ASTRONOMY. 425 



Las resulted in the discovery of seven such objects. Most of them are 

 so minute that they cannot be distinguished from stars by the ordinary 

 eye-piece. Photometric work on the satellites of Mars confirms that of 

 1877 and 1879, except that the brightness of Deimos, when preceding 

 and when following Mars, does not seem to change, as formerly noticed. 

 The determination of the brightness of various points on the Moon to 

 aid the work of the Selenographical Society is now completed. From 

 this investigation it appears that the scale of brightness, in use by 

 common observers of the Moon, is closely expressed in terms of stellar 

 magnitudes, each degree in the scale answering to the ratio of light 

 equivalent to six-tenths of a magnitude. The wedge photometer has 

 been used to measure the light of faint stars in zones. It is so placed 

 in the instrument that the diurnal motion of the stars carries them 

 from its thin to its thick portion, and the time of their disappearance 

 is noted to determine their brightness. The careful study of Saw- 

 yer's variable star, D. M. + 1°, No. 3408, proves it to be a very inter- 

 esting object. Its period of variability is 20h. 7m. 4s., 1.6 being the 

 shortest known belonging to the Algol class. Its variation is from 6.0 

 to 6.8. 



The telegraphic system devised by those in charge of the Science 

 Observer for the speedy transmission of comet news has been improved, 

 extended, and will probably soon come into general use. Progress has 

 been made in the reductions of the meridian circle work from 1870 to 

 1879. These observations will make about 1,200 printed pages, and 

 will fill three volumes of the Annals. Volume I will contain an intro- 

 duction with discussion of instrumental constants, &c; n will contain 

 all the zone observations in journal form, and in, observations of 

 secondary polar stars made in lS72-'73, a list of stars for United States 

 Coast Survey in 1878, and other similar work in 1879. This important 

 work is already well advanced, under the direction of Prof. W. A. 

 Rogers. The Coast Survey Catalogue is now ready for publication. 



The work of the meridian photometer has been considerable. Over 

 ninety thousand measures were made last summer on about 4,000 stars, 

 visible to the unaided eye. This work involves the discussion of sev- 

 eral problems of general interest in connection with the light of the 

 stars, among which may be mentioned atmospheric absorption. The 

 discussion of about fifteen thousand observations shows this curious 

 result: That we may assume the absorption at any altitude exceeding 

 15° to be equal in stellar magnitude to one-quarter of the secant of the 

 zenith distance, which agrees very closely with the empirical law de- 

 duced by Seidel. 



Though some have claimed that the Pole Star is variable, its con- 

 stancy is established by the photometer. 



Other valuable matter in this report pertains to variable star work, 

 equatorial observations, scientific papers published, and plans for the 

 future. (Sidereal Messenger.) 



