LESSON XXXI. 



ON THE TIDES. 



Now the mighty mass of water swells 



Resistless, heaving on the broken rocks, 

 And the full river turning, till again 

 The tide revertive, unattracted leaves 

 A yellow waste of idle sands behind. 



THOMSON. 



'PHILOSOPHERS in every age of the world have 

 been greatly puzzled to explain and account for 

 the Tides of the sea, which ebb and flow twice in 

 twenty-four hours ; but in despite of every attempt, 

 the doctrine of them remained in obscurity, until 

 the great Sir Isaac Newton developed the mystery. 

 This eminent philosopher having demonstrated 

 that there is a principle in all bodies, by which they 

 mutually draw or attract each other in certain pro- 

 portions according as their distances or size vary, 

 proved that as fluids are very easily put in motion 

 by any force acting upon them, those parts of the 

 sea which are immediately below the moon, must 

 be attracted towards it, and consequently wherevec 

 the moon is nearly vertical, the sea will be raised, 

 which occasions the flowing of the Tide there. A 

 similar reason occasions the flowing of the Tide 

 likewise in those places where the moon is in the 



nadir, 



