formation of rain clouds and the precipitation of their moisture usually begin on the coast near Vera Cruz, and the course of the rain storms advances from east to west, inundating the _tierra caliente_ along the eastern coast fifteen or twenty days before the table lands are moistened. There have been seasons in which it did not begin to rain until a month or two after the usual period. In 1802 such an event occurred; and, again in 1826, the vapors did not begin to form and descend until the end of July, in consequence of which the corn was totally lost. If the rains are withheld beyond the middle of June, all the cereal products are either destroyed or suffer greatly from the drought. The power of the sun, by that time, becomes so great that the ground is scorched and the air filled with clouds of dust which seem to gather and concentrate the blazing rays, until the falling particles surround or fall upon the traveller over the plains as if he were passing through a shower of heated cinders. The heat, and the masses of burning dust, are almost overpowering not only to vegetable but almost to animal life. The agricultural prosperity of Mexico, accordingly, depends either largely upon the relative duration of these two seasons, or on the power of the landed proprietors to supply the loss of water from the clouds, by IRRIGATION derived from the rivers or slender streams that meander through the interior of Mexico. Seldom, indeed, is the Mexican planter or farmer obliged to complain of too much moisture. Between the parallels of 24° and 30° the rains are of shorter duration, and the intervals between the showers greater. But, fortunately, beyond the 26th°, a copious supply of snow, during the winter, compensates for the want of rain at the regular season. Irrigation, therefore, is universally resorted to, wherever there is an adequate supply of water, and large sums are expended by the possessors of the principal estates, in the construction of _acequias_, or canals; _presas_, dams or reservoirs; and _norias_, or water wheels, by which the refreshing element is forced up and distributed over the thirsty fields. * * * * *