Numerous instances are on record of partial obscurations of the sun which could not be accounted for by any known cause. Cases of such phenomena took place, according to Humboldt, in the years 1090, 1203, and 1547. Another so-called _dark day_ occurred on the 12th of May, 1706, and several more (some of still later date) might be specified. Chladni and other physicists have regarded the transit of meteoric masses as the most probable cause of these obscurations. It is proper to remark, however, that the eminent French astronomer, Faye, who has given the subject much attention, finds little or no evidence in support of this conjecture. An examination of meteorological records is said to have established two epochs of abnormal cold, viz., about the 12th of February and the 12th of May. The former was pointed out by Brandes about the beginning of the present century; the latter by Mädler, in 1834. The May epoch occurs when the earth is in conjunction with one of the nodes of the November meteoric ring; and that of February has a similar relation to the August meteors. M. Erman, a distinguished German scientist, soon after the discovery of the August and November meteoric epochs, suggested that those depressions of temperature might be explained by the intervention of the meteoric zones between the earth and the sun. The period, however, of the November meteors being still somewhat doubtful, their position with respect to the earth about the 12th of May is also uncertain. But however this may be, the following dates of aerolitic falls seem to indicate May 8th-14th, or especially May 12th-13th, as a meteoric epoch: (_a_) May 8th, 1829, Forsyth, Georgia, U. S. A. (_b_) May 8th, 1846, Macerata, Italy. (_c_) May 9th, 1827, Nashville, Tennessee, U. S. A. (_d_) May 12th, 1861, Goruckpore, India. (_e_) May 13th, 1831, Vouillé, France. (_f_) May 13th, 1855, Oesel, Baltic Sea. (_g_) May 13th, 1855, Bremevörde, Hanover. (_h_) May 14th, 1861, near Villanova, in Catalonia, Spain. (_i_) May 14th, 1864, Orgueil, France. All the foregoing, except that of May 14th, 1861, may be found in Shepard's list, _Silliman's Journal_ for January, 1867.