[3] Limb is the word used by astronomers to denote the edge or circumference of the apparent disc of a heavenly body.
[4] "The Sun," p. 119.
[5] It has been frequently stated that the outburst in 1859, witnessed by Carrington and Hodgson, was immediately followed by an unusually intense magnetic storm, but the records at Kew and Greenwich show that the magnetic disturbances on that day were of a very trivial character.
[6] Some ungainly critic has observed that the poet himself seems to have felt a doubt on the matter, because he has supplemented the dubious moonbeams by the "lantern dimly burning." The more generous, if somewhat a sanguine remark has been also made, that "the time will come when the evidence of this poem will prevail over any astronomical calculations."
[7] This sketch has been copied by permission from the very beautiful view in Messrs. Nasmyth and Carpenter's book, of which it forms [Plate XI]. So have also the other illustrations of lunar scenery in [Plates VIII.], [IX.] The photographs were obtained by Mr. Nasmyth from models carefully constructed from his drawings to illustrate the features on the moon. During the last twenty years photography has completely superseded drawing by eye in the delineation of lunar objects. Long series of magnificent photographs of lunar scenery have been published by the Paris and Lick Observatories.
[8] At the British Association's meeting at Cardiff in 1892, Prof. Copeland exhibited a model of the moon, on which the appearance of the streaks near full moon was perfectly shown by means of small spheres of transparent glass attached to the surface.
[9] The duration of an occultation, or, in other words, the length of time during which the moon hides the star, would be slightly shorter than the computed time, if the moon had an atmosphere capable of sensibly refracting the light from the star. But, so far, our observations do not indicate this with certainty.
[10] I owe my knowledge of this subject to Dr. G. Johnstone Stoney, F.R.S. There has been some controversy as to who originated the ingenious and instructive doctrine here sketched.
[11] The space described by a falling body is proportional to the product of the force and the square of the time. The force varies inversely as the square of the distance from the earth, so that the space will vary as the square of the time, and inversely as the square of the distance. If, therefore, the distance be increased sixty-fold, the time must also be increased sixty-fold, if the space fallen through is to remain the same.
[12] See Newcomb's "Popular Astronomy," p. 78.