THE LAWS OF MOTION 293 



a phase of mechanism for the ether which is only true for 

 gross " matter," and which may indeed flow from the 

 particular type of ether -motion which constitutes gross 

 " matter." If the prime-atom be a vortex-ring it would 

 be impossible to describe in general the action between 

 two prime-atoms as a " mutual acceleration in the line 

 joining them," On the other hand, if the prime-atom be 

 an ether-squirt, this phrase would effectively describe the 

 action between two prime -atoms. In both cases the 

 statement that particles mutually accelerate each other's 

 motion in the line joining them would flow either as an 

 absolute or an approximate law from the particular struc- 

 ture of gross " matter," and would not be a mechanical 

 truth for all corpuscles from ether - element up to 

 particle. 



There are still several points to be noticed with regard 

 to the nature of the manner in which corpuscles spurt 

 and shunt each other's motion. We have said that this 

 depends on the relative position of the corpuscles — but is 

 the mutual acceleration never influenced by the velocities 

 of the corpuscles ? Do two of our conceptual dancers 

 influence each other solely by their relative position and 

 never by the speed and direction with which they pass 

 through that position ? It has been supposed that the 

 introduction of the relative velocity as a factor determin- 

 ing the mutual acceleration of two particles would be 

 contrary to a well-established physical principle termed 

 the conservation of energy. It is indeed a fact that 

 many writers, from Helmholtz downwards, have given a 

 mathematical proof of the conservation of energy which 

 depends on mutual acceleration being a function of rela- 

 tive position and not of relative velocity. But if two 

 moving bodies be placed in a fluid they will apparently 

 accelerate each other with accelerations depending upon 

 their velocities as well as on their relative position. The 

 conservation of energy still holds in this case for the 

 entire system of fluid and moving bodies, and yet to the 

 observer unconscious of the fluid the mutual accelerations 

 of the bodies would certainly appear to be determined by 



