NO. 8 SAMUEL PIERPONT LANGLEY ABBOT 35 



body is proportional to the fourth power of the temperature." Other 

 bodies not perfect radiators depart from this law in the sense that, 

 while radiating less absolutely than the perfect radiator, their emis- 

 sion is more nearly proportional to a power of the temperature higher 

 than the fourth." Suppose Ti to be the mean temperature of the Earth 

 corresponding to a rate of solar radiation Si, and T2, that correspond- 

 ing to ^2- Assume further that the reflecting power of the Earth 

 remains unchanged, and that no appreciable heat is received from 

 other sources than the Sun. Then 



( ^yT I = F" , where x>4. 



Accordingly if, as supposed, S2 is 9/10 Si, 



T2>o.974Ti. 

 " If Tiz=29o°, then To>282.°5, and Ti-To<7°.5C. 



"It may then be stated that if the solar radiation remained for a 

 long period of time at a value which would maintain the Earth's sur- 

 face at a mean temperature of 17° C, and then fell 10 percent, and so 

 remained indefinitely, the fall of temperature of the Earth's surface 

 would be less than 7°.5C. 



" But if the solar radiation fluctuated between limits separated by 

 10 percent, the fluctuation of terrestrial temperature would be less, 

 according to the frequency of the fluctuations of solar radiation. 

 Again, parts of the Earth's surface most closely associated with the 

 oceans by the influences of winds, ocean currents, and rainfall would 

 be least affected by such solar fluctuations, and would respond most 

 slowly to a permanent alteration of solar radiation. 



" From the foregoing considerations we may then infer that the 

 effect of a fall of 10 percent in the solar radiation should diminish the 

 mean temperature of the Earth not more than 7°.5C., and indefinitely 

 less according to the shortness of the time elapsing before the radia- 

 tion regained its former value. Stations near the sea, or subject to 

 ocean currents and winds, or to heavy rainfall, would lag far behind 

 stations in the interior of great continents in their temperature 

 fluctuations. 



" When we come to the study of actual temperatures over the 

 Earth's surface, we find that all collections of temperature data for 

 single stations in the interior of great continents, covering long periods 



" O. Lumnier, Rapports Presentes au Congres International de Physique, 2, 

 78-81, 1900. 

 " H. Kayser, Handbuch der Spectroscopic, 2, 77-82. 



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