PHYSICAL CONSEEVATIOF AND RESTORATION. 51 



tent of North American soil where the industry and the folly of 

 man have as yet produced little appreciable change. Here, too, 

 with the present increased facihtie-s for scientific observation, the 

 future effects, direct and contingent, of man's labors, can be 

 measured, and such precautions taken in those rural processes 

 which we call improvements, as to mitigate evils, perhaps, in 

 some degree, inseparable from every attempt to control the action 

 of natural laws. 



In order to arrive at safe conclusions, we must first obtain a 

 more exact knowledge of the topography, and of the present 

 superficial and climatic condition, of countries where the natural 

 sm-face is as yet more or less unbroken. This can only be accom- 

 plished by accurate surveys, and by a great multiplication of the 

 points of meteorological registry,* already so numerous ; and as, 

 moreover, considerable changes in the proportion of forest and of 

 cultivated land, or of dry and wholly or partially submerged sur- 

 face, wiU often take place within brief periods, it is highly desira- 

 ble that the attention of observers — ^in whose neighborhood the 

 clearing of the soil, or the drainage of lakes and swamps, or other 

 great works of rural improvement, are going on or meditated — 

 should be especially drawn not only to revolutions in atmospheric 

 temperature and precipitation, but to the more easily ascertained 

 and perhaps more important local changes produced by these 



which have long ceased to exist in the theatre of his researches, and of which 

 few other records are extant. 



* The general law of temperature is that it decreases as we ascend. But in 

 hilly re^rions the law is reversed in cold, still weather, the cold air descending, 

 by reason of its greater gravity, into the valleys. If there be wind enough, 

 however, to produce a disturbance and intermixture of higher and lower atmos- 

 pheric strata, this exception to the general law does not take place. These 

 facts have long been familiar to the common people of Switzerland and of 

 New England, but their importance has not been sufficiently taken into ac- 

 count in the discussion of meteorological observations. The descent of the 

 cold air and the rise of the warm affect the relative temperatures of hills and 

 valleys to a much greater extent than has been usually supposed. A gentle- 

 man well known to me kept a thermometrical record for nearly half a century, 

 in a New England country town, at an elevation of at least 1,500 feet above 

 the sea. During these years his thermometer never fell lower than 26° — Fah- 

 renheit, while at the shire town of the county, situated in a basin one thousand 

 feet lower, and only ten miles distant, as well as at other points in similar po 

 sitions, the mercury froze several times in the same period. 



