moment approaches for the appearance of the planet, the excitement of the moment increases. ‘The tremble of impatience for the entrance of the star on the field of view,’ says an Edinburgh Reviewer, ‘is like that of a sportsman whose dog has just made a full point, and who awaits the rising of the game. When a star appears, the observer, in technical language, _takes a second from the clock face_; that is, he reads the second with his eye, and counts on by the ear the succeeding beats of the clock, naming the seconds mentally. As the star passes each wire of the transit, he marks down in his jotting-book with a metallic pencil the second, _and the second only_, of his observation, with such a fraction of a second as corresponds, in his judgment, to the interval of time between the passage of the star, and the beat of the clock which preceded such passage.’ An experienced observer will never commit an error in this mental calculation, exceeding the tenth of a second, or six hundredth of a minute. When the star has been thus watched over the seven cobweb lines (or wires), the observer jots down the hour and minute, in addition to the second, and the task is done. Stars, not very near the sun, may be seen in broad daylight, but, at night, it is requisite to direct a ray of light from a lamp, so far to enlighten the field of the telescope, as to permit the spider lines to be seen running across the brighter ground on which the expected star is to be visible. The adjustment of the instruments is a task of great nicety. If they are out of trim only a shadow of a shade of a hair’s-breadth, the desired accuracy is interfered with, and they have to be re-adjusted. Temperature is of course an important element in their condition, and a slight sensibility may do mischief. The warmth of the observer’s body, when approaching the instruments, has been known to affect their accuracy; and to avoid such sources of error, instruments have at times been cased in flannel, that the non-conducting powers of that homely fabric might screen the too-sensitive metal. Sunday is a comparative holiday at the Observatory, for then, except when any extraordinary phenomena are expected, the only duty done is to drop the Time Ball, and observe the moon’s place. The moon is never neglected, and her motions have been here watched, during the last hundred and seventy years, with the most pertinacious care,—to the great service of astronomy, and the great benefit of navigation.