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Abstract On January 24, 1956 observations were made at a wavelength of 3.7 metres, of the lunar occultation of the Crab Nebula. A comparison of the time of obscuration of the nebula with the computed value enabled the refraction occurring in the lunar atmosphere to be estimated. An electron density at the moon's surface of about 103 cm×3 was derived for cases of both an atmosphere in hydrostatic equilibrium and for an atmosphere which is continuously escaping; a figure which corresponds to a surface density of the lunar atmosphere about 2 × 10×13 of that of the earth's atmosphere at normal temperature and pressure.
B. Elsmore (Thu,) studied this question.