VI 



Supplement to ''Nature" October ii, 1906 



used to denote special features. The list of terms is 

 very complete, and includes a few, e.^. " marcescent," 

 ■■ fovilla," and "sobole," that would not have been 

 missed. A few of the definitions, notably those of the 

 seed and leaf, niitfht be more accurately expressed, 

 and amonp misprints one of the most noticeable is 

 "aetoeris" for "etaerio"; but on the whole the 

 author has done her work wvll, and the book should 

 prove useful. 



THE PHOTOCRAPHV OF COLOUR. 

 \,itiiral-coh,ur Phntoi^raphy. By Dr. E. Konij;-. 



Translated from the (uTm.in, with additions, by 



v.. J. Wall. Pp. ,14. (London: Dawbarn and 



V\ard, Ltd., n.d.) 

 Colour-correct Photography. By T. Thorne Baker. 



Pp. 95. (London : Dawbarn and Ward, Ltd., 1906.) 



Price IS. net. 



'T^HE first of these volumes deals with the repro- 

 -L duction of colour and the second with the re- 

 presentation of coloured objects in black and white 

 or monochrome. 



'Powards the end of the first volume we read that 

 •■ colour photography is not a purely mechanical copy- 

 ing of nature, carried out with mathematical pre- 

 cision, and that, indeed, it will never be. He who 

 works quite automatically will never advance." The 

 statement as to the present is certainly true, and the 

 prophecy, though boid, is, literally, justifiable so far 

 as experience goes. The reproduction of colour is 

 thus essentially different from the representation of 

 form, for this latter depends only on the perfection 

 of one's instruments and a commonly intelligent use 

 of them. Colour photography, as at present practic- 

 able, may be described as a kind of simplified chromo- 

 lithography, inasmuch as the choice .of colours rests 

 with the worker or those who provide him with 

 materials, and the depth of tint depends on the 

 worker's judgment. Its distribution is mechanical, 

 but, again, this depends on the colour-screens or filters 

 used in the photography, which are never more than 

 approximately what they are desired to be. .And 

 when it is remarked that the colours used are none 

 of them permanent in the .sense in which carbon or 

 platinum is permanent, it is obvious that, so far as 

 the colour goes, colour photography does not furnish 

 more trustworthy records than painting or any other 

 colour-production method, except, perhaps, that the 

 possible errors of the unskilful may be a little more 

 limited. 



.\t the same time, there are certain principles 

 which, if they could be perfectly applied, would give 

 perfect colour reproduction. Remarkably fine work 

 has been done by those who have adhered as closely 

 as possible to these principles, as well as by those 

 who have trusted chiefly to empirical methods. The 

 volume before us is a small one ; it merely mentions 

 the underlying principles, being devoted almost 

 entirely to the practical details of the " subtractive 

 method " of three-colour photography, that is, where 

 the three coloured prints arc superposed so that their 

 NO. 1928, VOL. 74] 



absorptions arc added, and to the "additive method," 

 in which the three colours themselves are added to 

 each other, as when they are separatelv projected by 

 optical means on to the same screen, or united in 

 the eye itself by means of mirrors. That the two 

 methods are not so radically different as thev might 

 at first appear to be is obvious from the fact that, to 

 a certain extent, the colour-screens used are inter- 

 changeable. We think that a little more of the theo- 

 retical basis would have made the practical details 

 more understandable. Spectrum diagrams of the 

 effects of the various colour-filters might have been 

 given, and, in dealing with three-colour work, some 

 confusion might have been avoided by omitting the 

 reference to yellow as a fundamental colour, thus 

 giving four colours instead of three to deal with. 

 We are astonished to read at p. 47 that " it is a 

 recognised fact that photography always reproduces 

 shadows much too dark." It would have been better 

 to blame the photographer for this rather common 

 error than apparentlv to justifv him bv suggesting 

 that he is helpless. 



.\s to the scope of the volume, photo-mech.inical 

 methods are altogether and designedly excluded, as the 

 book professes to appeal to amateurs and others who 

 are |)hotographers, but not to commercial printers. 

 The direct processes such as Lippmann's, and those 

 in which the colour work is practically done by the 

 maker of the materials, are only shortly referred to 

 in the introduction. As a practical guide to the work- 

 ing of those methods that are now generally avail- 

 able for amateurs the volume will be found very 

 useful, as it gives formulae for the various colour- 

 filters and dyes for staining, quite practical instruc- 

 tions for making the filters and other apparatus, and 

 deals systematically with the subject. 



Mr. Thorne Baker's volume is more than the title 

 indicates, for he gives a chapter on the representation 

 of colours incorrectly, as may be sometimes desirable 

 for distinguishing emphatically between two or more 

 colours. To get a coloured flashlight that will 

 shorten the exposure by increasing the brilliancy of 

 the colours to which the plate is less sensitive, he 

 recommends to mix magnesium ]jowder with a 

 twentieth to a fortieth part of a mixture of equal 

 weights of calcium and lithium carbonates. The 

 author gives much other useful information in the 

 ten chapters that deal with the various branches of 

 the subject. We do not see, however, why the ex- 

 posure should be shortened when the studio blinds 

 are coloured instead of using a coloured screen as 

 usual, nor why metol should be " not recommended " 

 as a developer. Such advice would be more accept- 

 able if the reasons for it were given. The explan- 

 ation given at p. 85 of the fact that " the exposure 

 required with cells of different thickness does not 

 varv directlv as their width " is incorrect; it is not 

 a mailer of absorption by the glass sides of the 

 cell, but of the selective absorption by the coloured 

 liquid. But the book as a whole forms a useful 

 introduction to the subject, and contains some 

 formulae .-md suggestions rarelv met with. 



C. J. 



