The most interesting astronomical event of this month is undoubtedly the transit of Mercury, which takes place on the morning of the 14th. At this time the planet comes directly between us and the sun, so that it appears as a small round black spot upon his disk, which moves across it to the westward. If it went across the middle of the sun's disk, it would take nearly six hours to make the journey; but in the present case it passes far to the north of the cen ter, and its line of motion cuts off a little slice of the northern limb, whose width is only about one-tenth of the sun's diameter. In consequence the duration of the transit is much reduced, and it lasts absolutely less than three hours and a half. We are not very well placed to view the proceed ings, for the sun does not rise at Washington until the transit is nearly hal' over. Its later stages, and especially the egress of the planet, which occurs at about 8:48 A. M. (Eastern standard time), should, however, be easily seen, weather permitting. The apparent diameter of the planet is so small less than ten seconds of arcthat it will be invisible without a telescope, but with instrumental aid and suitable shade glasses it should be visible as a small dot, only about 1/200 of the sun's diameter. It takes about 2 minutes and 40 seconds to pass over the edge of the sun which it approaches very obliquelyand this will be the most interesting part of the affair to watch, provided one has a telescope of sufficient power. Transits of Mercury, while by no means as rare as those of Venus, are un usual enough to be some what of a rarity to the amateur astronomer. If the orbits of Mercury and the earth were in the same plane, the planet would transit over the sun at every inferior conjunc tion, that is, three times a year. But his orbit is actually m0re inclined than any other among the principal planets, and in consequence he usually appears to pass north or south of the sun at con junction rather than directly in front of him, and transits can only oc cur when the conjunction takes place near the nodes of his orbit. which the earth reaches on May 7 and November 9. At the May transits the planet is much nearer us than in November, and he has consequently to pass much closer (in miles) to the line joining the earth and the sun's center, in order to appear projected on the latter's disk. It follows that the May transits are much less frequent than the November ones. For example, there were four of the former and nine of the latter during the nineteenth century. After thirteen years tha earth and Mercury come around into nearly the same positions they occupied at first, and after forty'six years they do so almost exactly. The transits, therefore, are often repeated after thirteen years, and almost always after fortysix. THE HEAVENS, Looking at our map, we see that the Milky Way forms a great arch across the sky from east to west, passing north of the zenith, Right in its center, high up in the west, is the great cross of Cygnus the Swan. Below this is the bright star Vega in Lyra, and on the right is Altair in the Eagle. Hercules is setting il1 the northwest, and CapricornUs the Sea Goat is low in the southwest. The brilliant red object in this region is the planet Mars. Aquarius the Water Bearer is to the right, and below him is the Southern Fish, with the isolated bright star Fomalhaut. Above, and nearly overhead, is the great square of Pegasus. Saturn, which is in Aquarius, about midway between Fomalhaut and 7 Pegasi, is brighter than any star for a long way around. In the southeastern sky is Cetus the Whale. The star r in this constellation is one of our nearest neighbors in space, its distance being about nine light years, and the star u is the famous variable Mira. A maximum of this star is due this month, and it will be interestlng to compare its brightness with that of last December, when for a week or two it was the brightest star in the constellation. In the meantime it has been as faint as the ninth magnitude; that is, less than onetwentieth as bright as the faintest stars visible to the naked eye. Eridanus, now rising in the east, is not yet well seen; and the Phamix and the Crane, though conspicuous southern constellations, are so low that we never see them at any advantage. Orion is just rising, due east, and so is Gemini, farther to the north. Taurus the Bull is above the former, and Auriga the Charioteer above the latter. Still higher are Perseus in the Milky Way and Ariei the Ram south of it. Andromeda is right overhead, and the Great Kebula is almost exactly in the zenith. Of the circumpolar constellations, Cepheus and Cassiopeia are above the pole, Ursa Minor and Draco to the left of it, and the Great Bear below it on the horizon. THE PLANETS. Mercury is evening star until his transit on the 14th, and afterward morning star. At the end of tha month n is easily visible in the morning sky, rising about 6 A, M, Venus is evening star, but iG still so near the sun and so far south as to be seen with difficulty. Mars is in Capricornus, and is conspicuous in the southwestern sky early in the evening. On the 11th he is in quadrature with the sun, and comes to the meridian at 6 P. M. Jupiter is also in quadrature during the month, on the 5th, but being west of the sun, he souths at 6 A, M. and is to be seen only after 11 P. M. Saturn is in Aquarius, and is due south about 8 P. M. in the middle of the month, Uranus is in Sagittarius, too near the sun to be well observed. Neptune is in Gemini, and comes to the meridian about 3:30 A. M. in the middle of the month, THE MOON. New moon occurs at 6 P. M. on the 5th, first quarter at noon on the 12th, full moon at 7 P. M. on the 19th, and last quarter at 11 P. M. on the 27th, The moon is nearest us on the 9th and farthest off on the 25th, She is in conjunction with Venus and Mercury on the 6th, Uranus on the 9th, Mars on the 12th, Saturn on the 14th, Neptune on the 23d, and Jupiter on the 26th. A comet, visible in an opera glass, was discovered by Mellish at Madison, Wis., on the morning of Octo ber 14. It was at that time in R. A. 8h. 31m. Declination, 9 deg. 24 min., south, and moving slowly northwestward. It rises before 2 A. M., and may be cbgerved in the morning hours. It cannot yet be told whether, like Daniel's comet, it will become conspicu ous, or whether, like the majority of comets, it will remain faint. Princeton University Observatory.