Or, again, the mind's energy may be likened to the energy of sunlight as it falls in a flood through the window upon our desk. This diffuse sunlight will brighten the desk top and slightly increase its temperature, but no striking effects are seen. But now take this same amount of sun energy and, passing it through a lens, focus it on a small spot on the desk top--and the wood bursts almost at once into flame. What _diffuse_ energy coming from the sun could never do, _concentrated_ energy easily and quickly accomplished. Attention is to the mind's energy what the lens is to the sun's energy. It gathers the mental power into a focus on the lesson to be learned or the truth to be mastered, and the concentrated energy of the mind readily accomplishes results that would be impossible with the mental energy scattered or not directed to the one thing under consideration. The teacher's first and most persistent problem in the recitation is, therefore, to gain and hold the highest possible degree of attention. Three types of appeal to attention.--We are told that there are three kinds of attention, though this is not strictly true. There is really only one _kind_ of attention, for attention is but the _concentration of the mind's energy on one object or thought_. What is meant is that there are three different _ways of securing_ or appealing to attention. Each type of attention is named in accordance with the kind of compulsion or appeal necessary to command it, as follows: 1. _Involuntary_ attention, or attention that is demanded of us by some sudden or startling stimulus, as the stroke of a bell, the whistle of a train, an aching tooth, the teacher rapping on the desk with a ruler. 2. _Nonvoluntary_, or spontaneous, attention that we give easily and naturally, with no effort of self-compulsion. This kind of attention is compelled by _interest_, and, when left unhindered, will be guided by the nature of our interest. 3. _Voluntary_ attention, or attention that is compelled by effort and power of will, and thereby required to concern itself with some particular object of thought when the mind's pull or desire is in another direction. How each type of attention works.--The first of these types of attention, the _involuntary_, has so little place in education that we shall not need to discuss it here. The teacher who raps the desk, or taps the bell to secure attention which should come from interest must remember that in such case the attention is given to the _stimulus_, that is, to the signal, and not to the lesson, and this very fact makes all such efforts to secure attention a distraction in themselves.