one cortical area to another; meeting, they re-enforce or destroy one another; impinging upon a cell system which was in comparative quiet, they rouse it to activity, and are themselves modified by the pulses which it gives forth. At every second this mass of activities is receiving from the myriads of nerves that reach out to the eye, ear, skin, and other sensitive portions of the body countless other pulses of the same character, but initiated by the physical stimuli of the external world or by the chemical changes of the body. These pulses are not accompanied by consciousness, but when they reach the cortex they merge into the complex mass there existing and contribute their share toward the character of the total conscious state. And in the last place, the activities disengaged within the cortex are ever discharging downward through the outgoing channels into the co-ordinating mechanism at the base of the brain. This controls the systems of muscular contractions needed for the performance of our bodily movements much as the "combination stops" of an organ control the systems of pipes needed to produce any given timbre effect.
Thus the consciousness that you and I at any moment experience depends for its character upon the constitution of a system of activities as definite and determinate as any known to the physicist, although so complex that we can never hope to unravel it. To compare the complex with the simple, we have all seen the play of color upon the surface of a soap bubble. These colors depend for their character upon the constitution of a system of forces far more simple than that which underlies the human consciousness. They are due to the interference of waves of ether reflected from the inner and outer surfaces of the film; they depend, therefore, upon the angle of incidence and the thickness of the film. These two conditions again depend upon the tenacity of the film, the difference between the pressure within and that without the bubble, the action of air currents, the muscular tremor of the hand that holds the pipe, the action of gravity, etc. If any one of these conditions be in any way altered, some change will be made in the tint. This throws light upon one of the reasons why psychology lags so far behind the other sciences. Suppose the physicist should select that one square inch on the surface of the bubble where the colors were brightest, and should endeavor to formulate for each, in terms of the others, the laws of existence and sequence, ignoring the while the system of forces upon which those colors depend: however painstaking his efforts, they would meet with little success, and this has been the fate of the psychologist. Too often he has confined his attention to that portion of consciousness which was brightest, or for some other reason the most interesting, while if he had but looked into the marginal or
