272 



THE ATLANTIC. 



[chap. v. 



tlie Labrador Current below l°-5 C. 

 opposite Halifax, that temperature be- 

 ing only found at the bottom.) 



The isothermobaths of 2°, 2° -5, 3°, 

 and 4° C. are very constant at 1500, 

 900, 600, and 400 fathoms respective- 

 ly, for all the stations on the parallel 

 except Station CCCXXIII. on the 

 "cold wall," where all the lower tem- 

 pei'ature- lines are at a much higher 

 level, and at the shallow sounding at 

 Station CCCXXXI., where all the 

 lines below that of 4° C. rise slightly. 

 We must be careful, however, not to 

 attach too much importance to slight 

 deviations of the colder lines. On 

 the scale used in the plates, the mean 

 interval between the isothermobaths 

 of 2° and 3° C. in the Atlantic is 

 1000 fathoms; so that a rise or fall 

 of 100 fathoms, which is very prom- 

 inent on such diagrams, actually rep- 

 resents only one-tenth of a centigrade 

 degree, an amount very small in itself, 

 and quite within the limit of error of 

 observation with a deep-sea thermom- 

 eter. It is only where there is a con- 

 cordance among several isothermo- 

 bathic lines in sucli a rise or fall that 

 the indication is of any real value. 



From these observations we learn 

 that along the line where the south- 

 western trough of the Atlantic joins 

 the Southern Sea the temperature falls 



