. Discovery. Science. 196 DISCOVERY the painter. If, tlicrcforc, a motliod could be devised by which the person viewing the picture could sec it witlvmt hi-^ view being interfered with by this surface-. KOR PROJECTING POLARISED OLD PICTURES. effect, it would enable the person"to see the picture as it was when it was first painted or as it would be if it were properly restored. By means of his polarised- light apparatus M. Lambert has made this possible. A word now on polarised light. Ordinary hght, such as sunlight or electric light, consists of transverse vibra- tions, the vibrations tak
. Discovery. Science. 196 DISCOVERY the painter. If, tlicrcforc, a motliod could be devised by which the person viewing the picture could sec it witlvmt hi-^ view being interfered with by this surface-. KOR PROJECTING POLARISED OLD PICTURES. effect, it would enable the person"to see the picture as it was when it was first painted or as it would be if it were properly restored. By means of his polarised- light apparatus M. Lambert has made this possible. A word now on polarised light. Ordinary hght, such as sunlight or electric light, consists of transverse vibra- tions, the vibrations taking place in all directions at right angles to the direction of the rays. There are certain bodies, however, such that when light is passed through them the transverse vibrations all take place parallel to one definite direction only. The ray of light is then said to be plane-polarised. The usual means of obtaining plane-polarised light is by means of a prism called a Nicol's-prism, which is made from a crystal of Iceland Spar (calcium car- bonate). A Nicol's-prism may be used not only for producing polarised light (when it is called a polariser), but also for determining the plane in w^hich the light is polarised, when it is said to be used as_an analyser. Let us consider the Nicol's-prism as an analyser. If the light falling on the Nicol be nnpolarised, the intensity of the light which will get through will remain the same when the prism is rotated round the light ray as axis. If the light be polarised, however, the intensity of the light varies from a maximum to zero as the analyser is rotated. It is not hard to understand, therefore, that if a mixture of polarised and unpolarised light fall on the analysing prism, it is not a matter ot difficulty to rotate it so that the unpolarised light alone gets through— if the eye looks through the prism, only the unpolarised lighf is seen by the ob- server. When the analysing Nicol is so rotated that none of the polarised light
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