306 Mr. S. T. Preston on the Kinetic Theory of Gravitation. 



application of this theory to molecules in close contact (" co- 

 hesion " &c), is necessary and inevitable, and it serves to cor- 

 relate the molecular effects generally under one cause. The 

 explanation of the fundamental condition capable of producing 

 the recession of molecules, as above given, rests upon experi- 

 mental facts recently established, and upon a basis for the 

 constitution of the aether which is the simplest conceivable. 



12. We now propose to show some independent reasons in 

 support of this constitution for the aether, in addition to the 

 argument afforded by the numerous molecular effects which 

 this constitution, in principle, serves to explain. First, if 

 the subject be reflected on, it will be apparent that, in principle, 

 a movement of the component particles of the medium in 

 straight lines is the only possible constitution for the ultimate 

 medium in space. For a particle of matter cannot move in a 

 curved line unless it have a medium about it to control its 

 motion. Thus a planet can move in a curve because it has a 

 medium about it (the gravific medium) to cause it to move in 

 a curve. It is a known principle that a particle of matter can- 

 not of itself change the direction of its motion. The particles 

 of the ultimate medium in space must therefore move in straight 

 lines. This deduction is surely of great importance in the 

 inquiry as to the constitution of the physical media in space. 

 Also in addition to this, the observed facts of gravity prove 

 that the particles of the gravific medium move in straight 

 lines, since no other motion than this can harmonize with the 

 observed effects of gravity. It would therefore surely be a 

 strange thing if the particles of the aether, as a second medium 

 immersed in the gravific medium, did not move in straight 

 lines. To suppose this would be very like supposing that 

 when the particles of a second gas are immersed among those 

 of another, the particles of the first gas acted upon those of 

 the second to make them move otherwise than in straight 

 lines, which is known to be impossible. Moreover the fact 

 of the kinetic theory representing the simplest conceivable 

 constitution for a medium would by itself be a strong argu- 

 ment for this constitution in the case of the aether. The very 

 fact of the great precision and delicacy of the operations per- 

 formed by the aether as the mechanism for the transmission of 

 the varied phenomena of colour &c. would point to a simple 

 constitution ; just as the complex effects of sound with all its 

 intricate and varied gradations of tone are known to be trans- 

 mitted by a medium (the air) of the simplest conceivable con- 

 stitution, viz. that represented by the beautiful kinetic theory 

 of gases*. The more intricate the functions of a mechanism, 



* There would surely "be nothing to admire in complication in itself. 

 The whole aim of mechanical design is directed towards the attainment 

 of simplicity, which being unique, entails intellectual labour to find it. 



