ASTRONOMY. 311 



whole surface of the planet outside the margin of the equatorial belt 

 rotates with nearly the same rate." The approximate rotation -period 

 for the principal white spot between the edges of the great equatorial 

 belt was 9^ 50*" 9^8 from observations over more than eight months, 

 which is the same as for the second spot observed during 1880,- Hence, 

 these equatorial white spots drift in the direction of the planet's rota- 

 tion, at about 260 miles per hour, or through a complete revolution in 

 about 45 days. 



Twelve tinted drawings of the apjjearance of the disc of Jupiter 

 accompany the report. The first of two made on July 3, 1880, shows 

 the second satellite j ust entering on the great red spot at 15^ 43™.5, and 

 the other, made nine minutes later, shows it nearly over its center. A 

 notch was formed so soon as the satellite tonched the end of the red spot, 

 and when completely entered it appeared as white as when outside the 

 planet's disk. 



OBSERVATORIES. 



Observatories of the United States. — It will be remembered that at the 

 accession of Professor Pickering to the directorship of the Harvard 

 College Observatory he obtained by the subscription of some 70 persons 

 in Boston the sum of $25,000 ($5,000 a year for five years). A pamphlet 

 report on the scientific work accomplished has just been published, 

 which shall be summarized here. The work is spoken of under the head- 

 ings of tha various instruments employed. 



Large equatorial : This has been chiefly devoted to i^hotometry and 

 many new (successful) forms of photometers have been devised. The 

 brightness of the satellites of Mars, Jupiter, Saturn, Uranus (two only) 

 and Neptwie has been determined. Some 200 double stars ancf about 

 100 bright stars with faint companions have been measured in the same 

 way. All the planetary nebulae have been similarly measured and sev- 

 eral new ones have been discovered by their spectrum only. 



Many variable stars have had their light curves determined photo- 

 metrically, and several new ones have been discovered. Fifty points on 

 the moon have also been determined. Bond's zones of faint stars near 

 the equator are shortly to be revised. 



Meridian circle : The zone (50=^ to 55° If.) has been finished. It con- 

 tains 8,300 stars from 1 to 10th mag., each of which has been observed 

 twice. Two hundred and fifty-eight stars have been observed, each 6 

 times, for the Coast Survey, One hundred standard stars are regu- 

 larly observed with the sun. This work has continued for 3 years, and 

 will require 2 more. The graduation errors of one circle have been 

 determined. 



Meridian i)hotometer: Every star visible to the naked eye has had 

 its light determined photometrically on at least three nights, many on 

 more ; over 100,000 observations were made in 3 years, and this work is 

 now completed. Other similar work is planned. Other miscellaneous 



