138 THK entomologist's record. 



Scientific notes & observations. 



TDiscussion on the JNlature of certain Insect Colours. 



(Continued from p. 111. I 



I can hardly take upon myself to join in the discussion of the pig- 

 ment question. My microscoi)ical work seems now to be pretty nearly 

 over, and I find myself also quite behind the times in the use and 

 even in the comprehension of the highly technical terminology of the 

 subject. Ma_y I, nevertheless, offer a few remarks which may, I hope, 

 bring the matter down again to the level of ordinary mortals, without 

 in any way trenching upon the preserves of the " Giants " ? 



Colour is the result of the action of substances or surfaces upon 

 light, and is produced in various ways — either by the selective ab- 

 sorption of part of the light, and the reflection of the remaining part, or 

 by refraction, interference or diffraction, in each of which cases the 

 light is split up into its component parts, and the reflection of a part 

 or the whole of this decomposed light, gives colour. Therefore, without 

 light, there can be no colour, a fact Avhicli, though somewhat difiicult 

 to understand, is yet often forced upon our notice. If Ave walk 

 among our flowers in the evening Avith our net in hand, Ave must 

 notice how the colours gradually disappear as the light fails, initil 

 almost every flower (the Avhite last of all) becomes of the same 

 uniform shade. Of course in ordinary talk Ave say 'tis "too dark 

 to see ; " but the fact remains that we can see moths and can distin- 

 guish form but cannot see colour, because there is no longer light 

 enough to produce colour ; or, to put it the other Avay about, the sub- 

 stances, surfaces, or Avhat not, have no longer sufticient light from 

 Avhich to select their own particular fancy and to reject (reflect) Avhat 

 they do not want and Avhat Ave ought to see. I have often liked to 

 think that the photograph (negative or positive) gives us an idea of a 

 Avorld Avithout colour. We see then the familiar forms — but not in 

 their familiar colours. All are reduced to the same dead leA'el, i.e., 

 presented correctly as to form, bi;t all in one substance, and CA'ery- 

 Avhere able only to act in precisely the same manner upon the light 

 falling upon it. The whole surface absorbs the same rays and reflects 

 the same rays. The result is a monochrome. The conditions Avill not 

 reproduce the actual state of things ; there is total absence of the sub- 

 stances (surfaces) Avhich by absorption, reflection, &c., go to produce 

 what Ave call the true colour of the object. 



As to colour resulting from the action of substances (or surfaces) 

 upon light, it is certain that these surfaces or substances must liaA'e 

 white light to act upon, if they are to select (or reject) all colours, and 

 that liuht wliich lacks any constituent aviII not give what we conceive 

 to be the true natural colour of the particular object under examina- 

 tion ; hence the peculiar and unnatural appearance of objects under 

 monochromatic light. Now Ave come to the point under discussion as 

 far as I understand it. Is colour the effect of " j^igment " or of 

 "refraction" in the case of any particular object, e.g., a lepidop- 

 terous insect ? Pigment stands for matter Avhicli exercises this poAver 

 of absoiption and rejection of a part (colour), reflection of the whole 

 (white), or absorption of the whole (black) of the white light, e.g. 

 paint, &c. Eefraction, interference and diffraction, stand for the 



