AMERICAN INSTITUTE, 331 



always be found that the quantity of evaporation from land is far more 

 limited than from water, the one depending upon the capillary action and 

 retentive power of the surface soil, while the other arises from a compara- 

 tive inexhaustible source. The rate of evaporation from land depends in a 

 measure upon temperature, and is invariably accelerated by the effects of 

 a hot sun upon the earth's surface ; then again the temperature is affected 

 by elevation. The supply of water is somewhat dependent upon the geogra- 

 phy of the district ; close proximity, for example, to a large river, lake, or 

 sea, promotes the fall of rain. Thus one side of a mountain range, exposed 

 to oblique showers, will require much more draining than the other side, 

 not so exposed. So one country requires far more draining than another, 

 owing to the quantity of rain that falls annually. In England, the fall 

 ranges between twe ty-one and thirty-two inches ; in Brazil, 280 inches ; in 

 Bombay, 78 inches ; in South Carolina, 50 inches ; in Cumana, 8 inches. 

 The rain falls in large quantities near the equator, and diminishes toward 

 the poles. 



The agriculturist, before he commences to make his drains, must first 

 calculate the quantity of water required for the district in which he lives, 

 and its position relative to the surrounding country. If it is elevated, the 

 water will run off rapidly. Even before sowing, the germination of the 

 seed planted in it, if in a low situation, and the soil is of a retentive charac- 

 ter, the earth may become so saturated as to prevent the entrance of air, 

 and consequently impede if not prevent the germination of seed. 



All soils exist in one of three conditions : 



1st. Clay, which is a dense close mass of particles finely comminuted, 

 of an exceedingly tenacious kind, and when wet forms a paste impermeable 

 to water, and is rarely devoid of moisture under any circumstances, even 

 when its constituent particles are readily separable. 



2d. In the sandy or gravelly form, the particles are rarely if ever united, 

 consequently the soil is full of interstitial canals and passages for water, 

 and does not possess the power to retain or prevent its admission. 



3d. This soil is made up of calcareous or aluminous elements, sometimes 

 silicious, in an incalculable variety of proportions, and is filled with pores 

 for the ingress of air and water. 



In the first named soil, wet weather in the spring or fall frequently 

 retards the sowing of grain, even if partially drained, but if undrained, it 

 most completely prevents it, and absolutely compels the agriculturist to 

 change his system of farming, and sow other grains when the season is more 

 advanced. In this case efiicient drainage would carry off the water rapidly, 

 and rescue the farmer from the dominion of late or early seasons, and pre- 

 vent the failure of his crop, besides repaying the entire cost in two or three 

 years, particularly if his drains are deep and have a ready escape, as this 

 renders the soil available to deep-rooted plants, and enables them to send 

 down their fibres to the stores of abundant nourishment, which they help 

 to increase in permanent value by the excrementitious emanations from 

 themselves. 



