I never heard "sconce" used for anything but a candlestick, so, this quote puzzled me: see definition 4.
"With these triumphant expressions, he seized a hammer and dealt a heavy blow at a vice, which in his mindís eye represented the sconce or head of Joseph Willet. That done, he burst into a peal of laughter which startled Miss Miggs even in her distant kitchen, and dipping his head into a bowl of water, had recourse to a jack- towel inside the closet door, which served the double purpose of smothering his feelings and drying his face."

Sconce \Sconce\, n. [D. schans, OD. schantse, perhaps from OF.
esconse a hiding place, akin to esconser to hide, L.
absconsus, p. p. of abscondere. See Abscond, and cf.
Ensconce, Sconce a candlestick.]
1. A fortification, or work for defense; a fort.

No sconce or fortress of his raising was ever known
either to have been forced, or yielded up, or
quitted. --Milton.

2. A hut for protection and shelter; a stall.

One that . . . must raise a sconce by the highway
and sell switches. --Beau. & Fl.

3. A piece of armor for the head; headpiece; helmet.

I must get a sconce for my head. --Shak.

4. Fig.: The head; the skull; also, brains; sense;
discretion. [Colloq.]

To knock him about the sconce with a dirty shovel.
--Shak.

5. A poll tax; a mulct or fine. --Johnson.

6. [OF. esconse a dark lantern, properly, a hiding place. See
Etymol. above.] A protection for a light; a lantern or
cased support for a candle; hence, a fixed hanging or
projecting candlestick.

Tapers put into lanterns or sconces of
several-colored, oiled paper, that the wind might
not annoy them. --Evelyn.

Golden sconces hang not on the walls. --Dryden.

7. Hence, the circular tube, with a brim, in a candlestick,
into which the candle is inserted.

8. (Arch.) A squinch.

9. A fragment of a floe of ice. --Kane.

10. [Perhaps a different word.] A fixed seat or shelf. [Prov.
Eng.]
Squinch \Squinch\, n. [Corrupted fr. sconce.] (Arch.)
A small arch thrown across the corner of a square room to
support a superimposed mass, as where an octagonal spire or
drum rests upon a square tower; -- called also sconce, and
sconcheon.