5 36 THE GRAMMAR OF SCIENCE 



NOTE II 



On Newton's Third Law of Motio7i (pp. 292, 304, 311, and 325) 



We have seen on p. 303 that one fundamental part of Newton's third 

 law is involved in mutual accelerations being inversely as masses. 

 This leads at once to the equality in niagjiiiiide of action and reaction. 

 In the next place we conceive mutual accelerations to be parallel and 

 opposite in sense (p. 291). This does not, however, give us com- 

 pletely Newton's third law as it is usually interpreted, unless we 

 suppose these mutual accelerations to be in the same straight line as 

 well as parallel. In the case of particles this straight line is usually 

 taken to be the straight line joining them. 



Now it is not at all improbable that the mutual accelerations (and 

 therefore the mutual forces) which are ascribed to corpuscles will be 

 ultimately found to be better described by aid of the disregarded 

 kinetic energy of an intervening ether. For e.xample, oscillating and 

 pulsating bodies in a perfect fluid ether have mutual accelerations, 

 which may be described by action at a distance, but are really due to 

 the kinetic energy of the intervening ether. In the case of two small 

 bodies moving with velocities of translation or oscillating in such an 

 ether it by no means follows that the mutual accelerations (or the 

 apparent action and reaction) will necessarily lie in the same straight 

 line, and if they do, that this straight line will be the line joining the 

 small bodies. Further, on the supposition that apparent action at a 

 distance is due to the direct action of the ether, it does not seem 

 likely that, if a corpuscle P be suddenly moved, the result of this 

 motion will be immediately felt by a distant corpuscle Q, time would 

 be required to make the change in the position of P felt at Q. The 

 mutual actions might in this case be parallel, but it is hardly prob- 

 able that they would always be in the same straight line, that is 

 opposite in Newton's sense. 



Thus these considerations, taken in conjunction with those 

 referred to on p. 311 ct scq., suggest that greater caution is necessary 

 than is sometimes observed in extending Newton's third law to 

 molecules or atoms, which may really have considerable oscillatory 

 or translatory velocities relative to the ether. For the comparatively 

 small velocities of particles of gross "matter," the law is probably a 

 sufficient description of our perceptual experience. 



NOTE III 



William of Occam's Razor {^'^. 92 and 512) 



In the course of our work we have frequently had occasion to notice 

 the unscientific process of multiplying existences beyond what are 

 really needful to describe phenomena. The canon of inference which 

 forbids this is one of the most important in the who'e field of logical 



