The refractive indices of liquid oxygen, nitrogen, and hydrogen at temperatures ranging from the normal boiling point to the normal freezing point of the liquefied gases were determined by means of a Wollaston cell for the wavelengths 6939Å, 5461Å, and 4358Å. The values obtained at the normal boiling point for λ = 5461Å were: oxygen, 1.2242; nitrogen, 1.1990; hydrogen, 1.1120.