Such part of it as does not work mental changes works bodily changes -- contractionsof the involuntary muscles, the voluntary muscles, or both; as also somestimulation of secreting organs. That the movements thus initiated are everbeing brought to a close by the opposing forces they evoke, we have justseen; and here it is to be observed that the like holds with the cerebralchanges thus initiated. The arousing of a thought or feeling, involves theovercoming of a certain resistance: instance the fact that where the associationof mental states has not been frequent, a sensible effort is needed to callup the one after the other; instance the fact that during nervous prostrationthere is a comparative inability to think -- the ideas will not follow oneanother with the ordinary rapidity; instance the converse fact that at timesof unusual energy, natural or artificial, thinking is easy, and more numerous,more remote, or more difficult connexions of ideas are formed. That is tosay, the wave of nervous energy each instant generated, propagates itselfthroughout body and brain, along those channels which the passing conditionsrender lines of least resistance; and spreading widely in proportion to itsamount, ends only when it is equilibrated by the resistances it everywheremeets. If we contemplate mental actions as extending over hours and days,we discover equilibrations analogous to those hourly and daily establishedamong the bodily functions. This is seen in the daily alternation of mentalactivity and mental rest -- the forces expended during the one being compensatedby the forces acquired during the other. It is also seen in the recurringrise and fall of each desire. Each desire reaching a certain intensity, isequilibrated either by expenditure of the energy it embodies in the desiredactions, or, less completely, in the imagination of such actions: the processending in that satiety or that comparative quiescence, forming the oppositelimit of the rhythm. And it is further manifest under a two-fold form onoccasions of intense joy or grief. Each paroxysm, expressing itself in violentactions and loud sounds, presently reaches an extreme whence the counteractingforces produce return to a condition of moderate excitement; and the successiveparoxysms, finally diminishing in intensity, end in a mental equilibriumeither like that before existing, or having a partially different mediumstate. But the kind of mental equilibration to be especially noted, is thatshown in the establishment of a correspondence between relations among ourideas and relations in the external world. Each outer connexion of phenomenawhich we are capable of perceiving, generates, through accumulated experiences,an inner connexion of mental states; and the result towards which this processtends, is the formation of a mental connexion having a relative strengththat answers to the relative constancy of the physical connexion represented.
In conformity with the general law that motion pursues the line of leastresistance, and that, other things equal, a line once taken by motion ismade a line which will be more readily taken by future motion, we have seenthat the ease with which nervous impressions follow one another is, otherthings equal, great in proportion to the number of times they have been repeatedtogether in experience. Hence, corresponding to such an invariable relationas that between the resistance of an object and some extension possessedby it, there arises an indissoluble connexion in consciousness; and thisconnexion, being as absolute internally as the answering one is externally,undergoes no further change -- the inner relation is in perfect equilibriumwith the outer relation. Conversely, it happens that, answering to such uncertainrelations of phenomena as that between clouds and rain, there arise relationsof ideas of like uncertainty; and if, under given aspects of the sky, thetendencies to infer fair or foul weather, corresponds to the frequencieswith which fair or foul weather follows such aspects, the accumulation ofexperiences has balanced the mental sequences and the physical sequences.
When it is remembered that between these extremes there are countless ordersof external associations having different degrees of constancy, and thatduring the evolution of intelligence there arise answering eternal associationshaving different degrees of cohesion; it will be seen that there is a progresstowards equilibrium between the relations of thought and the relations ofthings. The like general truths are exhibited in the process of moral adaptation,which is a continual approach to equilibrium between the emotions and thekinds of conduct required by surrounding conditions. Just as repeating theassociation of two ideas facilitates the excitement of the one by the other,so does each discharge of feeling into action render the subsequent dischargeof such feeling into such action more easy. Thus it happens that if an individualis placed permanently in conditions which demand more action of a specialkind than has before been requisite, or than is natural to him -- if by everymore frequent or more lengthened performance of it under such pressure, theresistance is somewhat diminished; then, dearly, there is an advance towardsa balance between the demand for this kind of action and the supply of it.
