Roemer, a Danish
astronomer, first detected the cause of this variation. The second
method by which this time has been found is the aberration of stellar
light. This refined method was detected by the great English astronomer
Bradley.
About two years ago it occurred to me that a third method can be used
to solve this important problem. My plan is this: It is well known that
many variable stars, such as Algol, [sigma] Librae, U Coronae, and the
remarkable variable D.M. + 1.3408 deg., discovered by Mr. E.F. Sawyer,
fluctuate at regular intervals. Now, I believe it is possible to
determine very accurately the intervals between these changes, and,
by noting the change of time in these intervals, when the earth is in
different points of its orbit, we get the time light requires to cross
that orbit. For, as in the case of the satellites of Jupiter, when the
star is "in opposition," the changes will occur earlier than when it is
in conjunction or approaching that point. I have recently put this plan
to the test, and hope before long to make known the results.
In detecting the changes of variables, I have attempted to substitute,
in place of the ordinary eye observations, a very delicate thermopile,
which registers the changes in the star's heat.
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