Note 130 — Front matter (continued 2)

At a later period Mr. Darwin modified his views as to what he still termed "that wondrous organ the human eye," writing thus (Descent of Man, ii. 166): "We know what Helmholtz, the highest authority in Europe on the subject, has said about the human eye: that if an optician had sold him an instrument so carelessly made, he would have thought himself fully justified in returning it."

It is perfectly true that Helmholtz so expressed himself (Vorträge und Reden, i. 253, etc., English Edition, "Popular Scientific Lectures," pp. 219, etc.), adding that "the eye has every possible defect that can be found in an optical instrument, and some which are peculiar to itself." These utterances are frequently quoted, but Helmholtz says a good deal more of which we do not usually hear. He observes, in the first place, that in speaking as above he did so "from the narrow but legitimate point of view of an optician." Having then enumerated all the defects in question, he continues—"In an artificial camera, all these irregularities would be exceedingly troublesome. In the eye they are not so, so little troublesome, indeed, that it was occasionally a matter of extreme difficulty to detect them." He adds that men in general not only are unaware of the existence of such defects, but can hardly be induced to credit it. Also that they "almost always affect those portions of the field of vision to which at the moment we are not directing our attention." What is still more to the point, he observes, that the defects noted are all theoretical, while the purpose of the eye is practical, and that if theoretically more perfect as an optical instrument, it would be practically less serviceable. To complain that the eye is not adapted for the special purposes of a microscope or telescope is like condemning the boats of a sea-going ship because they lack some of the qualities found in racing outriggers or Rob Roy canoes. "As concerns the adaptation of the eye to its functions, [adds Helmholtz,] this is most thorough, and is manifest in the very limitations set to its defects.... A man of any sense would not chop firewood with a razor, and we may assume that any elaboration of the optical structure of the eye would have rendered it more liable to injury and slower in its development." Helmholtz therefore concludes that the eye is a product which "the wisest Wisdom may have pre-designed."

It thus comes very much to Pope's solution:

Why has not man a microscopic eye?

For this plain reason: man is not a fly,—

and in view of his subsequent admissions, Helmholtz's flourish about returning the eye to its maker looks very like theatrical clap-trap, unworthy of such a man.