'Nor a gum-gum?'

'Never.'

'What _is_ a gum-gum?' eagerly inquired several
young ladies.

The question is unanswered to this day, though Hardy afterwards
suggests it is another name for a humbug.

When Dickens visited the school where the half-time system
was in force, he found the boys undergoing military and naval
drill. A small boy played the fife while the others went
through their exercises. After that a boys' band appeared,
the youngsters being dressed in a neat uniform. Then came
a choral class, who sang 'the praises of a summer's day to
a harmonium.' In the arithmetical exercises the small piper
excels (_U.T._ 29).

Wise as the serpent is the four feet of performer on
the nearest approach to that instrument.

This was written when the serpent was practically extinct, but
Dickens would be very familiar with the name of the instrument,
and may have seen and heard it in churches in his younger days.

In referring to another boy's attempt at solving the
arithmetical puzzles, he mentions the cymbals, combined with
a faint memory of St. Paul.