INFLUENCE OF FORESTS ON CLIMATE. 73 



the influences they exert on climate. Climate is made up of deli- 

 cate and nicely adjusted elements, subject to disturbance through 

 various causes. Our summers, that preserve a genial temperature 

 from April to October, maturing' the crops of the field, often run 

 on the verge of destruction to those crops. A slight increase of 

 a disturbing power among the elements would lay waste the labors 

 of the husbandman — and this increase may be wrought by the acts 

 of man himself. 



The atmosphere at all times contains vapor of water that is 

 being constantly raised by the process of evaporation from land 

 and water surfaces. This vapor — usually about fourteen parts in 

 one thousand — is perpetually changing in amount and proportion, 

 and is almost always below the quantity that the atmosphere at 

 its existioig temperature is capable of sustaining. This circum- 

 stance causes wet bodies soon to become dry, and the surface of 

 the soil, though saturated with moisture, soon to become dusty. 

 Upon variations in the quantity of moisture present in the 

 atmosphere, the peculiarities of climate mainly depend. The 

 frequency of rain, and other phenomena of the highest interest 

 and importance, are greatly influenced by it. Evaporation 

 from moist surfaces is hastened by a breeze, and very much 

 increased by a strong wind. The evaporation must depend 

 on the nature of the surface ; and is less from naked earth than 

 from water surface. Experiments in this department of physical 

 science, being much more easily and simply conducted upon water 

 than upon other evaporating surfaces, we find most observers, so 

 far, confining themselves to the simplest form of such observa- 

 tions. This is to be regretted ; and the present national interest 

 attaching to this inquiry, should stimulate our scientific schools to 

 enter at once upon such a series of observations as may result in a 

 more thorough understanding of the whole subject than has hither- 

 to been reached. Such observations promise to be practically 

 useful, if continued through successive years in a primitive country 

 where the forests are being rapidly removed, and we fear we 

 have very little of country exempt from such changes, where any 

 great number of trees are remaining. In this field of inquiry we 

 are, at best, dealing with rather intractable elements. Some ex- 

 periments indicate that evaporation from the moist earth may be 

 from one-tenth to one-sixth of that from water. Other experi- 

 ments show that land, with the trees or other vegetables growing 

 upon it, emits considerable more vapor than the same space covered 



