"Besides all other uses, such lessons teach at once the necessity, as we said before, of observing your own observations. And as, first, the real witness of every observation is our mind; every fact which comes through our bodily senses being to us a mental impression, it seems but common sense to hear above all things what mind has to say for and about itself. Then, secondly, where would be the benefit derived from our observations, if we could not reason upon them, or could place no confidence in our own reasonings? Yet the art of reasoning is so purely a mental process, that it can be represented by symbols as abstract and free from material meaning as if they were bare algebraic signs. Thirdly, in the most accurate of sciences mind extends our knowledge far beyond the circle of observation, and gives us axiomatic assurance of its own accuracy. Who ever saw, or ever can see, all straight lines in all conceivable positions, yet who doubts that throughout the whole universe no two straight lines ever did inclose or can inclose a space? And, fourthly, can it be a matter of indifference to any of us what evidence the mind offers concerning its own moral nature, and what is the value of that evidence, and the laws deducible therefrom? How true it thus appears that 'know thyself' lies at the root of all knowledge, and that the man who receives no witness from within can know nothing as he ought to know it!" D.--POPULAR ACCOUNT OF PURE IDEALISM WITH CRITICAL REMARKS. "A classification of systems of philosophy according to the cosmological conceptions governing them has actually been made. It is founded on a consideration of the differences among philosophers as to what that totality of existence is which is to be accepted as really vouched for by Mind. All agree, as we have said, that Mind is the sole voucher for anything; but philosophers are divisible into schools according to the various views they have taken of the constitution of that phenomenal Universe, that Cosmos, that total round of things, of which we have a recurring assurance in every act of perception, and which is orbed forth more or less fully for each man in his wider contemplations.