632 TEMPEEATUKE OF THE SEA, ETC. 



are not prolonged so far north as on the first line, and that 

 the water at the bottom of the Bay is colder than in the Spitz - 

 bergen seas, approaching much nearer that of its maximum 

 density and of its point of congelation ; whence he concludes 

 that this is the main source of supply of the deep-seated cold 

 waters in the Atlantic, which, after attaining their greatest depths 

 between latitudes 40° to 50° N., are found 3,000 to 4,000 Veet 

 nearer the surface on approaching the Equator." 



2. Specific Gravity of Sea- Water. — J. Y. Buchanan. 



In No. 160 of the Proceedings of the Royal Society (just 

 published) is a paper on the determination at sea of the sj)ecific 

 gravity of sea- water which well deserves attention, being the 

 result of Mr. Buchanan's experience on board H.M.S. Challenger. 

 He draws attention to the great care required in the means used 

 for collecting the water and making the necessary measurements, 

 and for reducing the results, and describes the special instrument 

 (on the principle of Nicholson's hydrometer) which had been 

 made for him,, and which he had used and tested by comparison 

 with other methods. 



His mode of reduction by the graphical method in which he lays 

 down isothermal lines and forms a chart by means of which the 

 specific gravity of sea-water at any teniperature may be at once 

 read off from its observed specific gravity at any other temperature, 

 is also Avell worthy of adoption. 



3. Fokchiiammer's Researches on Sea-water and Currents. 

 (Report of British Association, 1846, p. 90.) 



The greatest quantity of saline matter is found in the tropical 

 regions far from land where there is 36*6 parts of salt per 1,000 

 of salt water. The proportion diminishes on the western side of 

 the Gulf Stream and near any coast. Towards the north-east it 

 decreases slightly, but is pretty constant over the North Atlantic, 

 about 35-7 per 1,000. 



More than 100 miles S. of Greenland the proportion of salt is 

 35-0 per 1,000 parts. 



In Davis Straits, 40 miles from land, 32*5 per 1,000, and this 

 is nearly the proportion in the Polar current. 



In latitude 43^° N. and longitude 46^° W., it is 33-8 per 1,000. 

 This points to the fact that the vapour rising in tropical regions is 

 condensed in Polar regions and flows back in the form of Polar 

 currents, so that more water flows away from than towards the 

 poles. 



[This seems clearly indicated by Parry's raj^id drift to the 

 southward off Spitzbergen, where some portion of the influence 

 of the Gulf Stieam might be supposed to extend to prevent such 

 a southerly drift.] 



The water of different seas may contain more or less salt, but 

 the relative [proportion of its constituent saline parts changes very 



