ASTRONOMY. 165 



beiu,ij O.OG, iu terms of the earth's mean distance irom the sun; it 

 would therefore seem to otier an additional means of determiuiug' the 

 value of the solar parallax. Number 270 also ai)])r()a<;hes (juite near 

 the earth, A =0.81. Jt will be noticed that 279, with its mean distance 

 from the sun of 4.25, considerably greater tlian that of any other aste- 

 roid, lies ui)on 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 furuish further knowledge of the mass 

 of that planet. Number 281, with its small mean distance of 2.19 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 Jahrbu(;h, relating to as- 

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

 discovered planets i)resenting interesting })eculiarities. 



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 Ai)ril to December, 1887. The 

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

 disappear after i)i*«sing a transit wire, the telesco]>e being stationary, 

 and the light of the asteroid or comparison star suffering diminution 

 <'iiher by a wedge or more frequently by a detlector — a piece of glass 

 with nearly parallel sides placed in the telescope tuJK\ 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 cases, after the ])hase collection has been determined, the 

 remaining unknown errors are less than the average variation of the 

 fixed stars. 



