A Remarkable Atmospheric Phenomenon at Ceylon. — The Rev. R. Abbay sent a communication on this subject to the Physical Society, May 27. In speaking of several of these phenomena he says that the most striking is witnessed from the summit of Adam's Peak, which is a mountain rising extremely abruptly from the low country to an elevation of seventy-two hundred feet above the sea. The phenomenon referred to is seen at sunrise, and consists apparently of an elongated shadow of the mountain, projecting westward to a distance of about seventy miles. As the sun rises higher it rapidly approaches the mountain, and appears at the same time to rise above the observer in the form of a gigantic pyramid of shadow. Distant objects may be seen through it, so that it is not really a shadow on the land, but a veil of darkness between the peak and the low country. It continues to rapidly approach and rise until it seems to fall back upon the observer, like a ladder which has been reared beyond the vertical, and the next instant it is gone. Mr. Abbay suggests the following explanation of the phenomenon: — The average temperature at night in the low country during the dry season is between 70° and 80° F., and that at the summit of the peak is 30° or 40 F.; consequently, the low strata of air are much the less dense, and an almost horizontal ray of light passing over the summit must be refracted upwards and suffer total internal reflection, as in an ordinary mirage. On this supposition the veil must become more and more vertical as the rays fall less horizontally, and this will continue until they reach the critical angle, when total internal reflection ceases, and it suddenly disappears. Its apparent tilting over on the spectator is probably an illusion, produced by the rapid approach and the rising of the dark veil without any gradual disappearance which can be watched and estimated. It will be evident that the illumination of the innumerable particles floating in the atmosphere causes the aerial shadow to be visible by contrast. Another interesting phenomenon visible in the mountain districts admits of an equally simple explanation. At times broad beams apparently of bluish light, may be seen extending from the zenith downwards, converging as they approach the horizon. The spaces between them have the ordinary illumination of the rest of the sky. If we suppose, as is frequently the case, that the lower strata of air are colder than the upper, the reflection spoken of in the case of Adam's Peak will be downwards instead of upwards. If several isolated masses of clouds partially obscure the sun, we may have several corresponding inverted veils of darkness, like blue rays in the sky, all apparently converging towards the same point below the horizon. This latter phenomenon is called by the natives "Buddha's rays."
Popular Science Review.
Periodicity of Hurricanes. — Vice-Admiral Fleuriot de Langle has published in the two last numbers of the Revue Maritime et Coloniale a long discussion on the periodicity of cyclones in all parts of the world. The paper seems to have been first read at the Geographical Conference in Paris last autumn. M. de Langle seeks to connect these storms directly with astronomical phenomena, as will be seen from the conclusions which he gives in the following sentences: —
- We may deduce from the preceding investigations that when the latitude of the place, the declination of the sun or the moon resume the same values respectively, and these phenomena coincide with an eclipse of the sun or the moon, or with a phase of the moon, on its approach to its apogee or perigee, there is danger of a hurricane. If at these critical periods there is any unsteadiness in the winds, extra caution is required when the apogee or perigee occurs near the time of full or new moon.
Of course, the statements are corroborated by a copious array of diagrams and tables, but after a careful study of the paper we fail to find that much has been added to our knowledge of the subject. There seems to be one radical defect in the reasoning, which influences all discussions of the relation between the moon and the weather. The hour of occurrence of a phenomenon at one station is taken, and the relation of that occurrence to the moon's age and position is investigated; but it is persistently ignored that the hurricane moves over the earth's surface, so that if its occurrence at A coincides with the period of any other phenomenon, it must necessarily fail to coincide with it at B.
Iron, on the authority of the Icelandic paper Nordlingr, states that two enterprising Icelanders, named Jow Thorkellsson and Sigindur Kraksson, have explored the volcanic region of the Dygyur Jelden. They started on their hazardous expedition from the Bardadal on Feb. 7, and in the course of their two days' exploration they succeeded, under great difficulties and dangers, in descending into the crater of the volcano Asya, where, at about three thousand feet below the upper margin, they reached the bottom, and found themselves on the brink of a lake of seething hot water, which was apparently of great depth. Near the southern extremity of this lake the ground was broken up by fissures and pools, which prevented further progress in that direction, while the entire space resounded with the noise of loud subterranean thunder. North of the great crater the explorers found an opening about six hundred feet wide, which appeared to be of about equal depth, from which issued dense masses of sulphurous smoke, accompanied by loud and deafening sounds.
