black Spot. And, on the contrary, by lifting up
the upper Glass from the lower, the diameter of the Rings would
decrease, and the breadth of their Orbit increase, until their Colours
reached successively to the center; and then they being of a
considerable breadth, I could more easily discern and distinguish their
Species than before. And by this means I observ'd their Succession and
Quantity to be as followeth.

Next to the pellucid central Spot made by the contact of the Glasses
succeeded blue, white, yellow, and red. The blue was so little in
quantity, that I could not discern it in the Circles made by the Prisms,
nor could I well distinguish any violet in it, but the yellow and red
were pretty copious, and seemed about as much in extent as the white,
and four or five times more than the blue. The next Circuit in order of
Colours immediately encompassing these were violet, blue, green, yellow,
and red: and these were all of them copious and vivid, excepting the
green, which was very little in quantity, and seemed much more faint and
dilute than the other Colours. Of the other four, the violet was the
least in extent, and the blue less than the yellow or red. The third
Circuit or Order was purple, blue, green, yellow, and red; in which the
purple seemed more reddish than the violet in the former Circuit, and
the green was much more conspicuous, being as brisk and copious as any
of the other Colours, except the yellow, but the red began to be a
little faded, inclining very much to purple. After this succeeded the
fourth Circuit of green and red. The green was very copious and lively,
inclining on the one side to blue, and on the other side to yellow. But
in this fourth Circuit there was neither violet, blue, nor yellow, and
the red was very imperfect and dirty. Also the succeeding Colours became
more and more imperfect and dilute, till after three or four revolutions
they ended in perfect whiteness. Their form, when the Glasses were most
compress'd so as to make the black Spot appear in the center, is
delineated in the second Figure; where _a_, _b_, _c_, _d_, _e_: _f_,
_g_, _h_, _i_, _k_: _l_, _m_, _n_, _o_, _p_: _q_, _r_: _s_, _t_: _v_,
_x_: _y_, _z_, denote the Colours reckon'd in order from the center,
black, blue, white, yellow, red: violet, blue, green, yellow, red:
purple, blue, green, yellow, red: green, red: greenish blue, red:
greenish blue, pale red: greenish blue, reddish white.

[Illustration: FIG. 2.]