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THE PHOTOGRAPHIC NEWS Vol. XXVII. No. 1297.—July 13, 1883. CONTENTS. Sensitive Bacteria, and their Employment in Photometry 133 Asser’s Photo-lithographic Method 433 Lenses for Instantaneous Work 434 The Tourist Photographer 435 Lighting and Posing the Human Model. By Cliff 437 Amateur Photography 438 Sulphur. By Charles Erhmann 438 Notes 440 Patent Intelligence 442 With the Eclipse Expeditions. By C. Ray Woods 442 Photographing a Dene-Hole. By Arnold Spiller 443 SENSITIVE BACTERIA, AND THEIR EMPLOY MENT IN PHOTOMETRY. It is well known to our readers that the motion of several of the lower organisms—as, for example, the so-called Bac teria—is influenced by light. The tiny beings thus influ enced do not, however, all behave in the same way when subject to light rays ; some are more, and some less, sensitive, while the cause of their motion under the action of light differs also. Certain Bacteria—as, for instance, the putrefaction Bac teria—only move, according to Engelmann, in the presence of free oxygen. If these Bacteria are under water in con tact with plant cells containing chlorophyll, they will not move so long as they are in darkness, and no oxygen is given off. On the other hand, as soon as light falls, the chlorophyll at once begins to generate oxygen, and the Bacteria get into motion. In this instance, therefore, the motion of the Bacteria depends upon an alteration in the nature of the gases. Other Bacteria there are, Engelmann tells us, called Bacterium pJiotometricum, which get into motion under no other circumstances but when light falls upon them. The animating power of the light is not instantaneous, but proceeds only after an interval, so that a certain prelimin ary action is necessary, as in certain photographic pro cesses ; to wit, in the case of a mixture of chlorine and hydrogen, which combines under the action of light. The animating action of the light in this case is not due to any development of oxygen. Light in great quantity, and of a constant nature, acts as a sedative. On sudden darkening, the Bacteria are frightened back. An illumin ated ball introduced into the fluid impels the Bacteria forwards, while a brightly-lit spot in an otherwise dark drop of liquid becomes a perfect trap to the little creatures ; they can get in, but they cannot get out. By directing a luminous ray into liquid in this way, Engelmann has suc ceeded within a few minutes in bringing together within the space of 0-1 of a millimetre several thousand Bacteria. The ultra-red rays seem to have the greatest power of animating Bacteria in this way, although the tiny organ isms are also sensitive to violet rays as well. It is apparent, then, that there are certain Bacteria which are exceedingly sensitive to light. For this reason they may be employed for photometry, and Engelmann, indeed, has actually experimented with this novel and original method of measuring light, and with no little success. Engelmann’s results furnish us with a satisfactory reply to the question why our eyes see no ultra-red. If the spectrum of a gas jet is permitted to pass through the re frangible medium of four fresh ox eyes, and with a micro spectroscope the action of the ultra-red is observed upon the bacterium photrometricum^ very nearly the same effect How to Make a Pictorial Background,. 443 The Use of the Diaphragm. By Charles Erhmann 444 Dust in the Eyes.—A Screw Loose, or What ■ By A. L. Henderson A Dictionary of Photography 444 Photo-Lithography and Photo-Zincography. By Major J. Waterhouse, B.S.C 445 Proceedings of Societies 447 Talk in the Studio 44 7 To Correspondents 448 Photographs Registered 448 will be seen as that produced by the direct spectrum. This proves that the boundary of vision of the spectrum at the red end is not in consequence of the absorption of ultra-red by the eye, but because the eye itself is not sensitive to these particular rays. The action of coloured light in bringing about the gene ration of oxygen in plant cells may also be verified in the micro-spectroscope by means of the Bacteria method. Engelmann found that in the case of green plant cells, the maximum action of the spectr :m in the red was between B and C, while there was a second maximum in the blue at F, and a minimum in the green. This observation, we may mention, is contradictory to the results of other investigators, such as Draper and Pfeffer ; but the last-mentioned experimented with whole plants, and hence it is likely that errors of observation crept in. Very important is the result that the maxima of assimilation (in the case of change of matter in the plant cell) coincides with the maximum of light absorption, and the minima with the minima. This observaton is really quite startling, and it harmonises with all our experiences in photo-chemistry. Very interesting, too, is the observation that coloured pigments are capable of forwarding the assimilation of un coloured vegetable substances. Apparently the coloured substances act upon the colourless vegetable bodies as optical sensitizers, in accordance with theory which Dr. Hermann Vogel holds. ASSER’S PHOTO-LITHOGRAPHIC METHOD. Nearly three months ago, we alluded to the facility with which the original pboto-lithographic method of Asser can be carried out; and the circumstance that the half tones of an ordinary negative may be reproduced as a grain or stipple. We now present our readers with a print from an etched zinc block, which Mr. Asser has kindly sent us; and although the original was a pen-and- ink drawing, there are several points of interest relating to it. Our readers will notice the very satisfactory manner in which the original spirit of the artist is rendered, and one may look on a reproduction of this kind as an etching in which the artist is spared all the troublesome details of work incident to the actual dissolving away of the metal. The original drawing, which represents a characteristically picturesque gateway to be found at Haarlem, made by Mr. A. W. Weissman, was executed in Indian ink on white paper, and an ordinary negative was taken of this on Asset’s prepared paper—which, as our readers know, is a highly starched paper made sensitive with bichromate— was next exposed under this until a vigorous brown im print of the subject became visible on the paper. Our readers are familiar with the remaining steps in the pro-