Origin and Development of the Theory of Relativity
William Wilson
There is an explicit statement of a restricted form. of what Einstein later called the Principle of Relativity in Sir Isaac Newton's Principia. It may be translated:
"The motions of bodies enclosed in a given space are the same relatively to each other whether that space is at rest or moving uniformly in direction [i.e. "moving with a constant velocity in a straight line] without circular motion." ...
