TO IANTHE.

Not in those climes where I have late been straying,

Though Beauty long hath there been matchless deemed,

Not in those visions to the heart displaying

Forms which it sighs but to have only dreamed,

Hath aught like thee in truth or fancy seemed:

Nor, having seen thee, shall I vainly seek

To paint those charms which varied as they beamed—

To such as see thee not my words were weak;

To those who gaze on thee, what language could they speak?

The musical effects in this stanza extraordinary.

First the rhyme scheme:  ABABB CBCC

Next the rhythms

NOT in those CLIMES where I have LATE been STRAYing

Though BEAUty LONG hath THERE been MATCHless DEEMED

NOT in those VISions to the HEART displaying

FORMS which it SIGHS but to have ONly DREAMED

Hath AUGHT like THEE in TRUTH or FANCy SEEMED

NOR, having SEEN THEE, shall I vainly SEEK

To PAINT those CHARMS which VARied as they BEAMED—

To such as SEE THEE not my WORDS are WEAK;

To THOSE who GAZE on THEE, what LANGuge COULD they SPEAK?

Next for some effects:

The first and third lines begin with the same introductory phrase (anaphora, http://rhetoric.byu.edu/Figures/A/anaphora.htm)

“Not in those”

The two lines set off two separate elements: The first goes to an investigation of the physical work ‘Not in those climes’. The second concerns an investigation of the imagination: “Not in those visions”. 

They are also paired in this manner: The climes are where Byron is:  “those climes were late I have been straying.” The second, his dreams, imagination, are the recollections and fancies of the absent woman. The word and his internal world are thus presented for review. 

He then brings both aspects together in a single conclusion: neither truth (the physical world) nor his fancy (imagination) was there anything so wonderful as you:

Hath aught like thee in truth or fancy seemed:

He begins with the answer to the proceeding by use of the word “nor” which echoes back to the “not” which opened the introductory concern. He then engages in the paradox of so much poetry: I cannot use words to express this thing which I am here expressing in words:

Nor, having seen thee, shall I vainly seek

To paint those charms which varied as they beamed—

To such as see thee not my words were weak;

To those who gaze on thee, what language could they speak?

The sixth line is quite wonderful. The pause coming after the first syllable creates sets off the words “having seen thee”.

Nor …. Having seen thee  … shall I vainly seek

Nothing in the world compares to you and an attempt by me to do so would be vain itself. 

There an interesting verb in the next line “paint”  which is picked up in the 8^th line as “my words”. The poem could be a painting in words.

There is an interesting contrast in these four lines between speech and sight: Having seen her, he cannot paint her by means of words (which would be heard), because words are “weak” in comparison to the sight. Indeed, there is no language adequate for the task:

To those who gaze on thee, what language could they speak?