131. Where many diverse means are to coöperate for the attainment of one end, where many obstacles have to be overcome, where persons of higher, equal, and lower rank enter as factors requiring consideration, it is always a difficult matter to keep the end itself, the one fixed goal, steadily in view. In instruction the difficulty is increased by the fact that no one single teacher can impart the whole, and that consequently a number of teachers are obliged to depend on one another. But for this very reason, however much circumstances may vary the courses of study, the common end, namely, many-sided, well-balanced, well-connected interest, in the achievement of which the true development of mental powers consists, needs to be lifted into prominence as the one thing toward which all details of procedure should point. 132. No more time, we need to realize at the outset, should be demanded for instruction than is consistent with the proviso that the pupils retain their natural buoyancy of spirits. This must be insisted on, and not merely for the sake of health and physical vigor; a more direct argument for our present purpose lies in the fact that all art and labor employed to keep the attention awake will be thwarted by the disinclination to study caused by sitting too long, and even by excessive mental application alone. Forced attention does not suffice for instruction, even though it may be had through disciplinary measures. It is urgently necessary that every school have not only spacious schoolrooms, but also a playground; it is further necessary that each recitation be followed by an intermission, that after the first two periods permission be granted for exercise in the open air, and that the same permission be given after the third period if there is a fourth to follow. Still more urgent is the demand that pupils shall not be deprived of their hours of needed recreation by an excessive amount of school work to be done at home. The teacher who loads pupils down with home tasks in order to dispense as much as possible with perhaps uncertain home supervision, substitutes a certain and general evil for a possible and partial one. The neglect of such precautions has given rise in recent times to very bitter complaints, which will continue to be heard in future for similar reasons. Violent gymnastic exercise is not the means to put a stop to them. They threaten to lead to another extreme--such restrictions upon instruction as will make an inner unity of work impossible.