on the Affections and Properties of Light. 375 
Obs. 10. and 11. The only difference in the circumstances 
is now to be reconciled. The rings surrounding the black spot 
on the top of a bubble of water, and those also surrounding 
the spot between two object glasses,* have dark intervals (ex- 
actly like those rings I have just now described, and the fringes 
surrounding the shadows of bodies) ; but these intervals trans- 
mit other fringes of the same nature, though with colours in 
the reverse order; from which Sir Isaac Newton justly in- 
ferred, that at one thickness of a plate the rays were trans- 
mitted in rings, and at another reflected in like rings. Now 
it is evident, that neither reflexibility nor refrangibility will ac- 
count for either sort of rings, because the plate is far too thin 
for separating the rays by the latter, and because the colours 
are in the wrong order for the former ; and also because the 
whole appearance is totally unlike any that refrangibility and 
reflexibility ever produce. To say that they are formed by the 
thickness of the plates, is not explaining the thing at all. It is 
demanded in what way ? and indeed we see the like dark in- 
tervals and the same fringes formed at a distance from bodies 
by flexion, where there is no plate through which the rays 
pass. The state of the case then seems to be this : “ when a 
“ phaenomenon is produced in a particular combination of cir- 
“ cumstances, and the same phaenomenon is also produced in 
“ another combination, where some of the circumstances, be- 
“ fore present, are wanting ; we are intitled to conclude that 
“ the latter is the most general case, and must try to resolve 
“ the other into it.” In the first place, the order of the colours 
in the Newtonian rings is just such as flexion would pro- 
duce ; that is, those which are transmitted have the red inner- 
• Optics, Book 1.1. P. 1. 
