OF MOLECULAR FORCES. 109 



If the ethereal medium consist of detached particles, the action of 

 which on each other is 'proportional to a power of the distance, that 

 power must be greater than 2, and the force must be repulsive. 



I have pleasure in remarking, that this result so far as it goes, 

 coincides exactly with that which M. Cauchy has obtained in his 

 " Me"moire sur la dispersion de la lumiere," page 191, where from his 

 investigations he infers respecting the mutual action of two molecules 

 of ether, "que, dans le voisinage du contact, cette action soil repulsive 

 et reciproquement proportionelle au bi-carre de la distance." 



20. If the particles of ether exert a repujsive action upon each 

 other, as we have just shewn must be the case, they will naturally 

 endeavour to disperse themselves through all space, and form a medium 

 coextensive with the boundaries of the universe. Here then a for- 

 midable difficulty presents itself to our notice. If the medium be of 

 finite dimensions it must be enclosed in an envelope, capable of re- 

 straining the expansive energy of the whole mass of particles. The 

 more extensive the medium the greater must be the strength of the 

 envelope. Is it probable that the constitution of the Universe is such 

 as to require that the whole should be enclosed in a huge vessel of 

 inconceivable strength? This objection would in my opinion be fatal 

 to the hypothesis of a system of detached particles, were it not for the 

 following considerations. 



Upon examining the preceding articles, it" will be seen that the 

 luminiferous ether must be such that d}V, d 2 g V, d\V are all equal and 

 negative. Now the properties of these quantities will not be in the 

 least affected, if we assume that the particles exert attractive forces as 

 well as repulsive forces, providing the attractive forces are proportional 



to -=p. For let us suppose that 



V = 



where n and m are respectively the attractive and repulsive forces exerted 

 by the same particle at the distance unity. 



