In a former chapter we had occasion to notice a fourth principle brought into operation by Nature in the acquisition of knowledge, which is the principle of Classification, or Analysis; and we shall now enquire how this principle may be successfully imitated by the teacher for the furtherance of his art. There are two forms, which in a former chapter we endeavoured to trace out and explain, in which this principle of Analysis appears in the educational process of Nature. We shall here again very shortly advert to them, beginning with that which in education is perhaps the most important, but which hitherto has certainly been least attended to,--that of teaching connected truths by progressive steps. When we read a connected section of history for the first time, and then examine the state of our knowledge respecting it, we find that we have retained some of the ideas or truths which we read, but that we have lost more. When that portion which we have retained is carefully examined, we find that it consists chiefly of the more prominent features of the narrative, with perhaps here and there occasional groupings of isolated circumstances. We have, in fact, retained upon the memory, little more than the general outline,--the great frame-work of the history. There will be the beginning, the middle, and the end, containing perhaps few of the minor details, but what is retained is all in regular order, bound together as a continuous narrative, and, however meagre, the whole forms in the imagination of the reader, a distinct and connected whole. There is perhaps no more of the intended fabric of the history erected in the mind than the mere skeleton of the building; but this frame-work, however defective in the details, is complete both as to shape and size, and is a correct model of the finished building from top to bottom. This is the state of every advanced pupil's mind, after he has for the first time closed the reading of any portion of history or biography. If the narrative itself has been correct, this general outline,--this great frame-work of the history,--remains on his mind through life, without any material alteration. Additional information afterwards will assist in filling up the empty spaces left between the more massive materials, but it will neither shake, nor shift them; and even the most minute details of individual or family incidents, connected with the general narrative, while they add additional interest, and fill up or ornament different and separate parts, will never alter the general form of the fabric, nor displace any of the main pillars upon which it is supported.