"Below"? Here is, at all events, a word added (instead of anything being taken away); invariable, certainly in the case of lakes, but not absolutely necessary.
The massy waters meet and flow.
"Massy"! why massy? Because deep water is heavy. The word is a good word, but it is assuredly an added detail, and expresses a character, not which the Lake of Geneva has in common with all other lakes, but which it has in distinction from those which are narrow, or shallow.
"Meet and flow." Why meet and flow? Partly to make up a rhyme; partly to tell us that the waters are forceful as well as massy, and changeful as well as deep. Observe, a farther addition of details, and of details more or less peculiar to the spot, or, according to Reynolds's definition, of "heavy matter, retarding the progress of the imagination."
So far the fathom line was sent.
Why fathom line? All lines for sounding are not fathom lines. If the lake was ever sounded from Chillon, it was probably sounded in mètres, not fathoms. This is an addition of another particular detail, in which the only compliance with Reynolds's requirement is, that there is some chance of its being an inaccurate one.
From Chillon's snow-white battlement.
Why snow-white? Because castle battlements are not usually snow-white. This is another added detail, and a detail quite peculiar to Chillon, and therefore exactly the most striking word in the whole passage.
"Battlement"! Why battlement? Because all walls have not battlements, and the addition of the term marks the castle to be not merely a prison, but a fortress.
This is a curious result. Instead of finding, as we expected, the poetry distinguished from the history by the omission of details, we find it consist entirely in the addition of details; and instead of being characterized by regard only of the invariable, we find its whole power to consist in the clear expression of what is singular and particular!