1919-20.] An Unnoticed Point in Theory of Newton’s Rings. 51 
YII. — An Unnoticed Point in the Theory of Newton’s Rings. By 
J. Marshall, M.A., B.Sc., University College, Nottingham. 
Communicated by Professor W. Peddie, D.Sc. 
(MS. received November 28, 1919. Read January 12, 1920.) 
become 
and 
f mZ 
- llY = — fxca 
uX = — yr/3 
mX - — ficy 
'my - nf 3 = — X 
K v 
Tl a = — 1 
The consideration of the passage of light waves through three media 
elucidates an interesting point in the Theory of Newton’s Rings. 
Let the three media be denoted by the 
numerals 1, 2, 3, and let 2 = 0 be the plane 
of separation between media 1 and 2 and 
z=—a the plane of separation between 
media 2 and 3. Also let the axis of x in ^ 
the plane z = 0 be parallel to the wave 
front of the incident plane waves. 
If f(my + nz -j™ ct) be taken to repre- 
sent the wave form, the electromagnetic 
equations 
curl E= - fxR 
and 
curl H = -o X 
c 2 
Z. 
Equations 1 and 2 can be replaced by 
P 
Ax 
fJLC 
, m Y 
y— + — A 
fXC 
v cn n 
Y = K 
and 
K 
5 
. m 2 + n 2 — /jlK.. 
