Otago Institute. 617 



by red, green, and violet (or blue -violet) mixed in proper pro- 

 portion. He then went on to explain the three sets of nerves in the 

 eye, and the sensation caused by the colours on the three nerves, after 

 the Young-Helmholtz theory. The primary colour-sensations were red, 

 green, and violet. Throwing discs of the three colours on the wall, he 

 showed that red and green together produced yellow, violet and red pro- 

 duced a purple, and green and violet produced a bluish green. By super- 

 posing the red, green, and violet a fair white light was produced. He 

 then projected the picture of an ordinary photograph on the wall, and by 

 superposing the three coloured discs in front of it the photograph stood 

 out in natural colouring, the result being received with prolonged ap- 

 plause. Various pictures were shown in the same manner, including a 

 beautiful sunset view, the red flush in the sky, the gold tinting of the 

 clouds, and the blue and green of the sea being seen to perfection. He 

 stated that not one of the negatives had been retouched, but were simply 

 taken through three coloured screens, and then projected through three 

 coloured glasses. Was it not possible to do away with the complex triple 

 lantern and superpose the three photos permanently? Certainly it was, 

 and that was just how the many modern beautiful reproductions of oil 

 and water-colour paintings were being formed. By placing the three 

 screens in the front of one lens there would simply be a subtraction and 

 consequent darkness instead of light. Evidently, if they wanted to repro- 

 duce in colour, they must make three gelatines and stain them, and use 

 complementary colours, so that each film would receive certain rays only. 

 The method was to take the three negatives from the three-colour screens 

 and then form three printing-blocks. The lecturer then explained the 

 technique of the printing-block colours, and concluded by saving that the 

 practical part of this process consisted of the decomposition of the 

 original colours and the printing. The problem of oolour-decomposition 

 by photographic means could be considered as solved, as by employing 

 different sensitive and light niters the condition of sensitiveness could 

 easily be regulated ; but the recompasition of the three-colour pictures by 

 the means of printing left much to be desired. The production of the 

 photo-mechanical printing-surfaces was uncertain, and the printing pro- 

 cess itself lacked that uniformity which three-colour printing required. 



The lecturer was tendered a hearty vote of thanks at the close of his 

 address. 



Fourth Meeting : 9th August, 1904. 



Professor Scott gave an address on " Primitive Man," illus- 

 trating his remarks by the exhibition of numerous models. 



The President, Professor Benham, exhibited "ski" that 

 had been used by members of the " Discovery " Antarctic Ex- 

 pedition, also a fossil crab from Waipara, and a fossil crayfish 

 from Ahuriri. 



Papers. — 1. Mr. G. M. Thomson : A Paper by Mr. J. A. 

 Thomson, B.Sc, "On a Small Salt Pool in the Barewood 

 District." 



2. " On Pecten huttoni," by Professor Park. (Trans- 

 actions, p. 485.) 



3. The President contributed a paper by Mr. W. Dunbar 

 " On the Skull of Begalecus parkeri." 



New Members. — Messrs. A. Bowman, C. W. Hay, and 

 F. W. Payne. 



