CHAPTER VII. THE SUMMER'S EVENING. "At summer's eve, when Heaven's ethereal bow More sweet than all the landscape smiling near ?" CAMPBELL. My readers will pardon me for having so suddenly shaken off the chill, cold garb of winter, and turned to the genial breath of summer, but the phenomena which we propose investigating in this chapter do not all occur during winter, and they will be much more pleasantly examined in our ramble through the flowery meads, than they could have been during the short evening of a winter's day. We will, therefore, bend our steps by the glassy margin of some silvery stream, and we shall presently be struck with the beauty of the reflections of the trees and cottages which diversify the opposite shore; we may, perhaps, be puzzled to account for seeing the reflection of the objects which are a considerable way removed from the banks; for the image of a person, we are sensible, is not seen by himself unless he bends perpendicularly over the stream. In reflection, the ray of light which strikes the water, or whatever reflecting object it may be, is always thrown off again at the opposite angle from that by which it arrives, and, therefore, to be seen by the person causing the reflection, he must be perpendicularly over it, or otherwise the ray will be projected in a different direction from him, and not come to his eye. Reflection follows the same law that a ball does when it rebounds from a hard substance. If we strike a ball perpendicularly against the floor, it rebounds again to our hand, as our reflected image is thrown back from the water to the eye; but if we throw the ball obliquely on the ground, it rises from the ground obliquely on the other side, just as the ray of light from the trees or cottage on the other side of the river may be considered to be thrown on the surface of the water, when it bounds off again in our direction, striking the water exactly at that part where a line drawn from the cottage to the water, and another from the water to our eye, would both approach the water at the same angle, though from different sides. A person stationed in the cottage would see our reflection, whilst we should see his. In the same manner, we do not see our own reflection in a looking-glass except when we are opposite to it; but if we stand on one side of the glass, we see the reflection of persons standing on the opposite side. The annexed diagram will explain this subject more clearly. The view represents a house a short distance from the bank, on one side of a river, whilst the spectator is standing on the opposite bank. The dotted lines represent the rays of light as they first strike the water, and are from thence reflected to the eye of the observer. The angle at which these lines touch the water is termed the angle of incidence, and that at which they again leave the surface and meet the eye, is called the angle of reflection, which two angles are always alike. The reflected landscape appears inverted, because the more elevated objects strike the water, and are again projected from it more perpendicularly than H those below them. Thus the ray from the roof falls on the reflecting surface nearer to the observer than the ray from the lower part of the building, and the image is, therefore, inverted, resembling a picture laid before the spectator in a reversed position. The effects of reflection are too beautiful, and too often brought under our notice, to pass unobserved by the most careless. They form a very prominent attraction in lake scenery, where the shores rise in bold and towering majesty, occasioning great depth of shadow, whilst the stillness of the water, caused by the shelter afforded by the precipitous shores, renders the surface of that glassy smoothness which so materially contributes to the beauty and perfection of the reflected image, rendering every leaf and spray as distinct as in the reality; and each appearing on the surface of the lake with mathematical exactness, in that part where the angle of incidence, or the angle by which the ray from it touches the water, exactly equals the reflected angle, or that by which it leaves the water to arrive at the eye of the observer. The slightest ripple on the surface disturbs the clearness of the reflection, by causing these various rays to be blended and confused. It is not uncommonly remarked, that when the reflections are very clear rain is at hand; and there may be some truth in the observation, inasmuch as the exceeding state of repose into which the elements are sometimes hushed, previous to a heavy rain, particularly in thundery weather, renders the water so calm as to be very favourable for the purpose of beholding the beauties of reflection. Another very curious circumstance may be observed if we place a walking-stick in the river, we shall perceive the part under the surface appears bent, so as to give the idea that the stick is broken at the water's edge. This is caused by refraction; by which is meant, that the rays of light when passing through a dense medium become bent downwards in their passage, giving the appearance just mentioned. Even in passing through the air this effect is produced in a small degree, and astronomers are obliged to make allowance for it in their calculations when observing the apparent position of the heavenly bodies, as this effect of refraction prevents their appearing where they really are. For instance, the rays of the sun being bent downwards in their passage to us, he will appear to rise, and be visible, before he is actually above the horizon, the rays having been bent downwards in their passage through the atmosphere. This may be prettily exemplified by placing a shilling at the bottom of a basin, then walking backwards till the edge of the basin hides the coin from our view; if, still keeping in this situation, we get some one to pour water into the basin, we shall find the shilling become visible, al |