IN May 1884 Mr. Peal, of Sibsagar, in Assam, who has studied the moon's surface with great attention, sent me a paper in which he maintained views closely resembling those of Capt. Ericsson (NATURE, p. 248) on the glacial origin of the lunar craters. In my answer I suggested that it was difficult to admit the existence of ice on the moon's surface, without a layer of water vapour over it, and that the telescope proves that if such vapour exists it is only in extraordinarily small quantities. It seems due to Mr. Peal, who was undoubtedly ignorant of Capt. Ericsson's paper of 1869, to draw attention to the correspondence. I am not sure whether the paper has been yet published.