230 PHILOSOPHICAL TRANSACTIONS. [ANNO 1797. 



pieces of transparent glass, tinged with various colours to the light of the sun, and 

 received what was reflected from them on white paper, in a darkened part of his room. 

 He then found, that each glass produced 2 luminous circles, which, when the paper 

 was sufficiently remote, were entirely separate from each other ; and that the circle 

 which proceeded from the upper surface of the glass was altogether without colour, 

 while that which arose from the under surface, was of the same colour as the glass 

 exhibited, when held between the light and the eye. From these experiments 

 Zucchius also concluded, first, that every coloured body must be in some degree 

 transparent, since a body absolutely impenetrable to light, could only reflect the 

 colours of other bodies, but possess none of its own ; and 2dly, that all bodies, 

 which appear coloured when seen by reflected light, must be in some measure opake; 

 for as the light which is reflected from their surfaces comes untinged to the eye, if 

 that part of it which penetrates their substance were afterwards to proceed in it 

 without impediment, no colour could be exhibited by them.* 



When Sir Isaac Newton began his experiments on light and colours, it was ge- 

 nerally believed, that colours in opake bodies arise from some modification given to 

 light, by the surfaces which reflect it. In opposition to one part of this opinion, 

 our great philosopher maintained, that such bodies are seen coloured, from their 

 acting differently on the different colorific rays, of which white light is composed; 

 but having established this point beyond dispute, he seems to have admitted, with- 

 out inquiry, that colours are produced at the surfaces of the opake bodies to which 

 they belong. For his experiments do not necessarily lead to such a conclusion ; on 

 the contrary, they are not more consistent with it, than they are with the opinion 

 of Kepler and Zucchius. This opinion indeed he appears not to have known ; since 

 he has taken for granted, what is contradicted by the experiments on which it is 

 founded, that the tinging particles of transparent bodies reflect coloured light.-}- 



The very splendour of Sir Isaac Newton's discoveries in optics, has probably 

 done some injury to this branch of knowledge; for soon after they were made 

 public, it became a common opinion, that the subject of light and colours had 

 been exhausted by that great man, and that no writer on it before him was now 

 worthy of being read. The former part of this opinion has long been generally 

 acknowledged to be unjust; but the latter part of it is still maintained by many, 



* The works of Zucchius seem very little known, though they contain a considerable number of ori- 

 ginal experiments, and though it is probable that he was the inventor of the reflecting telescope. For 

 he says (Pars 1, p. 126) it had occurred to him so early as l6l6, that the same effect which is produced 

 by the convex object-glass of a telescope, might be obtained by reflexion from a concave mirror; and 

 that, after many attempts to construct telescopes with such mirrors, which proved fruitless from imper- 

 fections in their figure, he at length procured a concave mirror very accurately wrought, by means of 

 which, and a concave eye-glass, he was enabled to prove his theory to be just. He does not mention at 

 what precise time he constructed this telescope: but his book was printed in lo"52, 1 1 years before the 

 publication of the " Optica Promota" of James Gregory. I have not met with any account of Zucchius, 

 in Montucla's or Priestley's histories; in the article " telescope," in the French Encyclopedia; or in any 

 Biographical dictionary which I have consulted. 1 Optics, book 1, part 2, prop. 10. — Orig. 



