22 POPULAR LKCTWES AND ADDRESSES. 



as it were, for the whole globe, the tidal effect 

 of the disturbing body considered. The tidal 

 spheroid averaging the moon's effect alone, is 

 called the luni-tidal spheroid ; and that for the 

 sun is called the soli-tidal spheroid. The resultant 

 tidal spheroid, representing on the same principle 

 the average displacement of the water produced by 

 the combined influence of the two bodies, is found 

 by simply adding the displacements from the un- 

 disturbed figure, represented respectively by the 

 luni-tidal and soli-tidal spheroids. 



9. If there were no frictional resistance against 

 the tides, each separate tidal spheroid would have 

 its longest diameter perpendicular to the line join- 

 ing the centre of the earth with that of the disturb- 

 ing body, whether moon or sun. 1 When the joint 



1 This assertion i> (minded not on observation, but on dynamical 

 principle.. Jt depends on the truth that, if the tidc-^cncratinn 

 inlluence of either sun or moon were suddenly to cease, the period 

 of the chief oscillation that would result \\ould be ^rcalcr than 

 either twelve solar or twelve lunar hours. The period of this 

 Oscillation would be /,,, than either twelve lunar or Iwche 

 hours, if ihe sea were very much deeper than it is, or if it were 

 lerably deeper, an. I also less obstructed by land. (Sec II.) 

 [f "" of the luni-tidal and soli- 



tidal Npheroi.U would be in line vvith the moon and sun respectively, 



