_Attention is the Will directing the Intellect into some particular channel and keeping it there._ There are virtually two processes involved in Attention. The Intellect is directed into a particular channel, but to keep it there, all intruders must be excluded. To illustrate. A student attempts to learn a proposition in Geometry. To do this he must keep his mind on the printed explanations, and if his thoughts attempt to fly away, he must repress that attempt. To guide his mind into the channel of the printed exposition, he calls into play the Directory power of the attention. To prevent intruders or extruders from withdrawing his mind from the text, he exercises the Inhibitory function of the Attention. 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_.