LIGHT. 137 



we find considerations offer themselves, similar to 

 those which occurred in the case of sound. The 

 vibrations of this ether affect our organs with the 

 sense of light and colour. Why, or how do they 

 do this ? It is only within certain limits that the 

 effect is produced, and these limits are compara- 

 tively narrower here than in the case of sound. 

 The whole scale of colour, from violet to crimson, 

 lies between vibrations which are 458 million 

 millions, and 727 million millions in a second ; a 

 proportion much smaller than the corresponding 

 ratio for perceptible sounds. Why should such 

 vibrations produce perception in the eye, and no 

 others? There must be here some peculiar 

 adaptation of the sensitive powers to these won- 

 derfully minute and condensed mechanical mo- 

 tions. What happens when the vibrations are 

 slower than the red, or quicker than the blue ? 

 They do not produce vision : do they produce any 

 effect? Have they any thing to do with heat or 

 with electricity? We cannot tell. The ether 

 must be as susceptible of these vibrations, as of 

 those which produce vision. But the mechanism 

 of the eye is adjusted to this latter kind only; 

 and this precise kind, (whether alone or mixed 

 with others,) proceeds from the sun and from 

 other luminaries, and thus communicates to us 

 the state of the visible universe. The mere ma- 

 terial elements then are full of properties which 

 we can understand no otherwise, than as the 

 results of a refined contrivance. 



