SUBMAEINE SIGNALIN( 



-BLAKE. 



209 



thence through the central stationary armature D, thence across the 

 other air gap to the lower pole face of the ring magnet, and thence 

 through the yoke of the ring magnet back to the upper pole face. 



This field is very much stronger than that in the ordinary dynamo, 

 there being more than 15,000 lines for each square centimeter of 

 cross-section. 



Around the armature is wound a fixed winding, which we will 

 call the armature winding and which is reversed in direction so that 

 one-half of the winding is clockwise and the other counterclockwise. 



When an alternating current is passed through this armature 

 winding it. induces another alternating current in the copper tube. 



Fig. 2. 



Only by this construction has it been found possible to obtain 

 the enormous force and rapidity necessary to compress the water 

 and to overcome the inertia of the moving parts of the mechanism. 



In order to apply this force to the work of compression, the cop- 

 per tube is attached to solid disks of steel, which in turn are attached 

 to a steel diaphragm 1 inch thick, which may be made part of the 

 side of the ship. In practice the tube is provided with lugs, and is 

 held between two disks drawn together on the tube by a 1-inch 

 vanadium-steel rod and a right-and-left-handed screw thread. 



Telegraphing is accomplished by means of an ordinary telegraph 

 key placed in the main armature circuit. 



Although an ordinary telegraph key is used, there is no sparking 

 at the contacts. This may surprise electrical engineers familiar 

 with the sluggish action and vicious arcing commonly found asso- 

 ciated with the operation of electromagnetic apparatus of this size 

 and power, more especially in view of the fact that a very high 

 18618°— SM 1915 14 



