the Cause of coloured concentric Rings. 2 6y 
the angle subtended by the bow «H e 21' 4,1 ",5 * For in con- 
sequence of the different reflexibility of the differently co- 
loured rays the violet, indigo, blue, and faintest half of the 
green rays will be reflected between « and [ 3 , if they fall on 
that space in any angle between the above mentioned ones 
contained between A « G and B jG G ; and will therefore meet 
at H, and form the greenish blue part of the bow. The red, 
orange, yellow, and the brightest half of the green rays, on 
the contrary being less reflexible, will be transmitted through 
the base between a and / 3 , and by refraction pass in proper 
angles into the air. The letters vib^g, which in the figure 
are placed within the space cc H jG, denote the reflected colours, 
and ~gy 0 r put under the base between a and (3 are the initials 
of the transmitted colours ; and in the same manner the re- 
flections and transmissions which must happen between (3 y, 
y and 3 e are expressed by the letters over the base for the 
former, and under it for the latter. The order of the colours 
of the blue bow, when it is seen at H, is perfectly explained 
by the letters in the reflected part; and the eye must be placed, 
for seeing it, at the mean obliquity between the angles AuG 
and E e G, which is 4,9° 57' 3", 3. 
In order to conform this account of the blue bow, to the 
manner in which it was viewed by Newton, I have preserved 
his way of ascribing the separation of the rays to their diffe- 
rent reflexibility, which however is merely the effect of their 
* There is a mistake in one of the angles given by Newton, when in his Optics, 
page 145, he explains the blue bow ; for 49 deg. -Jy taken from 50 deg, 4, makes the 
breadth of the bow i° 4' 3i",4, which contradicts he refractions he has given, page 
1 12. As he only takes in the blue, indigo, and violet colours, instead of 49x3- de- 
grees, it should rather be 49f-§> 
