WATER-BOTTLES 51 



Water-bottles may be used either from a davit or 

 from a swinging boom. The latter arrangement 

 requires at least one extra hand to work it, but it is 

 far preferable to the davit, and makes work possible 

 in decidedly rough weather. The depths at which 

 observations should be made cannot be laid down 

 beforehand. In areas which have been previously 

 examined the records of the earlier observations 

 give considerable help. In unknown waters one can 

 only go on the principle that the chief object is to 

 determine accurately the position of the dividing 

 lines between layers of different temperature and 

 salinity. As the latter can only be determined on 

 shore, the number of observations should always err 

 on the side of excess. 



As a rough guide for working in unknown waters 

 depths of o, 2, 5, 10, 15, 20, 25, 37, 50, 100, 200, 300 

 fathoms, etc., may be recommended. When the 

 depth of water does not exceed 200 fathoms, the 

 surface layers are of great importance. In the open 

 ocean, on the other hand, fewer observations near the 

 surface may suffice, if this should be necessary, in 

 order to allow time for the more complete examination 

 of the lower levels. 



The distance apart at which the stations should be 

 placed will also vary according to the locality. On 

 the Continental plateau to the north and west of 

 Europe they may be spaced as closely as tw r enty miles 

 with advantage, but in deeper waters the programme 

 can only be decided on after a careful consideration 

 of the time available and the records of previous 

 expeditions. 



With regard to surface samples the case is somewhat 

 different, as it is not necessary to stop the ship. In the 

 English Channel and in the Bay of Biscay the writer 



