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MECHANICAL ADJUSTMENT

a little girl, who was bending intently over her drawing, "Do not stoop so, my dear; you will make yourself near-sighted!" On the contrary, an old sailor, whose eye has long been accustomed to gaze on the distant horizon, straining its powers to catch a view of the lifting sail, or to obtain the first glimpse of land, though he has a power of distinguishing distant objects, which is truly wonderful, yet he often experiences some difficulty with regard to those which are very near him.*

By what mechanism does the eye adapt itself to these varying distances? It is by the pressure of certain muscles, which, when looking at a near object, render the cornea more round and prominent: the crystalline lens beneath it is also pushed forward; and these changes vary the power of the eye over the light, so as to produce the effect that is wanted. Birds require to see both very near and distant objects, with distinctness; they are, accordingly, supplied with a further provision for altering the focus of the

*Arnott, ib. 222.

TO VARYING DISTANCES.

205

eye-a bony rim, or hoop, which, by pressure, renders it more prominent and fit for inspecting near objects; and a muscle which, on occasion, draws the crystalline lens back; thus suiting it for viewing many distant objects.

Again, in the eyes of fishes, we perceive that a greater roundness of the crystalline humour makes up for the diminished power of light, which is enfeebled by passing through the water. The convex eyes of fish are already fitted for the view of near objects: they do not want the compressing muscle, or the bony rim, to render them more prominent; but they are furnished with what they do want-muscles to flatten the eye when occasion requires it.*

In speaking of the eyes of fish, I should like to bring the real thing to your recollection. When you have partaken of mackarel, cod, or other boiled fish, you have, doubtless, observed a round, white, bead-like substance, which lies loosely in the socket of the eye, or frequently, when the fish is served by the carver, drops out

*Paley, 19. 20.

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EYES OF FISH.

into the plate. That little globe is no other than the crystalline lens of the fish's eye: it was once a transparent jelly, but has been coagulated, or hardened, like the white of an egg, by boiling.

Compare the globular lens of the fish with the section of the crystalline lens in the human eye. What a difference! and why should this be? It is because the eye of a fish is intended to see in water, the eye of a man to see in air. If a man wished to see distinctly while his head was under water, he should put on a pair of very convex spectacles; and for this reason-the rays of light are not so easily refracted, or bent in water, as they are in air, and the converging power of a lens increases with its convexity. A small globe is the most powerfully converging of all lenses; hence it is the most suitable form for the lens of a fish's eye, which has need of great power to collect light in the water.*

Another peculiarity must be noticed. Light is not only refracted with more difficulty in

Arnott, p. 196 and 222.

DIVINE BENEVOLENCE.

207

water, but its brightness is sensibly diminished. And here we cannot help admiring the minute and tender care with which the Almighty has provided for the comfort of every thing that has life, by suiting its organs to its circumstances. Surely it is a proof that he intended existence should be a blessing! How unfit, then, are any to be called His children, who do not endeavour to promote the happiness of all around them. Can the cruel, the selfish, the rebellious say, "Our Father ?". -can they claim this connexion with Him "whose tender mercies are over all his works ?"—or can they wilfully give pain to creatures he made to be happy, without offending Him?

The care of Providence is as much shown in withholding a contrivance that is superfluous, as in bestowing it where it is needed. Light being much feebler in water, the iris in the eyes of fish is not furnished with those fibres which contract the pupil in land animals, probably because the light they receive is never too strong for the retina.*

* Paley, 20.

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MILTON'S BLINDNESS.

The goodness of the Creator is likewise shown in the means provided for the security of this most important organ, the great inlet of our knowledge, the medium through which we study the word and the works of God; and, by silent but most expressive language, communicate to each other our joys and sorrows, our hopes and fears. How pathetically does Milton lament the privations he sustained in consequence of his blindness!