Cryptogram from Frankenstein; or, the modern prometheus, chapter 7

I fear, my friend, that I shall render myself tedious by dwelling on these preliminary circumstances; but they were days of comparative happiness, and I think of them with pleasure. My country, my beloved country! who but a native can tell the delight I took in again beholding thy streams, thy mountains, and, more than all, thy lovely lake!

The sentence you are solving goes here.

It was completely dark when I arrived in the environs of Geneva; the gates of the town were already shut; and I was obliged to pass the night at Secheron, a village at the distance of half a league from the city. The sky was serene; and, as I was unable to rest, I resolved to visit the spot where my poor William had been murdered. As I could not pass through the town, I was obliged to cross the lake in a boat to arrive at Plainpalais. During this short voyage I saw the lightning playing on the summit of Mont Blanc in the most beautiful figures. The storm appeared to approach rapidly, and, on landing, I ascended a low hill, that I might observe its progress. It advanced; the heavens were clouded, and I soon felt the rain coming slowly in large drops, but its violence quickly increased.