It was the place whence proclamations were wont to be made, amidst an assemblage of the magistracy, with all the ceremonial that attended such public observances in those days.
Nor would it have been impracticable, in the observance of majestic ceremonies, to combine mirthful recreation with solemnity, and give, as it were, a grotesque and brilliant embroidery to the great robe of state, which a nation, at such festivals, puts on.
There are no more uses of "observance" in the book.
Show samples from other sources
As her release date neared, Vanessa got increasingly anxious, with a decided uptick in religious observance.
Piper Kerman -- Orange Is the New Black
"Religious observances shouldn’t be denied to anyone."