13H ASTRONOMY FOR 1889, 1890. 



iiK'tliod, and (lonbtloss fur surpassing the i)resent methods in ease of 

 nieasuieincnt and output of work. 



Tlie llenrv Brothers are reported to have made a decided advance 

 in lunar photo<;rai)li.v in the phites taken with the equatorial of 0"'.32 

 (12.0 inches) ap«rture intended for the chart work. The improvement is 

 attributed especially to the process of eidargemeut employed, which 

 makes the diameter of the moon about 1'" (39 inches). This photographic 

 work is to be continued with the great equatorial coude, which is soon 

 to be mounted and provided with a photographic objective. 



Mr. Ifoberts has devised a machine, which he calls a "pantograver," 

 for measuring the magnitudes of the stars depicted upon the photo- 

 graphic plates and transferring them to metallic plates for printing. 



COMETS. 



The origin of comets. — Dr. Bredichin, the present director of the Pul- 

 kowa Observatory, who has devoted much time to the study of comet- 

 ary i»henomena, has expressed theopinion that periodic cometsowe their 

 origin to the segmentation of ordinary parabolic comets, having been 

 thrown ott' from the latter by an eruption such as it is generally sup- 

 l)osed we have witnessed in the great comet of 1882, and earlier in 

 Biela's comet. Dr. Kreutz's monograph on this great September comet 

 of 1882 forms one of the most important of recent contributions to com- 

 etary literature. The formidable obstacles to an accurate determination 

 of its orbit presented by the disintegration of the nucleus into several 

 })oints of condensation seem to have been most skillfully surmounted 

 by the computer. His tiual value for the period of revolution is 772.2 

 years. 



Dr. lioletschek claims that the systematic grouping of cometary peri- 

 helia in certain directions (270° and 90° of heliocentric longitude) has 

 no connection with the general motion of the solar syetem in si)ace, 

 but is due to the position of the earth at the time that such discoveries 

 are most readily made. 



An important paper on the capture theory of comets will be found 

 in the Bulletin Antrnnomique for June, 1889, and in the same jouriuil for 

 December, 1890, M. Tisserand has a further contribution to the same 

 subject. 



The Observatory for August, 1889, has a useful table of the approxi- 

 mate positions at the time of discovery of all comets seen since 18(59, 

 with brief notes on the physical appearance of each. Mr. Denning, who 

 has compiled this table, proposes to supplement it by one with similar 

 data for the comets from 1840 to 1808. 



Brorseti's comet. — A careful seareh for Brorsen's comet, which passed 

 perihelion in 1890, was made by Brooks and Swift, but without eftect. 

 This comet was discovered in 1840, and was last seen in 1879; it could 

 not be seen at the return in 1884. Tempel's second comet, and Bar- 

 nard's comet 1884 II, were also expected to return to perihelion in 



