sion of my senses, which obliterate all these chimeras. I dine, I play a game of back-gammon, I converse, and am merry with my friends; and when after three or four hours' amusement, I would return to these speculations, they appear so cold, and strained, and ridiculous, that I cannot find in my heart to enter into them any farther." (Part iv., Section 7.)

Is not this good-humoured? Is it not a piece of pleasant bantering, to be equalled only by certain French philosophers? The real conclusion, however, winds up his First Book and runs as follows:-"A true sceptic will be diffident of his philosophical doubts, as well as of his philosophical conviction; and will never refuse any innocent satisfaction, which offers itself, upon account of either of them.

'Nor is it only proper we should in general indulge our inclination in the most elaborate philosophical researches, notwithstanding our sceptical principles, but also that we should yield (sic) to that propensity, which inclines us to be positive and certain in particular points, according to the light, in which we survey them in any particular instant. "Tis easier to forbear all examination and inquiry, than to check ourselves in so natural a propensity, and guard against that assurance, which always arises from an exact and full survey of an object. On such an occasion we are apt not only to forget our scepticism, but even our modesty too; and make use of such terms as these, 'tis evident, 'tis certain, 'tis undeniable; which a due deference to the public ought, perhaps, to prevent. I may have fallen into this fault after the example of others; but I here enter a caveat against any objections, which may be offered on that head; and declare that such expressions were extorted from me by the present view of the object, and imply no dogmatical spirit, nor conceited idea of my own judgment, which are sentiments that I am sensible can become nobody, and a sceptic still less than

any other.*

It is obvious to remark that no amount of easiness would maintain most minds in this balanced position of the pleasant know-nothing

The general tendency would be to acknowledge the negative side alone. And it would be well if an absence of serious convictions, seriously asserted, and acted on, did not gradually weaken the sense of Responsibility by making Truth appear indifferent because unattainable.

We, however, are just now more concerned with two other equally * All these quotations will be found between pp. 332 and 360 of the Treatise. Ed. 1817.

obvious comments. One, that Hume appears to take for granted the point at issue. Suppose it for argument's sake to be true that impressions and ideas (as described by him) make up our whole ordinary consciousness; does this shew that no latent power or entity exists by which we become conscious of those passing trains? When impressed by colours, are we conscious of an optic nerve, retina, crystalline lens and other instrumental powers of vision? Can we, if we try, perceive by sense the nerve-currents brainwards, or the sensory which receives and compares them? In both cases (eye and inward eye) pathology affords an evidence of consciousness which happy health refuses us. The brainsick sense sees colours and phantoms which are not-the disordered mind dwells on impressions and ideas absolutely unreal, and acts on them as stern realities. And thus our own purely subjective states reveal to us our own subjectivity. 'Tis so in fevers, in lunacies, in vices-'tis so to the drowning or the desperate man. These mournful changes which pass over ourselves issue from an interior activity of self-ness and form one of its commonest verifications.

This first comment admits of extension. If we endeavour to introduce experiment (as well as experience) into Mental Science, must we not ask a previous question:-Shall this or that experiment be tried? In other words, by what inner law shall we shape our inquiries so as to gain useful facts for our intended induction ?-Nay, we may further ask: What inner Being is to settle the questions, criticize them, and judge the final issue? And if we seem to see our way on these topics, we may feel pretty sure that whenever our psychology comes to practical trial, we proceed as being sure of a Self, more or less self-conscious of Self, and are quite confident that its self-ness will continue during the whole time of our investigations.

Our second comment may be simply summed, but the consideration given to it ought to be minute and careful. Suppose instead of successive perceptions, impressions, or ideas, we substitute a succession of phenomena, and then apply to them Hume's line of thought, we have an acute statement of the modern teachings which relegate the noblest part of our Nature, our reasonings and our beliefs to the territory of the Unknowable. In a word, all knowledge thus seems to be gained by "looking on," none by "looking in." Truth within ourselves especially if it manifests a Truth above ourselves is made to appear hopeless. And so far does the process of Elimination extend, that principles involved even in our "looking on " must not be drawn out of their latency, for fear they should become accepted parts of knowledge. Let any thinker repeat with this substitution

the Personal Identity argument in his own mind, and he will soon see what a shadow is cast over an infinitely wider world of thought.*

The same process of repetition ought in fairness to produce another effect. Are not these philosophic argutia, these Pyrrhonic subtilties closely akin to the difficulties raised against all first principles; and more particularly all Theistic principles ? But does anybody on their account doubt his own Self-ness or Identity? Or does any one refuse to act on the supposition of otherness, and outerness, or ignore his world of fellow-men and hard objectivities which press upon him from every side? Why then should anybody ignore on their account the great First-Cause?

In the text of Chapter III. the elements of our reasonable belief in our own Personal self-ness and sameness have been shortly mentioned; of such work-day belief, that is to say, as suffices for actual life, and gains from it, and throughout it, a perpetual verification. If any one wishes to go deeper than this, he must inquire upon what evidence first principles are accepted by reasoning men; what difficulties attach to such principles; and under what conditions these difficulties are held to be nugatory. This inquiry is troublesome but promises real satisfaction. We have not, therefore, declined it, as may be seen in the ensuing Chapter. One fact is manifest beforehand-that whatever evidence is presupposed valid by those first principles of every-day knowledge, may be safely presupposed, accepted, and reasoned upon, in the ground-work of Natural Theology.

It was Hume's object to push his scepticism to its most extreme verge. Thus pushed, it "so wrought upon him that he was "ready to reject all belief and reasoning" till a return to every-day life made his speculations appear in his own eyes "cold and strained and ridiculous." What then was the inference Hume himself intended? Which was really groundless-every-day belief or scepticism? Will his useful dilemma induce the reader to receive Kant's excuse for the celebrated doubter, when he bids us let the man alone because he is but trying the strength of human reason? At all events, Hume's way of stating his case seems to justify the old remark, that, while Superstition is refuted by Reason, Nature itself refutes the Sceptic.

*Compare Mr. Green's Introduction to Hume's Treatise on Human Nature, Vol. I., pp. 263, seq., where he discusses the bearing of this subject upon Hume's doctrine of Cause and Effect.

B.-EXTRACTS FROM POPULAR LECTURES, BY PROFESSOR HELMHOLTZ, ON THE RECENT PROGRESS OF THE THEORY OF VISION.

"If now we compare the eye with other optical instruments, we observe the advantage it has over them in its very large field of vision. This for each eye separately is 160° (nearly two right angles) laterally, and 120° vertically, and for both together somewhat more than two right angles from right to left. The field of view of instruments made by art is usually very small, and becomes smaller with the increased size of the image.

"But we must also admit, that we are accustomed to expect in these instruments complete precision of the image in its entire extent, while it is only necessary for the image on the retina to be exact over a very small surface, namely, that of the yellow spot. The diameter of the central pit corresponds in the field of vision to an angular magnitude which can be covered by the nail of one's forefinger when the hand is stretched out as far as possible. In this small part of the field our power of vision is so accurate that it can distinguish the distance between two points, of only one minute angular magnitude, i.e. a distance equal to the sixtieth part of the diameter of the finger-nail. This distance corresponds to the width of one of the cones of the retina. All the other parts of the retinal image are seen imperfectly, and the more so the nearer to the limit of the retina they fall. So that the image which we receive by the eye is like a picture, minutely and elaborately finished in the centre, but only roughly sketched in at the borders. But although at each instant we only see a very small part of the field of vision accurately, we see this in combination with what surrounds it, and enough of this outer and larger part of the field, to notice any striking object, and particularly any change that takes place in it. All of this is unattainable in a telescope.

"But if the objects are too small, we cannot discern them at all with the greater part of the retina.

'When, lost in boundless blue on high,

The lark pours forth his thrilling song,'

the ethereal minstrel' is lost until we can bring her image to a focus upon the central pit of our retina. Then only are we able to see her.

"To look at anything means to place the eye in such a position that the image of the object falls on the small region of perfectly clear vision. This we may call direct vision, applying the term indirect to that exercised with the lateral parts of the retina-indeed with all except the yellow spot.

"The defects which result from the inexactness of vision and the smaller number of cones in the greater part of the retina are compensated by the rapidity with which we can turn the eye to one point after another of the field of vision, and it is this rapidity of movement which really constitutes the chief advantage of the eye over other optical instruments. . . . .

66

A great part of the importance of the eye as an organ of expression depends on the same fact; for the movements of the eyeball-its glances are among the most direct signs of the movement of the attention, of the movements of the mind, of the person who is looking at us." Popular Lectures on Scientific Subjects, pp. 212-214.

The great German next proceeds to catalogue some principal defects of the Eye. 1. Chromatic aberration connected with 2. spherical aberration and defective centering of the cornea and lens, together producing the imperfection known as astigmatism, and 3. irregular radiation round the images of illuminated points. "Now," adds Helmholtz, "it is not too much to say that if an optician wanted to sell me an instrument which had all these defects, I should think myself quite justified in blaming his carelessness in the strongest terms, and giving him back his instrument. Of course, I shall not do this with my eyes, and shall be only too glad to keep them as long as I can defects and all. Still, the fact that, however bad they may be, I can get no others, does not at all diminish their defects, so long as I maintain the narrow but indisputable position of a critic on purely optical grounds." (p. 219.)

He then goes on to other faults. 4. Defective transparency. 5. Floating corpuscules (Muscæ Volitantes). 6. The "blind spot" with other gaps in the field of vision. "So much," he concludes, "for the physical properties of the Eye. If I am asked why I have spent so much time in explaining its imperfection to my readers, I answer, as I said at first, that I have not done so in order to depreciate the performances of this wonderful organ, or to diminish our admiration of its construction. It was my object to make the reader understand, at the first step of our inquiry, that it is not any mechanical perfection of the organs of our senses which secures for us such wonder