As to darknesses in Great Britain, one thinks of fogs--but in _Nature_, 25-289, there are some observations by Major J. Herschel, upon an obscuration in London, Jan. 22, 1882, at 10:30 A.M., so great that he could hear persons upon the opposite side of the street, but could not see them--"It was obvious that there was no fog to speak of." _Annual Register_, 1857-132: An account by Charles A. Murray, British Envoy to Persia, of a darkness of May 20, 1857, that came upon Bagdad--"a darkness more intense than ordinary midnight, when neither stars nor moon are visible...." "After a short time the black darkness was succeeded by a red, lurid gloom, such as I never saw in any part of the world." "Panic seized the whole city." "A dense volume of red sand fell." This matter of sand falling seems to suggest conventional explanation enough, or that a simoon, heavily charged with terrestrial sand, had obscured the sun, but Mr. Murray, who says that he had had experience with simoons, gives his opinion that "it cannot have been a simoon." It is our comprehensiveness now, or this matter of concomitants of darknesses that we are going to capitalize. It is all very complicated and tremendous, and our own treatment can be but impressionistic, but a few of the rudiments of Advanced Seismology we shall now take up--or the four principal phenomena of another world's close approach to this world. If a large substantial mass, or super-construction, should enter this earth's atmosphere, it is our acceptance that it would sometimes--depending upon velocity--appear luminous or look like a cloud, or like a cloud with a luminous nucleus. Later we shall have an expression upon luminosity--different from the luminosity of incandescence--that comes upon objects falling from the sky, or entering this earth's atmosphere. Now our expression is that worlds have often come close to this earth, and that smaller objects--size of a haystack or size of several dozen skyscrapers lumped, have often hurtled through this earth's atmosphere, and have been mistaken for clouds, because they were enveloped in clouds-- Or that around something coming from the intense cold of inter-planetary space--that is of some regions: our own suspicion is that other regions are tropical--the moisture of this earth's atmosphere would condense into a cloud-like appearance around it. In _Nature_, 20-121, there is an account by Mr. S.W. Clifton, Collector of Customs, at Freemantle, Western Australia, sent to the Melbourne Observatory--a clear day--appearance of a small black cloud, moving not very swiftly--bursting into a ball of fire, of the apparent size of the moon-- Or that something with the velocity of an ordinary meteorite could not collect vapor around it, but that slower-moving objects--speed of a railway train, say--may.