1870.] 



Light and Sound. 



15 



pare the result with the wave-lengths of the notes of the scale 

 reduced to the same ratio. Here are the limits of wave-lengths of 

 the different colours of the spectrum as most carefully determined by- 

 Prof. Listing.* In the third column the writer has added the mean 

 wave-length of each colour, and in the fourth column the ratio of one 

 colour to another, taking the mean wave-length of red as 100. 



Table of Wave-lengths of Colours in the Spectrum. 

 Wave-lengths : in Millionths of a Millimetre. 



Name. 



Limit. 



Red .. .. 



.. 723 to 647 



Orange 



.. 647 to 586 



Yellow .. 



.. 586 to 535 



Green 



.. 535 to 492 



Blue . . 



.. 492 to 455 



Indigo 



.. 455 to 424 



Violet 



.. 424 to 397 



685 

 616 

 560 

 513 

 473 

 439 

 410 



Ratio. 

 100 

 89 

 81 

 75 

 69 

 64 

 60 



Here next is a table giving the middle notes of the scale, their 

 wave-lengths, and their reduction to a common ratio, taking C as 100. 



Table of "Wave-lengths of Notes of Scale. 



Name. 



C . 

 D . 

 E . 

 F . 

 G . 

 A . 

 B . 

 C 2 . 



r ave-length 





in inches. 



Ratio 



52 



100 



46^ 



89 



42 



80 



39 



75 



35 



67 



31 



60 



27| 



53 



26 



50 



Putting together the two ratios, the following remarkable cor- 

 respondence at once comes out : — 



Ratio of Wave-lengths of Notes compared to Ratio of Wave-lengths 



of Colours. 



Notes. 



Ratio. 



Colours. 



Ratio. 



c .. . 



.. 100 



Red .. 



.. .. 100 



D .. . 



.. 89 



Orange 



.. .. 89 



E .. . 



.. 80 



Yellow . . 



.. .. 81 



F .. . 



.. 75 



Green . . 



. . . . 75 



G .. . 



.. 67 



Blue and 



indigoj 6? 







(mean) 



A .. . 



.. 60 



Violet .. 



.. .. 60 



B .. . 



.. 53 



[Ultraviolet .. 53] 



C .. .. 



.. 50 



[Obscure 



.. .. 50] 



Assuming the note C to correspond to the colour red, then we 

 find D exactly corresponds to orange, E to yellow, and F to green. 

 Blue and indigo, being difficult to localize, or even distinguish in 

 the spectrum, they are put together: their mean exactly corre- 

 sponds to the note G. Yiolet would then exactly correspond to 



* PoggendorfiPs ' Aimalen,' vol. cxxxi., p. 564. 



