350 Astronomy. [Lecture 22. 



call action, force, or attraction, solar or lunar. 

 The lunar action, as just noted, is thrice as 

 energetic as that of the sun. 



I shall now deduce from the doctrines which 

 have been advanced, what I hope will be found 

 a clear and convincing explanation of the principal 

 phsenomena of the tides. 



We have seen that the waters of the ocean 

 must rise at the same time at that part of the 

 ocean which is immediately under the moon, 

 and at the opposite point. Consequently, at 

 ninety degrees from these points on each side, 

 the water must be lowered. In the same manner 

 the solar action must elevate the waters in that 

 part which is immediately under the sun, and at 

 the part diametrically opposite. Combining the 

 two actions, we shall find that the elevation of 

 the water at the same place must be subject to 

 some variations both with respect to quantity 

 and time, according as the solar and lunar actions 

 are combined; or according as these forces act 

 differently, or against each other. 



In general, in conjunctions and oppositions of 

 the sun and moon, their forces are combined. 

 In conjunctions these bodies act on the same 

 meridian; and in opposition, they still act in 

 the same line, and each raises the water on that 

 side which is immediately under it. 



In the quadratures, on the contrary, the water 

 which is elevated by the sun, is depressed by the 

 moon's attraction, for the moon is then ninety 



