THE LAWS OF MOTION 317 



this atom were a vortex-ring aspect would be of import- 

 ance, but if it were an ether-squirt it would not. On the 

 other hand, in both cases, and probably in most other 

 conceivable mechanisms, aspect would play a great role in 

 the mutual actions between chemical atoms and between 

 molecules. These groups, built up of comparatively few 

 prime-atoms, can hardly accelerate each other's motion in 

 the same manner however they turn towards each other. 

 It is to this change of mutual acceleration with change of 

 aspect that we have probably to look for aid in our con- 

 ceptual attempts to describe such phenomena as crystal- 

 lisation and magnetisation. As to the particle, aspect has 

 probably little influence when we are dealing with particles 

 at distances great compared with their vanishingly small 

 size ; but it is still conceivable that if all the molecules in 

 a particle had a similar aspect, aspect might be important 

 in determining the action of this particle on an adjacent 

 particle. In the phenomenon of gravitation aspect does 

 not, however, play any part that we can perceptually 

 appreciate. On the whole we conclude that aspect must 

 be considered as a significant factor in determining the 

 absolute magnitudes of mutual accelerations, but the exact 

 influence which the " posture " of our dancers has upon 

 the mode in which they dance remains still one of the 

 obscure points of physics (see pp. 312, 326). 



^ 14. — TJie Hypothesis of Modified Action and the 

 Synthesis of Motion 



The next problem that we have to consider is one that 

 is of extreme importance when we are dealing with the 

 synthesis of motion, or the construction of the motion of 

 complex from simple groups of corpuscles (p. 236). It is 

 the problem of modified action. I may state it thus : — 



If we have found the acceleration of A in the presence of 



B, will the magnitude ^ of this acceleration be altered wJien 



1 We have already seen that the ratio of the mutual accelerations, or of the 

 masses of A and B, is not to be conceived as altered by the presence of other 

 corpuscles in the field ; but this leaves the question of absolute magnitudes 

 unsettled. 



