iManchester Memoirs, Vol. I. {igo6), No. 7. 3 



years since the first crude attempts were made to write 

 history, and early historians have been suspected of intro- 

 ducing eclipses into their narratives as scenic effects, much 

 as a painter might introduce into a picture figures or 

 clouds which might have been, but were not, actually there. 

 Within the last year, however, Mr. Cowell, of the Green- 

 wich Observatory, has thrown a new light upon some of 

 these old records. He has shown* that by a new and 

 simple supposition no less than five important records of 

 eclipses, which it had been previously considered difficult 

 if not impossible to reconcile with what we know of the 

 moon's motion from modern observations, could all be 

 brought into line. His hypothesis is indeed a little start- 

 ling, being no less than a gradual quickening of the 

 velocity of the earth in its revolution round the sun, which 

 we have been accustomed to regard as having been con- 

 stant for ages, if we disregard variations of a periodical 

 character. But there is more than one possible vera causa 

 for such a change of motion. We have long been familiar 

 with such a change in the case of the moon, and indeed 

 there has been a controversy of no mean order about this 

 same " secular acceleration," a controversy which is some- 

 what of a curiosity,! for it centred round a purely mathe- 

 matical calculation, about which it might have been 

 supposed there could be no doubt. But in the case of the 

 moon there is no difficulty in assigning the causes for this 

 change, whereas in the case of the newly discovered 

 change in the earth's motion difficulties do arise. We 

 may suppose, for instance, that there is a resisting medium 

 of an extremely tenuous character, and this would produce 

 the proper effect upon the earth ; but it would be natural 



*See Mon. Not. Roy. Astron. Sac, vul. 65, pp. 861, 867; vol. 66. 



PP- 3. 5, 35. 36. 



tSee, for instance, Mon. Not. Roy. Astron. Soc, vol. 53, p. 198. 



