1900] MICROSCOPICAL JOURNAL. 11 



Again, if we go and take a train, we observe the sig- 

 nal-boxes fitted with red and green lights which long ex- 

 perience has shown that the engine-drivers can distin- 

 guish most readily. But in using the microscope we do 

 not usually trouble about the sensitiveness of our eyes to 

 colors; in other words, we are much too apt to forget that 

 whilst our eyes are very sensitive optical instruments, 

 we must pay due regard also to their physiology. This 

 then is the keynote to the way in which multiple color il- 

 lumination acts in sharpening the vision. We get greater 

 perception of detail, of depth, and of solidity or gen- 

 eral form. 



At the same time knowing how we have arranged our 

 colored lights to fall upon our objects, and noticing which 

 parts are lighted up in the various colors, we are able to 

 draw additional inferences as to their size — even in mat- 

 ters of wave lengths — as to their shape, and as to whether 

 what we see is the true object, or a false light effect, for 

 such may frequently occur with bad illumination, and have 

 caused innumerable discussions. It is a lesson in micro- 

 scopic optics in itself to study the appearance of air or oil 

 bubbles in water with different kinds of multiple color 

 illumination, and I may safely say that most readers who 

 experiment with these kinds of illuminatiou will know 

 considerably more about their microscopes after than 

 before. 



The scope of multiple color illumination is a large one ; 

 it lends itself well to the study of botanical and physio- 

 logical preparations, to the study of living organisms, 

 to investigations on diatom structure, to commercial pur- 

 poses, as examining fibres, papers, etc., and to photo-mi- 

 crography. 



It has been my endeavour in this article to convey an 

 idea as to the methods and theory of multiple color illu- 

 mination in an intelligible manner, without going too 

 much into technicalities, and those who are sufficiently in- 



