Volltext Seite (XML)
684 THE PHOTOGRAPHIC NEWS. [Octobee 23, 1885. reverse the spectrum in that region. The lampblack showed a slight broad absorption band between F and G, with a maximum at G. Otherwise the spectrum was quite uniform between A 138 11204a D near wave-length 1’04. With the red and blue glasses, and with the asphalte, there was apparently no reversed area. The former had three maxima—at F, just below D, and just above A. The last was the strongest marked, and the one near D was very small. The asphalte had only one maximum, and that was just below D. If the length of the exposure with two pieces of red glass be increased, the limits of the reversed area will advance in both directions, as is shown by the figure, where abscissas represent the wave-lengths in the prismatic spectrum, and ordinates are proportional to the logarithms of the exposures. The shaded h m. a. 8 0 0 i 0 0 80 0 8 0 2 0 80 8 2 0.5 1.82 1.33 1.12 .94 . .76 .59 • A D area shows the darkened portion of the spectrum, while the deep notch represents the reversed portion. This series of exposures was taken on a fairly clear day, but occasionally wave-length 138 has been reached in from two to ten minutes, as is shown by the two crosses on the left. There was a great difference in the trausparency of the atmo sphere noted on different days. This was noted by Abney. Strangely enough, quite as good results have been obtained in December as in May and June. The A line is one of the easiest in the spectrum to photograph, and with the slit 5' in breadth it may be taken in one half- second. If the slit is 1‘ 20" wide, the spectrum may any day be photographed as far as wave-length 100 in two minutes, and under favourable circumstances as far as 1’38, but beyond that it is not easy to obtain satisfactory results. THE EASTMAN FILM. and H, and faded away at the two ends, disappearing at wave lengths ’37 and ’94 micron. If one wished for a photograph of the visible spectrum only, it would seem as if it might be obtained very satisfactorily by merely inserting a piece of smoked glass in front of the slit. The glass should be smoked until it is about as dark as two pieces of ordinary red and blue glass, placed together, appear when viewed by transmitted light. The hard rubber spectrum was obtained with a piece of rubber about '025 cm. in thickness. One could readily see the sun through it, and by close examination detect the window bars when no light came over the shoulder. In structure it was not transparent, but translucent like porcelain, and filled with little irregularities, consisting of short, narrow, opaque lines, lying in the direction in which the sheet had been rolled. On placing it in front of the slit, its spectrum showed a maximum photo graphic intensity in the neighbourhood of the A line, whence it gradually faded away to line '9 4, where it reversed, and became direct again near 1'12, where it disappeared. This reversing action was noticed more markedly in the case of the red glass, to be presently described. On the more refrangible side of the A line there was a faint absorption band extending half-way to D, and after that a uniform spectrum till D was reached. Here it began to fall off, and soon disappeared. Between F and G there was a small amount of light transmitted. With a single red glass there were three maxima, the largest between A and G, the next in size between it and D, and a small one in the neighbourhood of the line 112 micron. Between the last two maxima there was a reversed band culminating in the neighbourhood of line '94. By the insertion of another red glass the maximum between F and G was reduced to a small band in the vicinity of F, and the reversed area was transferred some what lower down in the spectrum, so that its maximum occurred BY HUGH REID.* Upon receipt of the films, and in order to secure as correct exposures as possible (for there was no number on the wrapper to indicate their rapidity), I tested a portion of one by Warnerke’s sensitometer, when the very high number 23 was registered, equal to 180 times the rapidity of the wet process. From the high number obtained, I had some doubts regarding its cor rectness, and wrote to the Company, requesting them to inform me of the number they gave by the standard sensitometer. In their reply they corroborated the number obtained by me. Here, then, to begin, I had very sensitive films to work with. One Saturday in September, having fine light (for the season of the year), with a high wind, I wished, if possible, to make an exposure or two, and for that purpose arranged for a short drive into the country, and endeavoured to get some quiet nook to secure a bit of landscape ; it was all to no purpose, on account of the wind. Failing in the landscape, the camera was rigged up, and an exposure made on the pony trap. Before exposing I had considerable doubts as to exposure and size of stop to use ; the wind being so high, I resolved to use the drop-shutter and stop , this being the smallest stop 1 had pre viously used for drop-shutter exposures. The formula for development used was that sent along with the films, easy to manipulate, the washing after fixing occupying about half an hour. After washing, the negatives are squeegeed, film side down, on to glass previously oiled or rubbed over with powdered talc. We now come to the oiling for the purpose of removing the grain of the paper. Castor oil is recommended. Knowing the disagreeable nature of it, I procured what was considered the • Abstract of a communication to the Glasgow and West of Scotland Amateur Photographic Association.