TITLE: who invented projective space $\mathbb{P}^n$?
QUESTION [12 upvotes]: Who invented projective space $\mathbb{P}^n$ as an extension of the usual affine space $\mathbb{A}^n$?
Who was the first person to consider projective closure of
plane affine algebraic curves (curves in $\mathbb{A}^2$)? Was it the same person?

REPLY [2 votes]: One should also mention 
Karl Georg Christian von Staudt (1798 – 1867), a German mathematician.
His book "Geometrie der Lage (1847)" was a landmark in projective geometry. 
Staudt was the first to adopt a fully rigorous approach. Without exception his predecessors still spoke of distances, perpendiculars, angles and other entities that play no role in projective geometry.