500 



THE POPULAR SCIENCE MONTHLY. 



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 in- 

 trepidity of the computers and the assidui- 

 ty 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 suc- 

 cessful expedition to observe the transit of 

 Yeuus, and one by Borelly, of Marseilles. 

 As a tour de force in finding asteroids may be 

 mentioned Watson's discovery of Xo. 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 re- 

 member that in 1800 not a single one of 

 these asteroids was known. 



Astronomical akd Meteorological Obser- 

 vations MADE DURING THE YeAR 1872, 



at the United States Naval Observa- 

 tory. Washington: Government Print- 

 ing-Office, 1874. 



This is the eighteenth regular volume of 

 the Observatory publications, which were 

 begun in 1845, and have been continued an- 

 nually since that time, with the exception 

 of the years 1853 to 1861. 



During 1872 the instruments at the Ob- 

 servatory were : 



1. The Meridian Transit of 5 inches ap- 

 erture, and 7 feet 1 inch focal length. 



2. The Mural Circle of 4 inches aper- 

 ture, 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 ap- 

 erture, and 12 feet 1 inch focal length. 



6. The Equatorial of 9.6 inches aper- 

 ture, 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 deter- 

 mined by the transit instrument, and which 

 are included in the Washington " Cata- 

 logue" of stars, in the observation of a 



large number of circumsolar stars from the 

 British Association " Catalogue," and in a 

 few miscellaneous observations, in aU about 

 1,400 observations. 



Tlie transit circle was devoted to the 

 observation of the stars of the American 

 Ephemeris, to observations of miscellane- 

 ous stars, and of the Sun, Moon, planets, 

 and asteroids (of the last, however, only 

 eight vrere observed during the year) ; 697 

 stars are found in the " Catalogue," and of 

 these, together with the Sun, Moon, and plan- 

 ets, 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 ob- 

 servations made of stars reflected from the 

 surface of Mercury lead to results more and 

 more discrepant each year, so that the lati- 

 tude deduced from direct observations dif- 

 fers from that from reflex observations by 

 nearly three seconds of an arc in 1872; under 

 these circumstances all the reflection obser- 

 vations of 1871 and 1872 have been rejected. 



The equatorial has been used in the ob- 

 servation 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 (meas- 

 ures on twelve nights), and of occultations 

 (ten immersions and five emersions). Be- 

 sides 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 ba- 

 rometer, 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 con- 

 sisted, 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 Navv, which 



