398 Mr. O'BRIEN, ON THE PROPAGATION OF LUMINOUS WAVES 



(3°) That the law of molecular force is not likely to be such as 

 to make C zero in all cases. (See § 16.) 



(4°) I have investigated the condition necessary in order that the 

 equilibrium of the etherial particles may be stable. (See $ 16.) 



(5°) Also the conditions necessary in order that the vibrations of 

 the ether may be wholly transversal or wholly normal. (See § 18, 19.) 



(6°) I have shewn that the equations of motion may be each solved 

 separately when the vibrations are wholly transversal or wholly normal. 

 (See § 20, 21.) 



(7°) That transversal and normal vibrations are in general propagated 

 with different velocities. (See § 25.) 



(8°) That the velocity of transversal vibrations may be of any 

 magnitude, the propagation of normal vibrations impossible, and yet 

 the equilibrium stable ; and here I have shewn that the law of molecular 

 force cannot be the inverse fourth power, nor the inverse square, if 

 the theory of transverse vibrations be true. (See § 20.) 



(9°) That the action of the material upon the etherial particles 

 produces an alteration in the velocity of light which is different for 

 different colours. (See § 28.) 



(10°) I have investigated the additional alteration which the motion 

 of the particles of matter produces in the velocity of light, and shewn 

 that it must be extremely small, and that it does not depend on the length 

 of the wave if C be zero; and that consequently the motion of the 

 material particles cannot produce dispersion independently of their direct 

 action on the particles of ether. (See § 29.) 



(11°) I have shewn that light cannot be propagated with a uniform 

 velocity in transparent bodies, unless the particles vibrate according to 

 the cycloidal law. (See § 33.) 



(12°) That the consequence of this must be a dispersion of homo- 

 geneous light in passing through a prism, when the vibrations are not 

 cycloidal. (See § 35.) 



