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310 THE PHOTOGRAPHIC NEWS. [May 15, 1885. limited means, and under the great disadvantage that he thought it necessary not to disclose his methods of working. J udging the mechanism by the work he did with it, there can be but one feeling among all who are familiar with his ruled test-plates—a feeling of intense admiration for the inventiveness and extra ordinary dexterity he brought to bear on the subject under the circumstances. For the production of diffraction gratings, interference- plates, and micrometers, where the equidistance of the lines would be of extreme importance, and where the breadth of space covered by the Hues is so large that the lever motion in arc would have produced errors in the evenness of the division, Herr Nobert removed the bent arm from the centre of the division plate, and substituted a vertical cylinder, on which he coiled an extremely thin, flat steet spring, having a hook at the free end. This hook he attached to a stud beneath the polished steel cylinder which carries the glass plate to be ruled under the diamond, and which takes the place of the carrier used for the test-plates. The rotation of the division-plate caused the vertical cylinder in the centre to rotate, coiling the steel spring, and thus, after the manner of a windlass, hauled along the diffraction-plate carrier at right angles to the ruling motion of the diamond. The preparation of the diamond points has long been con sidered as the grand secret of Nolest’s success. Beyond the admission of the bare fact that he did use diamonds, he kept the secret of their preparation. When the machine came into my hands, I expected to be able to explain the preparation of the ruling points immediately by inspection with the microscope ; but the matter was far more difficult than I had supposed. My appeal to diamond “experts” brought me face to face with absolute contradictions. There were ten diamonds with the machine. Two of them were technically termed “ points,” pyramidal fragments of diamond terminating in points. All were agreed that these were untouched by the polishing mill. The other eight diamonds each presented the general form of two faces meeting in an “ edge ; ” the difficulty was to decide whether the faces were in some cases (1) both polished, (2) both cleaved (cleavage-faces unpolished), or (3) one polished and one cleaved. The opinions of the diamond experts could not be reconciled, for in two instances they were wholly opposed, one party affirming that both faces were polished, whilst the other partj were equally positive that both faces were due to cleavage alone, and were not polished. Under these circumstances, it appeared to me essential to sub mit the diamonds to the test of the goniometer, with a view to determining whether the angles of the natural cleavage-planes had been altered, any such alteration being necessarily due to artificial polishing of one or both faces. I thought it would be most satisfactory to ask the assistance of a professional mineral ogist, and, therefore, applied to Mr. Lazarus Fletcher, of the Mineralogical Department in the British Museum, who very kindly undertook to examine the diamonds, and measure the angles with Fuess’s goniometer. In Mr. Fletcher’s opinion the two “ points ” were untouched by the polishing mill; diamonds No. 4 consisted of two cleavage-faces meeting in the edge, and was untouched by the mill; in each of the seven remaining cases one of the faces meeting in the edge was an untouched cleavage- face, and the other had been polished, and in some cases an additional facet or two developed on that side. The goniometer showed that in the polishing the angles had been altered from the natural cleavage-planes by quantities varying from a few minutes up to about six degrees, and as no two were exactly alike, it might be assumed that, as Mr. Fletcher suggested, “ the alteration of the angle is merely an incident of the polishing,” and not a condition distinctly aimed at by Herr Nobert. I had previously stated (at the Royal Microscopical Society) that some of the diamonds appeared to have two polished faces meeting in an edge. On closer examination in Mr. Fletcher’s presence, I found that certain striations on the faces, which I had regarded as imperfectly polished, were more probably untouched, and hence I have given my adhesion unreservedly to his judgment. Nobert’s original rulings appear to have been made on arti ficially polished surfaces. Later on, he experimented with thin cover-glass, ruling on the natural or melted surface. More recently, Dr. Schroder called his attention to a kind of glass technically termed mild glass, and instructed him in a method of polishing, which induced him to revert to artificial surfaces again. The plates ruled since 1869 are probably all of “ mild ” glass, thinned down to suit high powers. In 1869, he adopted a plan suggested by Dr. Woodward, namely, to rule ou thin glass, and mount the ruled plate on another thin glass, the whole dropping into a countersunk opening in a brass plate 3 by 1 inch, on which the data of the rulings were engraved. Dr. Wood ward suggested this plan in order to facilitate the employment of an achromatic condenser of large aperture and short focus. The memorandum-book shows that in ruling a 30-band plate, Nobert commenced with the coarser lines, using a weight-pres sure of 30 grammes of the diamond, which was gradually diminished until for the highest band he used only 3 grammes. A later entry seems to imply that he reversed the order of the ruling, commencing with the finest lines and the lightest pres sure. In conclusion, I may express my conviction that the publica tion of the data obtained from the examination of the machine, and especially of the diamonds, will further the interests of micrometry. Several ruling machines exist in Europe and America capable of dividing space as minutely and accurately as Nobert’s machine ; but most, if not all, of them refuse to rule lines at all comparable to his when the closeness exceeds about 50,000 to the inch ; and this is, I believe, mainly, if not wholly, due to imperfection in the diamond, or in the method of regu lating its pressure on the surface to be ruled. I venture to predict that when the. history of the mechanical inventions of our time comes to be written, a large measure of credit will be assigned to the mechanical genius of Herr Nobert, as embodied in this ruling machine. VIGNETTING. Having obtained a negative in which the background is neither too light nor too dark, how should it be vignetted ? Seeing that the whole principle which underlies vignetting consists in per mitting a dominant light to act upon the face and so much of the figure as is required to be shown, and shielding the light from all other portions, it will be at once evident that an opaque mask having an oval or other form of aperture inter posed between the negative and the light will not serve the intended purpose unless the light falls upon the negative from all directions. Such a mask interposed in the path of the direct rays of the sun would cause the print to have a sharp, hard edge, which would be fatal to artistic effect. But if an arrange ment of this nature were exposed to a cloudy sky, or to the sun’s rays previously broken up by having a diaphanous screen inter posed, then is the light distributed with a softness of margin dependent upon the distance between the vignetting screen and the negative. One of the most common methods of vignette printing is to place at a short distance in front of the negative a sheet of thin cardboard or opaque paper having an aperture cut into it of about the same dimensions as the portion of the figure that is required to be shown in the print. If the printing is to be done in the shade, this mask will answer without further preparation ; but if the direct rays of the sun are to be utilized, then must the aperture in the mask be covered over with thin tissue paper. This causes such a distribution of the light as to prevent it from forming a hard line. But in any case the distance at which the vignetting mask is mounted in front of the negative determines whether the vignette is to have a hard or soft margin. From half-an-inch to one inch between them will answer every purpose, unless in the case of very large pictures, when the distance may be increased with advantage. Vignetted portraits are to be met with everywhere, but this is not so with regard to landscapes. If photographers could only realize what a degree of beauty could be imparted to otherwise rather commonplace landscapes by the simple act of vignetting, they would adopt this method of printing to a greater extent than they do at present. Whether from a want of covering power in the lens, from defects at the ends and corners of the plates, or from other causes, it not unfrequently happens that in many cases the marginal defects are such as to necessitate a cutting down of the print to a serious extent. Seeing the remedy is so easy, why limit the dimensions of the picture in this manner ? By the judicious application of the vignetting mask not only may the defects referred to be cut off, but a positive charm be imparted. The fact also ought not to be lost sight of, that a photograph, if skilfully vignetted, may be printed upon a much larger sheet of paper than the negative. We have portraits which, to the observer, have apparently been made on a 10 by 12 plate, the paper being trimmed only a little smaller than these dimensions,