300 Chronicles of Science. [April, 



own; ill high, by water colder. This view earned with it the 

 support of so eminent a man as Sir J. Herschel, in his various 

 writings on Meteorology and Physical Geography. This tempera- 

 ture of 39" -5 is, however, that of the maximum density oi fresh 

 water ; whereas the behaviour of saline solutions is very difl'erent 

 from that of fresh water under similar circumstances. The direct 

 experiments of Despretz on sea water, brought from the South 

 Pacific by Freycinet, estabhshed beyond a doubt the following 

 facts :— 



The density of the water at 68° F. was 1-0273 under ordinary 

 circumstances, i. e. if slightly agitated, it froze at 27° • 4 ; but if it 

 were cooled very carefully, a maximum density was reached at 25° • 4. 



Subsequent to Despretz's experiments, Avhich were pubhshed in 

 the 'Comptes Kendus' for 1837, Sir J. Koss, in his Antarctic Expedi- 

 tion, tested the temperature at various depths, but failed to ascertain 

 the existence of any water at a lower temperature than 39°. How- 

 ever, long anterior to this date, General Sabine had obtained evidence 

 in the Arctic regions of the existence of water at a temperature 

 much below 32^, at depths of 700 fathoms or so. Eecent observa- 

 tions by Captain Shortland in the Indian Ocean have led to similar 

 results. 



The instruments, however, which have hitherto been used were 

 eminently untrustworthy, the indices, especially of the maximum 

 thermometer, being extremely liable to displacement by a jar, so 

 that frequently a temperature was recorded as maximum which was 

 not as high as the surface temperature. Such a fact as this throws 

 discredit on the observations of minimum temperature made by the 

 same instrument. In addition, these thermometers are hable to be 

 deranged if they are even laid in a horizontal position ; so what are 

 we to expect when the sounding line brings them up, as it sometimes 

 does, in a reversed position ! However, during the past year, the 

 Hydrographic Office has paid particular attention to the improve- 

 ment of these thermometers, and the ' Lightning ' was accordingly 

 furnished with the new pattern instruments, several of which were 

 brought home in good order, so that the results furnished by them 

 merit especial credit. 



The chief fact as to temperature ascertained by the expedition 

 is the existence, over a certain area between the Faroe and Orkney 

 Islands, of water possessing a temperature of aliout 32^ at a depth 

 of 500 fathoms, while in other soundings taken in the adjacent 

 districts, the temperature at equal or even greater depths was 

 persistently registered above 45\ On one occasion, within the 

 cold area, bottom was found at 140 lathoms, and the minimum 

 temperature recorded was 41''-' -7, showing the decrease in tempe- 

 rature to bo progressive with the depth. Each of the areas was 

 characterized by the presence of special organisms, leading to the 



