SCIENTIFIC NOTES AND OBSERVATIONS. 85 



coloured light that comes back after penetrating the pigment in the 

 scales. The pigments in these blotches, are those that have the greatest 

 brightness or luminosity — viz. — some shade of orange-3'ellow. This 

 pigment reflects, not only tlie yellow rays freely, but also some of the 

 other very luminous rays, which all added togcthei", make up yellow. 

 (If the luminosity is put down as lUO, that of chrome-yellow will be 

 7o or 80 — vermilion, 25 — emerald-green, 48 — blue, 35 — ultramarine, 7). 

 This highly luminous yellowish-white, mixed with the reflected masses 

 of white light (instead of very scattered white light) gives the metallic 

 appearance. The scales in these blotches are seen (under the micro- 

 scope) to have no teeth, or virtually none (merely slightly rounded 

 elevations) so that the white light is reflected in mass, so to speak, 

 and not scattered by the teeth as in the rest of the wings. The effect 

 is also heightened by darker, only slightly luminous patches, surrounding 

 the blotches more or less, just as the parts in shadow on a polished 

 metallic surface look almost black, and so hel}:) to increase the brilliant 

 appearance. 



The side issues in our discussion on the action of chemical re-agents 

 on the colour of pigments, seem to me, not merely relevant, but necessary. 

 We must have a clear understanding of the meaning of terms used, or, 

 we shall only wander in a maze of our own creation. The word 

 " pigment " is apparently the rock on which we are splitting. I 

 endeavoured to give a simple definition, according with present scientific 

 knowledge, which might help to clear that popular but erroneous one, 

 wliich makes pigment a material collection of atoms or molecules. The 

 late Professor Tyndall described the granules, etc., producing colour, as 

 having a sifting or selective power over white light, which enabled 

 them to extract from it what he described as "the luxury of colour." 

 He expressly stated that such power is not " creative " but " selective," 

 and further went on to say, " There is no colour generated by any natural 

 body whatever." How then about Dr. Freer's suggestion of the 

 " isolation of pigment ? " Dr. Freer may fairly retort that all text- 

 books speak of bile and blood-pigments, melanin, etc., but I think I 

 am not hair-splitting when I suggest caution in an acceptance of the 

 word in its popular sense, without conceding the scientific limitations 

 which ought to tpialify it. I must join issue with Dr. Freer and Mr. 

 Tutt as to there being any such thing as " black pigment." Blackness 

 is produced by the absorption of all the constituents of hght penetrating 

 an object, so that none are reflected (except, of course, from tlie surface 

 before the light penetrates, which has nothing to do with colour). How 

 few of our insects are really black ! What we call melanic specimens 

 are for the most part somewhat coloured, some few rays of light (more 

 or less) are reflected through the object from its internal surfaces 

 (the majority being absorbed) and it is these few reflected rays that 

 determine the amount of colouring. Did sucli a thing as black pigment 

 (in our qualified sense) exist, it would mean black rays amongst the 

 constituents of light, together with the red, green and violet ! Blackness 

 is simply a " quenching " of light. Of course, there is the quench- 

 ing due to interference of light, as well as that due to absorption. 

 There seem to me to be two objections to Dr. Freer's theory about the 

 change of colour in T. rubi, when wetted: — (I). The refraction caused 

 by water and the scale, must be in the same direction, because both are 

 denser media than air, and tlierefore, there can be no neutralisation as 



