in connection with the formulation of natural laws. Our course was more on the following lines. In the first place, we started out from the assumption that there exists a reference-body
, whose condition of motion is such that the Galileian law holds with respect to it: A particle left to itself and sufficiently far removed from all other particles moves uniformly in a straight line. With reference to
(Galileian reference-body) the laws of nature were to be as simple as possible. But in addition to
, all bodies of reference
' should be given preference in this sense, and they should be exactly equivalent to