C 180 3 
IX. Experiments for investigating the Cause of the coloured con- 
centric Rings, discovered by Sir Isaac Newton, between two 
Object-glasses laid upon one another. By William Herschel, 
LLD. F.R.S. 
Read February 5, 1807. 
T he account given by Sir I. Newton - , of the coloured arcs 
and rings which he discovered by laying two prisms or object- 
glasses upon each other, is highly interesting. He very justly 
remarks, that these phenomena are “ of difficult considera- 
tion/* but that “ they may conduce to farther discoveries for 
“ completing the theory of light, especially as to the consti- 
“ tution of the parts of natural bodies on which their colours 
“or transparency depend.”* 
With regard to the explanation of the appearance of these 
coloured rings, which is given by Sir I. Newton, I must con- 
fess that it has never been satisfactory to me. He accounts 
for the production of the rings, by ascribing to the rays of 
light certain fits of easy reflection and easy transmission alter- 
nately returning and taking place with each ray at certain 
stated intervals.-f* But this, without mentioning particular ob- 
jections, seems to be an hypothesis which cannot be easily 
reconciled with the minuteness and extreme velocity of the 
particles of which these rays, according to the Newtonian 
theory, are composed. 
* Newton’s Optics, 4th ed. p, 169. 
f Ibid. p. 256. 
