OCEAN CURRENTS 139 



Drift-bottles are also used for determination of ocean 

 currents. These bottles, which are suitably weighted with sand 

 so as to float just immersed, contain a stamped postcard asking 

 the finder to return them, with the locality and date of finding. 

 Floating bottles have long been used by seafarers in distress 

 to give information as to the accident which has befallen them 

 and their position. Bottles have been used for current deter- 

 mination for over 100 years, the first summary on a large scale 

 being that by the French hydrographer Daussy in 1839 m tne 

 North Atlantic. Sir John Ross criticised what he called the 

 " bottle fallacy," and of course, like all other scientific experi- 

 ments, these weighted drift-bottles are liable to give erroneous 

 or inaccurate or incomplete information. The chief difficulty 

 is that even when the points of origin and termination of the 

 bottle's journey are accurately known, it by no means follows 

 that the bottle has drifted in a straight line from one place to 

 the other. Again, if any portion of the bottle projects from 

 the water it comes under the influence of the wind, and is 

 therefore a measure, not of the ocean current alone, but of the 

 ocean current plus the wind. 



The Prince of Monaco distributed 1,675 weighted bottles 

 in the North Atlantic in 1885-1888, and of these 227 were 

 recovered that is, from one-seventh to one-eighth of the 

 original number. In limited areas, such as the Irish Sea, 

 the number recovered may be considerably larger. In 1894- 

 1895 the Lancashire Fisheries Committee distributed 1,045 

 bottles, mainly on the Liverpool-Douglas line, but also on the 

 Liverpool-Holyhead and Liverpool-Greenock lines. Of these, 

 440, or 42 per cent., were recovered. Again in 1898, of 101 

 bottles distributed, 41, or 40*5 per cent., were recovered. 

 Subject to certain limitations, the drift-bottle evidence is of 

 some value in the determination of ocean currents. Another 

 indirect method of determining the existence of ocean currents 

 is by means of the thermometer and aerometer. Bodies of 

 water which move as ocean currents have marked physical 

 features, and in particular the temperature and salinity vary 



