Few of our readers, probably, have failed to note the fact that brilliant sunsets have been unusually frequent since the latter part of November. Now a highly colored sunset is not, in itself, a remarkable phenomenon, and it may occur at any time of the year, and owe its origin to any one of several causes, very simple in themselves, as refraction by the atmosphere of the sun’s rays, which are thrown upon the sky after the orb itself has passed from sight, or a peculiarly humid condition of the upper air, or a remarkable electric condition, such as sometimes precedes a thunder storm. But the late brilliant sunsets do not belong to the category of ordinary phenomena. In the first place, they have not shown gorgeously hued clouds, as in usual sunset displays, but skies of dazzling tints and colors. In the second place, they have been prolonged for weeks, and have been seen, at intervals, over nearly every part of the globe. Evidently, some unusual circumstance must have given rise to these unwonted phenomena, and scientists in both hemispheres have been interested in seeking an answer to the problem. As it seemed very plain that no condition of humidity could account for such remarkable refraction, it was universally concluded that some substance, as dust, must exist in the upper air regions. This being accepted as probable another theory was needed to account for the presence of this dust. The first theory put forward by scientists in this country suggested the hypothesis of meteoric dust.
Meteors are gaseous bodies, which move through space in immense numbers, and in definite orbits. Drawn astray from these orbits by the attraction of the earth, they are set on fire on contact with the atmosphere, this ignition producing the phenomena of shooting stars. The product of this combustion is sometimes heavy enough as to fall rapidly, in the shape of stones, to the earth. More often it is an impalpable substance, which filters slowly down through the air, and is found in the shape of metallic dust, on the summits of snow-covered mountains and in the Arctic regions. About the middle of November the earth passes through a meteor zone—that is, an immense swarm of meteors revolving around the sun—and during this month there are always vastly more shooting stars to be seen than in any other month of the year. The brilliant sunsets being first seen in the latter part of November, their near coincidence in time with an unusual display of brilliant meteors, seemed to substantiate the theory that they were of similar origin. It is known that the telescope reveals immense numbers of these meteors too small to be seen by the naked eye, and it seems very probable that millions more are too small to be seen even with the telescope, mere meteoric dust that can only announce its presence to the eye by its refraction of the sun’s rays as they pass through it. When this dust falls it becomes visible otherwise, perhaps. We have spoken of its appearance on snow-covered hills. Sometimes it appears as a haze or dry fog. At least the appearance of any very remarkable haze, like that which obscured the light of the sun for weeks over Europe, in 1783, is now ascribed by science to the dust of enormous falls of meteors.
Had this theory of the cause of the bright sunsets been the true one, however, there should have been unusual displays of shooting stars visible as soon as darkness came on after the sunsets, for meteors are always ignited by the friction of the earth’s atmosphere. As these were not seen, the meteoric dust theory did not gain a very general support, and the opinion of many scientific men was that we must wait for a more probable theory. When it came to be known that these remarkable appearances of color in the sky had been visible from different points of the earth’s surface ever since last September, a theory was offered by Prof. Lockyer, the well-known English astronomer, and the editor of Nature, a leading scientific periodical, which is now generally accepted as solving the problem.
Mr. Lockyer thinks that these remarkable sunset glows are the late, but direct effects of the great volcanic eruptions which occurred in Java, last August. He believes that the enormous volumes of fine volcanic dust thrown out by these eruptions were carried into the upper air, and being borne by prevailing winds around and above the earth, the reflection of the sun’s rays upon them have produced the phenomena witnessed at so many different points.
The adequacy of this supposed cause seems plain, when we remember what a mighty convulsion of nature occurred at Java. Earthquake and eruptions followed one another with such force that they were felt for hundreds of miles distant. Large islands sunk from sight and new land appeared and the entire conformation of the Archipelago in that locality was changed. The great volumes of mud thrown out of the volcano Krakatoa fell in showers for over three hours in localities more than thirty miles away. With volcanic forces at work on this mighty scale, millions of tons of earth must have been hurled into the upper air. Of this the coarse and heavy material would naturally fall at once, but vast clouds of impalpable dust would be borne upward by the heated air, until they reached the region of the upper trade-winds, by which they would be borne westward in the circuit of the globe. Each evening these immense dust clouds would give a novel brilliancy to the skies, by reflecting the light of the setting sun, and during the day an unusual hazy appearance of the sky would probably be perceived.
This hypothesis of Mr. Lockyer was remarkably borne out by facts that actually occurred. The Java eruptions occurred August 26 and 27. On August 28, from the islands in the Indian Sea, near the African coast, Mauritias, Rodriguez, and the Seychelles, very singular sunsets and sunrises were observed, though not directly resembling those seen later, and a strange haze appeared, through which the sun seemed to be white and dim as the moon. On August 31, in the same latitude as these islands, in North Brazil, remarkable sunlight effects were observed, the sun appearing of a deep blue tint; the next evening similar appearances were seen in Venezuela. On September 1, also, a remarkable sunset was reported visible from the Gulf Coast, and one from Trinidad, Spain, at the same date. September 5, another was seen near Honolulu, in the Pacific ocean. This line of strange sunsets ran directly east and west. Another line ran from southeast to northwest, beginning with Ceylon and Madras and ending with England. Following this, the phenomena seemed to spread themselves over the whole portion of the earth’s surface, appearing at various points during four whole months. The points of difference between the earlier and later appearances were closely defined by Mr. Lockyer. At first the coarse particles suspended in the air obscured the sun’s light entirely, as was the case in the neighborhood of Java immediately following the earthquake. These disappearing, the sun seemed white and dim; the dust being still more thinned out, the blue and red molecules caused the appearance of a blue sun, and at last there was just enough of the finest dust left suspended to be carried by the various wind currents hither and thither and produce at the time of the setting of the sun, those singular reflected lights, which, at first almost unnoticed, became, when observed, the wonder of the world.
It may be admitted that there are gaps in the evidence supporting this last hypothesis, but it has the merit of probability, and must be accepted as the best theory of the brilliant sunsets yet offered.
A. C. C.
CHOCOLATES.