SCIENCE OF THE DAY.

New Zealand Herald, Volume LXVI, Issue 20264, 25 May 1929, Page 5 (Supplement)

SCIENCE OF THE DAY.

< MIRROR STOPS TRAIN.; A German scientist, Dr. Baeseler, a member of the technical staff of tho Bavarian railroads, has invented a wonderful method of stopping trains by means of a looking-glass. His invention, is based on tho fact that selenium becomes a conductor ot electricity when illuminated. A mirror of many facets, about four inches across, is placed in position on the semaphore. It reflects the light from passing locomotives exactly the same line to the point of its origin, no matter what angle the light conies from. The light*transmitter of tho locomotive is so arranged that the light reflected from the mirror strikes a selenium cell, communicates tho impulse to a relay equipped with an intensifier, and thus works the brakes on tile train. Not ono failure has been recorded in 4500 trials Nor has tho device ever operated needlessly, for only light from the locomotive sender is reflected to the selenium cell by the mirror. Light from other directions or objects is found to / hnvo no effect. While at the moment the new device has only been tested for working brakes on trains its possibilities are much more extensive. It could bo developed so as s to lessen ttie speed of a train when passing the first warning signal. Or it could bo so regulated as to prevent a speed i 1 higher than a certain speed being ati tained at all. It could also be used to transmit wirei less messages to the engine-driver. And as this new signal is quite unaffected by tho effects of fog, rain, sun, frost, or any other weather condition, it is likely to ! play an important part on the German railways in the near future. SECRETS OF HIGH SPEED. Tho introduction of slow-motion cinematography was instrumental in revealing hitherto unsuspected phenomena asso- [■ ciated with moving objects. Now, acI cording to -Mr. O. Hyatt-Woolf, editor > 1 of The Instrument World, this fascinating 5 I study has been greatly widened by an ' j instrument, the rotoscope, designed by a j British engineer, and made in this count try. The behaviour of instruments rotat- ? ing, for example, at such a great speed x as 500 revolutions a second can be studied, if An object revolving at this speed is seen t through the rotoscope as though moving 3 no quicker than at one revolution per minute.

Tho instrument consists essentially of a small, dynamically-balanced • cylinder, which can b.e rotated by a motor at high speeds on jewelled bearings. Its speed is controlled by an externally operated ball governor. Tho cylinder cpntains two rectangular apertures separated by tho width of an observer's eyes. Thus on each turn of the cylinder two separate glimpses of a moving' object are obtained. By approximating the cylinder speed to the speed at which an object is moving, the phenomenon of retentivity of vision produces tho effect of a continuous slow-motion view of the object. Many interesting effects have been studied with the instrument. For example, it has been observed that the flame from an ordinary gas jet fluctuates considerably instead of remaining steady, as it appears. Drops of water falling from a tap are always spherical and never, as popularly thought, pear-shaped. Lightning is revealed as a single intense spot of light which travels at so tremendous a speed that tho human eye and the photographic camera are deceived into registering it as a tortuous chain of light. CAMERA FOR OCEAN CURRENTS. The velocity and direction of current? beneath tho surface of water in Chesapeake Bay, Maryland, United States, have been recorded automatically by a unique motion-picture camera. This camera is designed to take the place of a complete observing unit composed of an officer, six men, and a boat. Within it is a compass and revolution dial of which pictures are made each half-hour. It works continuously without attention for a week. This camera was used in a survey of tide and current conditions, and from the data gathered current tables will be published from which at any future time the direction and velocity of currents at any place in the bay may be ascertained. Since certain fish are known to bite better at certain tidal stages than at other?., fishing interests will be aided.