THE FREEZING POINT OF SALT-WATER. 



729 



lead, the required quantity of line for each observation of the 

 series ran out, and the thermometers and lead are hove each 

 time. The operation is very tedious; a series of such obser- 

 vations in the Bay of Biscay, where the depth was 850 

 fathoms and the temperature taken for every fifty fathoms, 

 occupied a whole day. In taking bottom temperatures with a 

 self-registering thermometer, the instrument of course simply 

 indicates the lowest temperature to which it has been subject- 

 ed, so that if the bottom stratum is warmer than any other 

 through which the thermometer has passed, the result would 

 be erroneous. This is only to be tested by serial observations; 

 but from these it appears, wherever they have been made, 

 that the temperature sinks gradually, sometimes very steadily, 

 sometimes irregularly from the surface to the bottom, the bot- 

 tom water being always the coldest. 



Several important facts of very general application in phy- 

 sical geography have been settled by the deep sea tempera- 

 ture soundings which have been recently made, and the theories 

 formerly held on this subject shown to be erroneous. It has 

 been shown that in nature, as in the experiments of M. Des- 

 pretz, sea water does not share in the peculiarities of fresh 

 water, which, as has been long known, attains its maximum 

 density at four degrees, centigrade ; but like most other liquids 

 increases in densisity to its freezing point ; and it has also 

 been shown that, owing to the movement of great bodies of 

 of water at different temperatures in different directions, we 

 may have in close proximity two ocean areas with totally 

 different bottom climates, a fact which, taken along with the 

 discovery of abundant animal life at all depths, has most im- 

 portant bearings upon the distribution of marine life, and 

 upon the interpretation of palaeontological data. 



Mr. Wyville Thompson, who conducted the series of impor- 

 tant deep sea soundings undertaken in the Porcupine, says 

 very trulv " It had a strange interest to see these little in- 



