Page:Popular Science Monthly Volume 88.djvu/605

 Popular Science Monthly

��oil

��a vessel's position in a fog, when suffi- ciently near a signal station, was intro- duced and patented a few years ago by Capt. W. J. Smith, of Seattle. It is called the "fogometer." The use of this device depends upon the fact that the transmission of a radio signal is practical- ly instantaneous, while a sound signal requires an appreciable length of time to travel through either air or water. Moreover, the speed of sound in air is 1,090 feet per second, at a temperature of 32° Fahr., and increases with the temperature at the rate of about i foot per degree. Its speed in sea water is about 4,590 feet per second.

Gaging the Distance of a Ship in a Fog by Signals

Now suppose a vessel to be within hearing distance (by aerial or submarine signal) of a wireless station on shore, the ship having a wireless outfit. If the station gives a sound signal and a wire- less signal simultaneously, the distance of the ship from the station can be de- termined by noting the difference in time between the two signals, as re- ceived on board. Capt. Smith has pre- pared tables showing the distances corre- sponding to various intervals of time, for both aerial and submarine signals.

The construction and modus operandi of the fogometer will be clear from the accompanying diagram. The three rules here shown are graduated in arbitrary units representing nautical miles. We suppose a vessel to be approaching the Strait of Juan de Fuca from the south- ward, in a fog, within hearing distance of the lighthouse off Cape Flattery, which is equipped with wireless. First her course is laid off as to direction only, with a parallel rule. Calling the light- house by wireless she requests the opera- tor to despatch wireless and sound sig- nals simultaneously, and to repeat the dual signal at the end of thirty minutes. The first pair of signals gives the ship's distance from the lighthouse, as above explained. This is, say, 7.7 miles. After thirty minutes the second pair of signals gives the distance as 5.1 miles. The distance run in the interval is found by log to be 5^^ miles. We now have the three sides of a triangle, and set the fogometer accordingly, placing the ver-

��tex of the appropriate angle over the lighthouse. We next slue the triangle around until the offshore side, A, con- forms to the edge of the parallel rule con- taining the course.

Finally, we mark the chart with a pencil point through the aperture at the end of the run (the intersection of sides A and C), and take a line through this point and the lighthouse, which, with the aid of the parallel rule and the com- pass rose on the chart, gives us the cor- rect bearing of the lighthouse.

The distance of the lighthouse at the end of the run does not, of course, actual- ly correspond to the length of side C, unless it should happen that the arbi- trary graduations of the rules are identical with nautical miles on the chart; but this is immaterial, as the distance is known from the comparison of wireless and sound signals, as above described.

Objections to the Use of Combined Signals

It must be stated, however, in this connection that the determination of distances from the combined radio and sound signals is, in fact, not so easy as it might, at first sight, appear to be. During the past year the United States Bureau of Lighthouses made observa- tions from the tender Larkspur, cruis- ing near the Fire Island Light Vessel, which has a 12-inch steam chime whistle and a submarine bell, and was tempora- rily equipped with wireless. A report on these experiments states that "the com- paratively short ranges of the whistle and submarine bell lead to such a brief difference of interval between such sig- nals and the radio signals as to make highly accurate observations by stop- watches a necessity, thus limiting the usefulness of the method from a practical standpoint."

The Bureau is experimenting to de- velop an efficient fog-signal using radio only.

Detecting Flaws in Steel

RECEXT experiments in this country have shown that with the aid of a Coolidge X-ray tube, defects in steel castings can be detected c\'cn through metal of consicieralile thickness. Radio- graphs, not a lluoroscopc, arc used.

�� �