Emissivity ratio curves relative to the quiet Sun Skylab ATM observations 4′′ inside the limb reported by Nicolas et al. (1977), with the addition of an HRTS measurement of the 1312.59 Å line. Top: at a fixed log N_e [cm^-3] = 10.5; bottom: at a fixed log T_e[K] = 4.7. I_ob indicates the measured intensity of a line in erg cm^-2 s^-1 sr^-1.