124 



NATURE 



[December 12, 1895 



Livius, and Catullus being Caligula', Livii, and Cafulli, 

 I cannot accept such specific names as Dortat, Retziust, 

 Cafulloi, but consider that they should be corrected to 

 Dorics, Refzii, Catulli." 



With regard to genera, Dr. Thorell considers that such 

 terms as Scorpio and Aranea, cannot be used in a generic 

 sense, because in the plural form they are applied 

 respectively to the orders of Scorpions and Spiders. This 

 view, however, is, we venture to think, untenable. For 

 the terms were used by Linnaeus generically before they 

 were used ordinally; therefore, if it be considered necessary 

 to change either the generic or the ordinal name, it is 

 surely the latter that should be abolished. Moreover, in the 

 interests of nomenclature it is more important that the 

 generic name should be stable than the other. And 

 curiously enough. Dr. Thorell, with apparent inconsistency, 

 seems to take this view of the case when there is any 

 clashing between the name of a family and of one of its 

 genera. For he always, and we believe correctly, forms 

 he family-names with the termination — oidse, such as 

 Lycosoidai instead of the more usually accepted Lyco- 

 sida;. But he affirms that if there be a genus termed 

 Lycosoides contained in the family Lycosoidas, the latter 

 name must be altered, and a new one constructed from 

 some other genus, e.g. Trochosoida, be adopted. The prac- 

 tical application of this view has led him to abandon such 

 ong-established family-names as Epeiroidse, Thomisoidas, 

 Attoidas ; but if it were to be consistently and universally 

 adopted, it is clear that all the family-names now in 

 vogue, and every successive substitute, might have to be 

 changed and again changed ad infinitum. 



One other point deserving of notice is Dr. Thorell's 

 opinion that the priority of species-xi-3ss\f=, should be 

 reckoned from 175 1, when Linnaeus, in his " Philosophia 

 Botanica," proposed and gave rules for his binomial 

 nomenclature. Most zoologists now refer back to 1758, 

 the date of the pubHcation of the tenth edition of the 

 *' Systema." But Linnaeus's disciple Clerck published in 

 1757 his classical work "Aranei Suececi," in which he 

 -describes and gives good coloured figures of about 

 sixty species of Swedish, spiders, with binomial names 

 according to Linnaeus's system, and no arachnologist can 

 admit that these names ought to be rejected simply 

 because they were published before the tenth or twelfth 

 edition of the "Systema." Such questions as these, 

 however, we may perhaps leave with safety and con- 

 fidence in the hands of the two recently appointed 

 "bibliographical committees, from which so much is 

 expected. R- I- P. 



COLOUR VISION. 

 ■Colour Vision : being the Tyndall Lectures delivered in 

 1894 at the Royal Institution. By W. de W. Abney, 

 C.B., D.C.L., F.R.S. (late R.E.) Pp. ix. -1- 231, 8vo. 

 (London : Sampson Low, Marston, and Co., 1895.) 



CAPTAIN ABNEY has long been known as the 

 authority upon the scientific measurement of colour, 

 and his researches have naturally involved a continual 

 -attention to the problems of colour-vision. This, too, he 

 has made the subject of measurement in numerous ways, 

 .and in observations extending over many years. The 

 NO. 1363, VOL. 53] 



results of his work in the domain of colour-vision were 

 systematically expounded by him in the " Tyndall Lec- 

 tures" of 1894, and have now been recast in their present 

 form. The volume, which is sumptuously printed in 

 double-leaded type, is illustrated not only by numerous 

 cuts and process-blocks, but by an excellent chromolitho- 

 graphic spectrum chart of the typical cases of colour- 

 vision. It is worthy of the reputation of the President of 

 the Physical Society, and constitutes a distinct addition 

 to the literature of physiological optics. 



The work, as published, is now arranged in chapters 

 without reference to the original disposition of the subject- 

 matter when delivered in the form of lectures ; and a very 

 large portion of the book is devoted to the various cases 

 of colour-blindness, both congenital and acquired, in- 

 cluding the species of amblyopia due to excessive use of 

 tobacco. In the opening chapter, which deals with the 

 anatomy and physiology of the eye, the fascinating theory 

 of the " visual purple " is mentioned, only to be at once 

 dismissed as incompatible with the fact that that part of 

 the retina which is most sensitive both to light and colour, 

 the forea centralis, is destitute of the structures which 

 alone contain the substance which possesses the purple 

 reaction. The second chapter deals with the wave-lengths 

 that correspond to the several colours of the spectrum, 

 and with the apparatus devised by the author for pro- 

 ducing any desired mixtures of spectrum tints for the 

 purpose of colour-matching. The physical proofs that 

 green is a primary colour because it cannot be made up 

 by mixing any two other colours, and. that yellow is not 

 a primary because a yellow can be made by a mixture of 

 two others, are given very clearly. On p. 24 the author 

 remarks that " we are all familiar with the fact that there 

 are three primary colours," whereas the fact is not that 

 the colours are primary, but that the sensations are 

 primary ; and he assumes, without any proof save that of 

 indirect inference, that these primary sensations are three 

 in number. Indeed, in another passage the admission 

 seems to be made that the sensations which are primary 

 are four in number. 



Quoting from Prof Michael Foster's epitome of 

 Hering's theory of colour-vision, the author gives the 

 following statement. 



" The sensations caused by different kinds of light, or 

 by the absence of light, which thus appear to us quite 

 distinct, and which we may speak of as ' native ' or 

 ' fundamental ' sensations, are white, black, red, yellow, 

 green, blue. Each of these seems to us to have nothing 

 in common with any of the others, whereas in all other 

 colours we can recognise a mixture of two or more of 

 these. . . . Hering's theory attempts to reconcile, in 

 some such way as follows, the various facts of colour 

 vision with the supposition that we possess these six 

 fundamental sensations. The six sensations readily fall 

 into three pairs, the members of each pair having 

 analogous relations to the other. In each pair the one 

 colour IS complementary to the other, white to black, red 

 to green, and yellow to blue." 



Commenting on this theory as so stated. Captain 

 Abney says that it should be described as "tetra 

 chromic " (should it not be chromatic ?) rather than 

 " tri-chromic," for as far as " colour " is concerned, the 

 black-white sensation must be excluded But, surely 



