MODERN PRACTICE OF PHOTOGRAPHY. BY R. W. THOMAS, F. C.S. INTRODUCTORY SKETCH. HOW TO MAKE THE NEGATIVE. HOW TO CLEAN THE GLASS PLATE. HOW TO VARNISH THE NEGATIVE. HOW TO PRINT FROM THE NEGATIVE. PHILADELPHIA: INDUSTRIAL PUBLISHER, 406 Walnut Street. 1868. "I have said, and I abide by it," cries Voltaire, "that the fault of most books is their being too long." "A writer who has reason on his side will always be concise." BISHOP HORNE. H. C. BAIRD, Philadelphia, PUBLISHES THE PRACTICE OF PHOTOGRAPHY. BY ROBERT HUNT. With numerous Illustrations. 12mo. 75 cents. THE DAGUERREOTYPIST AND PHOTOGRAPHER'S COMPANIllustrated. 12mo. ION. $1 25 PHILADELPHIA: COLLINS, PRINTER, 705 JAYNE STREET. INTRODUCTORY SKETCH. PROBABLY no modern science or art can boast of so many roads to success, as that which owns itself the servant of the sun. It is easy to understand why this should be so, for all things, animate and inanimate, are affected by the sun, which at the same moment gives us both light and life, and is a fertile. source of chemical decomposition. It becomes, therefore, evident that the slightest investigation, the mere cursory examination of the many valuable storehouses of knowledge, is sufficient for developing that which at first sight appears new, but which, in reality, is only proof of the statement above made, that all bodies are more or less acted upon, and changed by the agency of light. Hence the innumerable processes in photography, which spring up daily, giving constant occupation and food to the experimentalist, engaging earnestly his attention, and so absorbing his interest by a success more or less certain, as to make the pursuit of this art, probably the most fascinating, the most exciting, and the most productive of results of any followed by the intelligent and intellectual classes of the present day. If the above paragraph has been carefully read, it will be easily seen that as there are many roads pointing to the same end, so, in proportion to their number, will be found the difficulty in selecting that path which the novice will gladly seek, as leading direct to a successful practice of the art in question. It will be my endeavor to point out that road, and in doing so, I would not for a moment disparage the opinions of others, but merely show, without turning either to the right or to the left hand, how perfect results may be obtained; but, in doing this, I feel that brevity must take the place of a system more prolix, and to some minds, more agreeable. Let, if you will, these pages be a primer-a first lesson on one of many processes; yet, the object I have in view is to put before those who require instruction on the subject of photography, a pamphlet which shall enable them at once, not only to succeed, but, with a little practice, to rival those who stand foremost as the most successful votaries of this engaging art. Now it would hardly do, from this preamble, to descend suddenly to a process, without feeling sure that the reader, who, perchance, may be altogether a novice, has some knowledge of the principles on which the art of photography is based; a writer must have no slight acquaintance with his subject who can make a complex matter clear and intelligible to the understanding of his reader by the use of a few paragraphs only. I despair of doing this to my own satisfaction, but, nevertheless, such an attempt has to be made, and in making it my aim shall be rather to excite the interest and attention of a student, so as to compel him to turn for fuller information on the various heads of the subject under notice, which may be found by making reference to works on optics and chemistry. The first question, what is light? naturally suggests itself. In answer, this much is known: light comes to us through the medium of our atmosphere, pure and white, yet it is easily decomposed; its rays, analyzed and divided by means of the prism, show seven principal colors, each color has its own property, and specifically its own chemical action; it is with this latter fact that we have to do, our whole practice of photography depending on the actinism of the violet color and the invisible rays beyond, as shown by chemical experiment to exist in the spectrum; the red and yellow rays at the opposite end, although most luminous, affect only in a slight degree, chemical bodies. It becomes, therefore, evident, bearing this fact in mind, that photographic lenses must be constructed, not possessing the power of giving the most luminous and, consequently, the most brilliant image only, on a ground-glass, placed at a point termed the focus of a lens, but the visual and chemical foci must be blended, so to speak; this, the skilful optician effects by combining lenses of various curves and densities, with a view of obtaining at the same focus two distinct powers, light and actinism, each, under ordinary conditions, being refracted at different distances. I need only remark that the problem has been well and satisfactorily worked out by our great opticians, who have also given to photographers a variety of useful combinations of lenses, not dreamt of in the earlier days of their art. I have shown already that light produces chemi |