Let me say a few words about my translation of the phrase des Nombres et des Êtres as from Numbers and from Souls. Baudelaire obviously chose the word êtres in part because it rhymes with fenêtres (windows), and scholars are not entirely sure what he meant by it. In French, être means being, and translators often translate this phrase literally, as Numbers and Beings. For example, see these translations. (I’ve noticed that translators tend to use literal translations for anything they don’t understand.)

My interpretation is that the word Nombres references Pascal, who was mentioned back in the first line. Furthermore, I think that by Êtres, Baudelaire also meant to reference Pascal, in particular, his other calling besides mathematics: religion. If this is the right interpretation, then souls is just as good a translation as beings. And if it’s the wrong interpretation, souls is still a fairly good synonym for beings. So it works either way (and also rhymes and fits the meter).

Finally, if it hasn’t occurred to you already, let me point out that both nightmares and windows are “big holes filled with vague dread leading who knows where,” i.e., abysses. (Windows, in particular, for people contemplating suicide by jumping out them.)