been a landmark in the history of the subject; but it is not cast in the form for a beginner in Geology.  It is, in its whole plan, argumentative; setting up and defending a special thesis in Geology; the facts being arrayed with that view.  Many other great works have assumed a like form; such are Malthus on Population, Grove’s Correlation of Physical Forces, Darwin’s Origin of Species.  Even expressly didactic works are often composed more to bring forward a peculiar view, than from the desire to develop a subject in its due proportions.  Locke’s Essay on the Understanding does not propose to give a methodical and exhaustive handling of the Powers of the Mind, or even of the Intellect.  That was reserved for Reid.

The question as between old writers and new, would receive an easy solution upon such grounds as the foregoing, were it not for the sentiment of veneration for the old, because they are old.  If an ancient writer retains a place by virtue of surpassing merits, as against all subsequent writers, his case is quite clear.  In the nature of things, this must be rare:  if there be an example, it is Euclid; yet his position is held only through the mutual jealousy of his modern rivals.

The only motive for commencing a study upon a very old writer is a desire to work out a subject historically; which, in some instances may be allowed, but not very often.  In Politics, Ethics, and Rhetoric, the plan might have its advantages; but, with this imperative condition, that we shall follow out the development in the modern works.  In proportion as a subject assumes a scientific shape, it must carefully define its terms, marshal its propositions in proper dependence, and offer strict proof of all matters of fact; now, in these respects, every known branch of knowledge has improved with the lapse of ages; so that the more recent works are necessarily the best for entering upon the study.  A historical sequence may be proper to be observed; but that should be backward and not forward.  The earlier stages of some subjects are absolutely worthless; as, for example, Physics, Chemistry, and most of Biology, in other subjects, as Politics and Ethics, the tentatives of such men as Plato and Aristotle have an undying value; nevertheless, the student should not begin, but end, with them.

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There is an extreme form of putting our present doctrine that runs it into paradox:  namely, the one-book-and-no-more maxim.  Scarcely any book in existence is so all-sufficient for its purpose that a student is better occupied in re-reading it for the tenth time, than in reading some others once.  Even the merits of the one book are not fully known unless we compare it with others; nor have we grasped any subject unless we are able to see it stated in various forms, without being distracted or confused.  It is not a high knowledge of horsemanship that can be gained by the most thorough acquaintance with one horse.