118 ANNUAL REPORT OF NE\7-Y0RK 



solid bodies become warmed according to their individual capac- 

 ity, and from tliem the air receives the heat which warms it. 

 From the moist surface of the soil goes on a rajoid evaporation, 

 which renders latent a large amount of heat, so that the temper- 

 ature of the soil is not rapidly but gradually elevated. The 

 ascent of water from the sub-soil to supply the place of that 

 evaporated, goes on as before described. The liquid water of the 

 soil has combined with (rendered latent) a vast amount of heat 

 therefrom, and passed as gaseous water (vapor) into the air. 

 When the sun declines the process diminishes in intensity, and 

 when it sets, the reverse takes place. The heat that had accu- 

 mulated on the surface of the earth radiates into the cooler 

 atmosphere and planetary spaces, the temperature of the surface 

 rapidly diminishes, and the air itself becomes cooler by convec- 

 tion. As the cooling goes on, the vapor suspended in tlie atmos- 

 phere begins to condense upon cool objects, while its latent heat 

 becoming free hinders the too sudden reduction of temperature. 

 The condensed water collects in drops — it is dew; or in the colder 

 seasons it crystalizes as hoar-frost. 



The special nature of the surface of the soil is closely connec- 

 ted with the maintenance of a uniform temperature, with the 

 prevention of too great heat by day and cold by night, and with 

 the watering of vegetation by means of dew. It is, however, in 

 many cases only for a little space after seed time, that the soil is 

 greatly concerned in these processes. So soon as it becomes cov- 

 ered with vegetation, the character of the latter determines to a 

 certain degree the nature of the atmospheric changes. In case 

 of many crops, the soil is but partially covered, and its pecu- 

 liarities are then of direct inliuence on the vegetation it bears. 

 Among these qualities the following remain to be noticed. 



1. The color of the soil. — It is usually stated that black or 

 dark colored soils are sooner warmed by the sun's rays than those 

 of lighter color, and remain constantly of a higher tempera- 

 ture so long as the sun acts on them. An elevation of several 

 degrees in the temperature of a light colored soil, may be caused 

 by strewing its surface with peat, charcoal powder or vegetable 

 mold. 'To this influence may be partly ascribed the following 

 facts. Lampadius was able to ripen melons even in the coolest 

 summers, in Friberg, Saxony, by strewing a coating of coal dust 



