932 CUTANEOUS SENSATIONS. 



11 go to overcoming resistances, and an ever smaller part to the production of the 

 feeling-bringing state " (James). When the pans of a balance are already loaded, 

 but in equilibrium, it takes a larger weight added to one of them to incline the 

 beam. As James says, Weber's law may be a sort of law of friction in the 

 neural machine. The molecules of the sensorial and neural cells are complexes of 

 atoms and atom-groups, spinning, oscillating, and colliding. They can be thought 

 of as embracing hundreds rather than tens of atoms, each possessing its motion. 

 The more violent the oscillations of an atom-group, or the further the group's 

 centre of oscillation from the systemic centre of the molecule, the greater risk 

 of its detachment altogether from the system. Each atom or atom-group, with 

 its kinetic and potential energy, when either of these energies, or both together, 

 exceed a certain amount, must leave the region of molecular affinities, and the 

 molecule be in so far decomposed. Constancy of composition exhibited by a 

 substance, and the uniformity with which it reacts in our testings, is no sign of 

 a dead sameness and calm within it, but merely means that the energy of its 

 molecular life is distributed so as to present a constant average. Among the 

 million molecules of living matter subjected to test en masse by even our most 

 delicate physiological experiments, there will at any given time be a certain 

 number in the act of decomposing, and a certain number more on the verge of 

 doing so. There will also be a certain number in the act of creation. The 

 majority of the molecules will be in that average phase of the molecular 

 existence in which the atomic movements most perfectly harmonise, somewhere 

 about the mean between the extreme phases of the molecular condition of 

 the particular substance in question. In addition to the molecules in this 

 mean phase exhibited by the majority, there will be numbers in condition 

 approximate to that critical for decomposition, and numbers the condition of 

 which is more than usually stable. If a formula analogous to Maxwell's for 

 the conditions of a gas is with modification, as urged by Ebbinghaus, 

 applied to the conditions of the molecules of protoplasm, the numbers 

 of molecules in degrees of more than average instability and of more than 

 average stability, arrange themselves about the majority possessed of the 

 particular stability which is average for the chemical substance in question, 

 approximately symmetrically. When the adequate stimulus impinges on such 

 a substance, one may suppose the energy of movement of all the particles 

 accessible to it to be increased. But the external result and the result upon the 

 chemical constitution of the substance must be different in the different 

 molecules. Those molecules already at verge of decomposition are doubtless 

 easily and at once -broken up, and likely enough also a number less near the 

 critical condition ; a number of which the stability is mean for the substance 

 may also be decomposed, and if not decomposed brought nearer toward easy 

 decomposition. If the stimulus is weak, the number of molecules sufficiently 

 liable to be decomposed by it is relatively small. When the stimulus is 

 sufficient to induce decomposition of the molecules of mean stability, they being 

 the most numerous, the condition as regards strength of stimulus will be 

 peculiarly favourable for producing a high ratio of released force to releasing 

 force. Since a great number of the molecules approximate to the mean mole- 

 cular condition of the substance, relatively small gradations in intensity of 

 moderate stimuli will cause relatively large differences of effect. As the 

 stimulus is progressively increased in strength, the further number of molecules 

 involved in decomposition becomes progressively less. Finally, even the last 

 and most stable that can be decomposed by the stimulus are reached. The 

 "maximal" stimulus is thus arrived at, beyond which further increase of 

 stimulus fails to cause further increase of effect. The reactions at base of 

 Weber's law can probably be pictured somewhat on the lines of such an hypo- 

 thesis as the above, but the total reaction must be the sum of an as yet unknown 

 number of such simpler ones. 



It must never be forgotten that Weber's law deals with judgments. 



