OMil the Molecular Energy of Matter. 89 



and though it became attenuated the further it spread, yet 

 it would as truly conform to the law of the conservation of 

 energy as light does when not intercepted, but allowed to 

 radiate into space. Thus^ though our ton of iron loses half 

 its weight, the loss could be easily accounted for without 

 supposing the annihilation of anything. 



Again^ it is known that all space is filled by a medium 

 which is capable of conveying molecular vibrations ; that it 

 conveys the motions of heat and light is certain; that it 

 likewise conveys the motions which constitute magnetism 

 and electricity was the belief of Faraday, and is now held by 

 Thomson, Tait, Maxwell, and others who have written on 

 the subject. 



Now Newton demands a medium for the conveyance of 

 the effects of gravitation. In his letter to Bentley, he says — 

 ■' That one body may act upon another at a distance, through 

 a vacuum, without the medium of anything else by and 

 through which their action and force may be conveyed from 

 one to another, is to me so great an absurdity, that I believe 

 no man who has in philosophical matters a competent 

 faculty of thinking can fall into it." 



This assertion has been severely criticised. Still the rea- 

 soning on which Newton bases it is sound, and it is now 

 generally held to be justifiable. 



Now since the ether which is known to fill space has the 

 power of conveying molecular vibrations, this fact tallies 

 very well with the supposition that gravitation is itself due 

 to waves of molecular vibration. 



Our supposed origin of gravitation satisfies sufiiciently 

 well the necessary condition of supplying an explanation of 

 the known laws to which gravitation is subject. 



First, the attraction which a body exerts is proportional 

 to the amount of matter it contains. This is consistent with 

 our supposition. For it has of late years been conclusively 

 shown that matter is simply a name for a collection of such 

 energies as are capable of making an impression on the 

 senses. Thus the qualities of a body are dependent on the 

 amount it contains of the various'forms of molecular energy ; 

 and its mass must depend upon the amount it possesses of 

 some constant form of energy. Hence if we suppose that 

 gravitation is proportional to this form of energy, it neces- 

 sarily follows that gravitation is proportional to the amount 

 of matter in the body. 



