12 X)r. Young’s Experiments and Calculations 
other, and of extinguishing the light, where they happen to be 
united; that these qualities succeed each other alternately in 
successive concentric superficies, at distances which are constant 
for the same light, passing through the same medium. From the 
agreement of the measures, and from the similarity of the phe- 
nomena, we may conclude, that these intervals are the same as 
are concerned in the production of the colours of thin plates ; 
but these are shown, by the experiments of Newton, to be the 
smaller, the denser the medium ; and, since it may be presumed 
that their number must necessarily remain unaltered in a given 
quantity of light, it follows of course, that light moves more 
slowly in a denser, than in a rarer medium : and this being 
granted, it must be allowed, that refraction is not the effect of 
an attractive force directed to a denser medium. The advocates 
for the projectile hypothesis of light, must consider which link 
in this chain of reasoning they may judge to be the most feeble; 
for, hitherto, I have advanced in this Paper no general hypo- 
thesis whatever. But, since we know that sound diverges in 
concentric superficies, and that musical sounds consist of oppo- 
site qualities, capable of neutralising each other, and succeeding 
at certain equal intervals, which are different according to the 
difference of the note, we are fully authorised to Conclude, that 
there must be some strong resemblance between the nature of 
sound and that of light. 
I have not, in the course of these investigations, found any 
reason to suppose the presence of such an inflecting medium in 
the neighbourhood of dense substances as I was formerly in- 
clined to attribute to them ; and, upon considering the pheno- 
mena of the aberration of the stars, I am disposed to believe, 
that the luminiferous ether pervades the substance of all material 
