GRAND METEORS.
I dare say that many of those present will, in the course of their lives, have opportunities of seeing some of the great meteors, or fire-balls, which are occasionally displayed. Generally speaking, about one hundred or so of these splendid objects are recorded every year. We are never apprised that they are coming; they take us unawares, and therefore we have no opportunity to make proper arrangements for seeing them. There is only the chance that such persons as have been fortunate enough to see them will have noted the circumstances with sufficient accuracy to enable us to make use of their observations.
Fig. 78.—How to find the Height of a Meteor.
The chief point to determine is the height of the meteor above the earth. For this we must have two observations at least, made in places as far asunder as possible. Suppose an observer at London and an observer at York were both witnesses of a splendid meteor; if they find, on subsequent comparison, that their observations were made at the same moment, there is no reasonable doubt that it was the same object they both saw. The observer at York describes the meteor as lying to the south, halfway down from the point directly over his head towards the horizon. The London observer speaks of the meteor as being to the north; and to him also it appeared that the object was halfway down towards his horizon from the point directly over his head. If you know a little Euclid, you can easily show from these facts that the height of the meteor must have been half the distance between London and York, that is, 85 miles ([Fig. 78]).
I do not mean to say that the mode of discovering the meteor’s height will be always quite such a simple process as it has been in the case of the London and York observations. The principle is, however, the same—that whenever from two sufficiently distant positions the direction of the meteor has been observed, its path is known—just as on [p. 21] we showed how the height of the suspended ball was obtained from observations at each end of the table. Generally speaking, bright meteors begin at an elevation of between fifty and one hundred miles, and they become extinguished before they are within twenty miles of the ground.
Sometimes a tremendous explosion will take place during the passage of a meteor through the air. There was a celebrated instance in America on the 21st of December, 1876, which will give an idea of one of these objects possessing exceptional magnificence. It began in Kansas about seventy-five miles high, and thence it flew for a thousand miles at a speed of ten or fifteen miles a second, until it disappeared somewhere near Lake Ontario. Over a certain region between Chicago and St. Louis, the great ball of fire burst into a number of pieces, and formed a cluster of glowing stars that seemed to chase each other over the sky. This cluster must have been about forty miles long and five miles wide, and when the explosion occurred a most terrific noise was produced, so loud that many thought it was an earthquake. A remarkable circumstance illustrates the tremendous height at which this explosion occurred. The meteor had burst into pieces, the display was all over, and was beginning to be forgotten, and yet nothing had been heard. It was not until a quarter of an hour after the explosion had been seen that a fearful crash was heard at Bloomington. The explosion actually occurred 180 miles from the spot, and as sound takes five seconds to travel a mile, you can easily calculate that the noise required a quarter of an hour for its journey. What a tremendous noise it must have been!
Shooting stars are of every grade of brightness. Beginning with the more gorgeous objects which have been compared with the moon or even with the sun himself, we descend to others as bright as Venus or as Jupiter; others are as bright as stars of various degrees of brilliancy. Fainter shooting stars are much more numerous than the conspicuous ones; in fact, there are multitudes of these objects so extremely feeble that the unaided eye would not show them. They only become perceptible in a telescope. It is not uncommon while watching the heavens at night to notice a faint streak of light dashing across the field of the instrument. This is a shooting star which is invisible except through the telescope.
THE GREAT NOVEMBER SHOWERS.
