26 ATMOSPHEKIC PRESSURE IN THE 



attraction tide must restore the general level of the 

 ocean before raising the level along the shores. We 

 must, however, from the greater average height of 

 the attraction tide, and the oscillations in longitude 

 of its highest point, expect to find that in the records 

 of disasters caused at seaports by unusually high tides, 

 such disasters will, in the northern hemisphere, have 

 occurred more frequently about the time of the Sep- 

 tember than the March equinox ; and in the southern 

 hemisphere more frequently about the time of the 

 March than the September equinox. We cannot, for 

 the present, do more than compare, the equinoctial 

 periods in the two hemispheres, because, as far as the 

 arguments which we have hitherto adduced are con- 

 cerned, we have no ground for determining what re- 

 lation the tidal forces which cause the annual tide 

 bear to those which cause the lunar and the solar tides. 



183. It will, however, be observed that, when the 

 annual tide, raised by attraction, is in the one hemi- 

 sphere, then the concomitant vis inertiaa tide is in 

 the opposite hemisphere, and that, therefore, though 

 the actual difference in the height of the water in the 

 two hemispheres is only the difference between the 

 relative height of those two tides, there is nevertheless 

 an intrinsic difference in the nature of those tides; 

 and this difference we may, not unreasonably, expect 

 to find more or less apparent in both the ocean and 

 the atmosphere. 



184. We have remarked, in section 143, that 



