faiiiKvv r^f//, /t^c'cS'.] Proc'EEDINGS. xiii 



of which the following is an abstract : — The development of 

 colour photography dates hack to the early part of the nine- 

 teenth century. The earliest methods were suggested by the 

 discovery that a solar spectrum decomposes silver chloride, 

 giving rise to a sympathetic colour change in the salt. 

 (Seebeck 1810, Herschel, Zenker, Du Hauron, Lippman and 

 many others). The next method consisted in using collodion 

 plates (Abney and others) but no reliable means of fixing the 

 pictures was known. The pictures obtained by the late Mr. 

 Joseph Sidebotham — one of a red geranium with green leaves, 

 and another of a landscape showing a red-tiled house and trees 

 in shades of green — were accidental, and were never repeated, 

 and it is curious that these results were fixed while others were 

 quite fugitive. The introduction of orthochromatic plates 

 made it possible to produce effects in colour not otherwise 

 obtainable. As early as 1873, Dr. Vogel used gelatine bromide 

 plates, and in 1879, Mr. F. E. Ives used coUodio-bromide plates 

 and obtained excellent results which could be used in the optical 

 lantern. Three negatives were required, each taken through a 

 differently coloured medium, the colours used being bright red, 

 puiple-blue and green. Transparencies wtre made which had 

 the ordinary appearance except that they varied in density. To 

 produce the colour effect three lanterns were used, the pictures 

 were projected through the same coloured media, their images 

 superposed, and the resulting picture approached very nearly the 

 colours of nature. Ives also used an instrument called the 

 Kromscop, which was stereoscopic and gave beautiful results. 

 Mr. Thorp, too, devised an instrument which showed effects very 

 similar to those of the Kromscop. Trichromatic printing or 

 the "three-colour" process is the outcome of the work alluded 

 to here. In this process, negatives are taken through colour- 

 screens. '1 he block from the negative of the red is printed in 

 blue ink, that from the green, in red, the one from the blue in 

 yellow. The combination of the three pigments gives results 

 which, in the ordinary way of colour printing, can only be 

 obtained by using from 5 to 15 or 20 colours. 



