CONTEXTS. vn 



The Zodiacal Light 329 



Polarization and Interfei'ence of Light 332 



Measurable Velocity of Light 333 



William Gilbert 334 



Edmund Hallcy 336 



Land and Sea Expeditions 336 



Instruments for measuring Heat 337 



The Electric Force 341 



Otto von Guericke 342 



Pneumatic Chemistry 343 



Geognostic Phenomena 347 



The Charm inherent in ^Mathematical Studies 351 



VIIL Retrospect of the Epochs considered 352-356 



Recapitulation 352 



The Power of penetrating Space 353 



Early Gems of Natural Knowledge 35-1 



The Advanae of various Scieacej .........v.....,....*..... S53 



