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47S W. R. BOYCE GIBSON : attentive mental process, I mean not on!}' an activity which in virtue of the continuity of interest shown succeeds in bringing into relation all the successive discriminations made during the process, but an activity which operates in such a way that its later discriminations could not be made unless the earlier ones had been previously made. This is a first cumulative factor in the process of mental growth. Each new acquisition of meaning becomes incorporated into the interpreting context of acquired experience by the help of which new acquisitions of meaning can alone be made. Meaning once acquired is instrumental in acquiring new meaning. A second cumulative factor is associated with the fact that the more attentively an interest is fed, as above described, the more effective does it become in diverting all fresh know- ledge to itself. Attention, as we say, becomes expectant on its behalf, sensitive, that is, to the presence of anything that in any way concerns it. In a word, there is a cumulative effect due not only to an increase in the number of feelers engaged in apprehending the new material, but due also to an increase in the sensitiveness of these feelers. The cumulative activity of consciousness is most effective when it works continuously within one and the same sphere of interest, the greater, that is, the vital unity of Consciousness. For in readopting a temporarily forsaken interest our first duty is always of a purely restorative character : an interest withers through neglect and in order to revive it to its former efficacy we have first to reassimilate a mass of half- forgotten material. Moreover, if this work of reassimilation is done too rapidly, the subtle associations of thought and fancy that gave the interest much of its previous force will not be won back. Where there is dissipation of interests there is always a dissipation of the results of previous activity going on in all the spheres of interest except one. This presupposes that the interests are alien to each other. In so far as they are co-operative they come within one and the same enlarged sphere of interest. The question before us now is whether the activity characteristic of the vital Unity of Consciousness can be said to involve a principle of Least Action. A principle of Least Action as expressive of psychical facts must mean, in the main, one of three things : l 1 It will be noticed that I make no attempt to deal with the Principle of Least Resistance, except by implication, though such a well-worn notion no doubt requires and would no doubt repay a direct attempt to elucidate it.