100 THE ANALOGY OF SOUND AND LIGHT. 



combined. So all the tints of a picture are the results of a few simple col- 

 ors variously combined. The musical scale sorts the complex notes in one 

 case, the spectrum sorts the complex colors in the other. Professor Barrett, 

 taking Professor Listing's determination of wave lengths, has made a most 

 interesting comparison. The wave lengths of the notes of the gamut he 

 expresses not in absolute but in relative measurement. Thus C is taken as 

 100, and all the other notes have their wave lengths expressed in percent;- 

 ages. Similarly, red is taken as 100, and the wave lengths of other colors 

 are expressed in percentages. This interesting result comes out in com- 

 paring the two columns; D and orange are each 89; E and yellow 80; F 

 and green, 75 ; G and the average of the blues, 67 ; A and violet, 60 ; B and 

 ultra violet, 53 ; C and the obscure rays (black), 54. Further, the compar- 

 ison of harmonies comes out in an interesting manner. Low C and uj^per 

 C sound well together, so red and black go well. together. Eed and green, 

 or C and F, harmonize well ; but red and orange no lady would wear, and 

 C and D make a combination by no means pleasant. lied and blue, or C 

 and G, also go well together. 7. The concluding part of the lecture was 

 devoted to an illustration of the figures described by vibrating bodies. 

 Several apparatus for this purpose were briefly referred to, but especial at- 

 tention was given to an apparatus of great ingenuity devised by Mr. S. F. 

 Pichler. Professor Barrett showed it with an electric light and a reflection 

 on to a screen. The principle of it may be thus described : Two metallic 

 vibrators, each with a small speculum, are fixed at right angles to each 

 other, and sounds are produced by a current of air acting on one or both of 

 them at pleasure. The perpendicular vibrator is tuned to a given note ; 

 the horizontal vibrator is fitted with a mechanical arrangement whereby 

 its pitch can be graduated to any degree of nicety within the compass of 

 two octaves. A.n apparatus is also provided whereby a pencil of light i& 

 concentrated upon the speculum of the perpendicular vibrator, whence it is 

 reflected to the speculum of the horizontal vibrator. For lecture purposes 

 artificial light is used, which is further reflected and magnified upon a 

 screen. When musical sounds are produced by the vibrators, various lumi- 

 nous geometrical figures are formed on the horizontal speculum and reflected 

 on the screen by the single or joint action of the vibrators described by the 

 pencil of light ; and the form and motion of such figures demonstrate the 

 exact relations to each other of the musical notes produced. Sounds which 

 harmonize to the ear produce regular figures to the eye, as, for example, 

 segments of the circle, ellipses, ovals, circles, or straight lines ; and if the 

 amplitude of each vibrator be equal, these luminous figures will hover on 

 the speculum or screen with an apparent steadiness like that of the heaven- 

 ly bodies hovering in the sky. If the sounds do not harmonize, the figures 

 are confused, unsteady and complicated, presenting an appearance as if the 

 wave lines were contending with each other. The mathematical relations 

 of musical notes are also demonstrated, regular simple forms being pro- 

 duced by combination of those notes which result from vibrations bearing 



