Body Under Experiment. Cube of sides (wind parallel to Cube of sides (wind parallel to Pyramid, square base of side h, Pyramid, square base of side h, height h (wind parallel to diagonal of base)... Cone, height = diameter of base =h (wind parallel to base)..... Total Resultant Pressure under 0.80 of total pressure on 0.55 of total pressure on 0.38 of total pressure on The method used with these bodies is similar to that described for plane sur-, faces; the different bodies are hollow and made of thin sheet iron; they are about 4 in. long, and provided with three holes in a row in the middle of one side. A hollow axis passes through the center, and communication is made with the pressure gauge in the same manner as before. In the case of the cylinder, which was examined by boring a single hole in it and revolving it gradually through 360°, it was found that pressure existed only between 0° and 35°, when the effect became a suction. Similar results were found for the sphere. Models were also experimented with representing buildings with roofs of various forms, and diagrams are given showing the distribution of pressure over leeward and windward sides. In all cases rarefaction on the side is quite as important a factor in the actual resultant force on the building as is the positive pressure on the windward side. The case of the pitched roof making angles of 45° with the horizontal on which a horizontal wind acts at right angles to the ridge is particularly worthy of note, and furnishes some food for thought. The normal pressure on the lee side due to suction is more than three times as great as that on the weather side. The resultant pressure on the two faces [neglecting the walls of the building] is inclined upwards and is about three and one half times as great as that on the weather side. On the weather side, the pressure is greatest near the lower edge, diminishes uniformly and becomes a suction near the ridge. A REDUCIBLE LIFE-BUOY, AND THE GALIBERT [Le Yacht.] Up to the present time solid bodies have commonly been used for rafts. Now the fact is, that the specific weight of the lightest of these rafts or floats is not much less than that of water, thus making it necessary to give them a great volume in order to obt indifferent floating capacity. M. Galibert has put them aside in constructing his buoy, which he has made of a special fabric perfectly water-tight and impermeable to water for several consecutive days. This reducible life-buoy has, when folded, a very small volume and an insignificant weight. It is easily inflated, and an air cushion is obtained, to which sailors have given the characteristic name of "turtle," owing to its shape and dimensions. The so-called personal buoy is so light, and presents such a small volume, that it may be kept in a small valise when the air is let out. Large buoys which have one thousand pounds resistance to submersion are so arranged that they can be immediately turned into a large raft, and be very useful in case of sudden shipwreck, taking the place of boats, which are often smashed in the breakers on landing, or which cannot be lowered owing to the position of the ship. Another contrivance very useful in the equipment of a vessel is the "respiratory apparatus," which consists essentially of an impermeable bag constructed on the principle of the reducible buoy, and which contains a sufficient supply of air to permit the saving of life in an asphyxiating locality. This pure air reservoir fixed upon the back so as to permit of free motion, and having a tube connecting with the mouth, with a nose compresser or pince-nez, allows a person to breathe normally without taking in any of the vitiated atmosphere by which he is momentarily surrounded. Suppose, for instance, a case of fire on board the ship; the smoke reveals the locality of the fire, but prevents getting at its origin, and putting it out in the beginning. Provided, however, with the above apparatus, any one among the crew can go down in the hold, and thus arrest the progress of the conflagration. The same would be true in case of foul gases developing in coal bunkers or any other part of the ship. Both apparatus have been successfully tested, and have received the official sanction of the (French) Government. J. L. BOOK NOTICE. DESCRIPTION ET USAGE D'UN APPAREIL ÉLÉMENTAIRE DE PHOTOGRAM- Photogrammetry is the science of making photographs in which the perspective is true, and in which, therefore, the dimensions of the objects photographed can be readily measured. Its most general application is to surveying. There are several claimants for the honor of inventing this application of photography to geodesy and, although of recent date, the history of photogrammetry is clouded with discussion. Frenchmen claim the honor for Colonel Laussedat, Germans for Dr. Meydenbauer. In Italy, the engineer PioPagiurni identified his name name with the subject in a practical way, by making an extensive photographic survey of the Alps. That was in 1875; ten years later, Deville, in the United States, completed a similar survey in the Rocky Mountains that had lasted five years, and covered 63 square miles of territory. Commandant Legros does not concern himself in his attractive little book either with history or polemics, but proceeds at once to explain, very clearly and concisely, the apparatus he has designed for photographic measurements. He disclaims any intention of adding a new instrument to the list that he says is already legion. "The point is this," he remarks, "we have sought only to make use of certain elementary means in such a way that they may be applied to all of the instruments now on the market." A photographic survey is based upon the fact that a photograph taken with a suitable lens is a true perspective in which the focal length is the distance M FIG. 1. line. By drawing in the hori- TT plane of picture. m perspective of M. If Pf is drawn parallel to MN, ƒ is the vanishing point of the line. PHH' plane of horizon. principal point. HH' horizon line. Pp=d principal distance. Every photogrammetric apparatus must be capable of tracing the horizon line, indicating the principal point and determining the exact focal length. The construction of Commandant Legros' instrument will be understood from Fig. 2. The essential features of it are the graduated circle K, with its ver d n P FIG. 2. อน m niers and the ruled ground glass (la glace quadrillée de precision) in the swing-back G. The camera is mounted on a double platform hinged at s, and supported by the uprights tt, fixed to the movable part of the circle. The axis of the swingback is at right angles to that of the hinge, and the combination of the movements of the swingback and hinge permit absolute vertical adjustment of the ground glass independently of the movement of the circle. The ground glass is accurately divided into small squares by a double system of very fine parallel lines I cm. apart. The lens has a vertical and horizontal movement by means of tangent screws a, e, the amount of which is measured in millimeters on the scales d and f. It is of the wide angle type and has a focal length of 5.51 in. to 5.707 in.; this corresponds to a plate 13 cm. by 18 cm. A lens of 20 cm. and an angle of 45° may be used with the same camera. The instrument is easily adjusted, and as may be seen from the sketch, the attachments can be readily applied to any commercial outfit at slight expense. Among the other many advantages claimed for it by Commandant Legros, is the facility with which the horizon line and the principal vertical line are obtained, and the extremely simple method of determining the effective focal length. A. G. BIBLIOGRAPHIC NOTES. AMERICAN. AMERICAN ENGINEER AND RAILROAD JOURNAL. VOLUME LXIX., No. 1, JANUARY, 1895. Water-Tube Boilers and their Application to War Vessels. Aeronautics; Captive Lookout Balloon on Board the French Battleship Formidable (illustrated). No. 2, FEBRUARY. Water-Tube Boilers, etc. (concluded). nautics; United States War Balloons (illustrated). Aero It is said that Captain Glassford "hopes to be able to take up the flying machine at the point it has reached through the remarkable experiments of Hiram S. Maxim, and build a machine that will carry a navigator through the air and at the same time will be under full control." BULLETIN OF THE AMERICAN GEOGRAPHICAL SOCIETY. DECEMBER 31, 1894. The Cape York Iron Stone, by R. E. Peary, C. E., U. S. N. CASSIER'S MAGAZINE. DECEMBER, 1894. The New American Navy. Some Possibilities of the Storage Battery. Producer Gas for Steam Raising. How Iron is Made. Edison's Kineto-Phonograph. Manufacturing Machinery-or Building It. John Ericsson, the Engineer. FEBRUARY, 1895. Recent American Direct Connected Engines and Dynamos. Preservation of Wood. Direct Electric Driven Machines. The Incandescent Lamp of To-day. Combined Efficiencies of Mechanical and Electrical Machines. ENGINEERING NEWS. VOLUME XXIII., No. 2, JANUARY 10, 1895. The Ritchie-Haskell Direction Current Meter. The Cost of Hydrographic Surveys. No. 4, JANUARY 24. The Puget Sound Dry Dock, Port Orchard, Washington. The Seattle Lake Washington Ship Canal. Chemical Methods of Preventing and Extinguishing Fires. No. 5, JANUARY 31. Rustless Coatings for Iron and Steel. |