CIRCULATION OF THE ATMOSPHERE 461 



different parts of the earth, especially of the United States, that there 

 is a definite though complicated synchronism, which connects the 

 variations of the solar action with the variation in the terrestrial cli- 

 matic effects. This is a large subject which can not be properly under- 

 taken in this lecture. It may be said in general that as the sun gets 

 more energetic in some parts of its period, the temperatures in the 

 earth's tropics are higher, and simultaneously in the temperate zones 

 they are lower. At the same time the barometric pressures in the 

 atmosphere of the earth centered around the Indian Ocean are higher, 

 while in North and South America they are lower. In the Pacific 

 states the temperatures increase with the solar energy, and in the cen- 

 tral and eastern states they decrease. The solar impulse which pro- 

 duces these effects tends to precede the terrestrial exhibit which depends 

 upon the solar impulse by some months, possibly by a year under certain 

 conditions, and this anticipation of course promises an opportunity 

 to develop what may become a rational ground for a seasonal forecast 

 for terrestrial weather. The entire field of operations is very compli- 

 cated, the circulation in both atmospheres tends to mask and make 

 more complex the pure variation of the solar radiation, so that we must 

 be very cautious in attempting to pronounce for or against certain 

 tentative conclusions regarding this subject. It will probably require 

 more than one generation of men to make practicable and popularize 

 the result of this research. Mathematicians as well as laymen are 

 cautioned to withhold negative evidence based upon half understood 

 phenomena, because it is in fact very difficult to disentangle the net 

 which nature has spread before us. The threads should not be torn and 

 distorted by the bungling hands of those who have not the training 

 required to unravel the several skeins which lead to the center of the 

 great mesh. It is certainly not saying too much to assert that there is 

 good ground for proceeding positively and firmly along this line of 

 research, and the fact that it has attracted the attention of many com- 

 missions, international committees, scientific societies, observatories 

 and institutions shows to what an extent the great problem has already 

 commended itself to the favor of scientific men. 



