endless variety of hues, thus presenting beauties even in their decay; these well-known autumnal tints are presumed to depend upon peculiar acid matters now formed in the leaves, which, acting upon the principle that during summer caused the reflection of green light, so modify it as to produce a reflection of red and yellow light, and various intermixtures of coloured rays.

The sight of a vast forest, thus variously tinted by the rays of the setting sun, is indeed magnificent; but the foliage soon loses its vital functions; the fall of the leaf arrives, and then the chill winds denude the trees, sweeping back their leaves to mingle with the earth, there to elaborate nutriment for the stems they once adorned.

During Autumn, we frequently see upon meadows, circles of green, much brighter than that of the surrounding grass; these are popularly known as "fairy rings," and probably they are due to the growth of a fungus, which dying away every year, leaves a rich soil, upon which the grass grows more luxuriantly than upon other parts of the meadow; these rings therefore annually increase in size, and in many localities they present an extraordinary appearance.

Slight frosts are common towards the close of Autumn, and therefore tender or valuable plants require protection by matting, or other bad conducting covering; and at this season may be often observed in the fields, marks of footsteps, which appear to have scorched the grass like heated iron; this phenomenon was formerly regarded with superstitious dread, but

can now be explained upon very simple chemical principles.

When the grass becomes crisp by frost, it is exceedingly brittle, and the foot of a man, or even of a child, is sufficiently heavy to break it completely down, and effectually to kill it; therefore when the sun has thawed the frosty rime from the fields, these foottracks appear brown and bare, in the midst of the surrounding and flourishing green grass.

Such are a few, and a few only, of the principal chemical phenomena of Autumn; and at its close, the frequent occurrence of frost warns us of the approach of Winter.

During the dark and dreary reign of this, the last of The Four Seasons, we shall still have to extol the power and appreciate the goodness of The Almighty, in providing for the welfare and protection of His creatures, although "the waters are hid as with a stone, and the face of the deep is frozen."

RESTO

1828

ATTUTIO

313

CHAPTER IV.

WINTER.

"HE casteth forth His ice like morsels; who can stand before His cold?

"He sealeth up the hand of every man that all men may know His work."

Decreasing days, gathering vapours, falling dews, piercing winds and chilling frosts, conclude the train of departing Autumn, and commence that of approaching Winter.

The most remarkable Chemical phenomenon of Winter, is the transition of water from the liquid to the solid state, and therefore its consideration will form the chief subject of this concluding Chapter.

The Chemist discovers during his manifold experiments and researches throughout the varied productions of Nature and of art, that all substances contract

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when cooled, and expand when heated; with the exception of water, which expands when cooled below a certain degree;—this departure from a law so general, or anomaly in the code of laws discovered by man, is productive of the most beneficial effects throughout the Creation; but to understand and duly appreciate these, a few preliminary experiments require to be performed, on the contraction and expansion of solids, liquids, and aëriform bodies generally.

Fig. 53.

First as regards solids;-Provide a smooth cylindrical bar of iron, about one inch in diameter and four inches in length, with a piece of iron wire about a quarter of an inch in diameter and ten inches in length, screwed into one of its ends, the other end of the wire being inserted into a wooden handle;-likewise a piece of iron-plate about three inches square, with a circular aperture in its centre, that will exactly allow the end of the cylindrical bar to pass through, or to use a more technical expression, that will "gauge the bar."

Mix together equal weights of finely-powdered ice, or snow and common salt, in an earthen or wooden bowl; this will form an intensely cold mixture, for a reason

hereafter to be given;-place the cylindrical bar in this for five minutes; then remove it, wipe it with a cloth, and apply it to the gauge; it will enter with extreme readiness, and indeed will be perfectly loose, but in the course of a few minutes it will only enter as exactly as it did at the outset of the experiment.

Ascertain this fact, then withdraw the bar from the gauge, and place it for five minutes over a clear glowing fire, so that it may become heated, but not to a degree approaching redness; then remove it, and apply it to the gauge; it will be impracticable to cause its entrance, until it is cooled down to the temperature that it had originally.

In these experiments, the bar of iron is said to contract by cold; and to expand by heat.

The contraction and expansion of a liquid by cold and heat, may be thus experimentally demonstrated :— Pour spirit of wine into a Florence flask, leaving only about half an inch of the neck unoccupied; with a sharp file make a mark upon the glass, or paste a small slip of paper around it, at the level of the spirit ; then place the flask in the mixture of ice, or snow and salt; as the spirit cools, it will contract in bulk, and at length remain stationary considerably below the mark ;-ascertain this fact, then remove the flask, dry it with a cloth, place it to stand upon a ring, as at page 58. As it gradually gains warmth from the surrounding air, the spirit will expand, and ultimately become stationary, exactly at the mark ;-now plunge the flask into hot water, the spirit will expand, and rise