986 



SCIENCE 



[N. S. Vol. XXXVII. No. 965 



reached the final stages, and a vast amount of 

 work had to be done over and over again as 

 advances were made. The manner in which 

 the more important of these problems have 

 been met is set forth below. 



This book is, of course, not the first attempt 

 that has been made to supply standards of 

 color. Ridgway himself had made an earlier 

 attempt.' On this subject the author, in his 

 preface, remarks : " Many works on the sub- 

 ject of color have been published, but most of 

 them are purely technical, and pertain to the 

 physics of color, the painter's needs, or to 

 some particular art or industry alone, or in 

 other ways are unsuited for the use of the 

 zoologist, the botanist, the pathologist or the 

 mineralogist; and the comparatively few 

 works on color intended specially for natural- 

 ists have all failed to meet the requirements, 

 either because of an insufficient number of 

 color samples, lack of names or other means 

 of easy identification or designation, or faulty 

 selection and classification of the colors 

 chosen for illustration." 



The scheme of classification used is essen- 

 tially that suggested by Professor J. H. 

 Pillsbury.^ The key to the arrangement of 

 colors in this scheme is the solar spectrum, 

 augmented by adding to the violet end of the 

 spectrum the hues obtained by mixing violet 

 and red in various proportions by means of the 

 Maxwell color disks.' 



In determining the number of color stand- 



" ' A Nomenclature of Colors for Naturalists, ' ' 

 etc., 1886. 



= See Science, June 9, 1893 ; also Nature, Vol. 

 LII., No. 1347, August 22, 1895, pp. 390-402. 



' If a wheel made up of sectors of different 

 color be rapidly revolved on its axis the various 

 colors will appear to blend into a single color. 

 This is the principle of the Maxwell color disks. 

 Throughout this review when reference is made to 

 the mixing of colors what is meant is the blend- 

 ing of colors produced on a rapidly revolving 

 Maxwell disk having its sectors differently colored. 

 In this sense we may with propriety speak of the 

 blending, say, of black and red as the mixing of 

 these two colors, using the term color in its 

 broadest sense. The mixing of pigments is a 

 different thing, and is not here referred to. 



ards to be used the first problem was to deter- 

 mine the number of segments into which the 

 original fundamental series should be broken. 

 It is both impracticable and unnecessary to 

 break this continuous series into the more 

 than one thousand hues that are recognizably 

 different to the normal eye. On the other 

 hand, the number of segments must be suffi- 

 ciently large that the gaps between them may 

 be small enough to serve the practical purpose 

 of identifying colors. On this point the 

 author says : " Distinctions of hue appreciable 

 to the normal eye are so very numerous that 

 the criterion of convenience and practicability 

 must determine the number of segments into 

 which the ideal chromatic scale or circle' may 

 be divided in order to best serve the purpose 

 in view. Careful experiment seems to have 

 demonstrated that thirty-six is the practicable 

 limit,'' and accordingly that number has been 

 adopted." 



As far as possible the gaps between each 

 successive pair of these 36 elements of the 

 fundamental series are in each case the same 

 in amount of visual color difference. The 

 scheme of nomenclature adopted provides for 

 an additional color in each of these gaps, so 

 tliat the fundamental series really consists of 

 72 named (or rather symbolized) colors, 

 though only 36 are given on the color plates. 



The fundamental series of colors thus ob- 

 tained is modified in three different ways in 

 order to cover the whole range of color varia- 

 tion. Each of these modifications produces a 

 continuous series, which we may call a sec- 

 ondary series. Each of these secondary series 

 begins with the fundamental series, either 

 pure or as modified in a previous secondary 



* The addition of the hues obtained by various 

 mixtures of violet and red renders the funda- 

 mental series a repeating one, and the various 

 hues of which it is composed may hence be ar- 

 ranged in a circle in which there is at all points 

 a gradual change of hue in passing from one 

 primary spectrum color to another. (Footnote by 

 the reviewer.) 



' ' ' That is to say, the practical limit for pic- 

 torial representation of the colors in their various 

 modifications." (Footnote of the author.) 



