CONTENTS. IX 



Page 



Polarization and interference oflight 715 



Measurable velocity oflight 716 



William Gilbert 717 



Edmund H alley 719 



Land and sea expeditions 720 



Instruments for measuring heat 721 



The electric force 725 



Otto von Guericke 727 



Pneumatic chemistry 728 



Geognostic phenomena 732 



The charm inherent in mathematical studies 737 



VIII. Retrospect of the epochs considered 738-742 



Recapitulation 738 



The power of penetrating space 739 



Early gems of natural knowledge 740 



The advance of various sciences . 741 



