AN APPARENT NEW POLARITY IN LIGHT. 
2 39 
The investigation of the effect of the different terms may be conducted in the very 
same words as in the second problem, and the result is precisely the same ; namely, 
that when the red end of the spectrum is on the same side as the mica, no bands are 
produced; but that when the blue end of the spectrum is on the same side as the 
mica, and the thickness of the mica is properly adjusted, the bands produced by the 
neighbouring colours will correspond, or nearly so, and strong bands will therefore be 
produced in the aggregate effect on the eye. 
With regard to the place at which any bright or dark band is seen, as depending 
on the place of the edge of the mica, the intensity will now be preserved the same 
cl 
by keeping — g the same ; that is, a band of the same character will be preserved 
qJ p 
by making the variations of l equal to those oi ~ , and in the same direction ; or the 
bands upon the retina will shift in the same direction as the shift of the mica, and 
the mind will therefore perceive bands to shift in the opposite direction to the shift 
of the mica. 
To exhibit more distinctly to the eye the cause of the annihilation of the bands 
when the red end of the external spectrum or the blue end of the spectrum on the 
retina is on the same side as the mica, and the cause of the formation of the bands 
when the blue end of the external spectrum or the red end of the spectrum on the 
retina is on the same side as the mica, I have constructed diagrams (figs. 3, 4, 5, 6, 7,) 
founded on the following calculations. The Table below contains computed values 
of 2 — G (s) . cos (p (s) + G (s) . cos {<p (s) — R} for all the values of s which are likely 
to produce sensible effects in the result ; and for the values of R, 0, 30°, 60°, 90°, 
120°, 150°, 180°, 210°, 240°, 2/0°, 300°, 330°. These of course apply also to the values 
of R, 2 n 7?, 2 n ic -j~ 30°, 2 n t -f- 60°, &c. 
