So many thanks indeed. As always your explanation made it all clear.See the Collins definition #9 of "by" in our dictionary:
(esp in oaths) invoking the name of: I swear by all the gods
(I swear) by the blushes of aurora etc...!
By invoking the names of these ancient gods of the morning, Thoreau light-heartedly shows his exasperation with "most men" and their preoccupations.
This may be obvious to you, Arietenata, but it is not apparent from post #4. The forum rules encourage you to quote up to four sentences, and I think at least this amount is needed here.Of course I did