304 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 70 



and will lower the temperature, while it may have an opposite effect 

 in the tropical regions, where a clear sky with calm weather will 

 raise the temperature, by increasing the effect of the insolation. 



Hence we cannot expect to find any perfect agreement between 

 the fluctuations in temperature and fluctuations in the barometric 

 gradient, /. e., in the horizontal atmospheric circulation, as there are 

 various other conditions that influence the temperature at the earth's 

 surface, especially in the regions of the barometric centers of action 

 in higher latitudes. 



We might expect the agreement between the fluctuations in 

 horizontal circulation and in temperature to be more complete in 

 regions lying between the barometric centers of action, than in 

 regions near these centers. Our investigations also seem to prove 

 that such is the case: e. g., the variations in temperature in 

 Norway show an almost complete agreement with the variations 

 in the barometric gradient of the North Atlantic (and the variations 

 in pressure at Ponta Delgada, and the inverse variations at Styk- 

 kisholm) while the variations in temperature in Iceland and the 

 Azores show no good agreement with the barometric variations, 

 neither one way nor the other. 



As was pointed out before, it has also to be taken into considera- 

 tion that the barometric centers of action may evidently shift their 

 position or be divided, often for some length of time, and then the 

 effect of the barometric changes on the temperature may in some 

 regions be inverted during this period. 



It is probable that changes in the sun's radiation may cause 

 changes in the transparency of the terrestrial atmosphere, which 

 again will affect the temperature in the various strata of the atmos- 

 phere, as well as at the earth's surface. 



We have not here mentioned that changes in the sun's radia- 

 tion of heat may naturally directly affect the temperature at the 

 earth's surface, but these direct effects are evidently of subordinate 

 importance as compared with the above mentioned indirect effects. 



We have already pointed out as a mistake of most previous 

 authors to suppose the temperature at the earth's surface to be a 

 measure for the temperature of the terrestrial atmosphere, and con- 

 sequently also for the variations in the quantity of heat received 

 from the sun. It has to be considered that 40 per cent of the solar 

 heat energy that reaches the outer layers o'f our atmosphere are 

 reflected to space, and are absolutely of no account for the terres- 

 trial temperature. Of the 60 per cent of the solar heat energy tha* 



