METHOD OF SAFE NAVIGATION IN FOG. 121 



on that day, and at a distance of 6 miles while still invisible from the U. S. S. Cas- 

 tine, the E-i rose to the surface and signaled the maneuver by this apparatus. 



A still larger set was next constructed using a 3 horse-power motor to drive 

 the exciter, and three ribbons each i^ inches in width and ^ inch in thickness. 

 The set was designed to be installed upon the U. S. S. Arkansas for test purposes 

 and is shown in Fig. 7, Plate 48. The frame here shown is necessary to anchor 

 the wires, as the beam of the ship at the place selected for installation was about 24 

 feet and it was believed that a wire of that length with a pitch of about 300 vibra- 

 tions per second might not give as good results. The riveted plate shown in the 

 figure represents the side of the vessel, and as installed the thickness of the plate 

 and side of the vessel was made 2% inches. Tests recently made between the 

 U. S. S. Arkansas and Utah showed the apparatus gave distinct signals at over 10 

 knots' range. The side of the Arkansas, where used as a diaphragm, consisted of 

 three thicknesses of plate riveted together, and was in no degree attuned to the 

 vibratory period of the wire. It is probable that diaphragms fitted to the system 

 would yield much better results, though those obtained are sufficiently remarkable 

 to demonstrate the efficiency of the method. 



Shortly after the government's tests on the submarines had demonstrated the 

 possibilities of the Berger apparatus to send Morse code signals under water. Pro- 

 fessor R. A. Fessenden, whose name is already well known in the aerial wireless 

 field, turned his attention to the development of an all-electrical apparatus for 

 submarine wireless. Efforts had previously been made in England and Germany 

 along this line, particularly by Evershed in England. The device which he designed 

 is termed an "oscillator" and is shown in Figs. 8 and 9, Plate 49, and consists 

 essentially of a massive ring magnet, "A," energized by the coil "C" producing an 

 extremely intense magnetic flux which flows from one pole of the ring magnet 

 across the air gap into the central stationary armature "D," thence across the lower 

 air gap to the lower pole face of the ring magnet, thence through the yoke of the 

 pole magnet back to the upper pole face. Lying in this air gap is the light moving 

 copper tube "A." The stationary armature "D" carries a fixed winding one-half 

 clockwise and the other counter clockwise. 



An alternating current is fed to this armature winding and induces another 

 alternating current in the copper tube of about 10,000 amperes. As the copper tube 

 lies in a field having an intensity of about 15,000 lines of force per square centi- 

 meter very strong forces are created and the light copper tube is driven back and 

 forth 1,000 times per second with a force equivalent to a pressure of two tons. By 

 attaching the shaft to a diaphragm in contact with the water these intense forces 

 are transmitted to the water in compressional waves 500 times per second, giving 

 a wave-length of a little more than 9 feet, which is heard as a clear musical note. 

 An interesting feature of this oscillator is that when acted upon by sound waves it 

 acts as a receiver, and is in effect either a reciprocating generator or motor. The 

 5-kilowatt oscillator weighs 1,200 pounds and the diaphragm has a diameter of 

 about 2 feet. 



