The modes of consciousness called pressure, motion, sound, light, heat,are effects produced in us by agencies which as otherwise expended, crushor fracture pieces of matter, generate vibrations in surrounding objects,cause chemical combinations, and reduce substances from a solid to a liquidform. Hence if we regard the changes of relative position, of aggregation,or of chemical union, thus arising, as being transformed manifestations ofcertain energies; so, too, must we regard the sensations which such energiesproduce in us. Any hesitation to admit this must disappear on rememberingthat the last correlations, like the first, are not qualitative only butquantitative. Masses of matter which, by scales or dynamometer, are shownto differ greatly in weight, differ as greatly in the feelings of pressurethey produce on our bodies. In arresting moving objects, the strains we areconscious of are proportionate to the momenta of such objects as otherwisemeasured. The impressions of sounds given to us by vibrating strings, bells,or columns of air, are found to vary in strength with the amount of forceapplied. Fluids or solids proved to be markedly contrasted in temperatureby the different degrees of expansion they produce in the mercurial column,produce in us correspondingly different degrees of the sensation of heat.
And unlike intensities in our impressions of light, answer to unlike effectsas measured by photometers.
Besides the correlation and equivalence between external physical forcesand the mental forces generated by them under the form of sensations, thereappears to be a correlation and equivalence between sensations and thosephysical forces which, in the shape of bodily actions, result from them.
In addition to the excitements of secreting organs, sometimes traceable,there arise contractions of the involuntary muscles. Sensations increasethe action of the heart, and recent experiments imply that the muscular fibresof the arteries are at the same time contracted. The respiratory muscles,too are stimulated. The rate of breathing is visibly and audibly augmentedboth by pleasurable and painful excitements of the nerves, if these reachany intensity. When the quantity of sensation is great, it generates contractionsof the voluntary muscles, as well as of the involuntary ones. Violent painscause violent struggles. The start that follows a loud sound, the wry faceproduced by an extremely disagreeable taste, the jerk with which the handor foot is snatched out of very hot water exemplify the genesis of motionsby feelings; and in these cases it is manifest that the quantity of bodily. action is proportionate to the quantity of sensation. even where pride causessuppression of the screams and groans expressive of great pain (also indirectresults of muscular contraction), we may still see in the clenching of thehands, the knitting of the brows, and the setting of the teeth, that thebodily actions excited are as great, though less obtrusive in their results.
If we take emotions instead of sensations, we find the correlation and equivalencesimilarly suggested. emotions of moderate intensity, like sensations of moderateintensity, generate little beyond excitement of the heart and vascular system,joined sometimes with increased action of glandular organs. But as the emotionsrise in strength, the muscles of the face, body, and limbs, begin to move.
