ON THE PHYSICAL THEORY OF UNDEU-CUREENTS. 153 



** (3) The movement of the upper oceanic stratum from the 

 equator towards the poles. 



'* (4) The dependence of these movements on the disturbance 

 of hydrostatic equilibrium constantly maintained by polar cold 

 and equatorial heat."* 



Although Arago, Pouillet, and other distinguished physicists 

 adopted similar views, and pointed out several inferences from 

 them, they were, in this country and in Prance, put aside in 

 favour of the doctrine of a uniform deep-sea temperature of 89° 

 Fah., which was supposed to have been established in D'Urville's 

 and Sir James Boss's expeditions, and was accepted by Sir John 

 Herschel. 



A short description, illustrated with elaborate diagrams, which 

 cannot well be reproduced here, was then given of the Challejiger's 

 temperature survey of the Atlantic, which had been characterised 

 by competent authorities as *' the most important single contribu- 

 tion ever made to terrestrial physics, presenting, as it does, the 

 whole thermal stratification of an oceanic area which may be 

 roughly estimated at fifteen millions of square miles, with an 

 average depth of fifteen thousand feet." 



The drawings exhibited represented sections of the Atlantic 

 Ocean, drawn on two scales, like a Geological section, the vertical 

 one being a scale of depth in fathoms, and the horizontal one being 

 a scale of nautical miles. The temperatures at various depths 

 being obtained by ''serial soundings," were then marked upon 

 the section, a series of " Bathy metrical isotherms" were drawn 

 across it, different colours being used for water ol different 

 temperatures, so that the relations of temperature and depth at 

 the various parts of the section were evident at a glance. 



The first section was from Teneriffe (28° N.) to St. Thomas's 

 (18° jS".), in which the chief points of interest were, the uniform 

 depth, 380 fms., at which 49° was reached ; and the fact that in 

 the Eastern basin the bottom temperature was 35°. 5, but in the 

 "Western (separated from it by, the Dolphin rise) it was 34°. 4, 

 * t5t. Petersb. Acad. «ci., Bull v., 1847. 



