THE TIDES, (APP. A.] 191 



APPENDIX A. 



[Extracts from a Lecture on " The Tides" given to the 

 Glasgow Science Lectures Association, not hitherto pub- 

 lished, and now included as explaining in greater detail 

 certain paragraphs of the preceding Lecture.] 



(i) Gravitation. The great theory of gravitation 

 put before us by Newton asserts that every portion 

 of matter in the universe attracts every other por- 

 tion ; and that the force depends on the masses of 

 the two portions considered, and on the distance be- 

 tween them. Now, the first great point of Newton's 

 theory is, that bodies which have equal masses are 

 equally attracted by any other body, a body of 

 double mass experiencing double force. This may 

 seem only what is to be expected. It would take 

 more time than we have to spare were I to point 

 out all that is included in this statement ; but let 

 me first explain to you how the motions of dif- 

 ferent kinds of matter depend on a property called 

 inertia. I might show you a mass of iron as here. 

 Consider that if I apply force to it, it gets into a 

 state of motion ; greater force applied to it, during 



