The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Photography in Natural Colours
and then immersed in a 3 per cent, solution of zinc chloride or nitrite of soda till it turns blue again, then blotted off between blotting paper, and exposed whilst damp under the coloured object. After exposure it will be seen that the green and yellow will be visible, but the other colours require developing, and for this the green and yellow must be covered with a varnish, and then the paper immersed in a dilute 2 per cent, solution of sul-phuric acid. In order to fix the print to some extent, it should be immersed in the mercury bath, then into the chlqride of zinc ;
Fig. 102.
wash and dry between blotting paper, and then coat with a solution of gum arabic with 5 per cent, of sulphuric acid added. The explanation of the theory of the formation of these colours is, according to Zenker, precisely the same as that involved in the following process : - 2. The interference method of Lippmann was announced by him in February 1891. This is founded on the theory of stationary waves, propounded by Zenker and
Fig. 103.
Wiener. . Let us assume abed, fig. 103, to be a ray of light proceeding in the direction of a d, and the small dots to be the particles of ether vibrating or in rapid motion, and on its reaching ^it meets with some reflecting surface v^hich sends the ray back. We shall have the second ray proceeding along the same line but in the opposite phase, and at b and c the pull or vibratory motion of the ether particle will be equal in both directions, as shown by the small arrows ; so that at these points there will be no light, whilst in the loops in between there will be increased light. Now in fig, 102 we see a ray of light proceeding in
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