Speed of light also explained why these emails were limited to a little over 500 miles: http://www.ibiblio.org/harris/500milemail.html http://www.ibiblio.org/h

Speed of light also explained why these emails were limited to a little over 500 miles: http://www.ibiblio.org/harris/500milemail.html http://www.ibiblio.org/harris/500milemail.html So it can be relevant, even as an approximation.