58o 



NA TURE 



[October 13. 1904 



that cannot be distinguished from the original 

 by simple obsetVation. Mr. Theodore Andrea 

 Cook, in his preface to the volume, refers to 

 " mechanical accuracy, assisted and improved by skil- 

 fully delicate and reverentially careful handiwork," and 

 thus sums up the position according to the facts of 

 the case. The colours are not accurate by reason of 

 the fact that the printing blocks are made by photo- 

 graphic means, although this may be claimed for the 

 drawing — that is, the outline. In describing the 

 process of three-colour printing, we have endeavoured 

 to show how that imperfection and compromise qualify 

 every step of the work. It is therefore necessary to 

 examine the first proof by critically comparing it 

 with the original, and then to make such alterations 

 as are required in the three printing plates, by 

 re-etching wholly or partially, by hand engraving, 

 burnishing, and similar methods, continuing to make 

 proofs and effect the needed changes until the differ- 

 ences are eliminated. At IVIessrs. Andr(? and Sleigh's 

 this examination and hand work are carried out by 

 trained artists, as distinguished, that is, from photo- 

 graphers and printers, and it is to the scrupulous care 

 bestowed upon this adjustment of the plates by hand 

 that the perfection of the prints depends. The justi- 

 fication lies in the result, and, whatever may be said 

 for or against any principle of work, it is by the 

 practical result only that it can, at present, be finally 

 judged. If a copyist were to paint a copy of a picture, 

 we should naturally seek the opinion of eminent 

 painters as to the merits of the copy. Three-colour 

 reproductions put forward as these are must naturally 

 be judged in the same way, and it is a source of gratifi- 

 cation to all interested in the technics of three-colour 

 work to know that these reproductions have received 

 the warm approval of many of our best known painters. 

 But it is easy to believe that there is room for a little 

 difference of opinion, and that a critical comparison 

 with the originals would reveal possibilities of improve- 

 ment. Such have been pointed out, and presumably 

 no three-colour work will ever be done for which 

 absolute faultlessness can be rightly claimed. But 

 there is a possibility of error even in this criticism. 

 For as the reproduction is not done in the same pig- 

 ments as the original it follows that the effect of a 

 difference of illumination will not be the same on 

 both. If the reproduction were perfect as compared 

 with the original by ordinary good daylight, there 

 would probably be differences noticeable to a trained 

 eye if they were compared on a dull day; and this prob- 

 ability must exist however the copy is made if the pig- 

 ments used are different from those in the original. 

 Moreover, no work in colour appears as it is 

 intended to unless it is illuminated by the light by 

 means of which it was produced or a quite similar 

 light, and this is a physical law which must ever 

 obtain. 



There have been a few attempts to simplify the three- 

 colour process by the use of one screen only, the three 

 colours being arranged upon it. Perhaps the best 

 known of these is due to Prof. Joly, who arranges his 

 colours in triple parallel lines. The most recent, and 

 the boldest in its conception, has only just been pub- 

 lished by Messrs. Lumiere. They sort out from potato 

 starch granules from 0.015 to 0.02 mm. in diameter, 

 and colour separate lots of these red, green, and violet 

 respectively. When quite dry the coloured granules 

 are mixed in such proportions that the mass appears 

 grey, with no predominance of either colour, and a 

 waxed glass is coated with them to form a layer only 

 one granule thick. To prevent the interstices from 

 passing white light, they are filled up with a fine black 

 powder. There is next applied a varnish which has 

 «s nearly as possible the same refractivity as the starch. 



NO. 1824, VOL. 70] 



By this means is obtained an irregular-grained triple- 

 colour screen. To prepare it for producing the picture 

 it is coated with a suitably sensitised emulsion. The 

 plate is exposed through the glass, developed, the silver 

 image dissolved away, and the remaining silver salt 

 reduced to the metallic state to form the image. Thus 

 is obtained the completed transparency. It is obvious 

 that if such plates ready for exposure were supplied 

 commercially, the making of coloured transparencies 

 would be much more simple than when three negatives 

 and three prints have to be made. There must be 

 many practical difficulties to surmount in the prepar- 

 ation of such compound plates, and, as in all cases of 

 three-colour work, the process must at present be 

 judged bv the results that it yields rather than by the 

 apparent soundness or otherwise of the theories upon 

 which it is based. 



The small volume by Mr. R. Child Bayley forms a 

 good introduction to the subject of colour photography, 

 as it is written in such simple language that it may be 

 " understood and followed by any reader, even by one 

 without the slightest acquaintance with photography," 

 as the author states in his preface. At the same time 

 sufficient formulae and precise details are given for the 

 practical working of those processes that are within 

 the experimental possibilities of the photographer. 

 Chapman Jones. 



iiOTES. 



The French physicians and surgeons who are visiting 

 London arrived on Sunday. On Monday the president and 

 council of the Royal College of Surgeons received the 

 visitors, who were shown the collections in the museum. 

 Parties have during the past three days visited the principal 

 hospitals, general and special, the physiological laboratories 

 of the University of London and the laboratories of the 

 Cancer Research Fund, the Lister Institute, the Middlesex 

 Hospital cancer department, the pathological laboratory of 

 the County Council Asylum at Claybury, and the London 

 School of Tropical Medicine. Receptions have been given 

 by the editors of the Lancet, Dr. and Mrs. Dundas Grant, 

 and the Dean of the Faculty of Medicine of the University 

 of London and Mrs. Butlin. On Wednesday night the 

 visit was brought to a close by a banquet at the Hotel 

 Cecil. 



Tut; Government of the Federated Malay States has 

 decided to establish an agricultural department in Malay, 

 and has appointed Mr. J. B. Carruthers, the Government 

 mycologist and assistant director of the Royal Botanic 

 Gardens of Ceylon, to be director of agriculture and Govern- 

 ment botanist. The Federated Malay States have an area 

 of more than 25,000 square miles, and the agricultural 

 potentialities are very promising. Large areas are being 

 planted with rubber plants, and sugar and cocoanuts are 

 extensively cultivated. There are two botanic gardens and 

 a rubber experiment station in the Malay States, and all 

 three are, we understand, to be administered by the new 

 department. 



On October 6 the Antarctic relief ship Morning arrived 

 at Plymouth from Lyttelton after an absence of about two 

 and a half years. 



The first monthly general meeting of the new session 

 of the Institution of Mechanical Engineers will be held 

 on Friday, October 21. A paper by Mr. R. M. Neilson on 

 " h. Scientific Investigation into the Possibilities of Gas 

 Turbines " will be read and discussed. 



