By T.S.H. EYTINGE, Cainsville, Canada.
It is well known that the sun's distance has been determined from the
velocity of light. It has been found, by terrrestrial experiments, about
how fast light travels, and, knowing from certain astronomical phenomena
the time light requires to pass from the sun to the earth, we have been
able to determine the sun's distance.
There are several methods of determining the velocity of light, but
hitherto only two plans have been used to detect the time light occupies
in passing from the sun to the earth. This time was first discovered
by observations of the satellites of Jupiter. It was found that the
interval between the eclipses of these bodies was not always the
same--that the eclipses occurred earlier when Jupiter was nearest the
earth, and later when he was at his greatest distance. 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°, 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. So far as I know, this
is the first application of the thermopile to variables.
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