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92 THE PHOTOGRAPHIC NEWS. [January 30, 1891. paper to be inserted is found by experiment for each variety of dry plates. Their use is to lessen the intensity of light passing through to the degree requisite to give correct results with the instrument ; this once found is constant for that variety of plate. To use the instrument, allow the hinged portion to fall, and so get the side with the luminous paint fully exposed to day light for thirty seconds. Place the eye at the end, then quickly close the hinged portion ; a blue luminous ground and a dark ground will be seen side by side. Count the number of seconds it takes for the blue luminous side to acquire the same tint as the dark side—that is, note when the difference in blue disappears. Refer to the table mentioned, and, opposite the number of seconds required for the two halves to appear alike, will be found the correct exposure to be given to the photo graphic plate to which the instrument is adjusted. The instrument I have constructed is adjusted to a plate of about 18 Warnerke sensitometer value, working with a stop or diaphragm in the lens of one-sixteenth of the focus of the same. The actinometer can easily be adjusted to a plate of any degree of speed by removing or adding to the layers of tissue paper behind the glass carrying the luminous paint. In adjusting the actinometer, any of the published tables of exposure may be employed, or, better still, that excellent little calculating machine for photographic exposures called the “actinograph,” invented, after much labour and study, by Dr. Ferdinand Hurter and Mr. Driffield, of Widnes. Or in very perfect instruments a clockwork, or its equivalent, can be set in action by closing the hinged portion, and arrested by open ing it; this can be arranged with a scale to show the requisite exposure in seconds. 2,671. February 1890.— “The Photometric Examina tion of Gases.” WILLLIAN Foster, 14, Clement's Inn, Lon don, Consulting Chemist. My invention consists of apparatus whereby the illuminating value of one and the same sample of gas can be rapidly ascer tained when consumed in a number of different burners. It consists ot a tap or cock the plug of which is fixed. A channel or passage for the gas is made along a portion of the longitudinal axis of the plug terminating laterally. Encircling the plug is a mass of metal carrying arms of equal length, at the end of each arm a particular but different burner being arranged. These arms, with the burners which they carry, rotate round the central fixed plug. In using the apparatus a particular burner is brought round to the end of the bar of the photometer, whereby the lateral channel in the plug, the arm of the burner required, and the bar of the photometer are all three in the same straight line. All the other arms, and, therefore, all the other burners of the apparatus, are cut off from gas communication. When flat flame burners are used, I arrange a form of tap at the extremity of the radial arm, whereby the flat surface or the edge of the flame can be opposite to the disc of the photometer. 9,422. June lith, 1890.—“Glazing Bars or Astragals for Roof-lights.” William Richard Lester, 11, West Regent Street, Glasgow, Engineer. My said invention has for its object to improve the form of glazing bars or astragals for roof-lights or windows, and to combine parts so that a soft material, such as lead, or an alloy thereof, may be satisfactorily used for securing the glass. Zinc, or other metals, or alloys, may also be used in combination with my improved bars. In carrying out my invention according to one modification, I employ a steel or iron bar rolled so as to be of a section having an upper vertical member or web, and on each side of its lower part a member or web shaped to form a gutter. In addition, there is formed on each side of the middle part a shoulder or projection, on which the edge of the glass is to rest. But these shoulders are a little higher than the outer edges of the gutter parts, so that such outer edges do not touch the underside of the glass. The lead or other metal combined with the bar is made to cover the vertical member, and is riveted thereto, or otherwise attached, so that it cannot lift off the bar ; and it is made with marginal parts, which are doubled close down to the shoulders, and which are folded down on the glass when it has been placed in position. The vertical member of the bar may be made to extend in part above, and in part below the other parts. An inner gutter may be formed on each side, and so as to have the glass resting on its outer edge, but not on the outer edge of the outer gutter, by suitably doubling and bending the lead, the shoulders below the lead being relatively lower than in the first modification; or inner gutters may be formed by fixing suitably shaped strips of zinc or other metal to the bar. In other modifications, the bar may be of cast iron or other suitable material ; or it may be of wood, in which last case the parts are made of such dimensions as to be of suf ficient strength ; or the bar may be made of sheet metal bended so as to present an outward form like what is herein before described for the steel or iron bar, wood or other suitable material being in some cases combined with such sheet metal. 19,658. December 2nd, 1890.—“Photographic Films.” A communication from George Eastman, Rochester, County of Monro, State of New York, United States of America, Manufacturer. Alfred Julius Boult, 323, High Holborn, London. Difficulty has heretofore been found in using photographic film—such, for instance, as is described in letters patent No. 19,897, dated December 10th, 1889, granted to me—com posed of a film support made from a compound of nitro-cellu lose camphor and other substances, and having applied thereto, after being dried, a film or layer of gelatino-argentic emulsion, especially if the photographic film be wide, owing to the tendency of such film to contract at the edges more than the central parts, so that it will not lie flat on the table or sup port of the roll-holder—such, for instance, as that of the Eastman and Walker roll-holder—but, when strained tight, the edges alone will be brought in contact with the table, while the central parts will bulge and buckle, thereby render ing it objectionable or unsuitable for photographic purposes. This unequal contraction and buckling is believed to be due to the drying out or evaporation of the volatile substance or substances used with the nitro-cellulose to make the compound from which the film support is produced, and which remain in it after it is dried. One reason for this belief is that it has been observed that such photographic film that has been kept on spools for some time becomes permanently set, and the buckling is more marked. It has been discovered that, by coating and thus protecting or sealing the film support on both of its surfaces with some material such as gelatine—-which, it is believed, prevents, re tards, or modifies the evaporation of said substance or sub stances in the film support when dried—the film is prevented from unequally contracting or buckling to an objectionable extent, and is caused to remain in good condition, and so that it may be kept in rolls or on spools for a considerable period of time without materially changing, thus enabling it to be employed in all cases where paper films are used. The Royal Institution.—Lord Rayleigh’s lecture on “Some Applications of Photography ’’ did not come off last Friday, and we regret to say that it was in consequence of domestic affliction ; its delivery has been postponed. In place thereof, Lord Justice Sir Edward Fry lectured on “ British Mosses.” Among the ob jects of interest exhibited in the library, were small photographs on Dagron and Co’s, collodion films, illustrating the French pigeon post, by Mr. John Spiller ; an excellent winter scene in the mountains, Piz Langard, Engandine, by Mr. Arnold Spiller ; some good primuline prints by Messrs. Green, Cross, and Bevan ; seascapes by G. West and Sons ; views of the moon by F. S. Wells ; camera with aluminium fittings by J. R. Gotz; opthal- mic refractometer by A. Fournet; a “ terpuescope ” by A. Wrench; exposure meter by Mr. Watkins; Gravell’s optical pointer, and his adjustable cut-off for limelight jets ; Newton’s new projection lantern for the Royal Institution ; a table polar iscope by Harvey and Peak; and photogravures by the Typo graphic Etching Co.