XCI
CHAPTER XII.
H. Decomposition of Light or Colour.
395–411.
§ 223. 1) The sensation of different colours is produc
ed by a different number of vibrations performed by the mole
cules of ether. 395.
Remark. Fresnel determined the length of the light-waves and the
number of their vibrations as follows:
| Length of the waves | Number of vibrations |
|---|---|
| violet 0.000423 | 759 Billions |
| indigo 0.000449 | 671 ″ |
| blue 0.000475 | 626 ″ |
| green 0.000571 | 579 ″ |
| yellow 0.000583 | 539 ″ |
| orange 0.000583 | 517 ″ |
| red 0.000620 | 478 ″ |
§ 224. White light in passing through prisms or lenses
(from one medium into another) is decomposed into seven dif
ferent kinds of light or colours (violet, indigo, blue, green,
yellow, orange, red). 396. (This decomposition of the sun's
light is called spectrum). The refraction of these different
colours is different; violet shows the strongest, red the least
refraction. As we have seen in No. 103, the image of the sun
is no longer a circularity, but a figure, limited on both sides by
straight lines and above and below by a circular arc, Hence the
sun's spectrum consists of infinite coloured circles, which cover
each other and the colours of which gradually succeed each other.
§ 225. The seven colours of the spectrum are simple, which
means each of them is indecomposable. By combining the
seven different pencils of one ray by the prism white light can
