In this paper the author gives an account of a further observation which corroborates the conclusion he had stated in a former communication “On the extensive atmosphere of Mars,” namely, that no indication now existed of any atmosphere being attached to that planet. A star retained its light blue colour, and its full brilliancy and comparative steadiness till the very instant of its occultation by Mars. At its emersion it was seen nearly dichotomised. The author concludes, that either some physical change has occurred in the atmosphere of that planet, or that the observations of Cassini and of Roemer were inaccurate.