Recent
observations of these eclipses, through glass of different colors, show
variations in the time of obscuration. Apparently, some of the rays
reach the earth sooner than others, although all leave the star at the
same time. As the entire time may amount to several centuries, an
excessively small difference in velocity would be recognizable. A more
delicate test would be to measure the intensity of different portions of
the spectrum at a time when the light is changing most rapidly. The
effect should be opposite according as the light is increasing or
diminishing. It should also show itself in the measures of all
spectroscopic binaries.
A third method of great promise depends on a remarkable investigation
carried on in the physical laboratory of the Case School of Applied
Science. According to the undulatory theory of light, all space is
filled with a medium called ether, like air, but as much more tenuous
than air as air is more tenuous than the densest metals. As the earth is
moving through space at the rate of several miles a second, we should
expect to feel a breeze as we rush through the ether, like that of the
air when in an automobile we are moving with but one thousandth part of
this velocity.
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