CLIMATOLOGY OF NEW HAMPSHIRE. 1 25 



fourths, and sand more than nine tenths." Farmers can determine the 

 capacity that different soils have for retaining moisture, by taking two 

 boxes, filling each with a different kind of soil, and pouring an equal 

 quantity of water on each, and then suspending each of the boxes at the 

 end of a balance, so adjusted that the bar shall be horizontal. Then, if 

 the soils are unequal in their capacity for retaining moisture, one box will 

 soon rise above the level of the other. This experiment was first per- 

 formed by D. Milne Home. When a mountain has been denuded of its 

 forests and vegetable mould, the rain that falls upon it flows immediately 

 into the streams, and is carried to the ocean; then, before another rain, 

 the streams are dried up, the rivers are greatly contracted, and the next 

 rain causes a freshet; so we have a succession of drouths and floods. 

 On the other hand, vegetable mould retains the moisture, and it is grad- 

 ually evaporated, a high relative humidity is maintained, springs gush 

 forth from the slopes of the mountains, the streams are full, but not to 

 overflowing, and a slight change in the temperature causes rain to fall in 

 gentle showers. 



There is one marked feature in regard to the mountains in New Hamp- 

 shire that have been burned, namely, the fact that the fire has, in 

 general, spread only over their eastern slopes, and when it has reached 

 the summits it has extended but a short distance down the western 

 slopes, showing that the moisture-bearing currents of wind come from 

 the west or south-west. Although it is of great importance that the 

 mountains should be covered with vegetation, yet it is of no less impor- 

 tance that there should be a certain amount of forest over the entire 

 country, and this amount should be at least thirty per cent, of the whole 

 area. In some parts of the state the area covered by forests is much less. 

 The general effect of forests on temperature is to make the nights 

 warmer and the days cooler, and to moderate the extreme heat of sum- 

 mer, making it less intense, and the cold of winter less severe. In New 

 Hampshire, during the winter, in calm, clear weather, the cold is more 

 intense, or, at least, the thermometer goes lower in the valleys than on 

 moderate elevations, or even on the summit of Mt. Washington. As the 

 stratum of air in contact with the earth often becomes colder by contact, 

 and as the cold air is heavier than the warmer currents, the cold air flows 

 down the valleys like currents of water. Hence in the Connecticut and 



