NEWTON S PRINCIPIA. 285 



CHAPTER VIII. 



THE THEORY OF THE TIDES. 



I. Newton s investigation on the Tides. 



o. The tides considered as a question in the motion of fluids, de 

 duced from the Lunar Theory. 



0. General explanations of eight phenomena of the titles. 

 7. The calculation of the height of the lunar and solar tides. 

 5. The tides in the moon. 



II. The theories that have been proposed since Newton s time. Note IX. 



1. The Equilibrium Theory. 



a. Its fundamental hypothesis. 



. The results of calculation made according to this theory, three 



kinds of tides. 

 7. Airy s opinion of this theory. 



2. The Hydrodynamic Theory. 



a. Its fundamental assumptions. 



& The results of calculation, three kinds of tides. 



3. The Wave Theory. 



a. Consideration of ocean tides. 



fr River tides, results of calculation and explanation of the chief 



phenomena. 

 7. Where this theory fails. 



III. Some results of observation. Note IX. 



THE cause of the tides in the ocean have always excited 

 the curiosity and wonder of mankind. Their regularity, 

 the magnitude of the scale on which they take place, the 

 difficulty of conceiving what that power could be that can 

 raise twice a day so vast a body of water, all render the 

 question one of the most interesting in the whole range of 

 science. Phitheas, it is said, was the first who remarked 

 that the tides followed the course of the moon. But the 

 &quot; why &quot; was still as great a mystery as before. Galileo 



