Polarity

Polarity, 

or action and reaction, 

we meet in every part of nature; 

in darkness and light, 

in heat and cold, 

in the ebb and flow of waters, 

in male and female, 

in the inspiration and expiration of plants and animals; 

in the equation of quantity and quality 

in the fluids of the animal body; 

in the systole and diasystole of the human heart; 

in the centrifugal and centripetal gravity; 

in electricity, 

galvanism 

and 

chemical affinity.  

– Ralph Waldo Emerson