The integrated intensity, I′, or
2πh1 + 2 cos ρw,
is thus
I′ = 2πh1 (11),
when g1 numerically exceeds 2h1; and, when g1 lies between ±2h1,
I = π{2h1 + (2h1 − √ g1²) cos ρ′} (12).
It appears therefore that there are no bands at all unless ω lies between 0 and +4h1, and that within these limits the best bands are formed at the middle of the range when ω = 2h1. The formation of bands thus requires that the retarding plate be held upon the side already specified, so that ω be positive; and that the thickness of the plate (to which ω is proportional) do not exceed a certain limit, which we may call 2T0. At the best thickness T0 the bands are black, and not otherwise.
The linear width of the band (e) is the increment of ξ which alters ρ by 2π, so that
e = 2π / ω (13).
With the best thickness