84 BOARD OF AGRICULTURE. 



Mr. Williams. The explanation is satisfactory. I misunder- 

 stood the statement. 



Prof. Fernald. Was it in the summer or winter ? 



Mr. Chamberlain. Winter. 



Pi'of. Fernald. The diflerence can be easily accounted for in 

 two ways. When the temperature is low, trees draw warmth 

 from the earth, which they impart to the surrounding air. Un 

 the other hand, when tlie temperature of the air is above a certain 

 mean, tKe temperature of the trees is less, and they abstract heat 

 from the air, and the result would be to establish an equality. 

 Then in the summer season, the effect would be to render the sur- 

 rounding air somewhat cooler ; in the winter, exactly the reverse 

 takes place ; the trees impart warmth to the surrounding air, and 

 thus a higher degree of temperature is attained. * 



Again, the prevailing wind, which is from the west, banks '^, 

 so to speak, on the western side of the forest, and forces its way 

 through the trees. Now, what is the effect of the friction as it 

 passes through the forest? There can be no friction without 

 heat, and the result is a slight elevation of temperature. 



Taking these two causes together, it seems to me we have 

 enough to account for the difference of six degrees between the 

 western and eastern sides. 



I saw, a few days ago, a pamphlet bearing on this same point, 

 and it was stated that near the Mississippi river, where an observa- 

 tion was made in the forest, it was found that on the western side 

 the temperature was four degrees ; in the centre of the forest, six- 

 teen degrees — a difference of twelve degrees. On the eastern 

 side the temperature was a few degrees lower than in the middle, 

 although higher than on the western side. Another illustration of 

 the same kind and in point here, and doubtless due to the same 

 causes— the warmth imparted by the trees to the surrounding air, 

 and also to the elevation of temperature caused by the friction of 

 the wind in passing through the forest. 



Mr. Williams. Do 1 understand the Professor to say, that the 

 mere friction of a current of air will lower the temperature ? 



Prof. Fkrnald. It will elevate the temperature. At least, it 

 has that tendency. Friction cannot take place under any circum- 

 stances without producing heat. Two masses of ice rubbed 

 together will generate sufficient heat to melt the ice. It is a law 

 of nature, that wherever there is an expenditure of power, that 

 power will manifest itself under the form of heat. 



