Cryptogram from Frankenstein; or, the modern prometheus, chapter 13

"I soon perceived that although the stranger uttered articulate sounds and appeared to have a language of her own, she was neither understood by nor herself understood the cottagers. They made many signs which I did not comprehend, but I saw that her presence diffused gladness through the cottage, dispelling their sorrow as the sun dissipates the morning mists. Felix seemed peculiarly happy and with smiles of delight welcomed his Arabian. Agatha, the ever-gentle Agatha, kissed the hands of the lovely stranger, and pointing to her brother, made signs which appeared to me to mean that he had been sorrowful until she came. Some hours passed thus, while they, by their countenances, expressed joy, the cause of which I did not comprehend. Presently I found, by the frequent recurrence of some sound which the stranger repeated after them, that she was endeavouring to learn their language; and the idea instantly occurred to me that I should make use of the same instructions to the same end. The stranger learned about twenty words at the first lesson; most of them, indeed, were those which I had before understood, but I profited by the others.

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"The next morning Felix went out to his work, and after the usual occupations of Agatha were finished, the Arabian sat at the feet of the old man, and taking his guitar, played some airs so entrancingly beautiful that they at once drew tears of sorrow and delight from my eyes. She sang, and her voice flowed in a rich cadence, swelling or dying away like a nightingale of the woods.