114 On the Surface Temperature and Great Currents 



organic life had all been gradual. He did not think that 

 even zoological terms would be universally applicable any 

 more than that the same species would be found everywhere 

 at the same time. The nomenclature must ever remain to a 

 certain extent arbitrary and conventional. The value of the 

 Cambrian and Silurian systems was not to be determined by 

 the pcr-ccntage of identical species so much as by the zoo- 

 logical affinities of the genera and large groups of fossils ; and 

 in this respect they were apparently more allied than the 

 Silurian was with the Devonian, or the Devonian with the 

 Carboniferous system. 



— — ■ — — — — ■ * 



On the Surface Temperature and Great Currents of the 



North Atlantic and Northern Oceans. By the Rev. Dr 



Scoresby.* 



The author commenced by pointing out the great impor- 

 tance to Physical Geography of the subjects which he pro- 

 posed to discuss, particularly as they tended, in the economy 

 of Nature, to furnish a compensating instrumentality against 

 the extremes of condition to which the fervid action of the 

 vertical sun in the tropical regions, and its inferior and more 

 oblique action in the polar regions, were calculated to reduce 

 the surface of the earth. Our knowledge of all the currents 

 of the ocean, with perhaps one exception, the Gulf Stream, 

 which had been, in its more important features, carefully ex- 

 amined and surveyed, and more especially in the American 

 Coast Survey, was derived from the comparison by naviga- 

 tors of the actual position of the ship as determined from 

 time to time, with its position as calculated from what sailors 

 technically called the " dead reckoning," or the course steered, 

 and the distance run as determined by the log, an instrument 

 by no means perfect. The determination, however, of oceanic 

 currents, to which the present communication referred, de- 

 pends simply on induction from observation of temperature, 

 and that mainly of the surface. Such observations, indeed, 

 only become available under considerable differences betwixt 



* Read before the Meeting of the British Association for the Advancement 

 of Science at Hull. 



