156 TABLES OF DIFFETIENCES OP MEAN TEMPERATURES. 





Max. at 



Mill, at 



Mea 



n at 



Range. 





P. M. 



A. M. 



A. M. 



P. M. 



Group I . . . 



jh^jm 



jhggm 



8" 0- 



7 0- 



4°-3 



II . . . 



I 20 



3 43 



8 23 



7 24 



7-2 



Ill . . . 



2 38 



4 31 



9 12 



8 II 



10.6 



IV . . . 



I 46 



4 24 



8 53 



7 42 



131 



V . . . 



2 28 



• 4 28 



901 



7 54 



13.6 



VI . . . 



2 12 



4 54 



9 °4 



9 02 



7 49 



5-9 



Mean III, IV, V 



2 17 



4 28 



7 56 



12.4 



The results of the daily fluctuation, as given above, may be summed up as 

 follows : — 



The daily range diminishes from about latitude 40° in either direction north or 

 south. The precise latitude of maximum range cannot yet be given. Diagram A 

 shows the extremely small ranges in latitude 75° and in latitude 27°, the former 

 produced by the small range in the sun's altitude during the Arctic day, the latter 

 by the equalizing effect of the aqueous vapor near the Gulf coast notwithstanding 

 the sun's great daily range in altitude near the tropic of cancer. Diagram B shows 

 the large daily range for the stations comprising groups IV and V, and the some- 

 what smaller one for group III. 



Md't 



Diagram B. 

 4 6 8 10 N. 2 4 6 8 10 Md't 



Diagram A. 

 Md't 2 4 6 8 10 N. 2 A C, S 10 M'dt 



+4° 



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vr— 



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1 



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M 



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2 



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—P- 



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w 



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i 



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1 — 



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—4 



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T.at. 27° 

 L:it. 75° 



The greatest heat of the day is reached earlier in the high than in the low 

 latitudes ; with the mean annual temperature near or below the freezing point, the 

 warmest time of the day is about 1| P. M., in the middle and lower latitudes this 

 epoch changes to 2^ P. M. The greatest depression in the daily fluctuation occurs 

 in the Arctic regions about tAvo hours after midnight, in the temperate zone about 



