230 THE POPULAR SCIENCE MONTHLY. 



themselves from the prejudice that nothing can be real which is not 

 absolute. 



Prof. Neumann is not content with showing, or attempting to show, 

 that the reality of motion necessitates its reference to a rigid body 

 unchangeable in its position in space, but he seeks to verify this as- 

 sumption by asking himself the question what consequences would 

 ensue, on the hypothesis of the mere relativity of motion, if all bodies 

 in s£ace, except one, were annihilated. " Let us suppose," he says 

 (he. cit., p. 27), " that among the stars there is one which consists of 

 fluid matter, and which, like our earth, is in rotary motion around an 

 axis passing through its centre. In consequence of this motion, by 

 virtue of the centrifugal forces developed by it, this star will have 

 the form of an ellipsoid. What form, now, I ask, will this star assume 

 if suddenly all other celestial bodies are annihilated ? 



" These centrifugal forces depend solely upon the state of the star 

 itself ; they are wholly independent of the other celestial bodies. 

 These forces, therefore, as well as the ellipsoidal form, will persist, ir- 

 respective of the continued existence or disappearance of the other 

 bodies. But, if motion is defined as something relative — as a relative 

 change of place of two points — the answer is very different. If, on 

 this assumption, we suppose all other celestial bodies to be annihilated, 

 nothing remains but the material points of which the star in question 

 itself consists. But, then, these points do not change their relative 

 positions, and are therefore at rest. It follows that the star must be 

 at rest at the moment when the annihilation of the other bodies takes 

 place, and therefore must assume the spherical form taken by all bodies 

 in a state of rest. A contradiction so intolerable can be avoided only 

 by abandoning the assumption of the relativity of motion, and con- 

 ceiving motion as absolute, so that thus we are again led to the prin- 

 ciple of the body Alpha." 



This reasoning of Prof. Neumann is irrefutable, if we concede the 

 admissibility of his hypothesis of the destruction of all bodies in space 

 but one. But the very principle of relativity forbids such an hypoth- 

 esis. The annihilation of all bodies but one would not only destroy 

 the motion of this one remaining body and bring it to rest, as Prof. 

 Neumann sees, but it would also destroy its very existence and bring 

 it to naught, as he does not see. A body cannot survive the system 

 of relations in which alone it has its being ; its presence or position in 

 space is no more possible without reference to other bodies than its 

 change of position or presence is possible without such reference ; and, 

 as I have abundantly shown, all properties of a body are in their na- 

 ture relations, and imply terms beyond the body itself. The case 

 put by Prof. Neumann is thus an attestation of the truth that the es- 

 sential relativity of all physical reality implies the persistence both 

 of force and of matter, so that his argument is a demonstration, not 

 of the falsity, but of the truth of the principle of relativity. 



