ECLIPSES. An eclipse is an obscuAttion of one of the heavenly bodies by the interposition of another, either between it and the spectator, or between it and the sun. The causes of E., as suggested in this definition, are so simple and familiar, that it is difficult for us to imagine how deeply E. affected men's minds before the dawn of astronomical science. To the ancients, they were without the order of nature—terrible presages of dire events; and at Rome, at one time, it was blasphemy, and punished by law, to talk publicly of their being due to natural causes. So strong a hold had this superstition on the popular mind, that even after it came to be generally believed that E. of the sun were caused by the moon coming betwixt us and that orb, E. of the moon were still referred to supernatural agency. When the moon was in eclipse, the people turned out and made a great noise with brazen instruments—the idea being, that by doing so they gave her ease in her affliction. According to some, Luna, when in eclipse, was in the pains of labor; according to others, she was suffering from the arts of wicked magicians. Similar notions have prevailed among all barbarian tribes. The Chinese, it is well known, imagine E. to be caused by great dragons trying to devour the sun and moon, and accordingly they beat drums and brass kettles to terrify the monsters into letting go their prey. Several stories are told of these popular superstitions being turned to good account by knowing persons; among which are those which represent Thales as bringing about peace between the Medes and Lyd inns; and Columbus, when in a great strait, procuring provisions from the natives of Jamaica through the pre diction of eclipses.
Stars, planets, and the satellites of planets, may stiffer eclipse. The principal E., however, are those of the sun and moon, called the solar and lunar eclipses. The transits of the lower planets over the face of the sun are partial solar E.; but solar E., properly so called, are those caused by the interposition of the moon between the sun and earth. Regarding solar E., it is observed that they happen
always at the time of new moon, when the sun and moon are in conjunction, i.e., on the same side of the earth. In a partial eclipse, the sun's disk suddenly loses its circu lar form; it becomes indented on one side, the indentation slowly increasing for some time, and then diminishing until it disappears altogether. In a total eclipse, the inden tation goes on increasing till the whole orb for a time disappears; after a short interval. the sun reappears again, passing through the same phases of obscuration in an inverse order. In an annular eclipse, the whole orb is obscured except a ring or annulus. Lunar E., again, it is observed, happen always at full moon, or when the sun and moon are in opposition, or on opposite sides of the earth, and are caused by the moon passing through the earth's shadow. Such E. are sometimes partial, and some times total, but never annular, and in their general phases they resemble those of the sun.
In speaking of E., we shall have occasion to use certain terms, which we shall now define. The duration of an eclipse is the time of its continuance, or the interval between immersion and emersion, Immersion or incidence of an eclipse is the moment when part of the luminary begins to be obscured; emersion or expurgation is the time when the luminary begins to reappear or emerge from the shadow. When the quantity of an eclipse is mentioned, the part of the luminary obscured is intended. To deter mine this part, it is usual to divide the diameter of the orb into twelve digits; and the eclipse is said to be of so many digits, according to the number of them contained in that part of the diameter which is obscured.
Having given this general explanation of the facts of observation on which the theory of E. turns, and of the language employed in speaking of them, we now proceed briefly to explain the theory itself, and how it is possible to predict the time of occurrence, and the duration and quantity of eclipses.