On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
Instantaneous Roentgen Ray Photography T HE sharpness of Roentgen ray skiagraphs of parts of the body is often impaired by voluntary or involuntary movements of the patient. This difficulty would not exist if “instantaneous” or exceedingly short exposures could be substituted for the usual “time” exposures. In order to obtain Roentgen rays of sufficient intensity for use in instantaneous exposures, the Roentgen tube must he excited by a single electric wave or pulse, produced by a very large induction coil. In the well-known Veifa apparatus this result is accomplished by melting a fusible plug in the primary circuit by an overload of direct current. The Erlangen firm of Reimger, Gebbert&Schall has recently put upon the market an apparatus in which the single wave or “un i-pulse” is produced by means of a specially constructed interrupter. This device consists of an amalgamated copper rod, surrounded by a closely fitting sheath of insulating materia., and dipping into a vessel which contains mercury, covered by alcohol. When the rod is drawn out of the mercury it draws some of the latter after it into the insulating sheath. The heat developed in the slender column of mercury by the strong current employed causes the column to break with explosive violence, and drives the mercury downward with great velocity, which is increased by the heat of the self. induction spark which immediately follows the rupture of the mercury column. The primary circuit is consequently broken with extreme suddenness, independently of the speed with which the rod is raised, and a spark of corresponding intensity passes between the secondary terminals. Fig. 1 shows the appearance of this spark in ordinary conditions and Fig. 2 sbows the deformation produced' by placing the spark gap in the strongest part of the coH's magnetic field. A Roentgen tube excited by this single induced wave, or “unipulse,” emits Roentgen rays of sufficient intensity to make strong skiagraphs of thick parts ot the body (Fig. 3). in 1/200 second. Why Fog Signals Fail IN a chart. published by the United States Weather Bureau, and reproduced here in abridged form, Prof. A. G. McAdie discusses some of the phenomena presented by fogs and the difficulties and dangers which arise therefrom to navigating vessels, especially near shore. The fogs of the Pacific, and especially those on the coast of California, Oregon and Washington, present some characteristic features of their own. They are low-lying, dense and of frequent and regular occurrence, and have been the cause directly and indirectly of a large per cent of marine disasters. In the vicinity of San Francisco, owing to the general movement of the air from the sea toward the land, and the climate of the great interior valley, fog is frequent and well marked. In summer the afternoon sea-fog varies in depth from 100 to 1,700 feet, but it rarely reaches far inland. On some afternoons the veloeity of the wind at San Francisco rises with almost clocklike regularity to about twentyctwo miles per hour, and a solid wall of fog, averaging 1,500 feet in height, comes through the Golden Gate, causing a fall in temperature to about that of the sea, namely, 55 deg. F. The upper level of the fog can be plainly seen from the hills in the vicinity, and it is interesting to note that above the fog level the air is cloudless, and the afternoon temperature ranges from 80 deg. F. to 90 deg. F. While the Pacific fogs occur with peculiar regularity, those of the North Atlantic Ooast, though at times persistent, are irregular both as to the time of their occurrence and their duration. The North Atlantic Coast fogs are probably due to thin strata of warm moist air passing over the cold water surface. The summer afternoon sea fogs of the Pacific are also quite different from the winter morning fogs. The laUer lie low, close to the surface of the water, and do not average more than 100 feet in depth. It is nearly always possible, by sending out a look-out, to get above the level of the fog and thus obtain proper bearings. With the summer afternoon sea-fogs this is out of the question. The distance which the fog extends seaward is not definitely known, but it is thought that an average would be about 50 miles. There are instances when a fog has been reported several hundred miles off shore. Whether a fog appears for a few hours at certain seasons, as on the Atlantic Coast,
