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The transmission took place more rapidly during the day, because of the exposure of the jar to the sun and wind, which, by the expansion caused within the vessel, and by the more rapid succession of aërial currents brought into contact with the external surface of the membrane, doubtless caused in a greater degree the transmission of the redundant oxygen. The average quantity that escaped per diem did not much exceed 11 per cent., or did not quite amount to one pint in the 24 hours; but of course the transmission was more rapid at first, and diminished gradually in quantity, as the condition of the air within the jar approached more nearly to that of the atmosphere surrounding it.

“To conclude this curious subject, Spallanzani proved that some animals possessed of lungs, - such as serpents, lizards and frogs, - produce the same changes on the air by means of their skin, as by their proper respiratory organs; and Dr. Edwards, in a series of masterly experiments, has shown that this function compensates so fully for the want of respiration by the lungs, as to enable these animals, in the winter season, to live for an almost unlimited period under the surface of the water."*

"It is scarcely possible” says Professor Daniel, “duly to appreciate, in the vast economy of terrestrial adaptations, the importance of this mechanism, by which gases and vapours rapidly permeate each other's bulks, and become equally diffused. The atmosphere which surrounds the globe consists of a mixture of several aëriform fluids, in certain fixed proportions, upon the proper maintenance of which, by measure and by weight, the welfare of the

* Turner's Elements.

whole organic creation depends. The processes of respiration and of combustion are perpetually tending to the destruction of the vital air, and the substitution of another which is a deadly poison to animal life; and yet, by the simple means which we have described, the poisonous air is not allowed to accumulate, but diffuses itself instantly through surrounding space, while the vital gas rushes, by a counter tendency, to supply the deficiency which the local consumption has created. Hence the invariable uniformity of this mixture, which is one of the most surprising phenomena where all is admirable. The most accurate examination has been made of air which has been taken from localities the most opposed to each other, in all the circumstances which can be conceived to affect its purity; by means of a balloon, from a height of 22,000 feet above the level of the sea ; from the surface of the ocean ; from the summit of Mont Blanc; from the heart of the most crowded districts of the most populous cities; from within the Polar Circle ; and from the Equator; and no difference has been detected in the proportions of its principal constituents.”

CHAPTER III.

ON THE IMITATION OF THE NATURAL CONDITIONS OF PLANTS

IN CLOSELY GLAZED CASES.

“Homo, Naturæ minister et interpres, tantum facit et intelligit quantum de Naturæ ordine re vel mente conservaverit : nec amplius scit aut potest." - Bacon, Novum ORGANUM, APHOR. 1.

“The power of man over Nature is limited only by the one condition that it must be exercised in conformity with the laws of Nature."-HERSCHELL.

CHAPTER III.

ON THE IMITATION OF THE NATURAL CONDITIONS OF PLANTS

IN CLOSELY GLAZED CASES.

THE science of Botany, in consequence of the perusal of the works of the immortal Linnæus, had been my recreation from my youth up; and the earliest object of my ambition was to possess an old wall covered with ferns and mosses. To obtain this end, I built up some rock-work in the yard at the back of my house, and placed a perforated pipe at the top, from which water trickled on the plants beneath; these consisted of Polypodium vulgare, Lomaria spicant, Lastræa dilatata, L. Filix-mas, Athyrium Filix-foemina, Asplenium Trichomanes, and a few other ferns, and several mosses procured from the woods in the neighbourhood of London, together with primroses, wood sorrel, &c. &c. Being, however, surrounded by numerous manufactories and enveloped in their smoke, my plants soon began to decline, and ultimately perished, all my endeavours to keep them alive proving fruitless. When the attempt had been given up in despair, I was led to reflect a little more deeply upon the subject, in consequence of a simple incident which occurred in the summer of 1829. I had buried the chrysalis of

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