_The Potato Disease._--This is altogether atmospherical. A new piece of land was cleared for potatoes. In the middle was a close muck, on a coarse, gravelly subsoil. In the lowest place a ditch was dug, to carry off the superabundance of water; from that ditch the coarse gravel was thrown out on one side, and suffered to remain at considerable depth. Only two or three rods distant, on one side the plat extended over a knoll of loose sand. Potatoes were planted, from the same seed, at the same time, and in the same manner, on these three kinds of land, side by side. They were all tended alike, needing little hoeing or care, the land being new. The rot prevailed badly that season. On digging the potatoes, it was found that in the coarse gravel, where the air could circulate almost as freely as in a pile of stove-wood, all the potatoes were rotten: on the muck, which was unlike a peat-bog, very fine and tight, almost impervious to the atmosphere, they were nearly all sound; on the sand, which was quite open, but tighter than the gravel, part were decayed and the rest sound. Their condition was graduated entirely by the condition of the soil. It is an apparent objection to this theory, that when the rot prevails, the best potatoes are raised on light, sandy soils. It is said that they are open to the action of air. To this it is replied, that whether they rot or not, in sandy soils, depends on the kind of sand. On some sand they rot very badly, on others hardly at all. Sandy soils differ very materially: some are almost pure silex; while others are filled with a fine dust, and, although apparently loose, are much more nearly impervious to the air than heavier soils; on the former, nearly all will decay, and on the latter, most will be preserved. Look at the immense potato crops near Rochester, N. Y., on sandy land. We have personally examined it, and find it to be filled with dust, that excludes the air, and saves the potato from rot. Why, then, is a heavy clay useless for potatoes? Is not clay a very tight soil? Unbroken it is; but, when plowed, it is always left in larger particles than other land--it is but seldom pulverized. The spaces between the particles are all open to the free action of the air; hence, instead of being close, it is one of the most open of all our soils. This confirms the theory.