18 REPORT 1853. 



be seen, and if a power of 3000 could under such conditions be effective, 12 feet 

 bands might be visible. How much of this the really/ unclear' condition of our 

 atmosphere will allow to be realized, remains to be determined by experiment. 



On the Surface Tempei'cdure and Great Currents of the North Atlantic and 

 Northern Oceans. By the Rev. William Scoresby, D.D,,F.R.S, L.l^E., 

 Cor. Mem. of Institute of France, &jc. 



The currents of the ocean, exerting as they do so great an influence on the condi- 

 tion of the air, the earth, and of the sea itself, constitute a subject of very important 

 consideration in [ihysical geography, and, indeed, in general science ; and they are 

 specially interesting as a compensating instrumentality against the extremes of con- 

 dition to which the fervid action of the sun in the tropics, and its oblique and inferior 

 action in the polar regions, tend, — an instrumentality serving not only to moderate 

 the extremes of temperature, but to render the general surface of the earth more 

 favourable for the comfort and benefit of its inhabitants. 



Our knowledge of the great currents of the ocean has hitherto been mainly derived 

 from the observations of navigators on the differences found betwixt the ship's 

 actual position during the voyage, as determined by celestial observations, and that 

 of the daily reckoning from the course steered and distance run. The results of 

 observations of this nature, extensively collected and collated, are found in the labours 

 of Major Rennell, Lieutenant Maury of the United States Navy, Mr. Findlay, &c. 



Dr. Scorest)y then noticed the errors to which this mode of investigation is ordi- 

 narily subject from defects in the log, compass action, and steerage of the ship — all 

 of which are liable to render the determinations uncertain unless where numerous 

 observations are found accordant, or those in diflFerent voyages made mutually cor- 

 rective. 



The process he had used, affording data for the present paper, consisted mainly in 

 the observing, during the progress of the ship, of the differences occurring in the 

 surface temperature of the ocean, which in many cases were such as to give unques- 

 tionable indications of currents coming from different regions, though not generally 

 serving to determine the exact direction or velocity. . 



His observations would refer, in the first instance, to the currents nf the North 

 Atlantic, as indicated by thermometric changes and peculiarities within a belt of 

 ocean about 220 miles in average width, extending in a VV. by S. direction from the 

 eptrance of the English Channel to Long Island, proximate to New York. 



Four transatlantic passages made by himself, with numerous voyages by Captain 

 Jos. Delano, a scientific American and excellent observer, who had furnished him 

 with the results of many of his researches, had supplied the materials for the present 

 determinations. These materials, extending to about 1400 observations (usually 

 taken six times a day) on the temperature of the sea, being placed on a chart along 

 with the projection of the ship's track on each voyage, were then tabulated, and the 

 leading indications finally represented in a diagram (Plate I.) before the Section. 



Of thirteen passages tabulated, seven were made in the spring of the year, two in 

 summer, one in autumn, and three in winter. Taking the middle day of each pas- 

 sage, the mean day at sea was found to be May 18-19, a day fortunately coincident, 

 with singular nearness, with the probable time of the mean oceanic temperature. 



The results indeed thus derived could not be considered as complete, nor the 

 normals of surface temperature in the different sections of the route conclusive ; yet 

 they exhibited, in certain particulars, facts of considerable interest and importance. 



The mean surface temperature of the whole range of observations was 56°, the 

 mean temperature nf the air in the same passages (the result of 1000 to 1500 obser- 

 vations) being 54''"2, indicating the prevalently received fact of the general superiority 

 of the temperature of the sea over that of the atmosphere. 



Though the observations were not sufficient for conclusive determinations of the 

 effects of latitude and season on the surface temperature, yet they obviously yielded 

 something sufficiently proximate to be not unworthy of notice, especially for the early 

 part of the passage westward, from longitude 12° to 36° W., and latitude 50° to 46°. 

 And within this limited range, the observations under discussion seemed, in respect 

 of latitude, to indicate an increase of the surface temperature, steering W. by S. from 



