had been half-a-dozen Chemical manuals in existence, he would probably have read them all, and fared much worse. It happens, however, that, in the more exact sciences, there is a greater sameness in the leading ideas, than in Politics, Morals, or the Human Mind; and the evil of distraction is so much smaller. Undoubtedly, the best of all ways of learning anything is to have a competent master to dole out a fixed quantity every day, just sufficient to be taken in, and no more; the pupils to apply themselves to the matter so imparted, and to do nothing else. The singleness of aim is favourable to the greatest rapidity of acquirement; and any defects are to be left out of account, until one thread of ideas is firmly set in the mind. Not unfrequently, however, and not improperly, the teacher has a text-book in aid of his oral instructions. To make this a help, and not a hindrance, demands the greatest delicacy; the sole consideration being that the pupil must be kept _in one single line of thought_, and never be required to comprehend, on the same point, conflicting or varying statements. Even the foot-notes to a work may have to be disregarded, in the first instance. They may act like a second author, and keep up an irritating friction. There is, doubtless, a consummate power of annotation that anticipates difficulties, and clears away haze, without distracting the mind. There is also an art of bringing out relief by an accompaniment, like the two images of the stereoscope. This is most likely to arise through a living teacher or commentator, who, by his tones and emphasis, as well as by his very guarded and reserved additions, can make the meaning of the author take shape and fulness. As the chief text-book is chosen, among other reasons, for its method and system, any defects on this head may be very suitably supplied, during the reader's progress, by notes or otherwise. When the end is clearly kept in view, we shall not go wrong as to the means: the spirit will remedy an undue bias to the letter. The subjects that depend for their full comprehension upon a certain method and order of details, are numerous, and include the most important branches of human culture. The Sciences, in mass, are avowedly of this character: even such departments as Theology, Ethics, Rhetoric, and Criticism have their definite form; and, until the mind of the student is fully impressed with this, all the particulars are vague and chaotic, and comparatively useless for practical application. So, any subject cast in a _polemic_ form must be received and held in the connection thereby given to it. If the arguments _pro_ and _con_ fall out of their places in the mind of the reader, their force is missed or misconceived.