CONTENTS. 



LETTER I. 



Page 

 GRAVITY AND ITS EFFECTS ... ... ... 1 



LETTER n. 



THE TIDES ... ... ... ... 16 



LETTER HI. 



THE HEAT WITHIN THE EARTH ... ... 33 



LETTER IY. 



WARM SPRINGS ... ... ... ... 44 



LETTER Y. 



HOT SPRINGS AND JETS OF STEAM ... ... 59 



