90 Mr. J. Croll on Ocean- currents in relation to 



this case the quantity of heat carried by the Gulf-stream into 

 the Atlantic through the Straits of Florida, to that received by 

 this entire area from the sun, is as 1 to 4- 12, or in round num- 

 bers as 1 to 4. It therefore follows that one-fifth of all the heat 

 possessed by the waters of the Atlantic over that area, even 

 supposing that they absorb every ray that falls upon them, is 

 derived from the Gulf-stream. Would those who call iu question 

 the efficiency of the Gulf-stream be willing to admit that a 

 decrease of one-fourth in the total amount of heat received 

 from the sun, over the entire area of the Atlantic from within 

 200 miles of the tropical zone up to the arctic region, would 

 not sensibly affect the climate of Northern Europe ? If they 

 would not willingly admit this, why, then, contend that the 

 Gulf-stream does not affect climate ? for the stoppage of the 

 Gulf-stream, taking it at Mr. Findlay's estimate, would deprive 

 the Atlantic of 77,479,650,000,000,000,000 foot-pounds of 

 energy in the form of heat per day, a quantity equal to one-fourth 

 of all the heat received from the sun by that area. 



How much, then, of the temperature of the south-west winds 

 derived from the water of the Atlantic is due to the Gulf- 

 stream ? 



Were the sun extinguished, the temperature over the whole 

 earth would sink to nearly that of stellar space, which, according 

 to the investigations of Sir John Herschel* and of M. Pouilletf, 

 is not above —239° F. Were the earth possessed of no atmo- 

 sphere, the temperature of its surface would sink to exactly that 

 of space, or to that indicated by a thermometer exposed to no 

 other heat-influence than that of radiation from the stars. But 

 the presence of the atmospheric envelope would slightly modify 

 the conditions of things ; for the heat from the stars (which of 

 course constitutes what is called the temperature of space) 

 would, like the sun's heat, pass more freely through the atmo- 

 sphere than the heat radiated back from the earth, and there 

 would in consequence of this be an accumulation of heat on the 

 earth's surface. The temperature would therefore stand a little 

 higher than that of space ; or, in other words, it would stand a 

 little higher than it would otherwise do were the earth exposed in 

 space to the direct radiation of the stars without the atmospheric 

 envelope. But, for reasons which will presently be stated, we 

 may in the mean time, till further light is cast upon this matter, 

 take —239° F. as probably not far from what would be the 

 temperature of the earth's surface were the sun extinguished. 



Suppose, now, that we take the mean annual temperature of 



* ' Meteorology/ Section 36. 



t Comptes Rendus, July 9, 1838. Taylor's Scientific Memoirs, vol. iv. 

 p. 44 (1846) 



