SURVEYING THE ROUTE. 



25 



fixed at the bulb end of the frame, so that, in descending, the 

 bulb is kept downwards. On starting to haul up, the resis- 

 tance of the water causes the frame to turn ; the shot then 

 takes the other end of the frame, the bulb comes uppermost, 

 and the temperature is registered as before. 



The Buchanan-Miller-Casella self-registering deep-sea ther- 

 mometer is the latest development of Six's original instrument. 

 Referring to the illustration (Fig. 18), this thermometer con- 



H[ 



/ 



Screw 



Fig. 16. 



Fan Capsizing Frame 



(Magnagni). 



Fig. 17. 

 Weight Capsizing Frame 

 (Negretti and Zambra). 



sists of a U tube with two upper bulbs. That on the left is 

 the one directly affected by the temperature, and is filled with 

 spirit in the bulb and partly down the stem. This bulb is 

 protected against pressure by being enclosed in another bulb 

 partly filled with spirit, a bubble of vapour being left to 

 allow for compression of the space when subjected to 

 pressure. The smaller bulb and a portion of the tube on 



