12 The Ethereal Hijpothesis of Light. [Jan,, 



to in our illustrations, we must be struck with the insufficiency of 

 the " ethereal " h}q^)othesis to afford an explanation of them. On 

 the contrary, I fear the remark of Dr. Frankland,* -which I appre- 

 hend he meant to be appHed to this hypothesis, holds good, that 

 " it hinders rather than expedites the advance of the experimenter." 

 Suppose we were to assume that the " ether suffers no rupture of 

 continuity " at the surface of glass, for instance ;t how is it that the 

 force, " light," acting upon that " ether," passes through the glass 

 freely, whilst one of its resolved forces or phases, heat, notwith- 

 standing that it operates solely upon the same hypothetical medium, 

 is unable to pass ? It cannot be merely because " light " proper 

 acts upon the ether ^^ith greater intensity, causing it to vibrate more 

 rapidly than heat ; for, according to Professor Tyndall, that would 

 result in the mere phenomena of light and darkness. " Darkness," 

 he says, " may be defined as ether at rest ; light as ether in 

 motion : " % and although the same author says the ether never is 

 at rest, and that when light-waves are not passing through it, heat- 

 waves are ; yet I do not see how the two forces can be severed, and 

 more especially how one can be reflected (or, more strictly speaking, 

 can reflect} back, whilst the other proceeds onwards, as we found it 

 to do in our insect scales and in the other cases described, unless 

 the medium which yields to one phase of the force, and resists the 

 passage of the other, is difierent from that which serves as the 

 vehicle of the reflected force, or is invested with the attributes of 

 various kinds of gross matter ; and, indeed, it appears to me that 

 there must be either a distinct form of " ether " for each force, or 

 one ]}hase of the force must act directly upon the constituent particles 

 of the object which is transparent to it, and the other react upon 

 the medium which served as its vehicle until it reached the surface 

 of the sohd ol)ject. Nor can we suppose " ether " to be invested with 

 attributes which cause it to change the character of the force with 

 the direction of its passage through it ; for although the Vi'Iociti/ of 

 heat travelling through certain crystals is greater in one dii'ection 

 than in another,§ and along the fibre of wood greater than across 

 it; II yet it always remains " heat," a force which is supposed by the 

 ethercalists to consist, like light, of the " vibration of ether " 

 everijwhere, so in whichever way we try to use the " ether," we 

 always find that it is the particles of matter wliich, after all, modify 

 the force. 



There is another circumstance which I should like to submit 

 for the consideration of those who are desirous of forming accurate 



* ' Prorcedings of Royal Institution,' June 12, 18G8. 



t I liiivc taken glaws as a familiar cxauiplo, but rock-snlt is a better one. 



j ' Radiation,' p. 'J. 



§ ' Heat as a Mode of Motion.' p. 221. 



il Ibid., p. 223. 



