the Inflection, Reflection, and Colours of Light. 265 
known accuracy in such matters, besides the singular inge- 
nuity of the methods he employed, made me more satisfied 
with these than any experiment I could make on the subject. 
In fig. 11. CS is the line perpendicular to the chart SU, and 
passing through the centre of the body, whose half is CD or 
SE ; EB is parallel to CS, and AI a ray incident at D ; ADB 
or EDI is the angle of incidence ; EDR that of the red's deflec- 
tion ; EDV that of the violet's ; and EDG that of the inter- 
mediate's. According to Newton* CD was -3-^th of an 
inch, DE 6 inches, SI °f an i nc h> RV y^th, anc * 
consequently RG T J^th ; GS was T y ; whence the angles IDE, 
EDV, EDG, and EDR, will be found to be 4', 30" ; 5 ' ; 7', 
and 9', respectively. Now the natural sines of 4', 30"; 5'; 7', 
and 9', are as the numbers 1309, 1454, 20354-, and 2617, 
which are as the sines of incidence, deflection, and inflection 
of the violet, green, and red. Thus the angles of flexion of 
the extreme and mean rays being given, those of the other 
rays are found by dividing the difference between 1454 and 
2617 in the harmonical ratio : for then the red will be equal 
to 145I; the orange 87^; the yellow 155^; the green 19344 
the blue 1934-; the indigo 12 9-4 ; and the violet 2584-; and by 
adding to the number 1454 the violet, and to their sum the 
indigo, and so on, we get the flexibility of the red, from 2617 
to 2471! ; of the orange, from 2471J- to 23844 ; of the yellow, 
from 23844 to 22294 ; of the green, from 22294 to 20354-; of 
the blue, from 20354- to 18414; of the indigo, from 18414 to 
1712J-; and of the violet, from 17124- to 1454: the common 
sine of incidence being 13 9. It is therefore evident, that the 
flexibility of the red is not to that of the violet as the refrangi- 
* Optics, Book III. Obs. 3. 
M m 
MDCCXCVI, 
