210 Royal Astronomical Society. 



connected by right lines. The groups thus formed sometimes do, 

 and sometimes do not, agree with those found in some European 

 maps. 



The map is executed coarsely by block-printing. The positions 

 and magnitudes are incorrect. There is no appearance of European 

 origin. The selection of stars of the fifth and sixth magnitude 

 could not well have been copied, and some stars are inserted which 

 are not to be found in any common catalogue or map. The epoch 

 seems to be about a.d. 173.5. 



A Historical Survey of Comets. By Dr. Michelsen. 



The author commences with a general review of the early history 

 of cometary astronomy, and notices the uncertainty attaching to 

 ancient European accounts of comets : the information given us by 

 the Chinese annalists, Ma-tuon-lin, as sketched by Mailla, Gaubil and 

 De Guignes, presenting a more definite aspect. He remarks that 

 the comet which appeared in the time of Anaxagoras may be con- 

 sidered the first established historically, though as yet unconfirmed 

 by any astronomical calculation. 



The author then proceeds to give a detailed description of the most 

 celebrated comets, commencing with Halley's, which he endeavours 

 to trace back as far as the year 426 b.c. The various confirmed 

 appearances of the comet since 1456 are then described, and also 

 circumstances relating to comets in previous centuries, which might 

 possibly be identical with Halley's. 



The comet of Encke is traced from its discovery by Mechain, in 

 1786, to the present time. The detection of a resisting medium in 

 space from the motion of this comet, and the determination (from its 

 perturbations) of the mass of Mercury, are also noticed. 



Biela's comet is described at its different appearances since the 

 year 1772. The author notices the supposed identity of the comets 

 of 1264 and 1556, and of those of 1532 and 1661. The great comet 

 of 1843 is described, and, assuming the period of revolution to be 

 about 175 years, some ancient comets are mentioned which might 

 possibly be the same. 



Those comets which, though only observed at one appearance, 

 yet remained visible long enough to allow their periodicity to be 

 determined, are placed in a separate class. The comet of Olbers in 

 1815 is computed by Bessel to have a period of 74 years, and the 

 next return is fixed for February 9, 1887. The comets of 1740 and 

 1666 do not show the least resemblance to this. The great comet 

 of 1811 was found by Argelander to have a period of 3066 years. 

 The second comet of 1811 was computed by Nicolai ; it was much 

 fainter than the first : the period assigned is about 763 years. Encke 

 made the time of revolution of the comet of 1812 about 71 years. 

 The comet of 1807 was computed by Bessel, who fixed the period at 

 about 1714 years. 



The author describes the celebrated comet of 1680, that of Lexell 

 in 1770, the comets of 1769, 1780, 1783, 1793, &c., and concludes 

 that there are three comets whose return is certain ; five probably 

 periodical, from the similarity of their elements with those of pre- 



