D O C U M E N T 2 5 4 O C T O B E R 1 9 2 1 1 6 5
1) The moving light source L with the coordinates can be substituted by
the observer, at time , by a light source with the coordinates at rest
relative to the coordinate system, where r is the distance: light source–observer,
measured with sufficient precision in the inertial system at time , if all body ve-
locities are small against c.
2) The influence of the observer’s motion on the observed locations of the light
source is a reduction[7] in the angle by .[8]
Example:
255. From Eduard Einstein
[Zurich,] 4 October
[1921][1]
[Not selected for translation.]
xr t
t0 L xr t0
r
c
-- –
t0
OL =
c
-- - sin =
L
v O
OL v rel. inertial system
2
-- - =
rel. mov. observer O
2
-- -
v
c
-- – =
OL v rel. inertial system
2
-- - =
rel. mov. observer O
2
-- -
2v
c
------. – =
v
L
v
O
v