Dr Goring on Monochromatic Light, fyc 51 



of direct and oblique incidence. I hope some person, better 

 able than myself to look into these things, and better furnish- 

 ed with apparatus, will examine this subject in a proper man- 

 ner. The impression produced in my mind was, that a cer- 

 tain quantity of white light enters into the constitution of each 

 of the seven coloured rays, as water does into the constitution 

 of alcohol, and may be rendered manifest by the dispersive 

 power of prisms and lenses under the circumstances I have de- 

 scribed. 



At all events, / think no effective monochromatic light is 

 likely to be obtained for illuminating chromatic microscopes, 

 so to render them equivalent in their action to achromatic 

 ones. 



I shall now proceed to notice some assumptions respecting 

 the achromatism of erecting eye-pieces and engyscopes, which 

 consist in supposing that, by arranging a system of glasses 

 with certain intervals, we may form an achromatic combina- 

 tion without correcting what I shall call the objective part sepa- 

 rately. Had these proceeded from more obscure and less in- 

 fluential persons, I should have allowed them to rest in peace ; 

 but the power of proficients in the exact sciences is so great, 

 either in retarding or advancing the perfection of optical in- 

 struments, that I feel it absolutely necessary for my own ho- 

 nour, and that of the improvements lately introduced into use, 

 to endeavour to rectify what seems to me retrogradations and 

 abuses. The dicta of mathematicians of high reputation are 

 generally received without examination, because it is conceiv- 

 ed, and not without justice, that they can hardly say or do 

 any thing wrong. If they could, many there are who will 

 think it more creditable to be in the wrong with them than in 

 the right with mere practical men. Yet optics is both an ex- 

 perimental and a demonstrative science ; and though experi- 

 ment ought certainly never to dictate to analysis, (which 

 would be placing the cart before the horse with a vengeance,) 

 yet the testimony of those organs which are to use optical in- 

 struments must not be wholly rejected. 



A telescope and what is usually termed a compound micro- 

 scope pass into each other by iiisensiblc degrees, so that it is 

 somewhat difficult to define the one distinctly from the other, 



