John Scott
Russell and the Doppler effect
It is not generally known
that John
Scott Russell (1808-1882), the discoverer of the soliton, made one of the
first experimental observations of what is now known as the Doppler
effect, and gave an independent explanation of the theory. The
Doppler effect was first described by the Austrian physicist Christian
Doppler (1803-1853) in 1842.
Scott Russell's short 1848 report gives no date for his original
observation, although he was Editor of the Railway Magazine from 1844
to 1847. The credit for first published account of this effect belongs
to the Dutch meteorologist Buys Ballot in 1845.
The following is a short note reprinted from the Report
of the Eighteen Meeting of the British Association for the Advancement
of Science, 1848, pt. 2, published by John Murray, London in 1849, pp 37-38.
On Certain Effects produced on Sound by the rapid motion of the observer.
By J Scott Russell, FRS Ed
Until the production of the very high velocities now given to railway
trains, no opportunities have existed of observing any phenomena in
which the velocity of the observer has been sufficient to affect the
character of sounds. The author having had occasion to make observations
on railway trains moving at high velocities, has been led to notice
some very curious effects in sounds heard at 50 and 60 miles an hour.
These effects are not heard by an observer who is stationary. He found
that the sound of the whistle of an engine stationary on the line was
heard by a passenger in a rapid train to sound a different note - in a
different key from that in which it was heard by the person standing
beside it. The same was true of all sounds. The passenger in rapid
motion heard them in a different key, which might be either louder or
lower in pitch than the true or stationary sound. The explanation of
this was given as follows. The pitch of a musical sound is determined
by the number of vibrations which reach the ear in a second of time
- 32 vibrations per second of an organ-pipe give the note C, and a
greater or less number give a more acute sound or one more grave.
These vibrations move with a velocity of 1024 feet per second nearly.
If an observer in a railway train move at the rate of 56 miles an hour
towards a sounding body, he will meet a greater number of undulations in
a second of time than if at rest, in the proportion which his movement
bears to the velocity of sound; but if he move away from the sounding
body he will meet a smaller number in that proportion. In the former
case he will hear the sounds a semitone higher, and in the second a
semitone lower than the observer at rest. In the case of two trains
meeting at this velocity, the one containing the sounding body and the
other the observer, the effect is doubled in amount. Before the trains
meet the sound is heard two semitones too high, and after they pass two
semitones too low - being a difference of a major third. There were
next explained the various effects which the noises of a train produced
on the ears of passengers at high velocities. The reflected sounds of
a train, from surfaces like those of bridges across the line, were at
ordinary velocities sent back to the ear changed by less than a tone,
so as to cause a harsh discord, which was an element of the unpleasant
effect on the ear, of passing a bridge. In a tunnel also the sounds
reflected from any irregularities in the front of the train or behind
it were discords to the sounds of the train heard directly. He showed
however that at speeds of 112 miles an hour these sounds might be those of
a harmony with each other and become agreeable, for the sounds reflected
in opposite directions would have the interval of a major third.
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Last updated 2 Mar 2000 (JCE)
Chris Eilbeck / Heriot-Watt University / chris@ma.hw.ac.uk
