especially true when the ideas presented are complex. A certain time is necessary for the attention to seize adequately the object or idea. When the relation is once established between the attending mind and the object, another should be immediately presented in order to prevent wandering to something irrelevant; but sometimes an exceedingly rapid speaker will present his ideas in such quick succession that the average hearer will be unable adequately to seize them, or "take them in." The result is a confused impression. Of course, the time required varies with the constitution of different minds—some normally acting more slowly than others; varies also according to age—the adult usually taking less time than the child, if the idea is at all complex; varies, too, according to the degree of culture or mental discipline—the trained mind acting more quickly than the untrained; varies further according to mental freshness fatigue lengthening the time necessary. But notwithstanding the many varying factors present in any situation, it is a safe rule that phenomenally slow as well as phenomenally rapid presentation should be avoided.
VI. Its intensity or degree. The concentration of consciousness varies in intensity, and tends to vary according to regular rhythms. Attention fluctuates, is wave-like. It is difficult to determine even approximately the normal length of these waves. Experimental psychologists have not been able to make much progress in reducing this aspect of attention to definite formulation. It is settled, however, that in visual impressions which are just strong enough to be perceived there is a fluctuation of a few seconds in length, which very closely corresponds to a certain rhythm of the breathing and the pulse-beat, known as the Traube-Hering wave. Experience teaches also that there are longer waves. They might be called minute waves and hour waves, were it not that the use of these terms would convey the impression that these periods of concentration and relaxation of consciousness bear some exact relation to these measures of time, which they do not. In fact, so many factors of
