LECTURE XII. 



EXPERIMENTAL PHILOSOPHY. 



RF.FLEXIBIL1TY OF LIGHT, OE CATOPTRICS. 



THERE is no part of the science of optics more 

 amusing, or indeed more astonishing, to un- 

 scientific readers, than that which regards the 

 reflection of light. How a looking-glass comes to 

 reflect images without their touching it ; how the 

 whole figure of a man, six feet high, shall be 

 seen in a glass not above three feet ; how, when 

 we look at some polished surfaces, as a watch- 

 case, for instance, a man's face seems not bigger 

 than his finger-nail ; while, if we look on other 

 surfaces, the face shall be of gigantic size ; these 

 are all wonders that the curious would wish to 

 understand, and the inexperienced to examine. 



The property which polished surfaces possess 

 of reflecting light, is referred by Newton to the 

 principle of repulsion. For it is justly remarked 

 by him, that those surfaces, which to our senses 

 appear smooth and polished, are found, when 

 viewed through a microscope, to be still rough 

 and uneven. It will, however, suffice for our 

 purpose, in describing the effects of reflection, if 

 we consider every particle of light as rebounding 

 from the surface of a mirror, like a tennis-ball 

 from the wall of a tennis-court. 



