556 



NA TURE 



[October 6, 1904 



of the simplest, and yet sacrificing nothing in the 

 way of accuracy and clearness; and, although the 

 book was written to aid artists in their study of 

 nature, it will none the less be welcomed by men of 

 science and those amongst the general public who 

 attach importance to accurate observation. 



There are some artists who make no secret of 

 their disdain for scientific methods as an aid to their 

 work ; but even these, on reading Sir Montagu 

 Pollock's book, will be forced to admit lli.ir in- 

 debtedness. Some sort of scien- 

 tific method is indispensable for 

 accurate observation of reflexions 

 in water. Even reflexions in still 

 water differ from what would be 

 expected by an untrained ob- 

 server; the reflected image is 

 indeed generally a counterpart 

 of the object, but it not un- 

 commonly presents an entireh 

 different "aspect. Many striking 

 instances of this are discussed 

 and explained in the first chapter ; 

 one of the most remarkable is 

 afforded by the reflexion of a rain- 

 bow in a lake, which is really 

 the image of a bow quite dis- 

 tinct from the one seen directly. 

 When we come to the study of 

 reflexions in rippled water, 

 further complications arise; in 

 I he second chapter, the reader is 

 led on from the most simple' and 

 elementary facts to appreciate 

 and understand complicated 

 effects such as are reproduced in 

 the accompanying illustration 

 (Fig. i). In such cases some 

 amount of scientific training is 

 absolutely necessary to one who 

 ■would give a faithful pictorial 

 representation of nature ; for the 

 appearance presented changes 

 every instant, and without the 

 aid of some sort of clue one can 

 scarcely avoid obtaining inhar- 

 monious effects. But even in 

 still water, where there is no in- 

 cessant change to distract the 

 attention, there are yet many 

 opportunities for the artist to go 

 wrong ; without a very accurate 

 knowledge of fundamental 

 principles, it would be impossible, 

 for instance, to deduce the nature 

 of the reflexions shown in Fig. 2 

 from the actual appearance of the 

 objects reflected. Notice, for in- 

 stance, that while the reflected 

 image of the spire of the distant 

 church is seen, the body of the 

 church and the dark hill behind 

 it are not present in the reflexion ; there is even no 

 image to be seen of the shore between the church 

 and the water. 



The third and fourth chapters are devoted to a 

 study of the colours in still and rippled water. This 

 part of the subject is exceedingly complicated, and 

 it is difficult to make any general statement which 

 will help us to predict the exact colours to be seen 

 under given conditions. The observed colour of the 

 ■water is due, partly to light reflected froni the surface 

 of the water; partly to light scattered by minute 

 particles floating on the surface; partly to the 



NO. 1823, VOL. 70] 



inherent colour of the water, modified, maybe, by the 

 presence of fine suspended particles ; partly to the 

 colour of the stones, sand, or mud at the bottom of 

 the water; and, lastly, the whole effect is complicated 

 by " contrast," which may modify greatly the various 

 colours observed. For instance, standing on one of 

 the cliffs of Sark, and looking out over the sea, the 

 latter often appears of a vivid green, dappled here 

 and there with patches of intense purple. Careful 

 ,)l)s,T\-,-iru.n sliows (li;il the pur|>Ic p.'ilcln'- -n,:r1c t'l, 



— Sils Basiglia, Upper Engad 



L'ght and Water." 



sites of submerged beds of sea-weed ; but the weed 

 is not itself purple, but of a dark olive-green colour, 

 so that the colour of the patches is not easily ex- 

 plained. The most probable explanation appears to 

 be as follows :— The sea-water is itself blue, i.e., it 

 is relatively opaque to red and partly opaque to 

 yellow light. Yellow light is most copiously reflected 

 from the sandy bottom of the sea, so that, on the 

 whole, the greater part of the light reflected from the 

 bottom of the sea which reaches our eyes is green. 

 The beds of sea-weed merely act as general 

 absorbers, and would give rise to dark patches were 



