oratory for five years. With these
appliances all the fundamental experiments may be performed, and the
apparatus is always ready at a moment's notice.

Fig. 81.

Though quartz does not condense moisture or gas to form a conducting
layer of anything like the same conductivity as in the case of glass
or ebonite, still it is well to heat it if the best results are to be
obtained. For this purpose a small pointed blow-pipe flame may be
used, and the rods may be got red-hot without the slightest danger of
breaking them. They then remain perfectly good and satisfactory for
several hours at least, even when exposed to damp and dusty air.

The rods are conveniently held in position by small brass ferrules,
into which they are fastened by a little plaster of Paris. Sealing-wax
must be avoided, on account of the inconvenience it causes when the
heating of the rods is being carried out.

One useful application of fused quartz is to the insulation of
galvanometer coils (Fig. 82), another to the manufacture of highly
insulating keys (Fig. 83); while as an insulating suspension it has
all the virtues. If it is desired to render the threads conducting
they may be lightly silvered, and will be found to conduct well enough
for electrometer work before the silver coating is thick enough to
sensibly impair their elastic properties.

Fig. 81A.

Fig. 82 is a full-size working drawing of a particular form of
mounting for galvanometer coils. The objects sought to be attained
are:
(1) high insulation of the coils,

(2) easy adjustment of the coils to the suspended system.

The first object is attained as follows. The ebonite ring A is bored
with four radial holes, through which are slipped from the inside the
fused quartz bolt-headed pins B. The coil already soaked in hard
paraffin is placed concentrically in the ring A by means of a special
temporary centering stand. The space between the coil and the ring is
filled up with hard paraffin, and this holds the quartz pins in
position. The system of ebonite ring, coil, and pins is then fastened
into the gun-metal coil carrier, which is cut away entirely, except
near the edges, where it carries the pin brackets C. These brackets
can swivel about the lower fastening at E before the latter is
tightened up.

The coil is now adjusted in the adjusting stand to be concentric with
the axis of symmetry of the coil carrier, and the supporting pins are
slipped into slot holes cut i