CHALLENGER 



which the whole hfe cycle of the deep sea fauna is completely 

 connected, but of which man as yet knows very little. 



As they probed into the depths of the ocean, scientists had 

 expected the temperature to decrease and the salinity and the 

 pressure to increase ; but it is found, in fact, that it is usually only 

 the pressure which increases at a steady rate with depth. The 

 different water masses moving beneath the surface cause irregular 

 fluctuations in both the temperature and the salinity, and such 

 fluctuations in turn affect the speed of sound in the water — and 

 hence soundings obtained with an echo sounder. 



Working on the returns of temperature and salinity at depth 

 recorded by many of the world's oceanographic expeditions, from 

 the Challenger of 1875- onwards, Dr. D. J. Matthews of the 

 Hydrographic Department had divided the world up into a num- 

 ber of areas, in each of which he considered the water conditions 

 to be similar enough for him to establish tables of corrections 

 to be applied to echo soundings to give the true depth; but so 

 few and far between were the available data that Matthews was 

 anxious to revise his tables, and by 1932 he was actively collecting 

 records for this work, which he completed in 1938. In the North 

 Atlantic over the next three or four years Challenger was to be 

 able to occupy a considerable number of stations to make oceano- 

 graphic observations of this nature as she voyaged between 

 Portsmouth and her survey grounds in the West Indies and in 

 Labrador. 



An instrument known as a 'reversing water-bottle' is used to 

 obtain this temperature and salinity data. A number of such bottles 

 are attached at set distances apart on a wire running from a winch 

 on the forecastle. The reversing water-bottle is an open-ended 

 cylinder with thermometers attached to the outside. When 

 lowered into the water these bottles are set like mousetraps, to be 

 sprung later by a small weight or 'messenger' which is sent down 

 the wire when the bottles have been lowered to the correct 

 depth. When thus sprung, the bottle turns upside down and 

 closes, trapping a water sample, which may later be bottled for 

 salinity analysis ; while the temperature at the time of the rever- 

 sal of the bottle may be read from the special thermometers which 

 are designed to record the temperature at the time of the arrival 

 of the messenger. 



