on the Colour of Blood. 419 
internal parts, and is thence sent hack through those sur- 
faces. The following are some of the experiments, upon which 
he. founded this doctrine. He exposed small round pieces of 
transparent glass, tinged with various colours, to the light of 
the sun, and received what was reflected from them upon white 
paper, in a darkened part of his room. He then found, that 
each glass produced two 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, se- 
condly, 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 co- 
lour could be exhibited by them.* 
* The works of Zucchius seem very little known, though they contain a consi- 
derable number of original experiments, and though it is probable that he was the 
inventor of the reflecting telescope. For he says (Pars i. p. 126.) it had occurred to 
him so early as 1616, 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 imperfections in their figure, he at length procured a concave mirror very accu- 
rately 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 
MDCCXCV 1 I. . 3 I 
