148 RECORD OF SCIENCE FOR 1887 AND 1888. 



tiekl, biXJ:! concliKled that mirrors are unsuitable for any extensive chart- 

 ing-, particuhirly mirrors of short focal length; at the same time there 

 is no doubt as to their capacity for the singularly accurate delineation 

 of small portions of the heavens, and for such operations as those con- 

 nected with stellar parallax or the charting of the moon. 



Mr. Roberts has described in the Monthly Notices (49: 5-13) an in- 

 strnment which he calls the ''stellar pantograver," intended to surmount 

 the difficulties of reproducing the negatives after they have been ob- 

 tained. It is essentially an instrument for engraving upon copper plates 

 ])oints of the same size and in the same relative i)ositious as those de- 

 picted by the photographs. 



In the long exposures of two hours and upwards that some of the 

 l)hotographs have required there is considerable danger of disidace- 

 ments of the images npon the plates due to variations in the refraction. 

 Dr. Dreyer has found that in latitude -fSO^ such displacements are not 

 likely to exceed 0".5 (and will therefore not affect sensibly the symmetry 

 of the images) in the case of an equatorial star moving from 27'" east 

 to L*7'" west of the meridian or in the case of a star of -|-25o declination 

 moving from 39'" east to 39"' west. 



The })liotographic work of Professor Pickering upon stellar spectra, 

 and of Gothard, Vogel and Roberts upon nebula?, has been mentioned 

 under these headings. Rai)id progress has been made by Dr. Gill with 

 his southern x)hotographic Durchmusterung. 



COMETS. 



Comet EmlcG (1888 II). — Encke's well-known periodic comet was 

 picked up by Mr. Tebbutt, of Windsor, New South Wales, with the 

 help of the ephemeris of Backhand and Seraphimoff, on July 8, 1888, 

 ten days after it had passed perihelion. In a 4i-inch telescope it ap- 

 peared as a small, bright, well-condensed nebula, about 1/ in diam- 

 eter, without a nucleus. It was observed at Windsor till August 1, 

 when it was "of the last degree of faintness," and at the Cape to 

 August 9, but it was unfavorably situated for observation in the 

 northern hemisphere. 



Berberich has discussed the brightness of Encke's comet as seen at 

 different returns from 178G to 1885, and calls attention to the rather 

 remarkable circumstance that the comet has been most conspicuous 

 when seen near a time of maximum of solar spots, and least when re- 

 turning near a minimum. 



Comet Faye (1888 IV). — Found by Perrotin, at Nice, August 9, 1888, 

 by the help of a sweeping ephemeris prepared by Kreutz. It was de- 

 scribed as a very faint, circular nebulosity about one minute in extent, 

 with a slight central condensation. Although it ren)ained visible as 

 late as February, 1889, on account of its extreme faintness but few 

 observations seemed to have been secured. Maximum brightness was 

 reached about the beginning of December. The correction to the 



