Great and small things / by Sir Ray Lankester.

  • Lankester, E. Ray (Edwin Ray), Sir, 1847-1929.
Date:
[1923]
Catalogue details

Licence: In copyright

Credit: Great and small things / by Sir Ray Lankester. Source: Wellcome Collection.

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    exactly the same extent or part of the spectrum ; nor are all yellow, or all green, or all blue liquids exactly alike in this matter. Their minor differences of “ tint ” are due to their absorbing or else letting pass more or less of the light of another colour. A very curious and important fact was discovered when various transparent coloured bodies (liquids and solids) were tested in this way. It was found that some (but by no means all) transparent coloured bodies cause detached black bands of absorp- tion in the spectrum (see Fig. 17). They are called Sun Light Blood Red COMBINED WITH OXYGEN Blood Red DEPRIVED OF OXYGEN Fig. 17.—To show the “ Absorption Bands ” seen in the “ Spectrum ” of Sunlight which has passed through a weak solution in water of Blood-Red or Haemoglobin. “ absorption bands ,” and can be accurately measured and their exact position in the spectrum fixed. Such coloured bodies as give detached absorption bands can be recognized and identified with absolute certainty by the position of those bands in the spectrum. As shown in Fig. 17, records of them are kept by which their position is shown as compared with that of certain fine dark lines always present in the spectrum of sun- light, called after their discoverer, “ Fraunhofer’s lines,” and named by letters, as seen in Fig. 17. And even more exactly the wave-lengths of the trains of light 4