IL. 
HISTORICAL SKETCH OF DEEP-SEA WORK. 
Our knowledge of the depths of the sea was only incidentally 
increased by the work of the great French, English, and Russian 
exploring expeditions, sent on voyages of circumnavigation. 
They collected interesting isolated facts regarding the distribu- 
tion of temperature, the density of the sea-water, and the exist- 
ence of animal life at great depths. Boyle and Hooke in the 
seventeenth century both speculated and experimented as to the 
saltness of the sea; Ellis, in the middle of the eighteenth cen- 
tury, observed the temperature of the water from a depth of 
nearly 900 fathoms. This observation, like many of the early 
deep-sea temperature observations, was made by bringing up the 
sea-water in a closed vessel and observing the temperature when 
it was brought on deck. To Sir Joseph Hooker, when naturalist 
of the Ross Antarctic expedition, we owe the interesting obser- 
vation regarding the occurrence of surface desmids in the bot- 
tom specimens of the dredgings of Sir James Ross. It was 
principally from observations made in the Arctic and Antarctic 
exploring expeditions that our first accurate knowledge was ob- 
tained of the distribution of the temperature of the deep sea, of 
the nature of the bottom, and of animal life at very great depths. 
The observations of temperature, however, were not sufficiently 
accurate for the requirements of modern physics, the thermom- 
eters used not being protected from the great pressure to which 
they frequently were exposed. 
Within the last twenty years the investigations of the depths 
of the sea have taken an immense development. Previous to 
1866 several important exploring expeditions had made it a part 
of their programme to sound at great depths and examine, as far 
as was possible with the instruments then in use, the physical 
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