The Structure of Coloured Bodies. 203 



effect, such as reflection, refraction, absorption, dispersion, 

 interference, diffraction,and double infraction, or polarisation. 

 What is the structural significance of these various phen- 

 omena, and to what extent we are justified in relying on 

 them as indications of structure, I have considered in 

 detail in a paper on "Ultra-microscopic Structure, and 

 Methods of its Investigation," which I hope to have the 

 opportunity of laying before the Society. 



In the present communication, dealing as it does with 

 coloured bodies, I purpose selecting from the various 

 divisions of the animal, vegetable, and mineral kingdoms, 

 typical examples of objects characterised by striking 

 or peculiar colour-production. Having drawn atten- 

 tion to the peculiar features of such appearances, and 

 the modification these undergo by varying conditions 

 of illumination, I shall, so far as I am able, describe 

 the structural or physical cause of these colours. This, 

 the main object of the communication, was in the first 

 instance my sole intention, and this more especially as 

 I have, in the previously mentioned paper, considered in 

 detail the methods for investigating ultra-microscopic 

 structures. It occurred to me, however, that without some 

 explanation of the methods by which I had arrived at the 

 results in the present instance, these might not be so 

 interesting or acceptable as if a sufficient reason were given 

 for them. Accordingly I have devoted preliminary sections 

 to the consideration of the nature and properties of colour, 

 and having described the different modes of colour-produc- 

 tion, and shown the relationship, so far as known, to the 

 structures producing them — in other words, their structural 

 significance. I have considered separately each of these 

 different modes of colour-production in order to ascertain 

 their characteristic features, so that they might, by exami- 

 nation, be easily recognised. 



The main object in such methodical examination has 



