ASTRONOMY. 1 G5 



beiurf O.OG, in terms of tlie eartli's ineaii distance from the snn; it 

 would therefore seem to otfer an additional means of determiuinj;- the 

 value of the solar parallax. Number 270 also ai)i)roaehes quite near 

 the earth, A =0.81. It will be noticed that 270, with its mean distance 

 from the sun of 4.25, considerably jireater than that of any other aste- 

 roid, lies upon the extreme outer limit of the grouj), and will at certain 

 times, therefore, be brought quite close to Jupiter, and by the pertur- 

 bations thus experienced may furnish further knowledge of the mas8 

 of that planet. Number 281, with its small mean distance of 2.10 lies, 

 on the other hand, near the inner border of the group; it is the sixty- 

 eighth asteroid discovered by Dr. J. Palisa. 



Prof. Tietjen discontinues with the year 1888, the regular issue of the 

 Circulars and Correspondence of the Berlin Jahrbuch, relatiug to as- 

 teroids. Special attention will be given hereafter to the orbits of newly 

 discovered planets presenting interesting peculiarities. 



The Annals of the Harvard Observatory, volume 18, No. 3. contains a 

 discussion of a series of photometric observations of the asteroids by 

 Mr. H. M. Parkhurst, extending from April to December, 1887. The 

 method of observation was to note the time that the asteroid took to 

 disai)pear after passing a transit wire, the telescope being stationary, 

 and the light of the asteroid or comparison star sufteriug diminution 

 either by a wedge or more frequently by a detlector — a piece of glass 

 with nearly parallel sides placed in the telescope tube, about one sev- 

 enth of the way from the focus to the object glass, and covering half 

 the field. The conclusions reached by the author are as follows: 



(1) The phase correction can not be neglected, and is peculiar to each 

 asteroid. 



(2) There may be, for certain asteroids, large errors from rotation. 



(3) In most eases, after the i)hase correction has been determined, the 

 remaining unknown errors are less than the average variation of the 

 fixed stars. 



