POPULAR SCIENTIFIC KNOWLEDGE. 37 



Hujgens first applied himself, in 1678, to the enigma of 

 the phenomena of polarisation of light exhibited in doubly- 

 refracting spar, and observed the difference between the two 

 portions into which a beam of light divides itself in passing 

 through such a crystal, it was not foreseen that through the 

 admirable sagacity of a physical philosopher of the present 

 day( 16 ), the phsenomena of chromatic polarisation would 

 lead us to discern, by means of a minute fragment of Iceland 

 spar, whether the light of the sun proceeds from a solid 

 nucleus, or from a gaseous covering ; whether comets are 

 self-luminous, or reflect borrowed light. 



An equal appreciation of all parts of natural knowledge 

 is an especial requirement of the present epoch, in which 

 the material wealth and increasing prosperity of nations 

 are in great measure based on a more enlightened employ- 

 ment of natural products and forces. The most super- 

 ficial glance at the present condition of European states 

 shews, that those which linger in the race cannot hope to 

 escape the partial diminution, and perhaps the final 

 annihilation, of their resources. It is with nations as with 

 nature, which, according to a happy expression of Goethe ( l7 ), 

 knows no pause in unceasing movement, development, and 

 production, and has attached a curse to standing still. 

 The danger to which I have alluded must be averted by the 

 earnest cultivation of natural knowledge. Man can only 

 act upon nature, and appropriate her forces to his use, by 

 comprehending her laws, and knowing those forces in relative 

 value and measure. Bacon has said that, in human societies, 

 knowledge is power, both must rise or sink together. 

 Knowledge and thought are at once the delight and the 

 prerogative of man; and they are also a part of the wealth of 



