For this purpose, let us suppose two children about to cross a piece of soft ground. The one goes forward, and his foot sinks in the mud. Does the other follow him? No indeed. The most stupid child we could find, if within the limits of sanity, would immediately stand still, or seek a passage at another point. Here then is an example of the way in which children, while entirely under the guidance of Nature, make use of their knowledge, by applying the principle of which we are here speaking in cases of urgency and danger; and we shall now endeavour to analyse the process, that we may the more readily arrive at some exercise, by which it may be artificially imitated, whether the application be urgent and required at the moment or not. We have supposed one child going forward on the soft ground, while the other is slowly following him. When the foot of the first sinks, the other instantly stands still; and a spectator can perceive, better perhaps than the child himself, that something like the following mental process takes place on the occasion. The child thinks with himself, "Tom's foot has sunk; if I go forward, I also will sink; I will therefore stand still, or cross at another place." This is an exact parallel to thousands of similar instances which come under the notice of parents and others every day; and is a process quite familiar to adults who have paid any attention to the operation of their own minds when similarly circumstanced. When it is analysed, we find it to consist, as shewn in a former chapter, of three distinct parts, not one of which can be left out if the effect is to be produced. There is always, at the commencement of such an operation, the knowledge of some fact; "Tom's foot has sunk." There is, secondly, an inference or lesson drawn from this knowledge, "If I go forward, I also will sink." And there is, thirdly, the practical application of that lesson, or inference, to the child's present circumstances: "I will stand still, or cross at another place." It is this process, or one in every point similar, that takes place in the mind, either of the young or the old, whenever they apply the facts gleaned by observation or experience for the guidance of their conduct. Now what we are at present in search of, is an exercise applicable to _reading_, as well as to observation;--to the _school_, as well as to the play ground or the parlour;--and to knowledge whose use may not be required at the instant, as well as that to which we are driven by necessity.