Page images

stantaneous gloom is overwhelming, and inspires with awe even the most careless observer. Curious custom among the Hindoos.—Among the Hindoos a singular custom is said to exist. When, during a solar eclipse, the black disk of our satellite begins slowly to advance over the sun, the natives believe that some terrific monster is gradually devouring it. Thereupon they beat gongs, and rend the air with most discordant screams of terror and shouts of vengeance. For a time their frantic efforts seem futile and the eclipse still progresses. At length, however, the increasing uproar reaches the voracious monster; he appears to pause, and then, like a fish rejecting a nearly swallowed bait, gradually disgorges the fiery mouthful. When the sun is quite clear of the great dragon's mouth, a shout of joy is raised, and the poor natives disperse, extremely self-satisfied on account of having so successfully relieved their deity from his late peril. THE SAROS.—The nodes of the moon’s orbit are constantly moving backward. They complete a revolution around the ecliptic in about eighteen and a half years. Now the moon makes 223 synodic revolutions in 18 yr. 10 da.; the sun makes 19 revolutions with regard to the lunar nodes in about the same time. Hence, in that period the sun and moon and the nodes will be in nearly the same relative position. If, then, we reckon 18 yr. 10 da from any eclipse, we shall find the time of its repetition. This method was discovered, it is said, by the Chaldeans. The ancients were enabled, by means of it, to predict eclipses, but it is considered too rough by modern astronomers: eclipses are now foretold centuries in advance, true to a second. In this manner historical incidents are verified, and their exact dates determined. METONIC CYCLE.—The Metonic Cycle (sometimes confounded with the Saros) was not used for foretelling eclipses, but for the purpose of ascertaining the age of the moon at any given period. It consists of nineteen tropical years,” during which time there are exactly 235 new moons; so that, at the end of this period, the new moons will recur at seasons of the year exactly corresponding to those of the preceding cycle. By registering, therefore, the exact days of any cycle at which the new or full moons occur, such a calendar shows on what days these events will occur in succeeding cycles. Since the regulation of games, feasts, and fasts has been made very extensively, both in ancient and modern times, according to new or full moons, such a calendar becomes very convenient for finding the day on which the new or full moon required takes place. Thus if a festival were decreed to be held in any given year on the day of the first full moon after the vernal equinox: find what year -it is of the . lunar cycle, then refer to the corresponding year of

* A tropical year is the interval between two successive returns of the sun to the vernal equinox.

the preceding cycle, and the day will be the same as it was then. The Golden Number, a term still used in our almanacs, denotes the year of the lunar cycle. Seven is the golden number for 1868. ECLIPSE OF THE MOON.—This is caused by the passing of the moon into the shadow of the earth,

Fig. 52.


and hence can take place only at full moon—opposition. As the moon's orbit is inclined to the ecliptic, her path is partly above and partly below the earth's shadow; thus an eclipse of the moon can take place only at or near one of the nodes. In the figure, the umbra is represented by the space between the lines Kc and Ib; outside of this is the penumbra, where the earth cuts off the light of only a portion of the sun. The moon enters the penumbra of the earth at a,—this is termed her first contact with the penumbra; next she encounters the dark shadow of the earth at b,—this is called the first contact with the umbra; she then emerges from the umbra at c,—which is called the second contact with the umbra; finally, she touches the outer edge of the penumbra at d,—the second contact with the penumbra. Since the earth is so much larger than , the moon, the eclipse can never be annular, as, however, the eclipse may occur a little above or below the node, the moon may only partly enter the earth's shadow, either on its upper or lower limb. From the first to last contact with the penumbra, five hours and a half may elapse. Total eclipses of the moon are rarer events than those of the sun, since the lunar ecliptic limit is only about 12°; yet they are more frequently seen by us, (1) because each one is visible over the entire unillumined hemisphere of the earth, and also (2) because by the diurnal rotation during the long duration of the eclipse, large areas may be brought within its limits. So it will happen that while the inhabitants of one district witness the eclipse throughout its continuance, those of other regions merely see its beginning, and others only its termination. The moon does not completely disappear even in total eclipsés. The cause of this fact lies in the refraction of the solar rays in traversing the lower strata of the earth's atmosphere; they are analyzed, and purple our moon with the tints of sunset. The amount of refraction and the color depend upon the state of the air at the time. HISTORICAL ACCOUNTS OF ECLIPSES.—The earliest account of an eclipse on record is in the Chinese annals; it is thought to be the solar eclipse of October 13, 2127 B. C. On May 28, 584 B. C., one occurred which was predicted by Thales, as we have before mentioned. In the writings of the early English chroniclers are numerous passages relating to eclipses. William of Malmesbury thus refers to that of August 2, 1133, which was considered a presage of calamity to Henry I. : “The elements manifested their sorrows at this great man's last departure. For the sun on that day, at the 6th hour, shrouded his glorious face, as the poets say, in hideous darkness, agitating the hearts of men by an eclipse; and on the 6th day of the week, early in the morning, there was so great an earthquake, that the ground appeared absolutely to sink down; an horrid noise being first heard beneath the surface.” The same writer, speaking of the total eclipse of March 20, 1140, says: “During this year, in Lent, on the 13th of the kalends of April, at the 9th hour of the 4th day of the week, there was an eclipse, throughout England, as I have heard. With us, indeed, and with all our neighbours, the obscuration of the Sun . also was so remarkable, that persons sitting at table, as it then happened almost every where, for it was Lent, at first feared that Chaos was come again: afterwards learning the cause, they went out and beheld the stars around the Sun. It was thought and said by many, not untruly, that the king [Stephen] would not continue a year in the government.” Columbus made use of an eclipse of the moon, which took place March 1, 1504, to relieve his fleet, which was in great distress from want of supplies. As a punishment to the islanders of Jamaica, who refused to assist him, he threatened to deprive

« PreviousContinue »