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Popular Science Monthly/Volume 54/March 1899/Minor Paragraphs

MINOR PARAGRAPHS.

A new and very ingenious method of space telegraphy is discussed at length in an article by Karl Zickler in the Elektrotechnische Zeilschrift It depends on a phenomenon discovered by Hertz in 1887, viz., the influence of certain short wave-length light rays upon electrical discharges. The ultra-violet waves, which are obstructed by glass but transmitted by quartz, are the most effective. The source of light is an arc lamp. The light is passed through a lens of rock crystal to the receiver. The receiver is a glass vessel partially exhausted of air, one end of which consists of a truly parallel plate of rock crystal. In front of the receiver there is a condensing lens of rock crystal, and within the exhausted chamber are the two electrodes, one of which is an inclined disk and the other a small ball. The electrodes are connected with the secondary portion of an induction coil, and when the ultra-violet rays fall upon the inclined disk and are reflected to the ball, a discharge will be produced which may be read either with a telephone or a coherer. The signals are sent by alternately interposing a plate of glass in front of the rays issuing from the transmitter and removing it therefrom. Herr Zickler has made many experiments to verify his conclusions and appears to have demonstrated the feasibility of his idea in practice.

Mr. Dawson Williams has announced in Nature the discovery in many susceptible persons of a periodicity in the effects that follow a sting. The immediate result, he says, is a small flattened wheal, pale and surrounded by a zone of pink injection. This is attended by itching, but both wheal and itching are gone in less than an hour. About twenty-four hours later the part begins to itch again, and in a few minutes a hard, rounded, deep-red papule appears, and is quickly surrounded by an area of œdematous skin. The formication is intense, and in the affected area, while the ordinary sensations of touch are dulled, those of temperature and painful feelings are exaggerated. In two or three hours the itching diminishes and the œdema disappears, leaving a small, red papule, which itches but little. The phenomena recur, with diminished intensity, in the course of another twenty-four hours, and may return in this way, growing fainter all the time, in four or five daily repetitions. After these returns have ceased, a small, indolent papule may persist for weeks or months. This periodicity is not observed in all subjects, but most generally in those who suffer most.

Among the advantages of Linde's liquid air process, Prof. J. A. Eving, speaking at the English Society of Arts, claimed its giving a means of separating more or less completely the oxygen of the atmosphere from its associated nitrogen. After describing a process by which a liquid consisting largely of oxygen may be produced, the author said that the most interesting application of the liquid which had hitherto been tried on a commercial scale was to make an explosive by mixing it with carbon. When liquid air, enriched by the evaporation of a large part of the nitrogen, was mixed with powdered charcoal, it formed an explosive comparable in power to dynamite, and which, like dynamic, could be made to go off violently by using a detonator. The chief advantage of the explosive was its cheapness, the cost being only that of liquefying the air. Even the fact that after a short time the mixture ceased to be capable of exploding might be urged as a recommendation, for if a detonator hung fire, there was no danger of the charge going off accidentally some time after the explosion was due, nor was there any risk of its being purloined or used for criminal purposes.