How does the poet show the contrast of ideas and emotions between the beginning and end of the first stanza of the poem "Dover Beach"?

The first stanza reads of "Dover Beach" reads as follows:

The sea is calm tonight.
The tide is full, the moon lies fair
Upon the straits; on the French coast the light
Gleams and is gone; the cliffs of England stand,
Glimmering and vast, out in the tranquil bay.
Come to the window, sweet is the night-air!
Only, from the long line of spray
Where the sea meets the moon-blanched land,
Listen! you hear the grating roar
Of pebbles which the waves draw back, and fling,
At their return, up the high strand,
Begin, and cease, and then again begin,
With tremulous cadence slow, and bring
The eternal note of sadness in.


The poem begins with a mood or emotion of quiet peace conveyed in the first six lines. The speaker uses such words as "calm," "fair," and "tranquil" to evoke this feeling. The speaker communicates the idea that all is good and restful in the beautiful moonlit seascape. The scene is called "sweet." It is so serene and lovely that the speaker beckons his unnamed companion with some joy—as indicated by the exclamation point—to come to the window and view it with him.

But in the next two lines, the speaker's perceptions begin to settle on the point where the tide meets the shore. This leads to the last six lines, where the mood changes. From the calm sea of the first line, we move to the commanding word "Listen!" that stops us and marks an alteration in the poem's tone. The "calm" sea develops a "grating roar," and the scene is no longer "tranquil." Instead, waves "fling" pebbles, a violent image. From "sweet" night air we move to the "eternal note of sadness."

The speaker's previous mood and ideas about the scene shift to become more troubled and unhappy as the stanza progresses.