LUMINIFEROUS ETHER. 75 



CHAPTER IX. 



INTERMINGLING OF UNDULATIONS. 



As has already been stated, there are, or, rather, have 

 been, two theories in respect to the physical nature of 

 light one, that it consists in the emanation of streams of 

 exceedingly minute particles, which fly through the air 

 with inconceivable swiftness, having in some mysterious 

 way the power of passing through glass and all transpa- 

 rent bodies ; and the other, that it consists in a vibratory 

 or undulatory motion in a subtle medium, which, in order 

 to have a name for it, has been called ether. The existence 

 of this ether is only imaginary, however, as nothing is di- 

 rectly known in respect to it, and it is only supposed to 

 exist, as the sole means that we can conceive of to render 

 the transmission of luminous undulations possible. 



It seems, however, as has already been said, very diffi- 

 cult to conceive of the possibility of undulations in such 

 infinite number and variety as must be moving at every 

 point in space, if this theory is true, meeting, and encoun- 

 tering, and crossing each other without in the least degree 

 interfering with or disturbing each other's motions. Still 

 we can not say that this would be impossible. There is 

 complete and positive proof that sound is produced by vi- 

 brations in the air; and yet, on a calm summer morning, 

 we can, by listening, hear a great many different sounds, 

 all clear and distinct, and each produced by its own undu- 

 lations, coming through the same medium with all the rest, 

 and each without being sensibly disturbed by the others. 

 We can hear the songs of two or three different birds, the 



