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BY referring 10 this figure, il We suppose the


line to represent plane 9 ass resting upon the
slightly convex lens represented by The arc a
u being the point OF contact in the Hr-t place It wl
be readily that knowing the radius of the cir
Gle of which the is part. aud knowing
likewise th- distances Il b, c. II d, Sc, the
eugth of the lines 2, = !, {, SC, Is matter
of easy ttgnometrica calculation that although
the distances z, T, &c, from ihe surface OF the
convex lens that OF the plane glass TOO small
Tor measurement, they msy still be computed with
the almost degree OF accuracy. Nsw NEWTON
did tins having arranged hi, apparatus
presented in the figure, be let fall precisely upon
the poin, of contact beam of light II pure red


light (You are dosbtless all aware that the whit.


light OF the is composed of light of seven differ
ent colors-oi as Others maintain OF e greater
number but in either the several colors com
posing white light called pre- coots.) Inn
mediateiy certain effect took place exactly at
the point OF. contact there va. Visible an intensely
black spot outside OF and surrounding this was
a ring oi red lisht outside OF this ring OF
blacA-then enc of red, &c. He h-d thcs sue
cession OF rings, black being IN the centre, alter
natcly black and red. Tie red light which fell
upon the point OF contact. was reflected and came
to MS eye IN some point, while in others II passed
through and left i black spot or ring


AEWroS at saw that the cause OF tnis phe-
nomenon was this; wherever red ring was 'isi'le
a complete pulsation Of the a.theriai fluid existed
a single was pcopagated between the t"o
surfaces. But in an interval less than rhl' the
wave wa- brehen;-ihe interva! was greater Than
the width OF one wave, and less tf,an the width Of
two, and no ish; was reflected consequently
black ring was seen The neN; red ring was seen
at that point where the interval between the
face of the convex lens and plane glass was equal
the width of two waves; the light was conse-
queutly reaecled AID red ring was seen. NeXt
came an interval greater than the width OF TWO
and less than that OF three consequently
black ring was seen. The distances between the
TWO surface then. represented by the lines 2 CT
and de, supposed to be infinitely small correspond
10 the width respectively OF one, tive and three
waves; and at these points red rings will be seen.
Ii then the length OF these lines 5e, CT and De can
be a,certaned, we shall know the width Of wave
of light. But a, showed Just now, these lines
easily computed knowing the radius OF the con-
leas aud the nesab, &c, and al Thus NV
rsS obtained the actual width of : wave of light
Though ne used different name, in accordance
with MS theory.


Having arrived at this result with red light. lie
tried II with al the ether colors OF the spectrum
and the hunber of waves n single inch for each
color he ascertaned to De as follows Use round
numbers, although ne computed it with extreme
accuracy