inverted position, so that the flowers may hang in the glass with their petals downwards.

Place a fragment of sulphur, about the size of a hazelnut, upon an egg-cup turned bottom upwards, and standing in the middle of a dinner plate; kindle the sulphur by touching it with a glowing coal, and then place the glass containing the flowers over this arrangement, as directed in the last experiment.

The sulphur will continue to burn for a considerable time, and during this combustion, the oxygen of the confined air combines with it, to produce Sulphurous acid vapor, fumes of which will be observed to ascend, and upon coming into contact with the flowers, the red rose will bleach, and the purple pansies will be more or less deprived of color.

If a similar experiment be made with autumnal dahlias of varied colors, they will present a still more striking example of the destruction or modification of their colors by the acid vapors.

In consequence of the existence of the above acid, and other vapors in the atmosphere of large cities, many plants cannot be grown exposed to its influence, and

therefore the following arrangement has been successfully adopted for preventing them from sustaining injury in such localities.

The engraving represents a circular wooden box, about. fifteen inches in diameter, and six inches deep, lined with sheet-lead, or sheet-zinc, so as to be water-tight; a stratum, about two inches thick, of clean gravel stones, is placed upon the bottom of the lining; then a stratum, about two inches thick, of turfy loam upon the gravel, and the remaining space filled with well-moistened loam; in this various small plants and flower-roots are set in the usual manner; and then covered with a large bellglass, that rests upon the rim of the box.

The arrangement of the earthy materials in the box closely resembles that of a naturally fertile soil, because the water filtrates by capillary attraction, and remains among the gravel, until the wants of the plants above require it for their support; the water cannot escape by evaporation into the external air, but it saturates that contained in the bell-glass, condenses as drops, and trickles down again to the soil, again to rise as vapor, and again to condense, and thus incessantly circulating,

Again; the same phenomenon is observed when we look at objects beyond the top of a chimney, from which the heated products of a clear burning fire are rising without smoke; and if the chimney belong to a cottage built in a small hollow, with rocks or trees immediately above it, the distortion of their positions is very remarkable.

The examination of this refraction of light belongs to the science of Optics, and not to that of Chemistry; but the reception of heat by the land, which is the cause of the phenomenon, is a legitimate branch of the latter science, and therefore demands our attention.

By the aid of the thermometer, the chemist has discovered that some soils are more easily heated than others, when equally exposed to the rays of the sun; and when they eventually acquire the same degree of temperature, some cool faster than others.

Soils principally consisting of white, and strongly adhesive clay, are not, generally speaking, easily heated, and containing a very considerable amount of water, the heat soon escapes, because it is immediately concerned in producing evaporation;-chalky soils agree with these, as regards heating with difficulty, but as they do not contain a large quantity of water, they do not lose much heat by evaporation.

The chemist has farther ascertained, that an exceedingly dark, or black soil, containing a large quantity of vegetable matter, becomes the most heated, both by the direct rays of the sun, and by warm air, that wafts over its surface from other localities; and that soils containing either much carbonaceous or ferruginous matter, exposed, under equal circumstances, to natural heat, acquire a much higher temperature than pale-colored soils.

"When soils are perfectly dry, those that most readily become heated by the solar rays, likewise cool most rapidly;" but it has been determined by accurate experiment, "that the darkest colored dry soil, (that which contains abundance of animal or vegetable matter, substances which most facilitate the diminution of temperature,) when heated to the same degree, provided it be within the common limits of the effects of solar heat, will cool more slowly than a wet pale soil composed entirely of earthy matter."

A specimen of rich black mould, which presented upon analysis nearly one-fourth its weight of vegetable matter, was exposed for an hour to sunshine, during which time its temperature increased from 65 to 88 degrees: whilst a chalk soil, under the same circumstances, had its temperature increased only to 69 degrees; however, upon removing the mould into the shade, where the temperature was 62 degrees, in half an hour it lost 15 degrees, whereas the chalk similarly situated lost only 4 degrees. Portions of brown fertile soil, and barren clay, were accurately dried, and then artificially heated to 88 degrees; they were afterwards placed in a room at 57 degrees; in the course of half an hour the brown soil lost 9 degrees, but the clay lost only 6 degrees of heat.

Throughout all these experiments, the temperatures were ascertained by a delicate thermometer, and the soils were placed upon equal-sized shallow trays, made of tin plate.

Upon considering the results of these experiments, “Nothing can be more evident than that the general heat of the soil, particularly in Spring, must be of the highest importance to the rising plant. And when the leaves are fully developed, the ground is shaded; and

any injurious influence which in summer might be expected from too great a heat, entirely prevented; so that the temperature of the surface, when bare, and exposed to the rays of the sun, affords at least one indication of the degrees of its fertility; and the thermometer may be sometimes a useful instrument to the purchaser or improver of lands."

The thermometer, although so frequently consulted throughout the Four Seasons, merely denotes the degree of heat that air, water, earth, and other media are capable of imparting, and not the actual quantity of heat therein contained; several experiments can be made concerning this fact, and they will lead to the elucidation of some curious natural phenomena.

Introduce the bulb of a thermometer into one pint of water, and then into four pints of water, drawn at the same time, from the same spring; the temperature of both portions of water will be found alike, although it is evident, upon the slightest reflection, that four times as much heat must be present in the one case as in the other; this the thermometer does not indicate.

To proceed further in this inquiry:-Provide two glass bottles, of equal size and thickness, and resembling each other in every respect as nearly as possible; pour into one of these a pound of Olive oil, and into

Fig. 22.