Structure of the Universe 399 



each ball strikes the front end it communicates a certain amount of 

 positive momentum to the mass as a whole, which travels through 

 the mass in a positive direction, and an equal amount of momentum 

 travels through the macs in an opposite, or negative direction, which 

 results in the motion in the opposite direction of the mass as a 

 whole. The real motion of the mass is in the opposite direction to 

 that of the impinging balls. If the balls moved quick enough the 

 eye would lead us to suppose that the motion of the lower row of 

 balls was continuous, and not done by successive impacts, just as in 

 moving pictures which appear to represent a continuous scene, but 

 which we know is made up of a multitude of separate scenes taken in 

 rapid succession. We may take the gap between the two rows of 

 balls to represent the inequality which is to propagate through the 

 medium, for instance the earth moving through space. There is an 

 incoming of grains in front and a leaving of grains in the rear, the 

 momentum of the incoming grains being transmitted instantaneously 

 throughout the whole mass from front to rear, the real mass of the 

 medium moving in the opposite direction to that of the inequality. 

 Reynolds says: "If the medium is stationary and the molecules are 

 moving with the earth the grains within the surfaces do not partake 

 of the mean motion of these surfaces, being replaced continuously by 

 other grains by the action of propagation, by which the singular sur- 

 faces in their motion are continually absorbing the grains in front 

 and leaving those behind without any mean effect on the motion of the 

 grains. And thus there is perfect freedom of the molecules or aggre- 

 gate matter, although the grains which constitute the nuclei are chang- 

 ing at the rate of 20 miles a second. To be standing on a floor that 

 is running away at a rate of 20 miles a second without being con- 

 scious of any motion is our continual experience, but to realize that 

 such is the case is certainly a tax on the imagination. Such motion 

 has all the character of a wave in the medium, and that is what the 

 singular surfaces which we call matter are — waves. We are all 

 waves." 



Cause of Gravitation. 



We now come to what is really the most important part of our 

 subject, namely, the cause of gravitation, and if you have been able 

 to comprehend what has already been stated, I think you will have no 

 trouble in understanding what is now to ba explained, that is, why 

 two bodies or masses of matter in space may approach each other 

 according to the Newtonian law of gravitation. 



In the first place we must rid our minds of the idea that there 

 is any such thing as "attraction" inherent in masses of matter them- 

 selves. Though in popular language we speak about the sun attract- 

 ing the earth, the earth attracting the moon, etc., in reality they do 

 not attract each other. All motions are really produced by pressure 

 of some kind or other exerted upon the bodies which move. Air cur- 

 rents, ocean currents, the tides, as well as movements of rigid bodies 

 are produced by pressure exerted in some way, and the gravitation or 

 motion of bodies in universal space is no exception to this. Reynolds 

 shows that wherever these "negative inequalities" or "singular sur- 

 faces of misfit" which we have seen to be matter, exist, there we have 



