204 Dr. a. Hod(;kinson on 



been so to vary the relationship of the various natural and 

 artificial bodies, or their parts, to the source of illumination 

 ^as to produce characteristic appearances, or colour changes. 

 When such colour effect has been found to agree in its 

 nature and properties with one of the known modes of 

 colour-production, it has itself been referred to such group, 

 and the same structural cause has been inferred to exist in 

 it as characterises the group even thongJi microscopic and 

 ■other methods of examination fail to reveal such structure. 

 Such method, which is only a part of a more extensive, 

 but similar, method framed to allow of the investigation of 

 all bodies, whether coloured or not, vide " Ultra-microscopic 

 Structure and Methods of its Investigation," I shall speak 

 of under the title of " Chromatic Analysis," and to facili- 

 tate such method, I have constructed a systematic table, by 

 following which, the different colour phenomena may be 

 the more readily grouped. I have felt justified in thus 

 taking colour-production as a manifestation of structure, 

 because I find that of all optical phenomena, excepting of 

 course image formation, those attended by the produc- 

 tion of colour are the most significant of structural con- 

 formation. 



Examination of bodies, according to the plan advocated, 

 naturally necessitated some modification in existing instru- 

 mental appliances. These I shall, as occasion arises, bring 

 before your notice. On the present occasion I will only call 

 your attention to a microscope, constructed for me by 

 Messrs. Smith and Beck, and so arranged as to allow of great 

 variety in the relationship of bodies, or their parts, to the 

 source of illumination. The moveable parts are all graduated 

 so that this relationship may be known and recorded. 

 Without some such appliance as this, I should have been 

 quiteunableto havedone evenwhat little I have accomplished. 

 In the preceding cursory sketch I have attempted to 

 convey some notion of the nature of the enquiry I have 



