Dr. Herschei/s Experiments for investigating 
From the complex nature of this figure, it will immediately 
be seen that we cannot attempt an investigation of the parti- 
cular streaks, that will be formed by the mixture of the trans- 
mitted with the reflected rays. An inspection of it, however, 
will be sufficient to show that streaky appearances must be 
produced. For instance, between a and the first red ray 
which re-enters the base, a narrow blue streak should be 
seen ; this will be broken in upon by the mixture of two sets 
of red, orange, and yellow rays, which together with the 
reflected colours of the bow, the green being still wanting 9 
must give a pale red division immediately joining the blue 
streak. When we advance farther into the figure, the great 
mixture of the colours and the different directions of the rays 
are so various, that nothing particular can be determined with- 
out entering into a very complicated calculation of the meeting 
and intersections of the rays ; we see, however, that these 
mixtures will produce a condensation of rays in some parts, 
and vacancies in others, so that no uniform tinge can remain, 
and consequently streaky appearances must be seen. The 
same conclusion may be drawn from an inspection of the 
places where the transmitted colours re-enter the base ; for 
the green, which is transmitted between a and (3 does not 
enter again till after the fourth division of the base ; the blue 
which begins to be transmitted at (3 cannot find admittance 
again till after the tenth ; the indigo transmitted from y to $ does 
not re-enter into the composition till after the sixteenth divi- 
sion ; and the violet transmitted between $ and s will only 
come in again after the nineteenth. There will consequently 
be a considerable space without green, another without blue, 
a third without indigo, and a fourth without violet; from 
