NATIONAL PHYSICAL LABORATORY.

Press, Volume LXVII, Issue 20308, 6 August 1931, Page 4

NATIONAL PHYSICAL LABORATORY.

SCIENCE AND INDUSTRY. & POPULAR DEMONSTRATIONS. irr.ou OUR OWN COEKEfII'UiiOESI-' LONDON, June 25. The great part the National Physical Laboratory now playa in the modern applications of science to industry was emphasised by Sir Joseph Thomson at the opening of the new physics building at Teddington. The completed portion of the new physics building will house the Heat and General Physics '"Section of the Physics Department, with part of the radiology and sound work, reports "The Times.'' Apparatus for the measurement of noises was on view in. this building. The loudness of the noise to be assessed is determined by varying the strength of a standard sound until ifc is either just "drowned" by the noise or judged to be equally loud. It was explained that, measured on a convenient scale of loudness with zero as the threshold of hearing, sounds become painful at about 130 "degrees" above threshold, where each "degree," known as a decibel, is approximately the least change in loudness preceptible to the oar. The level of conversational speech is at about 50-60 decibels above threshold. Aeroplane cabin noises are at present in the region of 80-110 decibels above the threshold. The lower of these levels corresponds to that of the noise in a tube train, and it is almost impossible to converse in a loudness level of 110 decibels, even by shouting. In street traffic and in ordinary trains the noise ranges from 50-70 decibels above threshold, and the laboratory is assisting the Aeronautical Research Committee in its endeavour to reduce noise in aircraft cabins to such a level.

New Exhibits and Tests. One of the new exhibits in the Aero Dynamics Department this year was a large steel tunnel, the equipment of which is nearly completed, in which compressed air at 25 atmospheres pressure can be circulated round an aeroplane model. Tests carried out under this high pressure are directly compare able with those on a full-scale machine —in other words, the "scale effect" which exists when working with a model in a tunnel at atmospheric pressure is eliminated. When the compressed air is circulated at full pressure by an airscrew the conditions will correspond with those surrounding a full-sized aeroplane flying at 150 miles au hour. In one of the older wind tunnels tests were shown in progress on a model of the Hill Pterodactyl, the ' new tailless aeroplane. A new and neat method of rendering streamline flow visible was displayed in the same department, A number of fine platinum wires, heated by an electric current, ara stretched across the airflow near a model. Each wire gives rise to a band of heated air, which follows the direction of the streamline passing the wire. The shadows of these heated air .filaments are cast on a screen and thus give a direct picture of the streamlines. Among the most popular demonstrations oJ: the afternoon were the tests carried out with a model ship in the vory large tank of the William Froude Laboratory, and the creation of electric

sparks some feet in length in front of i the High Voltage Laboratory, during the measurement of peak voltages up .to 1,200,000 volts. Some wind pressure experiments on buildings were shown in the Engineering Department. Here was displayed a type of liquid gauge used for measuring simultaneously the pressure of the wind at a number of points on a building. A flashlight photograph ia taken of the gauge when the wind conditions are steady, and the pressures are measured from the print. The same department showed a new plant which will measure "creep" rates in metals of the order of one hundred millionth of an inch an hour. At high temperatures metals fail under prolonged loading by gradual flow or "creep" at surprisingly low loads. Exactly how this happens is being | studied in the laboratory, and some new | alloys which are better able to resist • failure from "creep" have already been j developed ae a result.. • j