28 Chemical and Physical Notes 



of the bottom waters are sensibly increased by the " brining 

 down " of the Mediterranean. 



The common feature of Antarctic water found by all 

 expeditions is the thick warm layer lying between a cold 

 layer at the surface and another cold layer at the bottom. It 

 is very important to trace these two cold layers Southwards, 

 until they join and the warm intermediate layer has dis- 

 appeared. Every particular connected with this will be of 

 interest. 



Freezing Temperature of average Sea- Water. Sir James 

 Ross, in his description of his voyage, frequently refers to 

 39 F. as the temperature of maximum density of all waters, 

 and draws curious conclusions. Now it was well known 

 before the date of his voyage that average sea-water continues 

 to contract to a much lower temperature than 39 F. Indeed, 

 its temperature of maximum density is below that of its 

 freezing-point, which may be put at 29 F. A similar 

 mistake is often made at the present day by geographical 

 writers. Although everybody knows and recognises that 

 sea-water freezes at a temperature below that of fresh water, 

 and that this temperature is the lower the greater the quantity 

 of salt contained in the sea-water, it is to some extent not 

 known and to a great extent not recognised that pure ice, 

 which when left to itself melts at 32 F., begins to melt in 

 salt water at exactly the same temperature as that at which 

 the same water begins to freeze. A piece of pure lake-ice 

 immersed in average sea-water reduces its own temperature 

 and that of the sea-water in its immediate neighbourhood to 

 a temperature of roughly 29 F., which varies with the con- 

 centration of the resultant brine formed by the mixture of 

 the sea-water with the pure water formed by the melting of 

 the ice. An iceberg consists of pure land-ice, and if it is of 

 sufficient thickness to reach the layer of warm intermediate 

 water, its lower surface must be always melting at a tempera- 

 ture of about 29 F., and this temperature must in time be 

 communicated to the body of the ice, if it did not have it 

 before. But it must necessarily be at about this temperature, 

 because it separates from the parent land ice after it has been 



