Much have I travelled in the realms of gold, And many goodly states and kingdoms seen.
Yes, of course, you remember it, the first lines of On First Looking into Chapman's Homer. We remember George Chapman, if at all, only as the eponym of Keats's poem.
But Chapman was a successful playwright, and in one of his more celebrated oeuvres, The Revenge of Bussy d'Ambois, there are some interesting observations on the phenomenon of thunderstorms:
. . . the thunder which, by men's duller hearing than their sight, Seems a great time after lightning to break forth - Yet both at one time tear the labouring cloud.
Now Chapman did not have his facts entirely right. It is not a weakness in our hearing that makes us hear the thunder long after the associated flash has disappeared; the delay is a consequence of the differing speeds of light and sound.
Because sound travels relatively slowly - about 750 m.p.h. at sea level - its speed is relatively easy to pin down. But estimating the velocity of light is much more difficult.
The first successful attempt to do was in 1849 by a Frenchman called Armand Fizeau, who devised a very clever way to calculate the time it took for light to travel a distance of about five miles and back again.
He used a rapidly rotating cog-wheel to break up a beam of light. The flashing beam was aimed at a distant mirror, and the answering flashes were observed through the same toothed wheel.
With the wheel at rest, or rotating very slowly, the returning light passed through the same "cog-space" from which it had originated; at a high speed of rotation of the wheel, each flash was stopped on its return by the adjoining cog and was missed by the observer; and when the wheel revolved at twice this speed, each flash returned through the space next to the one which had allowed its original transmission.
In this last situation the time taken for the light to travel the five miles to the distant mirror and back again was the same as that required for the wheel to rotate "one cog" of its circumference, which could be calculated from the speed of rotation of the wheel.
The best estimate nowadays for the speed of light in a vacuum is about 186,282.3959 miles per second. Fizeau's cogwheel in 1849 gave him a figure of about 200,000 miles per second.
Not bad for a beginner!