i 62 Dr. Herschel’s Experiments for Investigating 
First remark. When we look upon this figure i 1 a cursory 
way, it may seem as if the vacancies corresponded with the 
assumed distances of the rays, but this is partly erroneous ; 
for even in the short extent of the figure, the vacancy between 
5 and 6 at the bottom, does not correspond with that a': the 
top. The lower single vacancy at 18, does not agree with 
the two vacancies above. Between 1 6 and 17 is a vacancy at 
the bottom, but none at the top. The lower vacancy at 11, 
has no corresponding one above ; nor has that between 4 and 
5 below, a corresponding vacancy at the top. 
Second remark. The rays 1, 2, 3, 4, & c. are by no means 
assumed as separated by blank intervals, but as rays at a 
certain distance from each other, one thousand times greater 
in the figure, than in their compressed natural state. 
Third remark. The appearance of the rays in my figure, 
was not intended to represent streaks such as will be seen, 
but to denote their incipient course in passing from the base 
of the prism, to an eye whose distance from that base we are 
to suppose not less than 3000 inches. The visible arrange- 
ment and colour of the streaks, erroneously conceived to be 
expressed in my figure, can only be deduced from the mix- 
ture of rays at the place where they enter the eye, the pupil 
of which it should be remembered, must have a proportional 
diameter of 200 inches. The angles also, it has been ex- 
plained, could not possibly be drawn of just dimensions, and 
from what has been said, we may conclude, that to make a 
calculation of the mixture and colour of all the rays when 
they reach the eye, even with the spare quantity of them 
which has been drawn in the figure, would be extremely la- 
borious, and that a thorough investigation of this particular 
