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. 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.