Double Spaces Between Sentences…NOT!
http://www.itcfonts.com/Ulc/4111/DoubleSpaces.htm

Strizver, Ilene
Upper and lowercase Magazine
2008

Abstract:

Typing two spaces after a period is a relic of the typewriter era that has hung around long past its sell-by date. Here’s how to make sure none of those double-space dinosaurs find their way into your typeset work.