the Cause of coloured concentric Rings. 287 
and reflected rays takes place, it will be seen that the rays 
transmitted through different points are among themselves 
subject to the same variety in the direction of their course ; 
■dr", o' 0", y' y", g' g", for instance, which passed through the 
point «, are parallel to each other ; but all of them converge 
respectively to rr', oo', yy',gg' transmitted through c ; and 
on the other handy'y", o' 0" , r' r" , diverge from g g'. 
Fig. 14, Plate XIV. is a general representation of the course 
of the rays of the blue bow, and of those that produce thestreaks. 
The base of the bow is divided into twenty equal parts, and 
one ray of the bow reflected from each of the points of the 
division is marked by a line. Twenty-one sets of rays of the 
different colours transmitted through the same points re-enter 
the base at their calculated places, and are represented by 
dotted lines drawn at proper angles ; but here it should be 
noticed, that the difference of the twenty angles being much 
too small to give any idea of their converging or diverging 
condition, the difference between each set has been expressed 
by one degree less towards the right, and one degree more 
towards the left ; the angle of the middle ray being of its 
proper magnitude. The strong lines marked A a, B / 3 , C y, 
D E g, show the division of the colours, and are the same 
which in fig. 1 were used to explain the construction of the 
blue bow. The rays incident on the base F G, in the direction 
of these lines, which are reflected in the same angles, and are 
also marked with strong lines, meet at the point where the 
eye is supposed to be placed. 
The figure has been drawn by the result of a strict calcula- 
tion contained in the following table. In the first column are 
the angles of the obliquity of the incident rays ; in the second 
P p 3 
