10 THE EXPLORATION OF THE SEA [PART I 



lower stopper: at the same time the upper stopper also slides 

 down the rods and closes the upper end of the bottle. Two spring 

 catches shewn at the sides then make fast the whole apparatus. 

 A sample of water at the depth to which the bottle is lowered 

 thus fills the cylinder ^ 



The bottle therefore collects a sample of water and isolates this 

 in a central chamber surrounded by three concentric shells of 

 water at the same temperature as that of the sample. These 

 shells of water insulate the sample, preventing the conduction of 

 heat from without, if, as is usually the case in a deep water 

 sounding, the water from the deep has a temperature which is 

 above that of the water strata through which the bottle has to be 

 hauled in coming to the surface. The same sounding therefore 

 enables us to ascertain the temperature of the water while 

 collecting a sample for further study. 



The determination of the temperature of the sea is obviously a 

 simple matter when it is the surface layers w^hich are being 

 investigated. All that is necessary is to lower a bucket over the 

 ship's side, fill it, and then immerse a thermometer in this. 

 Obviously the sample must be collected from such a situation that 

 it is not contaminated by the discharge from the engine-room or 

 from any exit-pipe from the interior of the vessel. But when a 

 temperature has to be taken from a water layer which is at some 

 distance from the surface the procedure is much more complicated. 

 In the time of the Challenger the only means of obtaining this 

 value was by the use of a " slow-reaction " thermometer, by using 

 a maximum and minimum thermometer, or by using a reversing 

 instrument. There were indeed other ingenious methods of 

 obtaining deep-sea temperatures, such as by the electrical thermo- 

 meter of W. Siemens. This depended on the fact that the electrical 

 resistance of water varies inversely with the temperature. If then 

 we balance the resistance of the water in situ with that of a sample 

 of water on board at a known temperature by means of a Wheat- 

 stone bridge the problem is solved. But this method demands 

 delicate apparatus not easily managed in a ship tossing in 

 a seaway, and as a practicable means of obtaining deep-sea 

 temperatures it has now been abandoned. The slow-reaction 



^ The water-bottle is described in detail in Publication de Circonstance of the 

 International Council for the Exploration of the Sea, No. 21. 



