Cryptogram from Frankenstein; or, the modern prometheus, chapter 16

The sentence you are solving goes here.

"When night came I quitted my retreat and wandered in the wood; and now, no longer restrained by the fear of discovery, I gave vent to my anguish in fearful howlings. I was like a wild beast that had broken the toils, destroying the objects that obstructed me and ranging through the wood with a stag-like swiftness. Oh! What a miserable night I passed! The cold stars shone in mockery, and the bare trees waved their branches above me; now and then the sweet voice of a bird burst forth amidst the universal stillness. All, save I, were at rest or in enjoyment; I, like the arch-fiend, bore a hell within me, and finding myself unsympathised with, wished to tear up the trees, spread havoc and destruction around me, and then to have sat down and enjoyed the ruin.