originates force from within myself, by calling it an 'immaterial' entity, mental principle, or soul.

But, so it is; in the endeavor to clearly comprehend and explain the functions of the combination of forces called 'brain,' the physiologist is hindered and troubled by the views of the nature of those cerebral forces which the needs of dogmatic theology have imposed on mankind.

How long physiologists would have entertained the notion of a life,' or vital principle,' as a distinct entity, if freed from this baneful influence, may be questioned; but it can be truly affirmed that physiology has now established, and does accept, the truth of that statement of Locke,-'the life, whether of a material or immaterial substance, is not the substance itself, but an affection of it.'* Religion, pure and undefiled, can best answer, how far it is righteous or just to charge a neighbor with being unsound in his principles, who holds the term 'life' to be a sound expressing the sum of living phenomena; and who maintains these phenomena to be modes of force into which other forms of force have passed, from potential to active states, and reciprocally, through the agency of these sums or combinations of forces impressing the mind with the ideas signified by the terms 'monad,' 'moss,' 'plant,' or 'animal.'

If the physiologist rejects the theological sense of the term 'life,' without giving cause for the charge of unsoundness in religious principles, does he lay himself more open to the charge, by rejecting also the theologian's meaning of the term 'spirit,' of the term 'soul,' of the term 'mind,' and, we might add, of

* CCCXXXVI", vol. i, p. 761. As the authority of a Physiologist and late President of the Royal Society may be cited for ascribing such vital phenomena to an invisible 'mental principle,' (a) I unwillingly refer to the remark by which Sir B. Brodie meets the obvious objection of the divisibility, without destruction, of acrite organisms: It is true that one of our most celebrated modern physiologists, from observing the multiplication of polypi by the mere division of the animal, has come to the conclusion that the mental principle, which to our conceptions presents itself as being so preeminently, above all other things in nature, one and indivisible, is nevertheless itself divisible, not less than the corporeal fabric with which it is appreciated.' (p. 115.) The reader, eager for new light and guidance toward truth, naturally here expects the facts and arguments exposing the weakness or fallacy of the inference deduced from the polyp-phenomena. The sole remark is a charge of that kind called 'argumentum ad hominem.' 'But it is to be observed,' (proceeds Sir B. B.) 'that, great as is the authority of Müller generally, in questions of physiology, in the present instance he is not quite an unprejudiced witness, inclined as he is to the pantheistic theory,' &c. (p. 116) Now, the charge is untrue; and, were it otherwise, affects not the point in question. Johannes Müller was of the school of inductive physiologists, opposed to Oken and others of the school of Schelling. He would not accept even the vertebral theory of the skull,' or 'general homologies;' but adhered to the party of Cuvier. He lived and died a sincere member of the Roman Catholic Church. Brodie's notion of a 'mental principle' seems to be a combination of 'vital principle' and 'soul,' πνεῦμα and ψυχή.

(a) Brodie's Sir B., 'Psychological Enquiries,' 12mo. 1854, pp. 103, 115, 167.

'sin,' or 'death' ? That is to say, arguments based upon scriptural expressions of thought-force may be drawn from the like personifications of the aberrations and cessation of such force. Both poets and painters have, in each case, endeavored to realize and give shape to the abstractions.

When doubting Thomas obeyed the Lord's command, his fingers met resistance below what seemed to him the surface of the side, and, entering the wound, were opposed by a 'force' exceeding the 'force' they exercised. The resulting idea was that the matter' of our Lord was there, but wanting where the spear had penetrated; the fact was the opposition of a force by a force, and the sensation of that opposition. We know of nothing more material' than the 'centers of force.' Our ideas of things without as within the ego,' are the action and reaction of forces, as 'material' or 'immaterial,' as the ideas themselves.

In this view is avoided the alternative of 'idealism' with denial of an external world, or that of the personifying the sum of mental phenomena as an 'immaterial indestructible. soul,' contradistinguished from other sums of forces which are as arbitrarily styled 'destructible matter.' Sleep, stimulants, drugs, disease, concur by their effects in testifying that the kinds and degrees of mental manifestations are the result of corresponding affections and changes of structure of the brain.

How the brain works in producing thought or soul, is as much a mystery in man as brutes-is as little known as the way in which ganglions and nerves produce the reflex phenomena simulating sensation and volition.

But it is a gain to be delivered from the necessity of speculating where the 'soul' wanders when thought and self-consciousness are suspended; or how it is to be disposed of until the resurrection of the body,' glorified or otherwise; of which reintegrated sum of forces'soul' will then, as now, be a parcel. If the physiologist and pathologist had done no more than demonstrate the universal law of our being,'† which cuts away the foundations of 'purgatory,' or other limbo, from the feet of those who trade thereon, which makes 'judgment' follow death, without consciousness of a moment's interval,§ they would deserve the gratitude of the Christian world.

* CCCXXXVI", vol. i, p. 656. The whole of Locke's 'Second Reply' to Bishop Stillingfleet may be read, with profit, in relation to the undesigned testimony borne by physiology to the clear good sense and affinity for truth in the philosopher's remarks on the relation of the dogma of 'immateriality,' 'indestructibility and separability' of soul, to a Christian's faith in the resurrection of the dead, as resting on the grounds of divine revelation.

+ cccxxxvII", p. 306.

Not to mention the kindred baser brood of 'Spiritualists and Spirit-Rappers.' For the importance of this conviction to 'practice,' see CCCXXXVI", vol. i, p. 156, § 63. 'In comparing present and future."

ART. VI.-On some phenomena of Binocular Vision; by JOSEPH LECONTE, Prof. Chem. and Geol. in University of South Carolina.

I. Adjustments of the eye.

Two kinds of ocular adjustment take place in every voluntary act of sight, viz: (1) a proper convergence of the optic axes so that they shall meet on the object of sight, and (2), an adjustment of each eye so that the diverging pencil of rays which enters the pupil shall be brought to perfect focus, and therefore produce a perfect image, on the retina. The first or binocular adjustment is necessary for single vision: the second or focal adjustment is necessary for distinct vision. The first is distinctly sensible for all distances within 100 yards and perhaps for much greater distances: the second is scarcely if at all sensible for distances beyond two yards.

To the two adjustments mentioned above may be added a third, viz contraction of the pupil. The design of the contraction of the pupil is probably to increase the clearness of definition of the retinal image by cutting off the most divergent rays from very near objects, and thus to decrease the spherical aberration which is not entirely corrected in the eye by the form of the lens. The pupil, however, also contracts involuntarily under the stimulus of strong light, without regard to distance. This must be carefully distinguished from the adjustive contraction, which is to some extent at least voluntary.

These three adjustments of the eye, viz: binocular or axial adjustment, focal adjustment and contraction of the pupil are associated in every voluntary act of sight. They are accomplished by one act of volition. They are so intimately associated that they cannot be voluntarily separated. It is usually impossible to converge the optic axes on any point, without at the same time adjusting the lens and contracting the pupil in a manner suitable for perfect vision at that distance. Such inseparably associated movements are called consensual movements.

The binocular adjustment is well understood; there is no difference of opinion as to its necessity nor the means by which it is accomplished. But in regard to the focal adjustment there has been much difference of opinion among the best physiologists and physicists. Some have denied altogether the necessity, and therefore the existence of any adjustment: attributing the phenomena which are usually explained by this means, to mere transference of attention from near to distant objects, or vice

versa. The large majority of the best physicists and physiologists, however, have for a long time regarded focal adjustment as an optical necessity and therefore a fact; but the real nature of this adjustment and the means by which it is accomplished, has been a question in doubt. It has been attributed by some to the elongation of eye by the action of the recti muscles,-by others to the change in the convexity of the cornea-by others to the structure of the crystalline lens combined with contraction of the pupil-by others to the pulling forward of the crystalline lens by the ciliary muscle so as to elongate the chamber behind the lens, and by still others to the change of form of the lens by the action of the ciliary muscle. Recent very ingenious observations by Donders, Cramer and Helmholtz, upon the images of external objects made by reflection from the anterior surface of the crystalline lens, and the changes in form and size, which they undergo when the eye is adjusted for near objects, have definitely settled the question in favor of a change in the curvature of the lens. The mechanism by which this change is effected is not clearly known but it is probable that it is effected by the action of the ciliary muscle.

Before giving some experiments which bear upon the question of adjustment, I will state that my eyes are perfectly normal. In youth and early manhood the natural distance for distinct vision of small objects was eight inches, but with effort I could see perfectly distinctly at five inches. At the present time my natural distance for fine print is ten inches, though with effort I see distinctly at eight inches. Beyond this there is for me no limit of distinct vision. My eyes define the edge of the moon as perfectly as they do an object at the distance of ten inches. Moreover, by long practice I have acquired considerable and perhaps very unusual facility in making experiments on binocular vision and in analyzing my visual impressions. The following experiments which I have practised from boyhood, are interesting not only as a beautiful illustration of the laws of binocular vision, but I believe as throwing some light on the subject of adjustment and also upon the difficult subject of the Horopter.

If a plane surface checkered or otherwise figured in regular pattern, such as an oil floor-cloth, a tesselated pavement or a papered wall, be placed before the eyes at the distance of several feet, and the optic axes be then voluntarily converged (the eyes crossed) upon some point in space nearer than the surface, the figures will of course be all seen double. If now the convergence be steadily increased until two contiguous similar images, one belonging to the right eye and one to the left,

1.

II

are made to coincide perfectly, and the eyes be then held steadily in this position for some time, the patterned surface will be distinctly seen in exquisite miniature, not at its proper distance but between the real object and the eye, at a distance depending upon the interval between the centers of the contiguous similar figures of the pattern. If the pattern be very regular the illusion is complete-we actually seem to be looking at a real object. In this experiment the position of the eyes is such that, of two contiguous similar figures, the right eye is directed toward the left figure and the left eye toward the right figure; and the image is seen at the crossing of the visual lines. Thus if one eye be directed toward a (fig. 1) and the cther toward b, a perfect image of these two figures will be seen at a'. So also b and c will be united and seen at c' and a and dat d', and so on

a

a.....

for all the figures of the pattern. The dotted line d' a' c' will be the position of the image surface. The image thus obtained may be a little indistinct at first, but it gradually grows perfectly clear. As soon as the image is distinctly seen and the outlines of the figures well defined, it may be retained without any difficulty; for we seem to be looking at a real object and therefore retain the necessary convergence of the optic axes with ease. The eyes may now be turned in every direction, viewing this extensive image surface precisely as if it were a real surface.

If now while viewing the image in the last experiment we repeat upon it the same experiment, i. e., if by increasing the convergence of the optic axes we bring again the two contiguous figures in coincidence, a new image is formed between the last and the eye and is seen in still smaller miniature. In this case the position of the optic axes is such that the eyes crossing are directed not toward contiguous figures of the real object but to figures separated by an intervening one. Thus in the figure (fig. 2) a and c will be combined and seen at a", d and bat d," and b and e at e".