What was James Bradley's calculation to calculate the speed of light? Looking into the history of how the speed of light came to be determined, to what we know it to be today, James Bradley is often mentioned. He was credited with the discovery of the aberration of light and having used the aberration of light to calculate the speed of light. There are many online sources that confirm this, though the year of discovery and calculated speed of light differs here and there.

I've read through Bradley's "A Letter from the Reverend Mr. James Bradley Savilian Professor of Astronomy at Oxford, and F.R.S. to Dr.Edmond Halley Astronom. Reg. &amp;c. Giving an Account of a New Discovered Motion of the Fix'd Stars" published in "Philisophical Transaction vol 35" which explains his findings of the aberration of light but makes no mention of calculating the speed of light.

How did James Bradley calculate the speed of light and what publication of his shows these calculation?
Despite many online sources crediting James Bradley with having calculated the speed of light to a 295.000 km/sec (britannica) or 301.000 km/sec (wikipedia), a small nuance ought to be added. Like Ole Romer before him in 1676, James Bradley calculated the speed of light relative to something else but both never provided a value in Earth-based units.

He wrote,


  This therefore being 20’’,2, AC will be to AB that is the Velocity of Light to the Velocity of the Eye (which in
  this Case may be supposed the same as the Velocity of the Earth's
  annual Motion in its Orbit) as 10210 to One from whence it would follow
  that Light moves or is propagated as far as from the Sun to the Earth
  in 8’ 12’’.
  
  (source)


The calculation to get to the ratio of 10210 is,

size of a radian (206265’’) / angle of aberration (20’’,2)


This ratio also holds for the speed of light to the speed of the earth. Not sure though exactly how britannica and wikipedia arrive at their respective values.