To fully understand what takes place when trying to study, let the pupil recall that there are three sources of knowledge.
First: The Senses carry into his mind reports from the outside world--Sensation--sight of the letters, words and sentences, &c. Second: The Intellect operates on these undigested elementary Sense-reports, or Sensations, and find _relations_ among them. This is Perception, or relations among Sensations. Third: The mind acts on the _perceived relations_ and finds relations among them. This is Reason or relations among relations.
Now the geometrical student in reading the printed instructions to himself or in reading them aloud, might simply occupy his _eye_, or _eye and ear_ with them and his Reason might soar away to other subjects, climes or ages.
Remember that the Intellect is always active and busy, and the question for us to answer in our own case is--shall it co-operate with the senses or the matter before us, or shall it wander away?
What the geometrical student requires and what we all require in such cases is to _compel the Intellect to stay with the Senses, and follow the printed train of thought_.
Interest in the subject helps to secure this co-operation. And the _Process or Method of study_, if it be an Assimilating one, also compels this co-operation. And one of the processes which is most of all effective in TRAINING the Intellect to obey the Will and thereby to stay with the Senses (where it is not a case of pure reflection), and thereby to institute and develop the Habit of the activity of the Intellect co-operating with the action of the mere senses, is practice in the use of the Laws of In., Ex., and Con. To illustrate: In reciting the last training example of one hundred words, the Directory power is exercised and then the Inhibitory power is brought into play, and so on _alternately_. Suppose the reciter has got to "Signatures." If he does not inhibit or exclude from his mind the word "Petition" he can make no advance. If he dwells upon "Petition" he will never reach "Cygnet." But if he inhibits "Petition" his Directory power sends him on to "Cygnet," and then inhibiting "Signatures" he proceeds from "Cygnet" to "Net," &c., &c. In this most simple, elementary way he exercises and trains the Directory and Inhibitory functions to co-operate in recalling the entire Series, and notice how many distinct and separate times he has exerted the Directory function and how many times the Inhibitory function in reciting a short series. And if _he has learned_ this and other Series _as I direct_ and then _recites them forward and backward as long as I require_, he is sure to greatly strengthen his Attention and thereby habituate the intellect to stay with the senses and thereby help to banish mind-wandering. And when the Intellect is thus trained into the Habit of staying with the sense of sight or hearing in reading or listening, the geometrical or other student can keep his mind on the subject before him until it is mastered.