The absorption of light and the colours of natural bodies / by Professor Stokes.

  • Sir George Stokes, 1st Baronet
Date:
1876
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Licence: Public Domain Mark

Credit: The absorption of light and the colours of natural bodies / by Professor Stokes. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    which, would he propagated from it in all directions. This I conceive to he a rough dynamical illustration of what takes place in this actual phenomenon, namely, that the incidence of etherial waves causes a certain agitation in the ultimate molecules of the body, and causes them to be in their turn centres of agitation to the ether; in fact that the incident light renders the medium so to speak self- ; luminous, so long as it is under the excitement of the incident light. That is the view which I maintained from the first, and which is clearly expressed in my original memoir, which was published in the Philosophical 1 'rant- actions of 1852. There is one phenomenon, that of phos-, phorescence, which I felt from the first to be exceedingly analogous to that which is now known by the name of fluorescence, a word I suggested in that original memoir, derived from fluor spar, which was one of the first minerals in which the phenomenon had been observed, as the analogous term, opalescence, is derived from the name of the mineral opal. I am unable to draw any sharp line of demarcation between fluorescence and phosphorescence. So far as I had observed, the effect was only of instantaneous duration, although, as I have expressly stated, I had not made experiments on a revolving mirror to determine whether a finite duration could be perceived With regard to the explanation of the law which I believed to be universal, that in this phenomenon the refrangibility is al- ways lowered, that is to say, the light coming out is always of lower refrangibility than t the incident light, I offered a certain conjecture, which I did] not hold to very tightly, and I have somewhat changed my views in that respect. but I held from the first that the effect is not a direct but an indirect one ; that the light is not simply reflected from the ultimate particles of bodies. It is curious that some two or three writers have attributed to me the notion that in this phenomenon the light reflected from the mole- cules of the body was changed in refrangibility. They have attributed that notion to me, and then contended against it; but if you will allow me to read a short passage from my original paper, it will show that I am not responsible for Chat. I wrote these words : “ In considering the cause of internal dispersion, we may, I think, at once discai a supposition of reflections and refractions of the vi ra ions