SITUATION. 63 



y ielded oftener than once in two years. But some situations 

 are so favorable, that a failure scarcely ever occurs. In plant- 

 ing out tender fruits, it is consequently very desirable to know 

 what places will prove the best. Even the apple, in re- 

 gions where the winters are rigorous, is sometimes destroy- 

 ed, by frost, and in some very unfavorable places rarely 

 escapes. 



It is familiar to many cultivators, that warm, low valleys 

 are more subject to night-frosts, than more elevated locali- 

 ties. Objects at the surface of the earth become chilled by 

 the radiation of heat to the cold and clear sky above, and 

 they cool by contact the surrounding air, which thus be- 

 coming heavier, rolls down the sides of declivities and set- 

 tles like the waters of a lake, in the lowest troughs. This 

 coldness is further increased by the stillness of those shel- 

 tered places favoring the more rapid cooling, by radiation of 

 the exposed surfaces ; while on hills the equilibrium is par- 

 tially restored by currents of wind. Superadded to these 

 causes, vegetation in low, rich, and sheltered places, is more 

 luxuriant, and wood less ripened, and hence particularly 

 liable to injury from frost. The mucky soil of vallies ra- 

 diates heat rapidly from its surface. The warmth of low 

 places, during the mild weather, often occurring in winter, 

 often swells fruit-buds, and succeeding cold destroys them. 

 On more elevated lands, vegetation escapes all these disas- 

 trous influences. 



The existence of colder air in valleys, on still, clear nights,, 

 is often plainly observed in riding over a rolling or broken 

 face of country. The thermometer has often shown a dif- 

 ference of several degrees between a creek bottom and a 

 neighboring hill not fifty feet high. A striking proof was 

 exhibited a few years since, after a severe night-frost early 

 in summer. The young and succulent leaves of the hicko- 

 ry were but partially expanded; and where the trees stood 

 in a valley, twenty feet deep, all the leaves had been frost- 

 ed, and were black and dead, up to the level of the banks 

 on each side, while all above the surface of this lake of cold 

 air, were fresh and green. 



In the winter of 1845-6, when the cold on a clear night 

 sunk the thermometer several degrees below zero, after the 



