76 ANNUAL KEPORT 



dry i^rairie for fifty to one hundred miles sonth and west, then? 

 climate would be so far changed that Wealthies would likely kill 

 to the snow line every three or four years as they uow do in un- 

 favorable sections. Then Gould and Latham, instead of exhibit- 

 ing grapes so large that they are obliged to stack them in order 

 to get five bunches on a large plate, would sneak around with 

 grapes inferior in size and quality and most varieties green at 

 that. Then the Mississippi Valley man would take all the pre- 

 miums, and if " turn about" is fair play perhaps we had better 

 ask that the change be made provided Gould and Latham do not 

 object. 



Wo now propose to consider another form of circulation of^ 

 air, the upward and downward flow. In discussing this question 

 we must exclude our usual horizontal winds; for though their 

 mixing in'would more clearly represent the actual condition of 

 things, yet we think it best to study each cause separately as far 

 as possible that we may the better understand the combination. 



Vfe are told that our vsurface atmosphere in summer is dense^ 

 moist and heavy, and that as we ascend it graduall}' loses these 

 properties and becomes very light, dry and cold in the -upper 

 regions. If the reverse of this was true winter would drop down 

 on us every night in summer, but as it is winter floats three or 

 four miles above us and only comes down on a somewhat pro- 

 tracted annual visit. Cold can only reach us from the upper 

 regions by the slow process of penetrating our atmosphere as it 

 penetrates other substances and in shore nights it has hardly 

 time to reach the earth's surface before the sun appears ^nd we- 

 are warmed up again. Thus our atmosphere is cooled from 

 above every night and warmed from below every day. As we 

 approach winter with shorter days there is less heat and with; 

 longer nights there is more cold till winter has reached us from> 

 above. 



Whilst we find no cause for upward and downward currents 

 in the upper region, yet in our surface atmosphere extending uj)- 

 ward a mile or so it is otherwise. Here the difl"erence in the 

 density of the upper and lower air will not be sufficient to coun- 

 teract the natural tendency of warm air to rise and cold air to 

 settle. From overheated places warm air is constantly rising, 

 cooler air moving forward from shaded places or settling down 

 from above to take the place; this again is slightly warmed and 

 rises so a current is formed which may continue till the earth ha& 

 imparted most of its surface warmth and is about as cool in one 



