Before 1846 when the doppler effect was first observed as an example of the effect Dopler had predicted, had people noticed the phenomenon of rapidly moving objects seeming to have a higher pitch as they approached and lower as they receded?
Steam locomotives existed before 1846. Did they move fast enough to produce the effect? Does a running horse produce the effect?
What theories did people have to explain the effect, if in fact it had been observed?
I often complain about people who mistakenly consider pre-20th-century humans to be far less sophisticated than they actually were, and I may become guilty of that myself, but here goes anyway…
The Doppler effect will change the perceived pitch of a sound. People might notice a change, but ascribe it to a change in volume, not realizing that both the volume and pitch are changing. The horses feet, for example, make a combination of sounds, and I think that the change in volume might be so overwhelming that it might be difficult for ANYone to notice the change in pitch. The sound of the locomotive might be a similar sort of white noise which Doppler might not change to a noticeable degree.
None of the above would apply to the train’s whistle, though.
Yes, but not MUCH before.
According to Wikipedia, Doppler first proposed his hypothesis in 1842 regarding light waves, and it was confirmed in 1845 regarding sound waves. I’m genuinely surprised that sound did not come first.
Before 1850, there weren’t any rapidly moving objects.
A horse is fast enough to produce the effect, but it is a series of clip clops, each of which is emitted from a stationary source. I presume the train whisle was the first conspicuous Doppler manifestation that people cold observe.
No one before 1846 ever noticed that one horses became blue-hued when running toward you and more red-hued as they ran away?
The horse feet are not moving forward when they contact the ground.
!! Good point!
But surely cannonballs are rapidly moving objects. There can’t have been a shortage of infantrymen and officers who were subjected to the approach and passing of a cannonball before 1850 - and for that matter rifle and musket bullets. Perhaps they simply went too fast. Or the soldiers were concentrating too much on the battle to wonder about the effect.
Which reminds me, John Keegan recently died, and I have a copy of The Face of Battle lying around - I remember it describing the noise and smoke of battle in vivid detail (soldiers in the Napoleonic era sometimes didn’t realise that (a) it was still daylight (b) they were being shot at, because of all the smoke), although I can’t remember if it said anything about doppler effects or relativity.
Touche!
But how much sound does a cannonball emit while it is moving? That’s why the train whistle is such a great example. Yet, as I pointed out earlier, Doppler’s actual first work regarded light, not sound.
Isn’t it possible to perceive the effect when a group* of ducks or geese flies overhead? Or were ducks and geese invented after 1846?
(*) Flock, skein, string, gaggle, badelynge, bunch, brace, flush, wedge, paddling, raft, team. And they say English is easier than French.
The fractional change in the pitch frequency is equal to the ratio of the speed of the emitter to the speed of the emitter: ∆f/f = v[sub]e[/sub]/c. The human ear can differentiate pitches whose frequencies vary by about 0.5–2% (sources seem to vary.) This means that to create a change in pitch that was noticeable to a human, the source would have to travel in the 5-15 mph range. This seems doable in and of itself; my guess is that it just wasn’t noticeable due to the reasons mentioned by Keeve above.
One of the real oddities of Physics is that Roemer got an estimate for the speed of light in 1676 while the first approximation to the speed of sound wasn’t figured out until 1709 by William Derham. (And the accuracy of the measure of the speed of sound noticably lagged that of light.)
Light was a far more interesting topic than sound and people expended significantly more effort (and still do) trying to understand it. So things like Doppler’s insight are to be expected.