ence and gratitude the Giver of every good and perfect gift!

The watery vapor thus present in the air is imbibed or attracted by soils with various degrees of energy, and is as much connected with their fertility as the direct absorption of the waters of the Spring showers. When this power of attracting aërial moisture is great, the plant is supplied with water even in the absence of rain; and the effect of the evaporation in the day is counteracted by the absorption of aqueous vapor from the air by the interior parts of the soil during the day, and by both the exterior and interior during night.

The compact, tenacious varieties of clay soils which absorb a great quantity of the water of the shower, do not attract a great quantity of moisture from the air during the absence of rain; they become hard, and the vegetation upon them is liable to wither away.

Chemical analysis of soils distinguished for their power of attracting aërial moisture, points out that they contain sand, finely divided clay, carbonate of lime, and organic manure, all so lightly bound together as to admit of the perfect access of air to a considerable depth; and the great utility of carbonate of lime, or chalk, and manure, consists in their conferring attractive powers upon the soil without rendering it adhesive and compact; sand likewise will destroy tenacity, but it appears also to impair this attractive power.

Soils which attract aërial moisture with the greatest avidity are always the most fertile; and very simple experiments upon this subject will afford means of judging of the value or productiveness of land.

One thousand grains of the soil, collected during dry weather, may be placed on a metallic "hot water plate,"

filled with boiling water; then let the soil be stirred with a piece of thick wire, until no dew or steam is deposited upon a cold glass plate or tumbler held about an inch above its surface.

This is a test that the soil is dried, and upon carefully removing it from the plate to the scale pan, the number of grain weights required to restore the original balance will indicate the quantity of water that was retained in the soil by capillary attraction, although it might have felt perfectly dry.

If this dried soil be left in the scale pan exposed to the air, it will gradually increase in weight by attracting aqueous vapor. The temperature of boiling water is directed to be used for the desiccation, because it is a good standard of comparison, viz., 212 degrees; and moreover such temperature will not alter the chemical nature of the soil by decomposing its organic constituents, like the greater heat of an open fire or lamp.

If it be required to ascertain the utmost quantity of moisture that the artificially dried soil is capable of attracting from the air, the following arrangement may be made:

Place the soil in an earthenware saucer, supported on an egg-cup, in the centre of a large dinner-plate full of

water; place a bell-glass, or a large earthenware jar, over this arrangement, that the rim of the glass or jar may stand in the water contained in the plate.

No liquid water can rise to the soil in the saucer, but the vessel with which it is covered contains air; this will excite the water to rise in vapor, and become saturated; a portion of this vapor will be attracted and condensed by the soil; examine its weight after a few hours, then replace it as before; and upon future examination, when it has ceased to gain weight, it may be considered to have attracted the greatest amount of water of which it is capable; again place it upon the plate to dry as before, and the water will evaporate.

Accurate experiments of this nature presented the first chemist who devoted his talents to agriculture with the following results.

I. One thousand parts of a celebrated soil from Ormiston in East Lothian, which contained more than half its weight of finely-divided matter, of which 11 parts were carbonate of lime, and 9 parts vegetable matter, when dried at 212 degrees, gained by exposure for an hour to air saturated with moisture, at a temperature of 62 degrees, 18 grains.

II. One thousand parts of a very fertile soil from the banks of the river Parret, in Somersetshire, under the same circumstances gained 16 grains.

III. One thousand parts of a soil from Mersea, in Essex, worth 45 shillings an acre, gained 13 grains. IV. One thousand parts of a fine sand from Essex, worth 28 shillings an acre, gained 11 grains.

V. One thousand parts of a coarse sand, worth 15 shillings an acre, gained only 8 grains.

VI. One thousand parts of the soil of Bagshot Heath gained only 3 grains.

A very considerable degree of chemical attraction is discovered to exist between the aluminous portion of soils, and the organic matter of manure; thus it is preserved from too rapid decomposition, and from being carried away by water; or, in other words, the soil remains rich, and capable of yielding nutriment to vegetation, whilst very silicious soils have little or no such chemical attraction, and therefore often remain poor, and incapable of yielding generous support to their produce.

When soils are immediately situated upon a stratum of rock or stone, they become dry much sooner than when the sub-stratum is of marl or clay, which are strongly absorbent of water, and accordingly in some cases this is of great advantage to light sandy soils, as a reservoir of moisture upon which they can draw in time of drought for the support of their vegetation; in other cases, where the external soils are too absorbent, this property is corrected by the sub-stratum being of sand or gravel; this admits of the percolation of the excess of water.

In limestone districts, the actual soil is a kind of marl, generally only a few inches deep, but highly absorbent, and capable of supporting vegetation, because the limestone rock upon which it rests does not allow the water to escape by rapid capillary attraction; whilst, on the other hand, in sandstone districts, where the sandy soil, although absorbent, rests on absorbent sandstone rock, vegetation frequently suffers from the capillary attraction of the latter, withdrawing the water too rapidly; indeed, during the height of summer, it is no uncommon thing

to see the grass on sandstone districts parched and browned, whilst that on limestone districts is luxuriant and green.

The student of Nature must bear in mind, that the enormous amount of fifty-four trillions, four hundred and fifty-nine billions, seven hundred and five millions of tons of watery vapor, is sustained by the atmosphere, which is a mechanical mixture of the elements Oxygen and Nitrogen, and the compound Carbonic Acid; and that during all the wonderful vicissitudes of the Four Seasons, the atmosphere is never sensibly altered in the due proportion of its constituents.

Even when replete with solar heat, gained indirectly by convection from the warm surface of the earth, the air is simply expanded in volume, not altered in actual constitution; and when from local causes it has parted with a certain degree of heat, or become cold, it is simply contracted in volume; the pure abstract effect of artificial heat and cold upon air, is likewise attended by similar phenomena; this can be experimentally proved by the following arrangement:

A Florence flask is placed with its neck dipping beneath the water contained in a glass; the flask, although empty, in the ordinary acceptation of the term, is actually full of air; this has no tendency to escape,