essential qualities, but without correspondence, and without co-operation. The moment that they ceased to coincide, they would cease to be useful. The whole system of the weather, and along with it, of organized matter, would be deranged; vegetable life would cease to be reproduced; and this being the case, animal life would necessarily perish. A much smaller alteration than this, indeed, would produce nearly a similar effect. Suppose that the law were, that light and heat should give out their influence in an inverse, instead of a direct ratio, —that the light was greatest when the heat was most diminished. We should thus have brilliant but cold suns in winter, and warmth but gloom in summer. The consequences of such an arrangement it might be difficult to trace in all its effects on the complicated machinery of the atmosphere; but that it would be altogether unsalutary, is easy to perceive. The heat of summer might be sufficient to cherish a pale and feeble vegetation, but the plants would be destitute of a vigorous fibre, the flowers would but languidly expand their petals, and the seeds would not ripen. In a few years, on the supposition of the constitution of plants remaining the same as at present, the powers of reproduction in most of the vegetable kingdoms would cease, and the soil would be left in possession of the few unimportant plants which now flourish in the shade.

There appears to be nothing in the nature of things to render such an arrangement impossible. How comes it, then, that light and heat increase and diminish in the same ratio, or, indeed, that they are combined at all? Or, granting that there is a natural necessity for this combination, how comes it that plants have received such a constitution that the increase of light is as necessary to their perfection as the increase of heat? Only one answer can be given to this question. It is the arrangement of an Intelligent Being. Chance is excluded. The law which connects vegetable life with the actual state of light and heat, must have been imposed by a wise and benevolent Creator.

If it be objected, that I have been speaking only of the properties of the sun in temperate regions, and that between

the tropics a different law prevails; I answer, the arrange ment is, in some respects, different, but not opposite: There is a smaller range in the alternations of heat and cold, of brightness and gloom, of night and day; and let it be remarked, that both vegetables and animals are singularly adapted to this peculiar condition. Organized existences are created with properties suitable to the state of the tropical weather, just as others are created for existing and flourishing under the arrangements of a temperate climate: And this, in fact, singularly strengthens our argument. How does it happen that tropical plants possess these properties? It is not from an inherent principle of accommodation to circumstances; for plants possess the property of acclimation, as it is called, only within a very narrow range. Change the arrangement with what caution you may, and the experiment will not succeed. Convey the tropical vegetation to the temperate zone, and that of the temperate zone to the tropics, and no favourable circumstances can prevent them from becoming extinct, when left to the natural agency of the climate. Can this be the effect of chance? Can it be mere accident, that the one set of existences is suited to the one set of conditions, and the other to the other? The reply may be safely left to the common sense of the reader; and here again we have a new subject of devout admiration.

FIRST WEEK-THURSDAY.

ELECTRICITY.

THE principle of electricity has been already mentioned as residing in the atmosphere; and as it frequently displays its tremendous powers during the summer months in the thunder stroke, it seems to demand some notice, although its properties have been more distinctly ascertained than its uses. The truth is, that notwithstanding the attention of philosophers has been very assiduously turned to this subject of late years,

especially since the discoveries of Franklin and Galvani, and many very singular facts have been established in regard to this remarkable agent, there is still so much obscurity attached to the whole subject, that, in the present state of the science, nothing very precise can be stated as to the important functions which it doubtless exercises in the economy of nature.

That electricity extensively pervades the fluid which surrounds our globe is certain; and it is not less distinctly ascertained that it performs a powerful part in influencing and modifying the changes which take place in the weather, both as relates to warmth and to moisture; but its substance is too subtle, and the laws by which it acts are too singular, to enable us, in the present state of our knowledge, to decide either as to the exact nature or the full extent of its operations. That it is extensively employed in the various modifications which the clouds undergo, may well be believed, since it has been ascertained, by means of Franklin's electric kite, that clouds are sometimes negatively and sometimes positively electrified; and, indeed, the copious falls of rain consequent on a thunder-storm, are themselves a sufficient proof of this influence. It has been supposed, that it is the electric power which preserves moisture in the form of mist or cloud while floating in a state of deposition,* and that when this influence is withdrawn, it necessarily falls in the form of rain. If this be the case, as is probable, an agency is assigned to the principle which is both extensive and highly important. Were rain always to be the consequence of the deposition of moisture in the atmosphere, a totally different, and certainly a less salutary, result would be produced. There would be no clouds, and the showers would fall almost without warning,— suddenly, violently, and frequently. It is probable, too, that rain would fall more partially and unequally than is the case at present, when clouds, once formed, are borne in all directions on the wings of the wind. At all events, we know,

* It has just been accidentally ascertained, that the electric fluid is abundantly contained in the steam generated in the 'boiler of the steam-engine.Fourth Edition, 1841.

that the present means, whatever they may be, by which the distribution of moisture on the surface of the earth takes place, is most skilfully adapted to the purposes of organic life.

Another property which has been said to belong to the principle of electricity, is the assistance which it affords to the processes of vegetation. While these processes proceed, it is ascertained by some late experiments, that there is a constant circulation of this fluid, if it deserves that name, between plants and the atmosphere, and there is, therefore, reason to believe, that this circulation is essential to the growth and health of the former. Various contradictory experiments, however, have been made on this subject, producing conflicting theories, and not ending in any very satisfactory result. The Abbé Nollet and the Abbé Bertholon, both made experiments, which seemed to prove that the artificial application of electricity considerably accelerated the vegetable process, and rendered it more vigorous; and the latter took so strong a view of this subject, that he seriously proposed the erection of what he named electro-vegetometers, or thunder rods, for bringing down the electricity of the atmosphere to the earth, for the purpose of fertilizing the soil. After describing his plans, he thus expresses himself:-'By these means we shall have an excellent vegetable manure, or nourishment, brought down, as it were, from heaven, and that, too, at so easy an expense; for, after the construction of this instrument, it will cost nothing to maintain it: it will be, moreover, the most efficacious you can employ; no other substance being so active, penetrating, or conducive to the germination, growth, multiplication, er reproduction of vegetables.' The Abbé's views, however, appear to be visionary; and the experience of several other philosophers are far from confirming the effects above mentioned; so that nothing more can be positively affirmed, from actual experiment, than the existence of a circulation of electricity in plants during vegetation. Further experiments are required to elucidate this very interesting subject.

It is now generally understood, that the phenomena of electricity depend on the existence of two fluids of different but corresponding qualities. Into this subject it scarcely lies within my province to enter; and all that is needful to be noticed is, that there is a negative and a positive electricity, each possessing peculiar laws, by whatever theory these laws may be accounted for. These agents, or properties, give rise to the remarkable natural phenomenon of thunder. This has been ascertained abundantly by direct experiment; and it may be held as proved, that the explosion takes place in consequence of a communication between two substances, of which the one is positively and the other negatively electrified. This chiefly happens in certain conditions of the clouds, when the equilibrium of the atmosphere has been disturbed. When different currents of air bring into contact two clouds differently electrified, the consequence is, that a sudden interchange of the electric principles takes place, which gives rise at once to the thunder-clap and the flash: a similar effect is produced by the electric or non-electric state of the earth, when the atmosphere is in an opposite state. The lightning in this case, does not flash from cloud to cloud, but descends in a thunder bolt to the earth, or issues from it in the form of a brilliant flame, Under any of these circumstances thunder is produced, but it is only when the interchange is with the ground that there is danger of fatal cousequences to organized existences. There is another form which the electric matter frequently assumes in the fine evenings of summer. It is called sheet-lightning, and bursts generally from behind a dark cloud near the horizon, in a broad and vivid flash, never accompanied with the sound of an explosion. In all these instances the intention is, that the atmosphere shall be restored to a salubrious state, by carrying the fluid from places which are over-charged, to others which are deficient.

Although we do not know the precise relations between electricity and the other elements which constitute the atmosphere, yet, so far as we can penetrate, these relations are highly salutary, and those who best know the properties of