The first measurement of the speed of light (approximate) is attributed to the Danish astronomer Olaf Romer in 1675. He used excellent reasonong and very crude tools by today's standards. There is also an intersting explanation on how the speed of light is defined and related maters at http://www2.corepower.com:8080/~relfaq/speed_of_light.html
My point being that good, logical reasoning and careful preciseness of language in discussion and writing go a long way toward arriving at good conclusions. Don't apply too much reverence to expensive scientific apparatus.