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STUDIES FOR STUDENTS 



But it is to the action of the air when in motion — to the 

 wind — that is due a very effective part of atmospheric work. 

 Particles of sand drifting along before the wind become them- 

 selves agents of abrasion, filing away on every hard object with 

 which they come in contact. As a matter of course this phenom- 

 enon is most strikingly active in the arid regions, though the 

 results, when looked for, are by no means wanting in the humid 

 east. It is thought by Professor Egleston that many of the tomb- 

 stones in the older churchyards of New York City, have become 

 illegible by the wearing action of the dust and sand blown 

 against them from the street. There is among the heteroge- 

 neous collections of the National Museum, at Washington, a 



Sandstone 

 Craigleigh 



II. SHOWING DEPTHS AT WHICH THE ANNUAL RANGE IS REDUCED TO 



0°.0I CENT. 



Observations on soil temperatures made at the Orono (Maine), Experimental Sta- 

 tion, showed the mean daily range of temperatures from April to October, at a depth 

 of 3 inches to be 5°. 26; at 6 inches i".9; at 9 inches i°.i8 ; and at 12 inches very slight. 

 At a depth of i inch the temperature vi^as lower than that of the air by 2°. 4; at 3 

 inches, by 2°. II; at 6 inches, by 3°. 16; at 9 inches, by 3". 94; at 12 inches, by 4°. 18; 

 at 24 inches, by 5°. 78; and at 36 inches by 7°. 10. 



The remarkable uniformity of temperatures at comparatively slight depths below 

 the surface is also well illustrated by limestone caverns and in mines. The highest 

 summer temperature of Mammoth Cave being reported as 56° F. and the lowest 

 winter as 52°. 5. The mean for the summer being 54° and for the winter 53°. 



