LUNAR TIDES AND ORBITAL MOTION. 19 



which it occupied in its orbit at the former period, 

 there may be a nearer approach to a similar recurrence 

 of storms than if there were only twelve hours' differ- 

 ence in the position of the moon. For, in the former 

 case there will be a recurrence of a similar influence 

 of the forces resulting from the orbital motion of the 

 earth, whereas in the latter case the action of these 

 forces would be completely reversed. With a differ- 

 ence of twenty-four hours in the position of the moon, 

 storms might recur in similar localities approxi- 

 mately ; which storms, if a change of only twelve hours 

 in the moon's position had occurred, instead of a 

 change of twenty-four hours, might not have recurred 

 in the same localities at all. That is to say; an 

 Atlantic storm which, at the end of a cycle of years, 

 might recur in the Atlantic with approximate simi- 

 larity in case of there being a difference of twenty- 

 four hours in the position of the moon ; might not, if 

 that difference of the moon's position were only 

 twelve hours at the end of the cycle, recur in the 

 Atlantic at all, but be transferred to the Pacific. 

 For there would in such case be in the Pacific a 

 nearer approximation than in the Atlantic, to the 

 recurrence of a combination of forces similar to that 

 which had been the cause of the Atlantic storm. 



179. The moon on an average oscillates backwards 

 and forwards between the northern and southern 

 hemispheres in 27'212^days. And therefore in that 

 period each of the lunar tides acts alternately in con- 



c 2 



