Physics. — “Motion relativated by means of a hypothesis of A. Förrr”. 
By H. Zanstra. (Communicated by Prof. P. Enarenrusr). 
(Communicated at the meeting of March 26, 1921). 
§ 1. The fixation of “inertial systems” in classical mechanics without 
applying the principle of absolute motion. 
It is well known that in the equations of motion of classical 
mechanics for a system of 7 material points: 
ey my, = ¥; ee ees EE 
WS Lek et n.) 
the position of those points is referred to a rectangular system of 
co-ordinates being at rest or moving uniformly in absolute space. 
But when we refer this position to another system of axes that 
does not move uniformly or rotates with respect to the above 
mentioned systems, the differential equation of motion assumes a 
more complicated form. E.g. if the system of axes has an absolute 
rotation, it is well known that we get on the left side of equation 
(1) terms of the type of centrifugal and Coriolis forces. 
Those systems of co-ordinates in which the equation of motion 
assumes the simplest form (1), the so-called ‘‘inertial systems” *), 
are consequently defined by means of the idea of absolute space. 
This idea, introduced by Newton, was at first retained in the later 
elaboration of Newron’s mechanics. Newton’s contemporary BERKELEY 
however already gave a criticism of this principle of absolute motion 
(motion in “absolute space’). The purport of his demonstration is 
that motion of bodies must be referred to other bodies and not to 
an absolute space *). 
In more recent times (+ 1870) this question was taken up again, 
especially by C. Neumann, LANGE and Macu *). While NruMANN still 
) The idea of “inertial systems” was introduced by LAnGE he calls them 
“Inertialsysteme’’. 
*) G. BERKELEY. The Principles of Human Knowledge, section 111. e.v. 
3) E. Macn. Die Mechanik in ihrer-Entwickelung. As for LANGE and NEUMANN 
see § 5. Literature is mentioned in the Enzyklopedie der Math. Wiss. VI 1, 
p. 30. See moreover H. SEELIGER. Ueber die sogenannte absolute Bewegung. 
Sitzungsber. der Math. Phys. Klasse der Bayr. Ac. der Wiss. 1906. Bd. 36, p. 85. 
