But
since a gravitational field exists with respect to this new body of
reference K1, our consideration also teaches us how the gravitational
field influences the process studied.
For example, we learn that a body which is in a state of uniform
rectilinear motion with respect to K (in accordance with the law of
Galilei) is executing an accelerated and in general curvilinear motion
with respect to the accelerated reference-body K1 (chest). This
acceleration or curvature corresponds to the influence on the moving
body of the gravitational field prevailing relatively to K. It is
known that a gravitational field influences the movement of bodies in
this way, so that our consideration supplies us with nothing
essentially new.
However, we obtain a new result of fundamental importance when we
carry out the analogous consideration for a ray of light. With respect
to the Galileian reference-body K, such a ray of light is transmitted
rectilinearly with the velocity c. It can easily be shown that the
path of the same ray of light is no longer a straight line when we
consider it with reference to the accelerated chest (reference-body
K1). From this we conclude, that, in general, rays of light are
propagated curvilinearly in gravitational fields.
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