November io, 1910] 



NATURE 



00 



more were on several occasions recorded in both the surface 

 current and the undercurrent; in the majority of cases, 

 howevrr the velocity varied between i and 2\ knots. 



On the slope south of the Azores the Michael Sars was 

 anchored in 500 fathoms. Here about ninety current- 

 measurements were made at different depths. In the deep 

 sea between the Azores and the Canary Islands a series 



Fig. 2. 



was taken right down to 2000 metres, from the vessel 

 while under slow, steady drift, with one of the large tow- 

 r.ets out as a drift-anchor. These measurements also show 

 considerable fluctuations, which are apparently connected 

 with tides. Similar investigations with modern methods 

 have never been undertaken before either in deep water or 

 in the Straits of Gibraltar. 



A number of measurements of light were also made in 

 the ocean south and west of the Azores. Mr. Helland 

 Hansen has constructed a new photometer which worked 

 well ; he determined the quantity of light by the aid of 

 panchromatic plates with and without gelatine colour filters. 

 The investigations showed a great influence of light rays 

 at too metres, red being the weaker, and blue and ultra- 

 violet rays the strongest ; at 500 metres blue and ultra- 

 violet rays were still found, and even at 1000 metres the 

 influence of the ultra-violet rays was clearly evident. No 

 trace of light could be noticed on the plates at 1700 metres, 

 after an exposure of two hours at noon with a clear sky. 



PhYTOPL-ANKTOX. 



Vertical hauls have been undertaken at various depths, at 

 fully forty stations, with a fine-meshed Nansen closing-net, 

 our object being to collect material for studying the vertical 

 and horizontal distribution of peridinae and diatoms in the 

 Atlantic Ocean. We specially aimed at obtaining material 

 fof comparing the plankton of the coast-banks with 

 plankton from purely oceanic waters, as also for comparing 

 subtropical and boreal conditions of existence. The coast- 

 banks off Ireland, Cadiz Bay, the west coast of Africa, and 

 the Newfoundland banks have a characteristic flora which 

 is sharply marked off from the oceanic flora, rich in 

 species but poor in individuals, which is met with in the 

 central parts of the Atlantic Ocean, especially the Sargasso 

 Sea south of the Azores. 



Largely owing to Lohmann's interesting researches in 



the Mediterranean, we arranged to devote a considerable 

 part of our work to the study of those organisms, especially 

 Coccolithophoridae and the naked flagellates, which pass 

 through even the finest silk net. These organisms have 

 been partly collected by filtering sea-water through sand 

 filters and partly by employing a large centrifuge driven 

 by a small steam winch. Altogether we have employed the 

 centrifuge in the case of about sixty 

 of these water-samples ; and, by 

 'means of a suitable contrivance. 

 Prof. Gran was able to examine 

 these samples on board in their 

 living state, both in regard to 

 quality and quantity. 



Examination showed a large 

 number of new forms, partly belong- 

 ing to quite new types, which will 

 be described by Prof. Gran. In the 

 central oceanic parts of the Atlantic 

 Ocean these small organisms were 

 found to occur in numerous forms 

 and in such large quantities that 

 they exceed in volume the plants 

 obtained through the medium of the 

 silk nets. In the neighbourhood of 

 the European coast-banks the 

 number of species was far smaller, 

 but the quantity of individuals was 

 particularly large. Thus we secured 

 in a single sample more than 

 200,000 individuals per litre of one 

 species alone. On the coast-banks 

 off Newfoundland and off Ireland 

 the peridinse far exceeded in volume 

 the Coccolithophoridae. 



Altogether the samples from the 

 more northerly waters show a 

 greater quantity of plants than the 

 subtropical portion of the ocean. 

 The material will likewise furnish 

 information with regard to the dis- 

 tribution of phytoplankton in rela- 

 tion to depth. In the more 

 northerly waters its range is limited 

 to a thinner, less deep-reaching 

 more southern portion of the area of 



Fig. 



layer than in 

 investigations. 



the 



ZOOPLANKTON. 



For the study of smaller plankton animals, of the size of 

 copepods, for instance, we employ a vertical closing-net, one 

 metre in diameter, with rather coarser silk. With this we 

 took samples at various depths and at many stations. 



However, I perceived from the very first that an appli- 



NO. 2 141, VOL. 85] 



F16. 4. 



ance of this sort would not be able to afford us much 

 information regarding the occurrence of the larger pelagic 

 animals, such, for instance, as cephalopods, decapod 

 crustaceans, and deep-sea fishes. Both the Challenger and 

 Valdevia expeditions employed, as will be remembered, a 

 big tow-net, with which they made many vertical hauls 

 from great depths to the surface of the sea. By this means 

 they . caught a certain amount, though by no m^ans a- 



