ASTRONOMY. 209 



of tlie minor planets, as follows: Pallas 1G7 miles; Juno 94zt4; Vesta 

 319ztl0; Antiope 51±3; Branliild 20±3; Eva U±l; Menippe 12±1. 



Though these equivalent diameters must not be accepted as actual 

 diameters, they doubtless give a pretty close approximation to the size 

 of the smaller members of the solar system, even allowing for a large 

 uncertainty in the albedo. It would seem from the Harvard College 

 determinations that some of the smaller asteroids are at any rate com- 

 parable in size with the satellites of Mars, and the step from these to the 

 larger meteorites is not a very large one. The volume also contains pho- 

 tometric measures of 103 unequal double stars and some miscellaneous re- 

 sults. Great care has been taken throughout to avoid systematic errors 

 by varying the methods of observation, but it is certain that some of the 

 measures of the light of faint companions to bright stars are in error, as 

 shown by comparison of pairs of the same assigned brightness. 



A work of some magnitude has been undertaken by Prof. Pickering 

 during the past year in the determination of the light of all the stars 

 visible to the naked eye at Cambridge (Mass.) As most of these stars 

 would be very troublesome to identify in the field of a photometer 

 mounted on an ordinary stand, they are observed in the meridian. The 

 photometer consists of a horizontal telescope pointing to the west, and 

 having two objectives. By means of two prisms mounted in front of the 

 telescope the pole star is reflected into one object-glass, and the star to 

 be measured into the other. The cones of light are made to coincide by 

 a double-image prism, the extra images being cut off by an eye-stop. 

 The star to be measured is thus seen in the same field with the pole star, 

 nnder exactly the same conditions. To determine the relative transpar. 

 ency of the air at different altitudes, a list of a hundred circumpolar 

 stars has been prepared, to be observed at both upper and lower culmi- 

 nations. Progressive changes in the light of the pole star may thus also 

 be detected and eliminated. 



A Persian IMS. of IJLUGn Beg's catalogue of stars recently presented 

 to the Eoyal Astronomical Society has been examined by Mr. Knobel 

 (M. jST. XXX, 337), and compared with Hyde's translation. A great many 

 discrepancies have (as was also the case with St>Fi) been found to arise 

 from certain characters being mistaken for others by the transcriber, 

 and Mr. K]n^obel was hereby led to examine those of Ibn Junis's lunar 

 eclipses, which Prof. Newcojib had found to be irreconcilable with the 

 computations, and he suggests explanations, founded on the assumption 

 of similar errors having been made in copying a MS. The magnitudes 

 of Ulugh Beg never having been properly translated, Mr. Knobel 

 gives a complete translation of the magnitudes as found in the MS. 

 under examination. 



Jupiter. — Dr. Schmidt has made a new determination of the time of 

 rotation of Jupiter upon its axis, from observations in 1879 and 1880, of 

 the red spot upon its disk. His preliminary discussion gives for the 

 time of rotation 9h. 55m. 31.42s. 

 S. Mis. 31 14 



