Count, by means of a watch, the number of seconds that elapse between
seeing the flash of lightning and hearing the report of the thunder;
allow somewhat more than five seconds for a mile, and the distance may
be ascertained. Thus, say the number of seconds is
5)20
——
4 miles distant;
or the distance may be estimated by remarking the number of beats of
the pulse in the above interval; provided, of course, that we know the
rate at which the pulse beats in a certain time. In a French work, it
is stated that if the pulse beat six times, the distance of the thunder
will be about 30,000 feet, or five miles and a half; thus reckoning
5000 feet for each pulsation.
In a violent thunder-storm, when the sound instantly succeeds the
flash, the persons who witness the circumstance are in some danger;
when the interval is a quarter of a minute, they are secure.