REVIEWS 



The Story of the Comets. By G. F. Chambers. [Pp. xvi + 256.] (Oxford: 

 Clarendon Press, 1909. Price 65-. net.) 



This book appears at an opportune season, when general interest is excited by 

 the return of the famous comet of Halley ; and it fills a gap in popular astro- 

 nomical literature, there being no work in English that confines itself to comets 

 and deals with them so exhaustively. The author has drawn on the stores of his 

 well-known Handbook of Astronomy both for text and illustrations ; but the 

 matter has been carefully brought up to date, including a beautiful series of 

 photographs of the remarkable comet discovered by Morehouse last year. These 

 show in a striking manner the complicated forms and rapid changes of comets' 

 tails, and give an idea of the intensity of the forces that produce them. 



After some general chapters on the physical appearance and tails of comets, 

 and the method of their discovery, the author proceeds to a description of 

 individual comets, dividing them into short-period, long-period, and remark- 

 able comets. In the first category Encke's comet naturally takes the place 

 of honour. Its earlier history is very fully told ; but more might have been 

 said about Backlund's remarkable researches on the variations in the rate of 

 acceleration, and his suggestions as to a possible connection with the sunspot- 

 curve. He also quotes with disapproval Miss A. M. Clerke's conjecture that this 

 comet, owing to its frequent returns to the sun, was likely to wear out quickly ; 

 this has, however, been already apparently verified by the remarkable faintness 

 of the object in 1908, though it has yet to be seen whether the loss of light is 

 permanent. Brorsen's comet is mentioned as though it were still in existence ; 

 but, like Biela's, it is now looked on as a definitely lost comet. 



Passing to the comets of long period, of which Halley's is the most famous, 

 it will probably be news to many that there are five others of the same type and 

 about the same period. One of these is Westphal's, found in 1852, for which 

 a period of 6o| years was calculated (Mr. Chambers erroneously gives 67J), so 

 that it is expected back in 191 3. Another of them, that of Pons, was quite 

 a conspicuous object in 1884 ; a drawing of it by Trepied is reproduced. Halley's 

 comet naturally claims a chapter to itself, in which the story of the detection of 

 its periodicity is once more told, and historical anecdotes recounted about the 

 different returns back to B.C. 240, the earliest appearance that can be identified 

 with reasonable confidence. Some account follows of the phenomena exhibited 

 by the comet in 1835, and an anticipation of the circumstances of the present 

 return, including an ephemeris computed by Dr. Smart. As the comet has now 

 been detected by photography, an estimate can be made of the time when it will 

 pass perihelion, which will be on or about April 20 next. As this is only 3A days 

 later than the date assumed by Dr. Smart, his ephemeris will not be much 

 in error. 



The next chapter deals with the remarkable comets of modern times, including 

 the six-tailed one of 1744, and those of 1811, 1843, 1858, 1874, and 1882. There 

 are numerous excellent illustrations, and the letterpress is interesting. 



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