the Inflection , Reflection, and Colours of Light. 249 
frangibilities inversely. But it is obvious that the sine of in- 
cidence is not the same in the two cases ; for in the one it is 
equal to that of the mean ray’s reflection, while in the other 
none of the rays are refracted at an angle equal to that of in- 
cidence, otherwise they would not be refracted at all. This, * 
however, being a consequence of the essential distinction in 
the circumstances, does not impair the beautiful analogy which 
we have seen is preserved in the two operations, and which 
proves them to be different exertions of the same power. 
Now we may find, from the data obtained, the sines of all the 
rays in the spectrum, by adding to 77 the lengths of the spaces 
into which it is divided, and which are without any sensible 
error as the differences of those sines. The sines of the red 
will be from 77 to 77! ; the orange from 77^ to 77^- ; the 
yellow from 7 7- to 77^ ; the green from 77^ to ; the blue 
from 774- to 77^ ; the indigo from 77-j to 77^ ; the violet 
from 77^- to 78. So that the sine of incidence being given, 
that of the reflection of all the different rays may be found ; 
and the angle of incidence being 50° 48', the angles of reflec- 
tion are as follows : of the extreme red 50° 21' ; of the orange 
50° 27' ; of the yellow 50° 32'; of the green 50° 39; of the 
blue 50° 48' ; of the indigo 50° 57'; of the violet 51° 3'; and 
of the extreme violet 51 0 if. 
I shall conclude this part of the subject with a few remarks on 
the physical cause of reflexibility. As light is reflected by a 
power extending to some distance from the reflecting surface, 
the different reflexibility of its parts arises from a constitutional 
disposition of these to be acted upon differently by the power. 
And as these parts are of different sizes, those which are largest 
will be acted upgn most strongly. I shall not hesitate to go a 
mdccxcvi. K k 
