide of the metal. But supposing this accident to have been guarded against, a very great number of copies can be obtained in succession, so long as great care is taken of the original picture. But being only on paper, it is exposed to various accidents; and should it be casually torn or defaced, of course no more copies can be made. A mischance of this kind having occurred to two plates in our earliest number after many copies had been taken from them, it became necessary to replace them by others; and accordingly the Camera was once more directed to the original objects themselves, and new photographic pictures obtained from them, as a source of supply for future copies. But the circ.u.mstances of light and shade and time of day, &c. not altogether corresponding to what they were on a former occasion, a slightly different but not a worse result attended the experiment. From these remarks, however, the difference which exists will be easily accounted for.