188 



.SUBMARINE CABLE LAYING AND REPAIBING. 



The wax should cover the silk close up to the edge of the 

 mirror, but not be allowed to run into the silk beyond, or it will 

 stiflfen the fibre where it should be perfectly free. 



The sensitiveness of the mirror on shore must be suited to 

 the distance away the ship is likely to cut in, always keeping 

 it in its most sensitive state until the ship's call. A spare 

 tube and mirror may be kept handy, with the mirror rather 

 stiffly suspended on a thick silk fibre top and bottom. This 

 less sensitive tube can be instantly put in the instrument if the 

 signals are too free. Wh • i speaking from a short distance, 

 say 50 miles or so, there is not sufficient capacity in circuit to 

 steady the signals, and back kicks destroy the legibility. The 

 instrument must then be shunted or damped to make the 



Mirror and 

 Soft Iron Strip 



^ilSLS^ 



Fig. 96a. — Bymer-Jones Mirror Tube. 



signals readable. But when speaking at 500 miles or more the 

 suspension must be very light and no damping or diminishing 

 devices applied. 



Mr. J. Rymer-Joues, of the Silvertown Company, has devised 

 an arrangement (Fig. 96a) whereby the sensitiveness of a mirror 

 can be varied over a wide range. In this instrument a soft-iron 

 flanged core wound with fine wire in the space between the flanges 

 is inserted into the mirror tube. This auxiliary coil is connected 

 in series with the main coil for the most sensitive condition, but 

 it can be used alone when speaking through a short length of 

 cable, the main coil being short-circuited. Instead of the usual 

 steel magnet on the mirror, a soft-iron strip is employed which 

 is magnetised by induction from the controlling magnet. The 

 latter is arranged to be adjustable in position through any angle 



