[44] Newton conjectured that comets formed “the aliment by which suns are sustained,” his opinion being that the former bodies finally coalesced with the suns round which they revolved. He remarked:—“I cannot say when the Comet of 1680 will fall into the Sun,—possibly after five or six revolutions; but whenever that time shall arrive, the heat of the Sun will be raised by it to such a point that our globe will be burnt and all the animals upon it will perish.” CHAPTER XV. _METEORS AND METEORIC OBSERVATIONS._ Ancient ideas concerning Meteors.—Meteoric Apparitions.—Radiation of Meteors.—Identity of Meteors and Comets.—Aerolites.—Fireballs.—Differences of Motion.—Nomenclature of Meteor-Systems.—Meteor-Storms.—Telescopic Meteors.—Meteor-Showers.—Varieties of Meteors.—Heights.—Meteoric Observations. “As oft along the still and pure serene At nightfall, glides a sudden trail of fire, Attracting with involuntary heed The eye to follow it, erewhile it rest; And seems some star that shifted place in heaven.” DANTE. No one can contemplate the firmament for long on a clear moonless night without noticing one or more of those luminous objects called shooting-stars. They are particularly numerous in the autumnal months, and will sometimes attract special attention either by their frequency of apparition or by their excessive brilliancy in individual cases. For many ages little was known of these bodies, though some of the ancient philosophers appear to have formed correct ideas as to their astronomical nature. Humboldt says that Diogenes of Apollonia, who probably belonged to the period intermediate between Anaxagoras and Democritus, expressed the opinion that, “together with the visible stars, there are invisible ones which are therefore without names. These sometimes fall upon the Earth and are extinguished, as took place with the star of stone which fell at Ægos Potamoi.” Plutarch, in the ‘Life of Lysander,’ remarks:—“Falling stars are not emanations or rejected portions thrown off from the ethereal fire, which when they come into our atmosphere are extinguished after being kindled: they are, rather, celestial bodies which, having once had an impetus of revolution, fall, or are cast down to the Earth, and are precipitated, not only on inhabited countries, but also, and in greater numbers, beyond these into the great sea, so that they remain concealed.” In later times, however, opinions became less rational. Falling stars were considered to be of a purely terrestrial nature, and originated by exhalations in the upper regions of the air. Shakespeare expressed the popular belief when he wrote:— “I shall fall Like a bright exhalation in the evening, And no man see me more.”