24 SUBMARINE CABLE LAYING AND REPAIRING. 



pressure. It is usual to make these instruments to stand 

 testing in an hydraulic press to pressures varying from 2^ to 

 5 tons per square inch according to the depth for which they 

 are required. 



There are several methods of capsizing the instrument at 

 any required depth in the sea. One is that suggested to the 

 makers by Commander Magnaghi, of the Royal Italian Navy. 

 This arrangement is shown in Fig. 16. The brass case T 

 containing the protected thermometer is held in the frame 

 by a screw at the top and supported on an axis H below. 

 The screw is part of the spindle of a small propeller or fan, F. 

 In descending, the fan is prevented from turning by the pin P 

 touching the stop E, the latter being capable of adjustment to 

 regulate the distance the screw enters the case. On ascending, 

 the fan revolves in a direction causing the screw to run out of 

 the case T : the instrument then falls over about the axis 

 H and registers the temperature at that spot. The tube in 

 this position is locked by the spring pin and cam at S. These 

 instruments are attached to the sounding line as shown, and 

 at different depths on the same line when serial temperatures 

 are required, the lowest thermometer being at a few feet above 

 the sounding tubes and sinker. 



The action of the rotating fan is not perfectly reliable : it 

 sometimes happens that the instrument reverses coo late or 

 too early. To obviate this, Messrs. Negretti and Zambra 

 devised a capsizing arrangement acting by means of a weight 

 let down the sounding line (Fig. 17). The weight hits against 

 the lever, L, which raises the spindle S and releases the 

 thermometer case T. This is pivoted on the axis H (but not 

 balanced) and as soon as released at the top it turns upside 

 down, at the same moment freeing the weight W, which falls 

 down the line and capsizes the next thermometer in a similar 

 manner. This releasing arrangement has been found very 

 certain in action. 



Another capsizing device by the same makers is very suitable 

 for temperature sounding in shallow water. The thermometer 

 is mounted on a hollow wooden frame loaded with shot, free to 

 move from end to end of the frame, and sufi&cient to render 

 the whole instrument just vertically buoyant in sea water. 

 The cord attaching the instrument to the sounding line is 



