316 Scientific Intelligence. [April 



excited by sonorous bodies, occasions motions in the membrana tym- 

 pani. These vibrations follow in regular succession, and according 

 as they are more or less frequent or rapid in succession, the sensation 

 of colour is produced. 



The following table exhibits the number of vibrations which are 

 distinguishable in a second, and the length of a wave : 

 Number of vibrations, Length of a wave. 



32 32 



64 16 



128 8 



4096 3 inches. 



8192 ... . li 

 The number of vibrations which produce the different colours of 

 the spectrum has been calculated with wonderful precision : 

 Red . . . 458,000,000,000,000. 

 Orange . . 506 „ 



Yellow . . 635 

 Green . . 577 a 



Blue ... 622 

 Indigo . . 658 „ 



Violet . . 727 

 The length of a wave is '0000266 inch, from which we can calcu- 

 late the vibrations. 



These numbers are so enormous that one is apt to be sceptical as 

 to their accuracy. Their computation is, however, extremely easy, 

 and we are perfectly certain that they form very close approximations 

 to the truth. 



By screwing two plates of glass together, the rays of light pass 

 through the first, and are refracted by the second, and when received 

 on white paper, exhibit the fits of Newton, consisting of alternate 

 light and dark colours. A happy idea struck Dr. Ritchie on the 

 morning previous to his lecture, that by a modification of this prin- 

 ciple, Newton's rings might be exhibited. He accordingly screwed 

 together two plates of glass, divided at their margins merely by a 

 layer of gold leaf, directing the pressure upon one central point with 

 the extremity of the screw, around which were beautifully displayed 

 the rings as he had anticipated. These may be enlarged by additional 

 pressure near their circumference. In this way these can be measured, 

 and the above numbers deduced. Frenelle, by means of ingenious 

 apparatus, has been enabled to exhibit the length of the waves, and 

 measure them by means of a microscope. His results were the same 

 as those given. Dr. Ritchie considers that the experiments of Frenelle 

 prove conclusively that light consists of the undulations of a fluid, 

 interfering with each other and producing darkness. 



A further proof in favour of the theory is, that when light is passed 

 through a small aperture, by reflexion, we have, if we place a sheet 

 of paper opposite to the hole, alternations of red and dark colours, 

 and M. Arago has shewn that light moves more slowly through glass 

 than air. M. Colladon, by some very interesting experiments at 

 the lake of Geneva, has proved that with sound as with light, the 

 angle of incidence is equal to the angle of reflexion. Newton ob- 

 jected that if light, like sound, consisted of waves, sound ought to 



