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THE POPULAR SCIENCE MONTHLY 



Hai.i.ey's Tomet in 1835 (by Sir John Herschel). 



As no method existed at that time for precise determinations of the 

 perturbations, there was considerable uncertainty as to when to look 

 for the next return, but Halley estimated that the general result would 

 be a retardation, and that it would not be visible much before the be- 

 ginning of 1759. This, as we shall see, proved to be a very fortunate 

 guess. 



Naturally, the old chronicles were now diligently searched for 

 records of earlier appearances. Beginning with 240 B.C., a continuous 

 series of supposed appearances is found at an average interval of 76.8 

 years, but with the very considerable range of a little more than five 

 years between the longest and shortest of these periods. With such a 

 range, naturally, the period alone furnishes a very slight foundation 

 for establishing identity, and, unfortunately, in many cases, the ac- 

 counts given are so meager and unsatisfactory as to leave the matter in 

 grave doubt. In a number of instances, where the comet has been 

 connected with natural events, such as conjunctions of planets, eclipses, 

 earthquakes and the like, or with important matters of history, the ac- 

 counts may contain, in connection with much rubbish, sufficient ma- 

 terial of value to leave no doubt as to identity. It has been thought 

 by many that this is the comet mentioned by Josephus in connection 

 with the destruction of Jerusalem. This would, perhaps, not be im- 

 possible, though a considerable stretching of the period would be 

 required. The appearance in a.d. 451 is the first record which seems 

 open to no doubt on the score of identity. In the autumn of that year 

 the Huns, under Attila, were defeated by the Eoman armies. Numer- 



