ESSAYS 309 



tracks must be more or less subject to voluntary control. Apparently the 

 resistance along any one or two tracks can be temporarily reduced, but, 

 since we are unable to attend to many things at once, it would seem that the 

 resistance of all other tracks must, for the time, be automatically increased. 



Everyone is aware that sensuous impressions usually continue to be 

 received even while the attention is engrossed with other idea^ ; an experi- 

 ence which might be expected if the reactions of the thalamus are not com- 

 pletely controlled by those of the cortex. Their independence would also be 

 a reason for sensations, however faint, being felt to differ in kind from 

 the most vivid recollections ; the thalamus co-operating with the cortex 

 only in direct sensation. 



It has already been shown that reactions may be almost as intimately 

 blended when the stimuli follow one another closely, as when they are simul- 

 taneous. In consequence of this blending of consecutive reactions, changes 

 are not felt as isolated events, but are presented in consciousness as stages 

 in continuous processes ; the change from one observed state to the next 

 being supposed to pass through every intervening state. Thus, if a body 

 be observed first in one position and immediately afterwards in another, it 

 is supposed to have occupied successively all the intermediate positions. 



The idea of continuity can be extended by means of appropriate hypo- 

 theses, and thus applied to sequences of change in which the stimuli are not 

 all closely consecutive ; it is then very helpful in the making of forecasts. 

 The method of extension is to suppose that the discontinuously observed 

 sequence exhibits stages in a series which, if its whole course were traced, 

 would be found to follow the same lines as some continuous process already 

 familiar. Astronomy gives the classic example of this method, the inter- 

 mittent observations of the motions of the heavenly bodies having been 

 paralleled with the more continuously observed motions of terrestrial bodies, 

 and successful forecasts having been framed upon the hypothesis of their 

 similarity. The whole system of science depends on applications of the 

 same method ; each newly observed sequence being hypothetically paral- 

 leled with some series already regarded as a known process, and the hypo- 

 thesis being verified by means of forecasts. 



In the present theory, comparison is made with more than one known 

 process. The distribution of the discharges of energy is likened to that of 

 discharges of electricity through a system of conductors, where the current 

 is inversely proportional to the resistance of the path. The discharges 

 themselves are supposed to be comparable with those in a pyrotechnic set- 

 piece, where communication is made between the different parts by tubes 

 filled with gunpowder, and the firework is activated by the successive 

 liberation of potential energy at one point after another in a tube. The 

 parallel, however, is not exact, since the single discharge of the firework 

 brings the whole of the gunpowder to a condition of chemical stability, 

 without further power of action ; whereas a disturbance of nervous equili- 

 brium, while reducing part of the material along its track to a stable 

 condition, yet renders the equilibrium of the remaining material even less 

 resistant to disturbance than before, and thus facilitates the passage of 

 subsequent discharges of energy. Nevertheless the reserve store of energy 

 is not unlimited ; it may be exhausted by a number of rapidly repeated 

 discharges, and the particular track of these discharges, being thus tired 

 out, needs time for recuperation before its activity can be renewed. 



The foregoing theory leaves no impassable gap between thought and 

 sensation, between mind and matter ; while, by reason of its analogies with 

 known physical processes, the hypotheses involved can be subjected to the 

 usual tests of scientific verification. In both these respects it contrasts 

 favourably with theories constructed on traditional lines. 



