Jan. :o, 1888,] 



SCIENTIFIC NE^VS. 



63 



REVIEWS. 



Colour: An Elementary Manual for Students. By 

 A. H. Church, M.A., F.C.S. New and Enlarged 

 Edition, with Six Coloured Plates. (Cassell 

 and Co., 1887.) 

 It is to be regretted that when revising and enlarging 

 this valuable little work, the main subject has not been 

 still further amplified, for we find the first fifty pages out 

 of a total of less than two hundred, are occupied by a 

 general account of the theory of light and production of 

 colour, and in the latter chapters the author enlarges on 

 the eesthetics of architecture, ceramics, and jewellery. 

 The list of contents is followed by a page of bibliographi- 

 cal notes, which are too rarely to be found in an English 

 text-book, and which remind us that only two other 

 modern English works are devoted to the subject of chro- 

 matics or the science of colour. We observe that no 

 table of wave-lengths is given, a rather serious omission, 

 when, owing to the " vagueness which seems to be in- 

 herent in the nomenclature of colour," a simple hue 

 can only be accurately specified by reference to its posi- 

 tion on the spectrum. The want is apparent, for 

 example, when the three primary sensations of IVIaxwell 

 and Helmholts are described on p. 68, " Maxwell's green is 

 to be found at one quarter the distance from E, between 

 E and F, and resembles emerald green in hue." We are 

 not informed whether the prismatic or the normal spec- 

 trum is referred to, and the position would be much more 

 accurately described by stating (in addition) that the 

 wave-length is 501 millioneths of a millimetre. Although 

 frequent mention is made of Maxwell's rotating discs for 

 the combination and study of colours, the method is not 

 recommended so strongly as it deserves ; offering, as it 

 does, the greatest facility for quantitative analysis, a large 

 area of perfectly uniform colour for examination, and the 

 advantage of being easily and cheaply constructed by one 

 who cares to experiment for himself We doubt if " it is 

 so easy for any one studying the subject of colour to 

 examine for himself the actual appearances presented by 

 the spectrum," for not only is the apparatus somewhat 

 expensive; but the management of a darkened room, and 

 an efficient substitute for sunlight on dull days, are 

 matters of considerable trouble to any one who has not 

 access to a properly equipped laboratory. The chapters 

 on contrast, contact, and separation, mutual influence, 

 harmonies and balance are full of matter which must be of 

 the highest importance to manufacturers of textile fabrics, 

 as well as to those engaged in decorative and pictorial art 

 The coloured plates aim only at the simplest effects, and 

 are offered as rough approximations to the true hues ; and 

 thus succeed in forming a valuable feature instead of a 

 misleading eyesore. A number of useful tables of classi- 

 fied colours are given, and some attention is directed to 

 the " broken hues " such as russet, olive, sage, slate, " of 

 which ornamental art constantly makes such admirable 

 use." Most of these are defined and the components and 

 complementaries specified, but " puce " and " buff " are 

 only alluded to, and not appear in any of the lists. The 

 chemical propensities of the author come out in calling 

 the familiar " hypo " of the photographer, " sodium thio- 

 sulphate " ; and in attempting to describe a certain kind of 

 pink, it is likened to the rose acacia, the almond 

 blossom, the flowers of the double peach, and finally, " it 

 is, perhaps, more closely represented by the flame of 

 burning cyanogen. " 



A few slips occur, is in Fig. 3, where a beam of light 

 after passing two prisms in Newton's second experiment, 

 is shown as parallel, instead of diverging ; and a triangle 

 is spoken of on p. 59, as being a figure of one dimension. 

 Green is printed for yellow on Fig. 31. The author 

 acknowledges his indebtedness to Ogden Rood, the 

 author of "Modern Chromatics," and cites a curious obser- 

 vation as being due to him, relating to the admixture of 

 black and white. "It is generally allowed that even the 

 purest black pigments, as free as possible from any tinge 

 of colour, yield, when mixed with white pigments, a bluish 

 grey. This has been usually attributed to the fineness 

 of the particles producing a blue colour by the same 

 notion on the light as an opalescent medium. But it has 

 been shown that when white and black are mingled 

 opticalh' on a rotating disc, the grey they yield is matched 

 in hue (not in brightness) by a white disc into which 

 1 7 per cent, of blue, in the form of a strong wash of 

 indigo, has been introduced. The real cause of the blue 

 tinge produced in these cases seems to be traceable to the 

 fact that, with a low illumination, the nerve-fibrils of the 

 retina which correspond to the sensation of the blue are 

 called into action more energetically than those which 

 give the sensations of red and green, and so the white we 

 see on looking at a neutral grey is tinctured with blue." 

 Mr. Church's manual cannot fail to be a useful supple- 

 ment to the artistic instincfof the designer, who plays so 

 important a part in many manufacturing industries con- 

 tributing to the beauty and comfort of our homes, and 

 will explain in a popular manner the leading facts of a 

 very attractive science to those vi'ho may take it up for its 

 own interest. 



Lectures on Bacteria, by A. De Bary. Translated by 

 H. E. F. Garnsey, M.A., and J. B. Balfour, M.A., 

 M.D., F.R.S. Second edition. Oxford: Clarendon 

 Press. 

 This is the book our readers want. The translators 

 say there is no other book in English which gives a 

 general view of the subject, and sets forth the known 

 facts in the life of bacteria in their connection with those 

 with which we are acquainted in other branches oi 

 natural history ; and the author says he has had to make 

 himself intelligible to all who were not strangers to the 

 elements of a scientific training. The translators are 

 right, and the author is successful. A difficult but deeply 

 interesting subject is here brought before us clearly and 

 simply, as clearly and simply as is possible consistently 

 with scientific accuracy and completeness. We are 

 tempted to quote largely, but our limited space forbids ; 

 we cannot refrain, however, from speaking of the in- 

 genious way in which Professor De Bary has refuted 

 Wigand's theory of equivocal generation. Wigand states 

 that motile bacteria are found in the healthy living cells 

 of the leaf of a South American water-plant, Trianea 

 Bogotcnsis. Professor De Bary makes the following 

 remarks on this : — " If living tissue from the fresh 

 healthy leaf is placed under the microscope, we shall 

 really see in many cells the prettiest representations of 

 the appearance of bacteria, small slender rods, isolated 

 or attached together in short rows, and actively following 

 the movements of the protoplasm and other cell con- 

 tents. An excellent representation, as 1 said, or model. 

 But a drop of dilute muriatic acid destroys the illusion." 

 The pseudo-bacteria are simply small crystals oi 

 calcium oxalate, and with them dissolves the elaborate 

 superstructure built upon their misleading forms. 



