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showed men the bonds that hold our world in its 

 place and course. 



6th. The existence of the ethereal medium was 

 postulated by Newton as essential to the theory of 

 light and to the existence of gravitation. The 

 theory of an interplanetary Ether has been held 

 since more than 500 years B. c. The doctrine then 

 rested on a-priori reasoning only ; since Newton's 

 time the study of the conditions of light, heat and 

 electricity has necessitated the assumption that such 

 a medium fills interstellar space and the interstices of 

 matter. From the very nature of its supposed pro- 

 perties it must be impossible to show its physical pre- 

 sence; but the coincidence between the observed phe- 

 nomena in the transmission of the three forms of 

 energy above named, and the properties that such a 

 medium would necessarily possess, are so many and so 

 varied that the non-existence of the Ether seems 

 impossible. 



The nature of the cause of gravitation, though 

 most probably dependent also upon the Ether, or being 

 one of its forms of motion, is still an undetermined 

 problem. It is probable that the Ether possesses the 

 characteristics of a gas, as known under the Kinetic 

 theory, excepting that its atomic motion is inherent 

 in itself, and that its vibratory molar or isotropic 



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