JOHN MURRAY 95 



Norwegian Government for the North Atlantic cruise, Sir 

 John Murray undertaking to pay all the expenses. The 

 scientific reports on the expedition will be published in a 

 series of volumes by the Bergen Museum ; but the more 

 general results have appeared in popular form in a volume 

 entitled The Depths of the Ocean (Macmillan, 1912), by 

 Murray and Hjort, with contributions by several other 

 naturalists, which gives a condensed account of the modern 

 science of oceanography, with special chapters on the latest 

 discoveries, based largely upon the experiences of this North 

 Atlantic cruise taken along with the previous cruises of the 

 " Michael Sars " in the Norwegian seas. 



Amongst noteworthy matters that are discussed in this 

 volume we find : — 



(1) Methods of plankton collecting, including the towing 

 of as many as ten large horizontal nets, at various depths, 

 simultaneously. The pelagic plants collected, either in the 

 nets or by centrifuging the water, are discussed in a notable 

 chapter by Gran. 



(2) The " Mud-line," a favourite subject with Murray, as 

 being the great feeding-ground of the ocean. He places it at 

 an average depth of 100 fathoms, on the edge of the " Con- 

 tinental-shelf," at the top of the " Continental-slope," which 

 descends more or less precipitately to the floor of the Atlantic 

 at an average depth of 2,000 fathoms. We know from 

 Murray's careful estimations that, if all the elevations of the 

 globe were filled into the depressions, we should have a 

 smooth sphere covered by an ocean 1,450 fathoms deep. 

 The floor of this ocean is the " mean sphere level." 



(3) Dr. Helland-Hansen, the physicist on board the 

 " Michael Sars," had devised a new form of photometer, 

 which registered light as far down as 500 fathoms in the 

 Sargasso Sea. At between 800 and 900 fathoms, however, 

 no trace of light was registered on the photographic plates, 

 even after two hours' exposure. The observations show that 

 light in considerable quantity penetrates to a depth of at 



