f to
be guided. Although thus there was no special effort made to reach a
connection with the theory of Newton, it was evident, fortunately,
at the end of the experiment that the connection existed. If we
avail ourselves of the simplifying circumstance that the velocities
of the heavenly bodies are slight in comparison with that of light,
then we can deduce the theory of Newton from the new theory, the
"universal" relativity theory, as it is called by Einstein. Thus
all the conclusions based upon the Newtonian theory hold good, as
must naturally be required. But now we have got further along. The
Newtonian theory can no longer be regarded as absolutely correct in all
cases; there are slight deviations from it, which, although as a rule
unnoticeable, once in a while fall within the range of observation.

Now, there was a difficulty in the movement of the planet Mercury
which could not be solved. Even after all the disturbances caused by
the attraction of other planets had been taken into account, there
remained an inexplicable phenomenon--i.e., an extremely slow turning
of the ellipsis described by Mercury on its own plane; Leverrier had
found that it amounted to forty-three seconds a century. Einstein
found that, according to his formulas, this movement must really
amount to just that much. Thus with a single blow he solved one of
the greatest puzzles of astronomy.

Still more remarkable, because it has a bearing upon a phenomenon which
formerly could not be imagined, is the confirmation of Einstein's
prediction regarding the influence of gravitation upon the course
of the rays of light. That such an influence must exist is taught
by a simple examination; we have only to turn back for a moment to
the following comparison in which we were just imagining ourselves
to make our observations. It was noted that when the compartment is
falling with the acceleration of 981 the phenomena therein will occur
just as if there were no attraction of gravitation. We can then see
an object, A, stand still somewhere in open space. A projectile,
B, can travel with constant speed along a horizontal line, without
varying from it in the slightest.

A ray of light can do the same; everybody will admit that in each case,
if there is no gravitation, light will certainly extend itself in a
rectilinear way. If we limit the light to a flicker of the slightest
duration, so that only a little bit, C, of a ray of light arises,
or if we fix our a