The Lippmann Procesf

THE LIPPMANN PROCESF.

The Lippmann process, which depends on the effects of the phenomenon known as " interference," was announced by Pro fessor Gabriel Lippmann to the French Academy of Sciences in 1891. A perfectly transparent and very finely grained plate is placed with its film side in contact with a reflecting surface consisting of a trough of mercury, in such a manner that the plate forms one of the sides of the trough. During exposure, the light waves instead of rushing through the sensitive film with inconceivable velocity, and so obliterating all record of their form and structure, arc reflected and thrown back upon them selves by the surface of the mercury. The result is that stationary waves of light are formed in the film itself, which are cap able on development of yielding micro scopically fine latninre or divisions of metallic silver, each colour of the original having its own particular wave length re modelled with exactness in the structure of the developed image. The consequence

is that, although, if looked through in the usual way, the negative seems to present no special features of interest, if viewed by reflected light at a certain angle the colours of the original are at once ap parent. The light has been decomposed by the metallic laminae of the film, and as these exactly reproduce the wave structure of the original colours of the image, the latter is necessarily viewed in its own correct tints. Although the honour of the actual achievement belongs to Professor Lippmann, he was not the first who had suggested the possibility of producing stationary light waves in a photographic film. Dr. Wilhelm Zenker, Otto Wiener, and Lord Rayleigh had pre viously made valuable contributions to the theory of the process.