ASTRONOMICAL NOTES: by C. J. Ryan
THERE has lately been an interesting correspondence in The English Mechanic upon the subject of meteorites, and a remarkable conflict of opinion has been manifested, showing that there is really not much positive knowledge about them. The Earth's atmosphere is continually being bombarded by these missiles, and the dust into which they are transformed during their passage through it falls upon the Earth, sprinkling it annually with a layer of dark mineral substance, which if evenly spread, would cover the surface to about the thickness of a match. For long it was denied by the Academies of Science that mineral masses, varying in weight from a few ounces to several tons, ever fell from the sky, although they had been frequently seen in the act of falling and had been handled while still warm. But the incredulity of the astronomers was broken down about a century ago and they could no longer hold to their axiom that "as there are no stones in the sky, they cannot fall out of it." The careful study of "shooting-stars" has not been undertaken for much more than half a century. Although there is no doubt that meteoric masses do fall to the ground occasionally and that the meteoric dust which is found in the enduring snows on high peaks and in the Arctic regions comes from the disintegration of such objects, it is not certain that all of the shooting stars that flash across our night skies (and day ones too, though we rarely see one by day) are of the same nature as the meteoric stones which we can examine in our museums.
One of the most difficult problems to explain is the cause of the luminosity of the meteors. Many of them start into brilliancy at the enormous heights of eighty or ninety miles above the Earth and, after dashing at planetary speed across a distance of perhaps a hundred miles or more, disappear at heights of thirty or forty miles from the surface. Compared with the rapidity of their motion the quickest bullet is practically at rest. The explanation most widely accepted is that the friction of the meteorite in passing through our atmosphere at such an enormous speed ignites it and rapidly destroys it. Objection has been raised to this theory on the ground that the atmosphere at great heights is exceedingly rare and that it is difficult to believe it could offer enough resistance. Another problem has hitherto proved quite insoluble; i. e., the long persistence of the train of luminous particles which remain drifting in the upper air after the disappearance of the explosive bolides. For instance, on February 22, 1909, such a luminous train was seen for several hours drifting across the sky at high speed. Its height was so great that it was visible over a large part of England and France. Why these sparks do not go out instantly, in the same manner as those which follow the ordinary shooting-stars, is an unsolved mystery.
The only thing that is well established about meteor showers is that most of them are periodic and come from well-defined quarters of the heavens. From the study of the directions from which these streams come, it has been calculated that they travel round the sun in long elliptical orbits, and are members of his family. An orbit of thirty-three years has been computed for the famous November meteors. They probably extend about as far as the planet Neptune on one side of the Sun. The wonderful displays of November meteors seen in 1833 and 1866, which astonished the whole world, were probably caused by the passing of the Earth through a particularly dense portion of the stream. In 1866 we met the same portion that we had encountered in 1833. It was again looked for in 1899, thirty-three years later, but, to the surprise of the astronomers, there was but a very ordinary display. Many reasons have been offered for this, but no one really knows enough to explain it satisfactorily. A few of the meteoric streams follow the tracks of comets, and it is supposed that they may be the disintegrated remains of comets, particularly in the cases where the latter have faded away. There are many other peculiarities in the behavior of meteorites and of the meteoric streams which are quite incomprehensible, but enough has been said to show that the problem is full of interest to inquiring minds.
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Students of H. P. Blavatsky's teachings will not have failed to notice that there is a continual effort being made by astronomers to find some really satisfactory theory to explain the formation and behavior of comets' tails. She discusses the subject in The Secret Doctrine in such a way and gives such suggestive hints as to make it clear that when we do get the real clue to the mystery there will be need for further readjustments in our theories of matter. She also leads us to understand that partly through the discoveries which will be made in connexion with the anomalies of comets' tails, science will find that the present theory of gravitation is highly incomplete, and that there is an opposite force—repulsion—to be understood. Gravitation is only one aspect of a mysterious force which is as definitely polarized as electricity or magnetism. It is of interest to notice that Professor Kapteyn, the famous Dutch astronomer of Groningen, has just declared at the thirteenth Science Congress of Holland that the law of gravitation is abrogated among the spiral nebulae. His words are:
All the known facts indicate that the so-called universal force of Gravitation exerts no influence upon the primordial matter from which all stars have been produced.
A few years ago—even to a date considerably later than the time when H. P. Blavatsky wrote the daring suggestions in The Secret Doctrine—such a statement would have been considered the rankest heresy; no scientist would have dared to throw doubts upon the universal supremacy of the law of gravitation. Truly, indeed, did she prophesy that in the twentieth century it would be recognized that she had but sketched an outline, which, though rejected at its first appearance, was based upon real knowledge.