The Middle Ages have left us descriptions of comets, which show only too well how the imagination will run riot under the stimulus of terror. For instance, the historian, Nicetas, thus describes the comet of the year 1182: "After the Romans were driven from Constantinople a prognostic was seen of the excesses and crimes to which Andronicus was to abandon himself. A comet appeared in the heavens similar to a writhing serpent; sometimes it extended itself, sometimes it drew itself in; sometimes, to the great terror of the spectators, it opened a huge mouth; it seemed that, as if thirsting for human blood, it was upon the point of satiating itself." And, again, the celebrated Ambrose Paré, the father of surgery, has left us the following account of the comet of 1528, which appeared in his own time: "This comet," said he, "was so horrible, so frightful, and it produced such great terror in the vulgar, that some died of fear, and others fell sick. It appeared to be of excessive length, and was of the colour of blood. At the summit of it was seen the figure of a bent arm, holding in its hand a great sword, as if about to strike. At the end of the point there were three stars. On both sides of the rays of this comet were seen a great number of axes, knives, blood-coloured swords, among which were a great number of hideous human faces, with beards and bristling hair." Paré, it is true, was no astronomer; yet this shows the effect of the phenomenon, even upon a man of great learning, as undoubtedly he was. It should here be mentioned that nothing very remarkable happened at or near the year 1528.
Concerning the comet of 1680, the extraordinary story got about that, at Rome, a hen had laid an egg on which appeared a representation of the comet!
But the superstitions with regard to comets were now nearing their end. The last blow was given by Halley, who definitely proved that they obeyed the laws of gravitation, and circulated around the sun as planets do; and further announced that the comet of 1682 had a period of seventy-six years, which would cause it to reappear in the year 1759. We have seen how this prediction was duly verified. We have seen, too, how this comet appeared again in 1835, and how it is due to return in the early part of 1910.
[26] With regard to the words "Isti mirant stella" in the figure, Mr. W.T. Lynn suggests that they may not, after all, be the grammatically bad Latin which they appear, but that the legend is really "Isti mirantur stellam," the missing letters being supposed to be hidden by the building and the comet.
CHAPTER XXI
METEORS OR SHOOTING STARS
Any one who happens to gaze at the sky for a short time on a clear night is pretty certain to be rewarded with a view of what is popularly known as a "shooting star." Such an object, however, is not a star at all, but has received its appellation from an analogy; for the phenomenon gives to the inexperienced in these matters an impression as if one of the many points of light, which glitter in the vaulted heaven, had suddenly become loosened from its place, and was falling towards the earth. In its passage across the sky the moving object leaves behind a trail of light which usually lasts for a few moments. Shooting stars, or meteors, as they are technically termed, are for the most part very small bodies, perhaps no larger than peas or pebbles, which, dashing towards our earth from space beyond, are heated to a white heat, and reduced to powder by the friction resulting from their rapid passage into our atmosphere. This they enter at various degrees of speed, in some cases so great as 45 miles a second. The speed, of course, will depend greatly upon whether the earth and the meteors are rushing towards each other, or whether the latter are merely overtaking the earth. In the first of these cases the meteors will naturally collide with the atmosphere with great force; in the other case they will plainly come into it with much less rapidity. As has been already stated, it is from observations of such bodies that we are enabled to estimate, though very imperfectly, the height at which the air around our globe practically ceases, and this height is imagined to be somewhere about 100 miles. Fortunate, indeed, is it for us that there is a goodly layer of atmosphere over our heads, for, were this not so, these visitors from space would strike upon the surface of our earth night and day, and render existence still more unendurable than many persons choose to consider it. To what a bombardment must the moon be continually subject, destitute as she is of such an atmospheric shield!
It is only in the moment of their dissolution that we really learn anything about meteors, for these bodies are much too small to be seen before they enter our atmosphere. The débris arising from their destruction is wafted over the earth, and, settling down eventually upon its surface, goes to augment the accumulation of that humble domestic commodity which men call dust. This continual addition of material tends, of course, to increase the mass of the earth, though the effect thus produced will be on an exceedingly small scale.