In this instance, as well as in many others, we behold a specimen of the admirable and diversified effects, which the Creator can produce from the agency of a single principle in nature. By means of optical instruments, we are now enabled to take a more minute and expansive view of the amazing operations of nature, both in heaven and on earth, than former generations could have surmised. These views tend to raise our conceptions of the attributes of that Almighty Being, who presides over all the arrangements of the material system, and to present them to our contemplation in a new, a more elevated, and expansive point of view. There is, therefore, a connection which may be traced between the apparently accidental principle of the rays of light forming images of objects, and the comprehensive views we are now enabled to take of the character and perfections of the Divinity. Without the existence of the law or principle alluded to, we could not, in the present state, have formed precisely the same conceptions either of the Omnipotence, or of the wisdom and intelligence of the Almighty. Had no microscope ever been invented, the idea never could have entered into the mind of man, that worlds of living beings exist beyond the range of natural vision, that organized beings possessed of animation exist, whose whole bulk is less than the ten hundred thousandth part of the smallest grain of sand; that, descending from a visible point to thousands of degrees beyond it, an invisible world exists, peopled with tribes of every form and size, the extent of which, and how far it verges towards infinity downwards, mortals have never yet explored, and perhaps will never be able to comprehend. This circumstance alone presents before us the perfections of the divinity in a new aspect, and plainly intimates that it is the will and the intention of the Deity, that we should explore his works, and investigate the laws by which the material world is regulated, that we may acquire more expansive views of his character and operations. The inventions of man in relation to art and science, are not therefore to be considered as mere accidental occurrences, but as special arrangements in the divine government, for the purpose of carrying forward the human mind to more clear and ample views of the scenes of the universe, and of the attributes and the agency of Him “who is wonderful in counsel and excellent in working.”
CHAPTER IV.
ON THE REFLECTION OF LIGHT.
The reflection of the rays of light is that property by which—after approaching the surfaces of bodies, they are thrown back, or repelled. It is in consequence of this property that all the objects around us, and all the diversified landscapes on our globe, are rendered visible. It is by light reflected from their surfaces that we perceive the planetary bodies and their satellites, the belts of Jupiter, the rings of Saturn, the various objects which diversify the surface of the Moon, and all the bodies in the universe which have no light of their own. When the rays of light fall upon rough and uneven surfaces, they are reflected very irregularly and scattered in all directions, in consequence of which thousands of eyes, at the same time, may perceive the same objects, in all their peculiar colours, aspects, and relations. But, when they fall upon certain smooth and polished surfaces, they are reflected with regularity, and according to certain laws. Such surfaces, when highly polished, are called Mirrors or Speculums; and it is to the reflection of light from such surfaces, and the effects it produces, that I am now to direct the attention of the reader.
Mirrors or Specula, may be distinguished into three kinds, plane, concave, and convex, according as they are bounded by plane or spherical surfaces. These are made either of metal or of glass, and have their surfaces highly polished for the purpose of reflecting the greatest number of rays. Those made of glass are foliated or quicksilvered on one side; and the metallic specula are generally formed of a composition of different metallic substances, which, when accurately polished, is found to reflect the greatest quantity of light. I shall, in the first place, illustrate the phenomena of reflection produced by plane-mirrors.
When light impinges, or falls, upon a polished flat surface, rather more than the half of it is reflected, or thrown back in a direction similar to that of its approach; that is to say, if it fall perpendicularly on the polished surface, it will be perpendicularly reflected; but if it fall obliquely, it will be reflected with the same obliquity. Hence, the following fundamental law, regarding the reflection of light, has been deduced both from experiment and mathematical demonstration, namely, that the angle of reflection is, in all cases, exactly equal to the angle of incidence. This is a law which is universal in all cases of reflection, whether it be from plane or spherical surfaces, or whether these surfaces be concave or convex, and which requires to be recognized in the construction of all instruments which depend on the reflection of the rays of light. The following figure (fig. 14) will illustrate the position now stated.
Let AB represent a plane mirror, and CD a line or ray of light perpendicular to it. Let FD represent the incident ray from any object, then DE will be the reflected ray, thrown back in the direction from D to E, and it will make with the perpendicular CD the same angle which the incident ray FD did with the same perpendicular, that is, the angle FDC will be equal to the angle EDC, in all cases of obliquity. The incident ray of light may be considered as rebounding from the mirror, like a tennis ball from a marble pavement, or the wall of a court.
figure 14.
In viewing objects by reflection we see them in a different direction from that in which they really are, namely, along the line in which the rays come to us last. Thus, if AB (fig. 15) represent a plane mirror, the image of an object C appears to the eye at E behind the mirror, in the direction EG, and always in the intersection G of the perpendicular CG, and the reflected ray EG—and consequently at G as far behind the mirror, as the object C is before it. We therefore see the image in the line EG, the direction in which the reflected rays proceed. A plane mirror does not alter the figure or size of objects; but the whole image is equal and similar to the whole object, and has a like situation with respect to one side of the plane, that the object has with respect to the other.