From JOHN WILLIAMS
When I was a child, it was common knowledge that you could calculate
the distance of thunder and lightning based on the time between the two
measured in seconds: for example, ‘Flash – one thousand and one, one thousand
and two . . . one thousand and seven – Bang!’ That was seven miles away.
Recently I experienced a thunderstorm in the presence of my brother-in-law
(who is French) and he used exactly the same calculation, but his answer
was in kilometres! This seemed both to confirm the widespread use of the
method and to imply this is due to its simplicity rather than its validity.
As I see it, the calculation is still extremely simple, since the light
is seen virtually instantaneously while the thunder travels at the speed
of sound, approximately 760 miles per hour, and thus 0.211 miles per second.
Therefore the time lag in seconds should be divided by five (4.7 if you’re
using a stopwatch) to get the distance in miles, or divided by three (2.9)
for a distance in kilometres.
John Williams St Galmier, France
Advertisement
