The superstition here assumed is so familiar from the Classics as well as from modern tradition that it scarcely needs illustration or commentary. But see Plato, 'Phaedrus', xxxi., and Shakespeare, 'King John', v., 7.
The plain was grassy, wild and bare,
Wide, wild, and open to the air,
Which had built up everywhere
An under-roof of doleful gray. 
With an inner voice the river ran,
Adown it floated a dying swan,
And  loudly did lament.
It was the middle of the day.
Ever the weary wind went on,
And took the reed-tops as it went.
Some blue peaks in the distance rose,
And white against the cold-white sky,
Shone out their crowning snows.
One willow over the water  wept,
And shook the wave as the wind did sigh;
Above in the wind was  the swallow,
Chasing itself at its own wild will,
And far thro'  the marish green and still
The tangled water-courses slept,
Shot over with purple, and green, and yellow.
The wild swan's death-hymn took the soul
Of that waste place with joy
Hidden in sorrow: at first to the ear
The warble was low, and full and clear;
And floating about the under-sky,
Prevailing in weakness, the coronach  stole
Sometimes afar, and sometimes anear;
But anon her awful jubilant voice,
With a music strange and manifold,
Flow'd forth on a carol free and bold;
As when a mighty people rejoice
With shawms, and with cymbals, and harps of gold,
And the tumult of their acclaim is roll'd
Thro'  the open gates of the city afar,
To the shepherd who watcheth the evening star.
And the creeping mosses and clambering weeds,
And the willow-branches hoar and dank,
And the wavy swell of the soughing reeds,
And the wave-worn horns of the echoing bank,
And the silvery marish-flowers that throng
The desolate creeks and pools among,
Were flooded over with eddying song.
[Footnote 1: 1830. Grey.]
[Footnote 2: 1830 till 1848. Which.]
[Footnote 3: 1863. River.]
[Footnote 4: 1830. Sung.]
[Footnote 5: 1830. Through.]
[Footnote 6: A coronach is a funeral song or lamentation, from the Gaelic 'Corranach'. 'Cf'. Scott's 'Waverley', ch. xv.,
"Their wives and daughters came clapping their hands and 'crying the coronach' and shrieking".]
[Footnote 7: 1830 till 1851. Through.]