On 11-08-25 10:33 AM, Abd ul-Rahman Lomax wrote:
At 06:55 PM 8/24/2011, Jed Rothwell wrote:
Here is an interesting footnote to history. I believe the speed of
sound was not established with this much precision until later. This
was done by assuming for simplicity that the speed of light is close
to infinite over short distances, and firing a cannon. The time delay
from the flash to the sound of the explosion gave the speed of sound.
This was done in 1826 at Lake Geneva to establish a value to within
1% of the modern figure. I don't know how they recorded it. I guess
by pressing buttons to start and stop a timer. You would think this
would mainly record human reaction time but I suppose it depends on
how far away the cannon was.
The reaction time would affect both start and stop timing, probably
about equally. Only if the interval were short such that variation in
reaction time would be a major chunk of it would reaction time be a
serious problem.
Since the human reaction time is added to the clock reading at both
ends, and you're taking the difference, the error it introduces should
be essentially random, due to variation in the reaction time. And in
that case, you can just repeat the test a dozen times and average the
results. Noise which is largely random will tend to cancel out, leaving
you with something very close to the true "noise-free" result. (That
assumes, of course, that the same person notes both the bang and the
flash -- if two different people record the two events, using two
different nervous systems, you've introduced a possible source of
systematic error!)
Errors in reading a sweep hand should also be random, and hence should
also cancel out when averaged over many trials.
And after that, the biggest source of error may be the accuracy of the
clock itself. Clock technology was driven by the need for accurate
navigation, and was pretty good pretty early. So it seems reasonable
they could have gotten a very good result with that technique.
The main problem for anyone trying to precisely replicate the result, of
course, will be the limited availability of really good cannons. (Maybe
try Ebay...)
