-"The vine was violently agitated while under the closest scrutiny from root to tip, nor did their combined strength applied to the trunk serve to still it."
To whom "their" refers?
They who tried to steady the vine.
- "After an hour's observation they retreated, no less wise, it is thought, than when they had come."
What does "no less wise" mean?
They were not less wise afterwards.
They were as wise, or more wise, afterwards.
-"But in the ensuing excitement as many courses of action were proposed as there were incapable counselors."
What does the whole sentence mean?
Something was exciting after whatever had happened.
Actions were proposed - I guess related to whatever happened.
(Probably) Each councelor suggested a different action = there was no concensus.
as many actions - as - counselors
The writer considers the counselors incapable.