he lac might be as wide there as possible. In order that at
every re-attachment of the stem to the upper hemisphere the ball _h_ might
have the same relative position, a gauge _p_ (fig. 105.) was made of wood,
and this being applied to the ball and hemisphere whilst the cement at _m_
was still soft, the bearings of the ball at _qq_, and the hemisphere at
_rr_, were forced home, and the whole left until cold. Thus all difficulty
in the adjustment of the ball in the sphere was avoided.

1191. I had occasion at first to attach the stem to the socket by other
means, as a band of paper or a plugging of white silk thread; but these
were very inferior to the cement, interfering much with the insulating
power of the apparatus.

1192. The retentive power of this apparatus was, when in good condition,
better than that of the electrometer (1186.), i.e. the proportion of loss
of power was less. Thus when the apparatus was electrified, and also the
balls in the electrometer, to such a degree, that after the inner ball had
been in contact with the top _k_ of the ball of the apparatus, it caused a
repulsion indicated by 600 deg. of torsion force, then in falling from 600 deg. to
400 deg. the average loss was 8 deg..6 per minute; from 400 deg. to 300 deg. the average
loss was 2 deg..6 per minute; from 300 deg. to 200 deg. it was 1 deg..7 per minute; from
200 deg. to 170 deg. it was 1 deg. per minute. This was after the apparatus had been
charged for a short time; at the first instant of charging there is an
apparent loss of electricity, which can only be comprehended hereafter
(1207. 1250.).

1193. When the apparatus loses its insulating power suddenly, it is almost
always from a crack near to or within the brass socket. These cracks are
usually transverse to the stem. If they occur at the part attached by
common cement to the socket, the air cannot enter, and thus constituting
vacua, they conduct away the electricity and lower the charge, as fast
almost as if a piece of metal had been introduced there. Occasionally stems
in this state, being taken out and cleared from the common cement, may, by
the careful application of the heat of a spirit-lamp, be so far softened
and melted as to restore the perfect continuity of the parts; but if that
does not succeed in replacing things in a good condition, the remedy is a
new shell-lac stem.

1194. The apparatus when in order could easily be exhausted of air and
filled with any given gas; but