It may be said that of the 142 planets known up to February, 1875, at least 92 have their orbits fully determined, while only four are for the present lost. This is a most admirable showing both for the intrepidity of the computers and the assiduity of the observers. Since February three new planets have been found, two by Dr. Peters, of Clinton, New York, apparently in honor of his safe return from a most successful expedition to observe the transit of Venus, and one by Borelly, of Marseilles. As a tour de force in finding asteroids may be mentioned Watson's discovery of No. 139 in Peking, China, during the residence of the American Transit-of-Venus Expedition in that place. It may add to one's conception of the assiduity of astronomers if we remember that in 1800 not a single one of these asteroids was known.
This is the eighteenth regular volume of the Observatory publications, which were begun in 1845, and have been continued annually since that time, with the exception of the years 1853 to 1861.
During 1872 the instruments at the Observatory were:
1. The Meridian Transit of 5 inches aperture, and 7 feet 1 inch focal length.
2. The Mural Circle of 4 inches aperture, and 5 feet focal length.
3. The Prime Vertical Transit of 4.8 inches aperture, and 6 feet 6 inches focal length.
4. The Transit Circle of 8.52 inches aperture, and 12 feet 1 inch focal length.
6. The Equatorial of 9.6 inches aperture, and 14 feet 4 inches focal length.
6. Meteorological Instruments.
Of these instruments the first and third were not in use during the year, for lack of observers.
The mural circle was employed during the year in observations of stars whose right ascensions had previously been determined by the transit instrument, and which are included in the Washington "Catalogue" of stars, in the observation of a large number of circumsolar stars from the British Association "Catalogue," and in a few miscellaneous observations, in all about 1,400 observations.
The transit circle was devoted to the observation of the stars of the American Ephemeris, to observations of miscellaneous stars, and of the Sun, Moon, planets, and asteroids (of the last, however, only eight were observed during the year); 697 stars are found in the "Catalogue," and of these, together with the Sun, Moon, and planets, about 3,700 observations were made. The methods of reduction have remained substantially the same since the instrument was mounted. It is to be noted that the observations made of stars reflected from the surface of Mercury lead to results more and more discrepant each year, so that the latitude deduced from direct observations differs from that from reflex observations by nearly three seconds of an arc in 1872; under these circumstances all the reflection observations of 1871 and 1872 have been rejected.
The equatorial has been used in the observation of the asteroids, of which ten have been observed during the year (a very fine series having been made for three months on Alceste), of the companion of Sirius (measures on twelve nights), and of occultations (ten immersions and five emersions). Besides this a good series of observations was made on the comets of Encke and Tuttle.
The regular meteorological observations (seven observations in twenty-four hours) have been kept up and are given in detail and in means. The indications of the barometer, wet and dry bulb thermometers, maximum and minimum thermometers, solar thermometer and rain-gauge, are recorded at suitable times, and the direction and force of wind (force by estimation only) and cloudiness of sky are also noted. No self-recording meteorological instruments are provided.
The personnel of the Observatory consisted, in 1872, of a superintendent (rear-admiral U. S. Navy), of five Professors of Mathematics and three aids (observers), of an instrument-maker, and three watchmen (meteorological observers).
Besides this force several officers of the line of the Navy were detailed to take charge of the chronometers of the Navy, which