In seeking a plausible hypothesis to explain comets' tails, Signor Luigi Armellini, an Italian astronomer, has advanced the revolutionary idea that they are optical illusions, merely the effect of light passing through the more or less lens-shaped head of the comet. He publishes, in the Astronomische Nachrichten, fourteen photographs of comet-like forms which he produced by passing beams of light at various angles through lenses so as to fall upon sensitized plates. He claims that the different angles at which the solar rays fall upon the nucleus of a comet as it moves round the sun sufficiently explain the familiar changes in shape of the tail.
This hypothesis has not been favorably received, for it provokes more difficulties than it solves, plausible though it may seem at first sight. For instance, there is the undeniable fact that comets' tails display an entirely different spectrum from that of the Sun. Then there is the fact that they are frequently most irregular in shape, with strange bends and gaps in them, and sometimes they show bright projections pointing towards the Sun. Everyone who saw the great daylight comet of the winter before last (Comet 1910 a) will remember the curious bend half way down the tail which was plainly visible without optical aid. This was a curious freak for a comet!
It is singular that a somewhat similar hypothesis to that of Signor Armellini was offered by a correspondent to the Century Path not long ago (April 24, 1910), the difference being that he suggested that the comet's tail was a shadow of the nucleus thrown upon a surrounding spherical nebulosity and which became visible as a bright object when relieved against the intensely black background of the sky. This hypothesis lies open to the same objection as the lens theory, and also to others. But the important thing is that the mystery of comets has not been cleared up, nor will it be until the properties of other states of matter than those with which we are familiar are discovered by science.
The following quotation from The Scientific American shows some of the difficulties which comet theorists have to meet:
The tail of Halley's comet has conducted itself in the most whimsical fashion.... It seems to have split longitudinally into three more or less well-defined parts. When we consider that Morehouse's comet of 1908 exhibited some extraordinary changes; that it repeatedly formed tails which were discarded to drift out bodily into space until they finally melted away; that in several cases tails were twisted or corkscrew shaped, as if they had gone out in a more or less spiral form; that areas of material connected with the tail would become visible at some distance from the head, where apparently no supply had reached it from the nucleus; that several times the matter of the tail was accelerated perpendicularly to its length; and that at one time the entire tail was thrown forward and curved perpendicularly to the radius vector in the general direction of the tail's sweep through space (a peculiarity opposed to the law of gravitation) it is evident that a comet presents important problems for the future astronomer to solve. (May 28, 1910, Italics ours).
In connexion with the profoundly interesting problem of gravitation and the dead mechanical theory of the universe versus the living, spiritual teachings which H. P. Blavatsky brought us, the student should consult Sections III and IV of Part III of The Secret Doctrine, Vol. I. Nothing displays more forcibly the strength and beauty of the Theosophical position, which sees the working of Divine Intelligence and Control in every thing, from the least to the greatest.
To the general public as well as to astronomers the question of the habitability of the planets is a perennial subject of interest, and it is curious to observe how the opinions of experts have been modified lately. A few years ago it would have appeared most unlikely that the time was quickly coming when it would be seriously advanced by a distinguished astronomer that with the exception of Mars all the planets are probably inhabited! Yet that is the position taken today by Professor T. J. J. See of the U. S. Observatory, Mare Island. "Mars has been inhabited in the past, but life has doubtless vanished there, as but little of the Martian atmosphere remains." Until recently it was thought that the extensive dark shadings on Mars were oceans, but the numerous observations made of late with finer telescopes and under more favorable conditions than were formerly available have proved that these dark areas, instead of being the smooth, even surfaces they should be if composed of water, are irregularly mottled and actually crossed in places by some of the fine lines called "canals" about which so much controversy has raged. Very limited dark blue regions surrounding the white "snowcaps," which are most distinctly visible during the Martian summers, are most probably water, but these are so small that conditions must be very different on Mars from those on the Earth or any similar planet. The state of things upon Venus appears to be far more like that to which we are accustomed. No mountains such as Venus possesses are to be traced on Mars. Professor See feels sure that Mars must have been the seat of life in the past, and with respect to the families of planets which we are morally certain must surround the myriads of gigantic suns which we see only as twinkling stars, he is convinced that they also must have been formed for the habitation of intelligent beings, for to regard them as barren deserts would make Nature ridiculous.
H. P. Blavatsky, in The Secret Doctrine and elsewhere, and William Q. Judge in his writings, have plainly stated the Theosophical teaching about the condition of Mars in its present cycle. According to this, the planet is under "obscuration," that is, it is not the seat of full and complete active life, though there may be some lower vital forces at work. But this does not mean that Mars is becoming extinct or that it is a dead planet. According to the Esoteric philosophy, of which H. P. Blavatsky was permitted to unveil a little and to give a partial outline, the planets are subject to great periodic changes of state. From a high condition of activity in which life in every form flourishes, they decline to a state of quiescence during which the vital forces are active in the unseen planes; but in due course the nearly extinct fires are re-lighted and a further and higher evolution commences. We see this taking place on a smaller scale around us; civilizations rise and fall only to rise again; nations and even races disappear to be replaced by others commencing their upward march.