The Optical Magic Lantern Journal (February 1898)

20 The Optical Magic Lantern Journal and Photographic Enlarger. the two side scales immediately opposite the water, the two cclumns of which will be level (as at CC). forced down the pipe at one side and up the other, as shown at p D, Fig. II. is read from the scale by calculating the difference between the two levels. In this diagram the fall and rise are both 4 inches, so the difference between the two must be 8 inches, which gives the water pressure of the | gas under the circumstances stated. sites > CONS The Jersey City Acetylene Explosion. that a telegram stated that a fi gas had occurred the day before ¢ Christmas. Since then we have received fuller particulars. A company called the United Liquefied Acetylene Distributing Company, situated in Montgomery Street, Jersey City, U.S.A., was formed some time ago for supplying © liquefied gas to various parts of the country. In one building the gas was generated, then conveyed through tubes to an adjacent building where by compressors it was rendered liquid, the gas being, during process, kept cool by means of , refrigerated brine. The liquefied gas is pumped © into small steel cylinders, which are previously . examined and “blown off,’ this latter con sisting of admitting a small quantity of the gas . During this | and then allowing it to escape. operation a sheet of flame was suddenly seen in the room and this was followed bya tremen° dous explosion, which blew a 20 feet hole in the side of the building. So far this seemed the extent of the damage, but a few minutes later a serics of explosions took place, the last of which blew the factory to pieces and set fire to the ruins. Houses, which were adjoining, were greatly damaged, and there was great consternation in the neighbourhood. The firemen were placed at a great disadvantage, for the water supply acting on the large quantity of calcium carbide in stock, at once generated more gas to feed the flames. The loss in connection with the Acetylene Works is estimated at about £5,000, but the loss in connection with the wrecking of adjacent buildings which has not yet been computed, is said to | reach a very large figure. If the gas piping be connected at © B, and pressure admitted, the water will be | The pressure | tremendous explosion of acetylene | tes | *. States | view to subsequent work. For example, a len Some Simple Lens Tests. By EDGAR CLIFTON, F.R.P.S. NW oe T cannot fail to strike even the least K\v{ observant that while our exhibitions are full of pictures in which, to put it mildly, sharpness of defi LS) 2 nition is not the most pronounced 7) characteristic, our opticians are neveran theless urged to produce still more optically perfect instruments. A little astigmatism, more or less, would certainly make but little difference in the artistic effects of the modern school, and yet there is a great and growing demand for stigmatics, anastigmate, collinears, planars, and the like. This must be taken as an unmistakable sign that the bulk of | photographers still respect the exquisite power On page 2 of last journal we announced of rendering detail, which one of our most talented teachers has termed the photographer’s birthright. Now, a winter’s evening may be profitably spent in ascertaining the true capabilities of such lenses as we possess, and making notes of any peculiarities which may be detected, with a which has an amount of . spherical aberration sufficient to render it useless for rapid work with full aperture will probably be found to yield softly defined and pleasing images when used for portraiture. Again, flatness of field is a most desirable quality for most subjects, but for many interior views a lens with great curvature of field may often be used with a larger aperture and consequently a shorter exposure than one of the newest “ flat field” instruments. No special appliances are necessary for such rough tests, a candle or small oil lamp without a chimney being the chief requisite. This should be placed at a convenient height, say 4 feet from the floor, upon a shelf, chest of drawers or other suitable support, a black focusing cloth being tacked to the wall behind it to avoid reflections which might be found misleading. The camera with its lens attached should be fastened upon its stand as usual, leaving the screw slightly loose, so that the camera may be rotated, turntable fashion, without disturbing the stand. The camera should be placed as far as possible from the light. If the distance be less than 10 or 12 feet the consequent lengthening of focus on the camera side of the lens will somewhat interfere with the . accuracy of the observation.