234 Mr. Brougham's Experiments and Observations on 
bolic fringes described by Newton,* and these being always 
of the colour in which they were held, moving the angle a 
little, so as to make the fringes out of the light that went to 
the top of any one division of the spectrum and also out of 
that which went near the bottom of the next, the fringes were 
made of two colours ; one part was of the highest colour, and 
the other of the lowest, but both were on the ground of the 
highest. Thus if held on the confine of the green and blue, 
the upper half of each fringe was blue, the under green, but 
both parts in the blue division of the spectrum ; and trying 
the same in all the rays, it was evident that the red was moved 
farther into the orange, and the orange into the yellow, than 
the blue was into the indigo, or the indigo into the violet. 
Now, in Obs. 3. the fringes were formed by the infection of 
one knife, and were moved into its shadow, and separated and 
dilated by the defection of the other ; and this most in the red 
and least in the violet : likewise in Obs. 4. the fringes of one 
colour were deflected into the region of the next, and this 
most in the red, and least in the violet ; although in both ob- 
servations the violet, from the position of the chart, was 
farthest from the angle, and consequently had the rays been 
equally deflected, the violet should have been farthest moved, 
and most dilated by the deflection ; but seeing that at equal 
angles of incidence in the third, and at less in the fourth obser- 
vation, the red was most and the violet less deflected, it is 
evident that the most infexible rays are also most defexible. 
Having thus found that the parts of light differ in flexibility, 
I wished next to learn two things ; in what proportion the 
angle of infection is to that of deflection at equal incidences ; 
* Optics, Book III. Obs. 8. 
