37 o DISCOVERY REPORTS 



alternate stations (usually in the morning) the series was taken only to 2000 m. instead 

 of to the bottom. At each station also the 70 cm. closing plankton nets were hauled 

 vertically at six different depths between the surface and 1000 m., with an additional 

 haul from 1500 m. at some stations in September, and various hauls were made with 

 other nets, both vertical and oblique. It is with the samples from the vertical closing 

 nets that this paper is principally concerned. 



Except in October the ' Discovery II ' began each line in the south and worked north- 

 wards, and in all five of the lines the most southerly station was at the edge of the pack- 

 ice. It is desirable to extend such lines as far south as possible, but no useful purpose 

 would have been served in any attempt to penetrate farther south, for the gear cannot be 

 used in the pack. The most northerly station lay between 55° and 56 S in each line 

 except the last which was cut short owing to the necessity for refuelling the ship. How- 

 ever it came only a fortnight later than the preceding line and it was not considered 

 necessary to carry it so far north. It will be seen that the lines varied in longitude from 

 about 78 to 81 ° W. This slight deviation from a fixed longitude is probably of no im- 

 portance, and it would in any case have been extremely difficult to bring the lines closer 

 together without loss of time and working stations at irregular hours. 



The distances between the stations can be read without difficulty from Table I. 

 Since the lines run almost due north and south the difference in minutes of latitude 

 between successive stations is equivalent to the number of miles which separates them. 

 Thus St. 1220 is i° 19' south of St. 1221, i.e. 79 miles. The total length of each line and 

 the average distance between the stations are as follows : 



Length Av. intervals 

 miles miles 



December Sts. 1220-29 754 84 



March „ 1312-20 753 94 



September „ 141 5-21 499 83 



October „ 1441-50 624 69 



November „ 1472-76 371 93 



The construction and method of handling the 70 cm. closing plankton net, which is 

 hauled vertically for quantitative investigations, has been described in detail by Kemp 

 and Hardy (1929, pp. 183 and 199). The effective straining part of the net is made of silk 

 with 74 meshes to the linear inch; the opening is 70 cm. in diameter and the speed of 

 hauling is 1 m. per second. The net is closed on the Nansen principle by messenger, 

 release gear and throttling rope. At all the stations in 8o° W this net, which is usually 

 referred to as the N 70 V, was hauled through the usual series of six depths. These are 

 from 50 m. to the surface, 100 to 50 m., 250 to 100 m., 500 to 250 m., 750 to 500 m. and 

 1000 to 750 m. At three of the winter stations (1415, 1419 and 1421) an extra deep haul 

 was made from 1500 to 1000 m. 



In working the lines of stations in 8o° W we were extremely fortunate in meeting with 

 no gales or strong head winds which might have resulted in an incomplete series of 

 samples and irregularity in the spacing of the stations. Actually out of 250 samples 

 required, 248 were successfully collected and analysed, one was spilt in the laboratory 



