( 130) 
ples common to both, and some peculiar to each. 
The common principles are, 
Ist. Such command of water as will cover the 
largest surface with the least labor and expence. 
2d. Muddy water, (the effect of loosened soil and 
heavy rains,) is most favorable to vegetation, be- 
cause, besides giving the necessary moisture, it fur- 
nishes a considerable portion of alluvial matter. 
3d. Water, charged with sand or gravel, or con- 
taining iron or vitriol, or of a temperature very hot 
or very cold, is unfavorable to vegetation, and ought 
not to be employed, until, by standing in reservoirs, 
it deposits these injurious matters in the one case, 
and in the other acquires the temperature of the at- 
mosphere. 
Ath. Clay and calcarious soils require less water- 
ing than others, 
Sth. Irrigation is of Jess importance in northern 
than in southern latitudes; and, 
6th. In cold climates, or in situations of much ele- 
vation, irrigation is most usefully employed in the 
spring and autumn; and in hot climates and sandy 
soils in the summer. 
The principles peculiar to the two modes, may be 
collected from the following brief detail of the labors 
necessary to’ each. In irrigating by submersion, the 
first and great labor is to make a dam of such strength, 
as shall ‘resist the volume of water by which it may 
be pressed—of such height as will raise the water 
above the level of the ground you wish to overflow, 
and of such structure as will enable you to discharge 
the water it collects promptly and entirely. The 
