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. 



