40 THE WATER 



After allowing it to remain down for two or three 

 minutes to take up the temperature of the water, a 

 weight or " messenger " is fixed over the wire and 

 allowed to slide down until it hits the striker plate. 

 This releases the catches at the top of the thermometer 

 guard, and the lid faUs on to the body and the two 

 together fall on to the bottom plate. The two locking 

 levers open and engage with the locking lugs on the 

 guide bars and keep the water-bottle tightly closed. 

 The lugs are adjustable, and their position can be 

 altered if necessary. Before the bottle can close it is 

 necessary that some water should escape through a 

 relief valve fitted under one of the catches of the ther- 

 mometer guard, and the time required for this can be 

 determined by making an experiment just below the 

 surface ; or in moderately good weather one can feel the 

 shock of the water-bottle closing, by keeping one's hand 

 on the wire. After allowing a sufficient interval for 

 this purpose, the bottle is hauled up as quickly as 

 possible, and the temperature is first read. At night 

 an electric torch, held behind the thermometer, is of 

 great assistance. One of the air valves in the lid is 

 then opened, and the water drawn off from below. 



The insulating water-bottle is a very efficient piece 

 of apparatus, and can be used in any weather in 

 which it is possible for men to work without risk of 

 being washed overboard ; it is not easily put out of 

 order except by being allowed to strike against the 

 ship's side. The continual blows of the messenger 

 tend to distort the striker plate, but this is easily 

 prevented by interposing a small piece of leather 

 perforated for the- passage of the wire. The leather 

 should be fastened to the upper part of the frame by 

 a few inches of string, to prevent its floating up the 

 wire and checking the fall of the messenger. 



