200 nutting: the ether 



venes. Electric and magnetic forces may be either positive or 

 negative, gravitational and chemical forces are negative only. 

 The signs of these forces can not be altered by ai^ intervening 

 medium. Electric forces are a maximum when no matter inter- 

 venes. Magnetic forces are intermediate in value while gravi- 

 tational force is the same whatever the intervening medium. The 

 speed of propagation of electric and magnetic forces across space 

 is a finite constant independent of the sign or magnitude of those 

 forces. The speed of propagation of gravitational forces is cer- 

 tainly greater than 10 14 cm/sec and probably infinite. In no case 

 is there any evidence of a force too small or too great to be propa- 

 gated; that is of any finite maximum or minimum load.- In other 

 words, there is no evidence that the ether, if the ether be respon- 

 sible, has any finite inertia or viscosity on the one hand or break- 

 ing strength on the other, certainly not in any mechanical sense. 



(b) The absence of matter is no bar to induction. An electric 

 charge induces an electric charge as readily across a vacuum as 

 through matter, and similarly with magnetic and electromagnetic 

 induction. Induction is always of the same sign, unlimited in 

 magnitude and propagated with the speed of light. 



(c) Electromagnetic radiation is propagated across a vacuum 

 as freely as through matter. Beams of light and electric waves, 

 whatever their nature, travel independently of each other, i.e., 

 no matter how filled with radiation of one kind and direction a 

 certain space is, neither the wave length, velocity, direction, damp- 

 ing or polarization of any other beam traversing the same space 

 at the same time is in any way affected. Neither electric nor 

 gravitational strain of any amount produces birefraction in a space 

 devoid of matter nor does a magnetic field affect the plane of 

 polarization unless matter be present. That these effects do exist 

 in matter indicates an actual mechanical strain. Of the two 

 astronomical methods for determining the velocity of light, the 

 satellite method gives the group velocity, while the aberration 

 constant gives the waoe velocity; the close agreement between 

 the values obtained indicates that wave and group velocity is 

 the same, hence that there is no dispersion in space, waves of 

 all frequencies travel with the same velocity. 



