360 On the Mechanical Energy of the Universe. 



based on experimental data, and to represent truly the present 

 condition of the universe, so far as we know it. 



]\Iy object now is to point out how it is conceivable that, at 

 some indefinitely distant period, an opposite condition of the 

 world may take place, in which the energy which is now being 

 diflfused may be reconcentrated into foci, and stores of chemical 

 power again produced from the inert compounds which are now 

 being coutinvially formed. 



There must exist between the atmospheres of the heavenly 

 bodies a material medium capable of transmitting light and heat ; 

 and it may be regarded as almost certain, that this interstellar 

 medium is perfectly transparent and diathermanous ; that is to 

 say, that it is incapable of converting heat, or hght (which is a 

 species of heat), from the radiant into the fixed or con ductible form. 



If this be the case, the interstellar medium must be incapable 

 of acquiring any temperature whatsoever ; and all heat which 

 amves in the conductible form at the limits of the atmosphere of a 

 star or planet, will there be totally converted, partly into ordinary 

 motion, by the expansion of the atmosphere, and partly into the 

 radiant form. The ordinary motion will again be converted into 

 heat, so that radiant heat is the ultimate form to which all phy- 

 sical energy tends ; and in this form it is, in the present con- 

 dition of the world, diffusing itself from the heavenly bodies 

 through the interstellar medium. 



Let it novvf be supposed, that, in all directions round the visible 

 world, the interstellar medium has bounds beyond which there 

 is empty space. 



If this conjecture be true, then on reaching those bounds the 

 radiant heat of the world will be totally reflected, and will ulti- 

 mately be reeoncenti-ated into foci. At each of these foci the 

 intensity of heat may be expected to be such, that should a star 

 (being at that period an extinct mass of inert compounds) in the 

 courseof its motions arrive at that ])art of space, it will be vaporized 

 and resolved into its elements ; a store of chemical power being 

 thus reproduced at the expense of a corresponding amount of 

 radiant heat. 



Thus it ajjpears, that although, from what we can see of the 

 known world, its condition seems to tend continually towards 

 the equable diffusion, in the form of radiant heat, of all physical 

 energy, the extinction of the stars, and the cessation of ail phse- 

 nomena, yet the world, as now created, may possibly be pro- 

 vided within itself with the means of reconcentrating its ])hysical 

 energies, and renewing its activity and life. 



For aught we know, these opposite ])rocesses may go on 

 together ; and some of the luminous objects which we see in 

 distant regions of space may be, not stars, but foci in the inter- 

 stellar aether. 



