The blazing star, Threat'ning the world with famine, plague, and war; To princes death; to kingdoms many curses; To all estates inevitable losses; To herdsmen rot; to ploughmen hapless seasons; To sailors storms; to cities civil treasons. Although comets are no longer regarded with superstitious awe as in old times, mystery still clings to them. Astronomers can tell what path a comet is travelling upon, and say whence it has come and whither it will go, can even in many cases predict the periodic returns of a comet, can analyse the substance of these strange wanderers, and have recently discovered a singular bond of relationship between comets and those other strange visitants from the celestial depths, the shooting stars. But astronomy has hitherto proved unable to determine the origin of comets, the part they perform in the economy of the universe, their real structure, the causes of the marvellous changes of shape which they undergo as they approach the sun, rush round him, and then retreat. As Sir John Herschel has remarked: 'No one, hitherto, has been able to assign any single point in which we should be a bit better or worse off, materially speaking, if there were no such thing as a comet. Persons, even thinking persons, have busied themselves with conjectures; such as that they may serve for fuel for the sun (into which, however, they never fall), or that they may cause warm summers, which is a mere fancy, or that they may give rise to epidemics, or potato-blights, and so forth.' And though, as he justly says, 'this is all wild talking,' yet it will probably continue until astronomers have been able to master the problems respecting comets which hitherto have foiled their best efforts. The unexplained has ever been and will ever be marvellous to the general mind. Just as unexplored regions of the earth have been tenanted in imagination by anthropophagi and men whose heads Do grow beneath their shoulders, so do wondrous possibilities exist in the unknown and the ill-understood phenomena of nature.