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THE PHOTOGRAPHIC NEWS. Vol. XXYII. No. 1272.—January 19, 1883. CONTENTS. PAO® .. 42 .. 43 .. 44 .. 45 .. 45 .. 47 .. 48 PAGE 33 33 .. 35 .. 35 .. 38 .. 40 .. 41 Photographic Action in Minerals Photographing a Ship’s Course " Patents and Patenting Carbon Printing. By J. C. Annan ...................... Pry Plates and their Development. By S. Tamkin Notes Patent Intelligence Notes on Photography. By E. Howard Farmer Green Fog. By C. Ray Woods 4-; Lockyer’s Dissociation-Theory. By Dr. II. W. Vogel. Correspondence Proceedings of Societies Talk in the Studio To Correspondents ••!•••••••••••••••••••••••••••••••••••••••••• PHOTOGRAPHIC ACTION IN MINERALS. In a recent number of the News we commented on the change that certain organic bodies undergo under the influence of light, and we then communicated some recent discoveries in this connection. But changes, due to light, quite as surprising, are to be found among minerals, which are usually regarded as the most stable of bodies. According to a new observation of Erdmann’s, it seems that certain kinds of felspar are sensitive to light. Green felspar, which is sometimes called Amazon-stone, and is found in certain localities in Sweden, is one of these. This green felspar is generally discovered in zinc- mines, and the miners, when they first come upon it, notice that the mineral is of a light emerald green. But on ex posure to light the colour changes, and becomes a very dark green indeed. The interesting experiment was made to seal up in glass tubes of different colours pieces of this felspar, so as to prevent any influence from air or damp ; but after eleven months’ exposure to light the same change in colour was remarked, so that light rays, and these alone, are shown to bring about the change. Heated, however, to a moderate temperature, the dark green felspar becomes once more light green. While on this interesting subject, we may refer to a former observation of G. F. Richter’s, in which an analagous change in the mineral Jacinth through the action of light was remarked. There are hyacinth-red varieties of this mineral, as also those coloured yellow and greenish-grey. Richter showed that sunlight changed the red variety into brown. Four-and-twenty hours were sufficient to work a perceptible change, and after this period the colour of the mineral became quite brown. At the same time its former diamond brilliancy was lost, and it appeared more like glass. In order to find out whether its original brilliant appearance could be restored to it, Richter placed some of the mineral in the dark under black paper for a period of fourteen days, and was sur prised to see that there certainly was a restoration in this respect, albeit the mineral did not attain the full force of its pristine beauty. Finally, it may be remarked that warmth behaves in a most singular manner in respect to these changes by light. In ordinary photographic processes, warmth frequently assists the photographic action of light; indeed, as our readers are aware, it is possible to produce and develop heat pictures (Thermographs) in the same way as light-pictures. In the case of felspar and glass, it is, however, different. Felspar darkened by light, or window-glass rendered violet or green under the action of the sun’s rays, are bleached when submitted to heat. So, again, bicumen or asphalte rendered insoluble by the action of light, and anthracene acted upon by light, are both bro ught back to their original condition by heat. So that we have here some remarkable examples of the fact that heat can at times act in opposition to light. PHOTOGRAPHING A SHIP’S COURSE. A fortnight ago we referred to an invention by Mr. Pick well, Civil Engineer, of Hull, for registering a ship’s course by the unerring pencil of photography. That gentleman has been good enough, not only to furnish us with further details touching his invention, but also to forward some sketches which will make more clear to our readers the nature of the apparatus involved. As we before mentioned, sensitized sheets of paper—or, rather, tables printed on sensitive paper (see fig. 5)—are used to receive the impression of the ray of light, which comes from the daylight or a lamp above the compass. The paper is prepared after the manner of that employed at the Greenwich and Kew Observatories; in fact, Mr. Pickwell exposes his paper wrapped round a barrel, in the same way precisely as do the Astronomer-Royal and Mr. Whipple. The paper keeps very well for weeks with a little care, and its development is, as our readers are aware, a very simple matter. Our sketches will be readily understood. Fig. 1 repre sents an elevation of a compass binnacle and stand, of the pattern used by the inventor, and fig. 2 a cross section, showing the inside compass and lamp, and the adaptation of the patent self-registering apparatus under the compass card. A is the wooden stand lashed and screwed to the deck, which carries the ordinary bowl, B, covered by the binnacle top, C, with glass windows, the stand being of any convenient height. Inside the outer bowl the compass bowl is hung on gimball rings in the usual way, and the compass card is seen below the glass cover or lid of the inner bowl, light being supplied at night by a top lamp, as shown in fig. 2. The registering apparatus is fitted in the bowl below the card, and is indicated by the letter E on the engraving. It consists of a barrel (figs. 2, 3, and 4) containing clockwork, which causes a second barrel within the first to continuously revolve at a given speed, the outer barrel being fixed and having two slots, e e, cut through on its upper surface parallel to the axis. The compass card has also a slot, shown by the line G G G, curved in such a manner that some one part of it is always across one or other of the straight slots in the drum; and as the inner barrel is, when in use, covered with sensitized paper, it will be at once understood that, in whatever course the ship is being steered, a ray of light, either from the sun or from the lamp, will pass through the small opening made at the intersection of the curved slot in the card with one or other of the straight