LECTURE VI. 

 ON LIGHT, 



PART I. REFLEXION REFRACTION DISPERSION 

 COLOUR ABSORPTION. 



|N a conversation held some years ago by the 

 author of these pages with his lamented 

 friend, Dr Hawtrey, Head-Master and late 

 Provost of Eton College, on the subject of 

 Etymology, I happened to remark that the syllable Ur 

 or Or must have had some very remote origin, having 

 found its way into many languages, conveying the sense 

 of something absolute, solemn, definite, fundamental, or 

 of unknown antiquity, as in the German words Ur-alt 

 (primeval), Ur-satz (a fundamental proposition), Ur-theil 

 (a solemn judgment) in the Latin Oriri (to arise), 

 Origp (the origin), Aurora (the dawn) in the Greek 

 'Ogos (a boundary, a mountain, the extreme limit of 

 our vision, whence our horizon), 'O^aw (to see), '0^05 

 (straight, just, right), "O^xos (an oath or solemn sanction), 

 r n0a/ (the seasons, the great natural divisions of time), 

 &c. "You are right," was his reply, "it is the oldest of 



