We derive the radio spectral index of the Barnard Loop ( BL ) from large-scale radio surveys at four frequencies and find it to be a thermal source .
We use the radio data together with H \alpha data to determine the electron temperature in BL , the \lambda Ori HII region , and a high-latitude filament ; all of these regions are somewhat cooler than typical HII regions .

We perform least squares fits of the DIRBE diffuse IR intensities to the 21-cm line and radio continuum intensities .
After the resolution of a “ geometrical conundrum ” , this allows us to derive the electron density n _ { e } ; we find n _ { e } \approx 2.0 cm ^ { -3 } and pressure { P \over k } \approx 24000 cm ^ { -3 } K .

Grains within BL are warmer than in HI regions .
Trapped L \alpha accounts for the extra heating that is required .
This is a general effect that needs to be accounted for in all analyses that examine IR emission from H ^ { + } regions .
Very small grains that emit 60 \mu m radiation are enhanced in BL relative to HI by a factor of 2-3 , while PAH ’ s that emit 12 \mu m are probably deficient by a factor \sim 2 .