Researches on the molecular asymmetry of natural organic products (1860).

  • Pasteur, Louis, 1822-1895.
Date:
1905
Catalogue details

Licence: In copyright

Credit: Researches on the molecular asymmetry of natural organic products (1860). Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    FIRST LECTURE. i. AT the end of the year 1808, Malus announced the discovery that the light reflected by all objects, whether opaque or transparent, acquired new properties of a very extraordinary character, which dis- tinguished it essentially from the light sent to us directly from luminous bodies. Malus gave the name polarisation to the change which the light underwent in the process of reflection. Later, the expression plane of polarisation was used to designate the plane of reflection, that is to say, the plane containing the incident ray and the normal to the reflecting surface. Malus' discoveries in connection with polarised light were not limited to this. It had long been known that a ray of direct light was always separated into two beams of white light, of equal intensity, in its passage through a rhomboid of calcium carbonate. Thus the flame of a taper viewed through such a rhomboid is always double, and the two images are equally bright. Huygens and Newton had already noticed that light, after its passage through a crystal of Iceland spar, no longer behaves like direct light. Thus, when we study one or other of the images of the taper, just mentioned, through a second rhomboid, we observe (1) that there is not always bifurcation of the ray; (2) that when bifurcation does take place, the two new images have not the same intensity. So that the light which has traversed a doubly refracting crystal is different from