New measurements of the solar limb emission in the OI 777.4 and 844.6 nanometer lines

Slit spectra of the solar limb emission in the 777.4 and 844.6 nm O I lines are calibrated against the solar disk center brightness. Data from CCD spe ctrograph instruments at two different observatories show limb emission wit h identical line intensities and measure a value of R-4 = Sigma I(844.6 nm) / Sigma I(777.4 nm) = 0.20 +/- 0.02, very different from the ratios compute d from early photographic measurements of these Lines. Implied by this new value of R-4 is that O I lines in the solar chromosphere are formed in regi ons with electron densities log (N-e) > 11.5 and that collisional excitatio n is more important than the photoexcitation by accidental resonance mechan ism.