Imagini ale paginilor

their nourishment and increase very materially depend.

Dr. Priestley's experiments on this subject were made in 1771 and 1772; and his account of them was presented to the Royal Society in 1773. He has since discovered, that light is necessary to enable plants to purify air; that pure air, however, is not produced by light or plants, but only by the purification of the impure air to which plants have access 1.


This subject has been since pursued by Dr. Ingenhousz, who, in 1779, published Experiments upon Vegetables,' discovering their great power of purifying common air in the sunshine, and of injuring it in the shade, and at night, &c.-From these experiments he has observed, that plants correct bad air, in a complete manner, in a few hours; that this wonderful operation is not owing merely to the vegetation of the plant, but to the influence of the light of the sun upon it: that plants, exposed to the light of the sun, have likewise the surprising faculty of elaborating the air which they contain, and have absorbed from the common atmosphere, into real dephlogisticated air; which they emit, principally from the under surface of their numerous leaves, into the common mass: that this

Observations on Air, vol. i. p. 49, 87, vol. iv. p. 293, 305, vol. v. p. 12, 18, &c. The experiments, just related, induced Dr, Priestley, in 1776, to consider the subject with more attention. But, as in all the experiments which he made, the plants, confined in carbonic acid gas very soon died, he concluded that carbonic acid gas was not a food but a poison to plants. But, in the year 1784, Mr. Henry, of Manchester, found, by a series of experiments, that carbonic acid gas, so far from killing plants, constantly promoted their growth and vigour. The experiments also of M. Sennebier, in the year 1780, and of Saussure, jun. in 1797, have, at last, put the subject beyond the reach of dispute.

operation does not commence till after the sun has appeared for some time above the horizon, and is carried on more or less briskly, in proportion to the clearness or dulness of the day; that this production of pure air diminishes toward the close of the day, and ceases entirely at sunset, except in a few plants which perform this function somewhat longer than others: that acrid, illscented, and even the most poisonous plants, perform this office in common with the mildest and most salutary.

Dr. Ingenhousz has further observed, that all plants whatever emit a noxious air in the night; and even those which excel others in yielding the purest air in the sunshine, surpass them in the power of infecting the circumambient air in the dark, and to such a degree, that, even in a few hours, they render a large quantity of good air so noxious, that an animal confined in it loses its life in a few seconds'; and that, even in the daytime, plants shaded by high buildings, or growing under a dark shade of other plants, emit an air that is noxious to animals.

This intelligent philosopher has likewise observed, that the flowers of plants, universally, render the air highly noxious, equally by night and by day:

'Dr. Ingenhousz, however, has observed, that the quantity of noxious air which plants emit at night, is very inconsiderable in comparison with that of the oxygen gas which they give out during the day.

2 A few flowers of the honeysuckle exposed even to the sun's light in the middle of the day, rendered a body of air, equal to two pints, highly noxious, in three hours. These flowers, says the doctor, like all others, after having thus rendered truly fatal a body of air equal to two pints, have lost nothing of their fragrance. The air itself, which they have poisoned, is impregnated with the same fragrant smell as the flowers themselves; so that a person shut up in a small and close room, containing a large quantity of

that their roots, detached from the ground, possess the same property, some few excepted: that fruits, in general, even the most delicious, have this deleterious quality (but principally in the dark) to such an astonishing degree, as to endanger the life of a person who should happen to be shut up in a small and close room, where a great quantity of them is stored up: and lastly, that the light of the sun, singly, has not the power of purifying any quantity of air exposed to it, without the concarrence of the plants.

The experiments of Dr. Ingenhousz, united with those of subsequent philosophers, indubitably prove that the action of vegetables upon air, at least in the day, is directly opposite to that of animals. The latter inspire the common atmospherical air into their lungs, and then emit it thence, loaded with a foreign and noxious principle. Vegetables, on the contrary, absorbing carbonic acid gas, decompose it, give out the oxygen, and retain the carbon which forms a part of their nourishment; thus affording to man and animals that vital air which their existence depends.


It has been already said, that neither candles will burn, nor animals live, beyond a certain time, in a given quantity of air; yet the cause of such speedy extinction and death was unknown, and no method was again found out for rendering that empoisoned air fit for respiration, until the experiments and discoveries of the eminent philosophers whom I have mentioned last. Some provision there must be for this purpose, as well as for that of supporting flame; for, without such a provision, the whole atmosphere would in time become unfit for animal

the most fragrant flowers, might lose his life by this most treacherous of all poisons. He has heard of more than one instance of sudden deaths, which were too probably

life, and the race of men, as well as of beasts, would die of a pestilential distemper. And yet we have reason to believe, that the air is not less proper for respiration in our days, than it was above 2000 years ago, which is as far as we can go back in natural history.

For this important end, therefore, Dr. Priestley has suggested to the divine, as well as to the philosopher, two grand resources of Nature-the vegetable creation already mentioned, and the sea and other great bodies of water.

With respect to the last, Dr. Priestley has observed, that both the air corrupted by the breath of animals, and that vitiated by other putrid matter, was sweetened, in a great measure, by the septic part infusing itself into water. He concluded, therefore, that the ocean, and the great lakes and rivers, that cover so large a proportion of the globe, must be highly useful by absorbing what is putrid, for the further purification of the atmosphere; thus bestowing what would be noxious to man, and other animals, upon the formation of marine and other aquatic plants, or upon other purposes yet un


In fine, we are assured from these great discoveries, that no vegetable grows in vain : but that, from the oak of the forest to the grass of the field, every individual plant is serviceable to mankind: if not always distinguished by some private virtue, yet making a part of the whole which cleanses and purifies our atmosphere. In this the fragrant rose and deadly nightshade alike co-operate. Nor are the herbage and woods that flourish in the most remote and unpeopled regions unprofitable to us, nor we to them, considering how constantly the winds convey to them our vitiated air, for our relief, and for their nourishment. And if ever these salutary gales rise to storms and hurricanes, let

us still trace and revere the ways of a beneficent Being, who, not fortuitously, but with design; not in wrath, but in mercy; thus shakes the waters and the air together, to bury in the deep those putrid and pestilential effluvia, which the ve getables upon the face of the earth had been insufficient to consume.

Let no presuming impious railer tax
Creative Wisdom, as if aught was formed
In vain, or not for admirable ends.-
Lives there the man, whose universal eye

Has swept at once the unbounded scheme of things;
Marked their dependence so, and firm accord,
As with unfalt'ring accent to conclude
That this availeth nought?-

Till such exist, let zealous praise ascend,
And hymns of holy wonder, to that Power,
Whose wisdom shines as lovely on our minds,
As on our smiling eyes his servant-sun.

No. XVI.



Nymphs! your bright squadrons watch with chemic eyes
The cold-elastic vapours, as they rise;
With playful force arrest them as they pass,
And to pure air betroth the flaming gas,
Round their translucent forms at once they fling
Their rapturous arms, with silver bosoms cling;
In fleecy clouds their fluttering wings extend,
Or from the skies in lucid showers descend;
Whence rills and rivers owe their secret birth,
And ocean's hundred arms infold the earth.


IT was the opinion of Thales, and other antient

« ÎnapoiContinuați »