Radio age (Jan 1927-Jan 1928)

26 RADIO AGE for May-June, 1927 tionally lucky we may see at the north pole, just before the bubble breaks, a black spot. It is as if the store of colors had been exhausted. "It may be perhaps a new idea that anything can be so thin that it cannot reflect light ; but the study of thin films such as found in bubbles teaches us that light is not reflected strictly from the surface of bodies, but that it must penetrate a very little way into the substance of the body itself before it can be turned and sent back. Like a motor car, the beam of light requires a little room in which to turn. And if this necessary turning space is not to be found, the light will not be able to turn at all, but will pass through the film and out at the other side. "This is true in the case of bodies ordinarily considered to be opaque, such as polished surfaces of metal. But even metals are transparent in thin enough layers, as is evidenced by ordinary gold leaf. "In penetrating the reflecting surface to this minute depth certain qualities characteristic of the reflecting material are impressed upon the light, so that by examining the reflected beam, even many miles away from the reflecting body, we can tell something about the material of the reflector. In fact certain scientists have attempted to gain by this means some idea of the different materials composing the surface of the moon. The moon shines by reflected sunlight, and the idea is that the light reflected from different areas of the moon's surface may, by its characteristically altered quality, betray the nature of the material which has reflected it. "How thin is this black spot in a bubble, and what sets a limit to it? Why cannot a bubble thin out indefinitely? These questions lead to one of the most interesting things which a bubble can teach us. Water is made up of molecules, particles so inconceivably small that a soap bubble when freshly formed may be many molecules thick. But as the film thins out it is gradually reduced to a thickness of but a few molecules ; and obviously this process cannot go on forever. The film cannot be less than one molecule thick. Any further thinning out is bound to break it. "Every liquid acts as though it were encased in a stretched elastic skin. Liquids in quantities such as are ordinarily handled do not show this property because so much of them is inside and so little on the outside, and the surface properties are masked by the properties characteristic of the inside. But a soap film is nearly all surface, and very little inside, and the contractile property of the surface becomes evident. This contractile property (surface tension is its scientific name) is responsible for a great many happenings in nature. It is the cause of the globular shape of a dew drop, of a rain drop, of water sprinkled on a dusty floor; it causes the ascent of oil in a lamp wick and is responsible for the absorbent property of a towel or of blotting paper. It governs the curious changes of shape in that wonderful little speck of protoplasm called the amoeba, and it is suspected of having much to do with the contraction of a muscle." But hubbies are useful in everyday life. "They play an important part in modern mining industry," said Dr. Heyl. "Often the valuable mineral is mixed with much rock from which it must be separated. Various methods of concentration are employed to effect this purpose. One which has been developed in comparatively recent years makes use of bubbles to this end. The mineral bearing rock is crushed to a powder and stirred up in water to which a very small amount of a special oil is added. The agitation of this mixture produces a froth of bubbles which rises to the surface, each of these little bubbles bearing attached to itself a particle of mineral, while the worthless rock is left at the bottom of the liquid. This froth is skimmed off, and a valuable concentrate obtained from it. This process is called flotation, and is one of the most important of modern developments in the art of mining. "And the moral of all this is, as the Duchess might have remarked to Alice, that there is nothing in Nature so simple and commonplace as to be unworthy of our serious attention." Grid Control Tube Is a New Marvel A DEVICE more sensitive than anything yet developed in electrical research, a grid tube that operates on an infinitesimal fraction of energy — approximately one-billionth of an ampere — was recently demonstrated. Termed the "grid controlled glow discharge tube" the device, perfected by D. D. Knowles, shown above, a young scientist in the research laboratories of the Westinghouse Company, is so sensitive that a human hand placed near a grid plate is sufficient to operate it. This act causes the tube to glow and discharge energy efficient to actuate a relay. Analyzed briefly the apparatus consists of three electrodes — a negative electrode and a positive electrode, the latter being surrounded by a grid, which constitutes the third electrode. Differing from the ordinary vacuum tube, this glow tube has no heated filament and therefore does not consume any energy when not operated. If a voltage is applied between the positive and negative electrodes particles of electricity called "free electrons" attach themselves to the grid. When this grid is thoroughly insulated these minute charges of electricity cannot escape, thus preventing the tube from passing any current. When a spectator's hand nears the plate a means is thereby provided for removing the small charges of electricity. The result is that the tube immediately passes a current large enough to operate commercial relays.