CALORIC. 447 



scribed by meteorologists than any other of the United 

 States. Its mean temperature is 47, or nearly the same as 

 that of Great Britain, whose mean latitude is about 54, 

 ivhile that of Pennsylvania is not 41. 



Mr. Blodget gives the mean average temperature of the 

 spring months of the whole State as 41, or its mean annual 

 temperature.* The mean temperature of summer is thus 

 stated by observers : from tide to mountain range, 12-2- ; 

 mountain belt, 67 ; western end of State, TO , or 2J of dif- 

 ference between the east and west plains. The climate of 

 the mountains, then, it seems, gives an average summer 

 temperature of 67. On the heights of the Alleghanies it 

 is much less. The autumnal mean of the State is 50, the 

 Atlantic side 54, and the western slope 52. The winter 

 mean of the mountain group is 24, the western slope 28, 

 and the eastern 30. The maximum summer tempera- 

 ture of the whole State is 74, the summer minimum 

 65. The low mean summer temperature of 67 gives a 

 delightful climate to the mountain district of the State, and 

 constitutes it one of the most attractive regions on the con- 

 tinent. That belt of mountains, as will be seen from the 

 above data, has a calorical range, from mean winter to mean 

 summer temperatures, of 42. 



The climatal vibrations of the State exhibit of course the 

 general extremes of temperature which characterize the 

 eastern side of the continent. This statement applies to 

 annual, monthly, and diurnal changes, also to those depend- 

 ent upon accidental atmospheric vicissitudes, which often 

 amount in a short time to enormous thermometric ranges. 

 The regular diurnal changes are, perhaps, the most con- 

 siderable in the mountain regions, the surfaces of the moun- 

 tains being more covered with forests, thus preventing uni- 

 form and extensive heating of the surface by the direct rays 

 of the sun. This range of protected surfaces has over it 

 a stratum of cold air, which, as soon as the sun declines 



* "Pittsburg has a summer mean of 71-4, and Marietta, Ohio, 

 71-3, while Philadelphia is 72-5 to 73-7." BLODGET. 



