oS MGHT. 



between the surfaces was sufficient for one wave, at the second for two, 

 &.C. From these calculations it appeared that the waves of red light 

 were so minute that 40,000 of them would be comprised within an inch, 

 and that 60,000 violet waves were included in the same space; the 

 waves of other colors being of intermediate magnitudes. 



From these results it is inferred that lights are of various hues ac- 

 cording to the amplitude of the" pulsations, exactly as musical tones vary 

 with the magnitude of the aerial vibrations, and as the altitude of the 

 sonorous undulations determines the loudness of the tones, so the alti- 

 tude of those of light determines the intensity of the color. A singular 

 analogy is thus exhibted between the laws of transmission of light and 

 sound. 



Another curious result is obtained from data which these considera- 

 tions furnish us. As sounds are produced by vibrations communicated 

 to the tympanum by means of the air, the number of which in a given 

 time is susceptible of calculation, so the sensation of sight may be con- 

 sidered, in accordance with the undulatory theory, to be produced l)y 

 vibrations communicated to the membrane of the eye, the rapidity of 

 whose contracting can be thus determined. 



Since light travels at the rate of 200,000 miles in a second, a line of 

 light 200,000 miles in length must enter the eye during this interval ; 

 this length is equivalent in round numbers to 12,000,000 of inches, 

 which, multiplied by 60.000 for the violet rays, would give for the 

 number of vibrations of the retina, during a single second, more than 

 some hundred millions of millions. 



In meditating upon these celebrated theories, we are forcibly re- 

 minded of the insignificance of all human attainments when compared 

 with the vast resources of knowledge which lie hidden from our view. 

 We have seen that the patient, long continued labors of individuals, 

 have sometimes snatched a single jewel from the treasury of Nature's 

 truths to adorn their names with immortal honor; but how small is this 

 in comparison with what remains unknown. On every side we experi- 

 ence difficulties, and the more deeply we penetrate into the mysteries of 

 nature the more we are enabled to perceive that the limit of knowledge 

 is unattainable, and that eternity itself would be too short to enable man 

 to become acquainted with all tlie works of the Creator or to compre- 

 hend his glorious attributes. 



Whichever theory be taken, difficulties still remain ; if light be ma- 

 terial and possessed of tlie ordinary properties of matter, it would seem 

 that it must exert an influence upon the heavenly bodie.s, forming, in 

 fact, a resisting medium, and however slight the resistance might be, 



