CAUSES OF THE SEASONS.

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though there are some circumstances, which can be more effectively explained afterwards, that render the rate of change variable at different stages of its taking place.

What we have stated will, we trust, be sufficient to explain to those who are not conversant with such subjects, that application to each other of the two motions of the earth, which brings about the sun and all the other seasonal changes. At the medium points between the extremes of alternation, which are called equinoctial points,—from the equality of day and night in every latitude at those times, - the momentary influence of the sun is the same upon both the northern hemisphere and the southern one; and were it not for the continued operation of the former inequality, these would be the times of mean season in both hemispheres.

The equinox which happens on the twenty-first day of March, is called the vernal equinox; and from the time of this to our midsummer the influence of the sun upon the northern hemisphere is increasingly greater than on the southern. This happens about the twenty-first of June. From this time the influence of the sun upon the northern hemisphere continues diminishing till the autumnal equinox, about the twenty-third of September; at which time the momentary influence upon both hemispheres is again equal, though the modified influence which results, is affected by the previous state of things.

From the autumnal equinox, the sun's influence becomes greater on the southern hemisphere than on the

northern, and continues to do so till our midwinter, which is about the twenty-second of December, and after this it continues to lessen on the southern hemisphere, and to increase on the northern one, until the vernal equinox is again arrived at, and the momentary influence upon the two hemispheres is again equal. These motions, in their regular succession, produce all the seasons, of which our conventional distinction into Spring, Summer, Autumn, and Winter, is more imaginary than real. In as far as the sun is concerned, there is a waxing of solar influence upon the northern hemisphere, and a waning of the same upon the southern, during the half of the year from December to June; and in the other half of the year the waxing is upon the southern hemisphere, and the waning upon the northern.

Whether the changing position of the earth to the sun, arising from the change of the angle which the plane of the rotation makes with the plane of the orbit, produces a return of solar influence to the one hemisphere or to the other, some time always elapses, not only before the effects of the change begin to be apparent, but before the previous effects have ceased. In like manner the energy upon either hemisphere does not begin to slacken exactly at its midwinter; nor are the mean temperatures at the astronomical times of the equinoxes. These differences between the observed states and the astronomical times, do not depend upon any difference whatever in the solar influence taken upon the earth as a whole. We have no means of estimating this originally and in itself; for a sunbeam

THE HEMISPHERES.

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is so exceedingly swift, that it will not linger till the most expert of the human race is able to make a single experiment upon it. We can judge of the action only from the effect produced upon terrestrial substances; and this is so different on substances of different kinds, and there are so very many substances differing from each other in so many ways, that it is impossible to state any thing with precision on this part of the subject. We are in consequence reduced to actual observations, in places differently situated and circumstanced; and these are so complicated, that nobody has yet been able, or in all probability will ever be able, to generalize them in a systematic and satisfactory

manner.

Still, the real seasons of each hemisphere are reduced to two,-a season of increasing action, and one of decreasing. It is when the former has acquired a certain degree of strength, and produced certain effects upon the susceptible parts of nature, that we call it Spring. A greater degree of strength we call Summer. The first marked decrease is Autumn; and the last one Winter. But none of these is distinctly marked from the other; they differ, in different latitudes and countries, and even in the same country, during different years, in their various lengths and characters.

Spring is unquestionably the most variable of the whole; and the one most difficult to characterize. It is easy to make calculations as to what should be the character, the time, and the duration of the season in all latitudes, if there were no element in the

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ACTION OF NATURE

calculation but the unvarying action of the sun, and those changes of the earth's position with regard to the sun, of which we have given some account. But such calculations are never near the observed truth; though they are a sort of approximation, and serve as a general framework on which to arrange our observations of particular places.

One reason why Spring is more variable and less manageable in this respect than any other season, arises from those parts of nature upon which the sun has the chief influence, having most work to do in the Spring. Cultivation must in some measure be put aside, if we would understand the seasons; for a skilful cultivator is always able to work to the weather, at least in some of his labours. Putting this aside, Spring is the season of toil both with wild plants and wild animals; and the more marked the seasons are in any country, this toil is the more severe.

Almost all our natural plants, except the fungi, which are in great part autumnal, and those plants which keep growing at all seasons, if they have enough of moisture and not too much cold,—these excepted, our wild plants make the greater part of their growth in the Spring. They also have the beginning of their annual growing then. In every case it is more difficult to start, than to proceed after starting. There is also more danger to plants at this season than at any other. The young bud is always tender; because the different parts of which it is composed have just come out of their winter hiding-places, and are not inured

to the weather. They are not hurt by cold alone, but also by too severe exposure to heat or to drought; and the weather is generally so unsettled at this time, that though its changes are evidently healthful upon the whole, they are severe and even fatal in many instances.

Spring is also the busiest time of the year with the birds; because they have their nests to build and their broods to rear. It is true that the waste left by the winter furnishes the materials of the nests; and that many insects and other small animals are, especially during the advanced part of the Spring, in that condition in which they serve best for the food of birds. But notwithstanding this, the labours of the winged creatures are exceedingly severe; and many of them fly thousands of miles for the purpose of finding breeding places for their young. It is clearly shown, however, that He, without whose knowledge not even a sparrow can fall to the ground, extends his fatherly care to all His creatures, and strengthens each of them in proportion for every labour they have to perform.

The effects which the Spring produces upon all the tribes of the vegetable and the animal kingdoms, are among the most striking and instructive features of the season. Their dependence on the solar influence is secondary, however, and comes to them through the medium of those more general portions of terrestrial nature, upon which the sun produces seasonal changes. They can therefore be more clearly, and also far more briefly noticed, after we have cast a passing glance upon