264 



THE PASSAGE OF STOEM-AEEAS OVER FORESTS. 



years, and a part of a third year, from June to October inclusive. The 

 means by mouths combined for this period give the following results at 

 1.4 meters above the ground : 



Mean differences of temperature hetween open fields and xooods. (Centigrade.) 



January . 

 Febrnary 

 March . . . 



April 



May 



June 



Months. 



July 



August... 

 September 

 October... 

 November 

 December 



—0.83 

 —0.77 

 —0.77 

 —0.20 

 —0.50 

 —0.25 



—1.27 

 —1.43 

 —1.30 

 —0.90 

 — 0. 45 

 —0.40 



1^ 



as 



-0.44 

 — 0.G6 

 —0. 53 

 -0.70 

 +0. 05 

 + 0.15 



It would appear from this, that pine-woods have generally greater 

 effect in cooling the air near the surface than leaf-woods, but these ob- 

 servations have not been continued long enough to enable us to arrive 

 at any very definite results. 



SWEDEN. 



During the two years, the Swedish Government has ordered the es- 

 tablishment of scientific stations at Upland, in Scania, in the southeast- 

 ern part, and at Skasaborg, with the view of studying the influence 

 which forests exert upon the surrounding country, by registering cli- 

 matological and meteorological observations. We have seen no results 

 of these observations. 



There are understood to be comparative observations going on at 

 other places in Europe, but we are unable to state particulars. 



THE PASSAGE OF STORM- AREAS OVER FORESTS. 



With respect to storms, it is now quite well established, that they are 

 coincident with areas of low barometric pressure, which are often many 

 hundred miles across, and when oval, usually longer from north to south. 

 These low-areas generally move eastward in north latitudes, and upon 

 an average of thirty miles an hour. The air itself does not travel with 

 them, any more than the waters of the ocean in tides. There is an 

 inward tendency of the winds towards an area of low barometer, and 

 were it not for the earth's motion, these might be towards a central point; 

 but in foct, their course is more or less oblique, generally from 30'^ to 

 60° from a radial line, and in northern latitudes always toward the 

 right. 



These areas of low barometer are not always stormy, and over a wide 

 arid region might not be cloudy. But they are generally attended with 

 cloudy weather, and when the conditions are favorable, with rain. 

 These circumstances depend upon the relative humidity of the atmos- 

 phere, and as this varies, the width of cloudy or rainy area is constantly 

 changing. With respect to the degree of saturation of the atmosphere, 

 it is found to increase from below upward, to the level where clouds 

 form, and to diminish above this, to the highest limit of the clouds. 

 There is reason to believe that the higher regions of the atmosphere are 



