McCormmach looks into the personal friendship of Michell and
Cavendish, their scientific collaboration, and their common Newtonian
philosophy.
Michell wanted to weight the stars by the gravitational
retardation of their light. He was under the notion that light was something
that was also acted on upon gravity, and that this would be measurable. If
this were indeed the case, it would be possible to determine how much a star
massed based on the amount that the light emitted by it was retarded.
It is interesting to note that they believed that light was
affected by gravity. Thanks in part to this work, we know that light is not
directly altered by gravity. Thanks to General Relativity, we know that
space-time itself is warped by any gravitational field, and the light travels
along these fluctuations as if it was still traveling in a straight line.
Going back to the paper at hand, Michell and Cavendish
attempted to extend Newton's achievement by following the philosophical path
that led to it. They took the force of gravity which was known and sought to
deduce new phenomena from it. They looked to new stellar, terrestrial, and
optical effects of gravitation.
Michell's early work dealt with the distances to the stars
and their real positions in space. This led him to see the correlation between
stars and their proximity to one another possibly being due to their mutual
gravitation.
Here I see usage similar to applying p-prims when it comes
to gravitation. Michell is clearly intrigued by gravity and feels that it can
be used to help determine the mass of stellar objects. This is because he knows
that gravity affects everything, and particles of light are no different. He
had calculated the force with which light must be sent forth, and so he felt he
had a great basis to go off of. Cavendish encouraged Michell's work.
Even though Michell was unsuccessful (there was no chance of
success, but he did not know that), his methods were sound. It was also from
the torsion balance made by Michell that Cavendish was able to determine G.
Michell never got to do the experiment himself, the reality
that awaits us all at the end of life finally claiming him, but his work
allowed Cavendish to complete it.
There is another great thing to tell to students here in how
the work that is started today and passed on can lead to the discoveries of
tomorrow; standing on the shoulders of giants as Newton put it.
Russell McCormmach, "John Michell and Henry Cavendish: weighing the stars," British Journal for the History of Science, Vol. 4, pages 126-155 (1968)
