ON THE ELECTRICAL PROPERTIES OE PURE SULPHUR. 
91 
We believe that it is not only feasible but advisable to further increase the uni¬ 
formity of the controlled field. 
Insulation of the Coils from the Frame.- —-If the quartz is protected from dust it 
insulates very well, better than anything else we know of in places which can not be 
got at constantly for treatment. After being in use for some months, the total insula¬ 
tion of the coils and terminals from the frame was 1 '2 X I0' J ohms, the measurement 
being made by means of an electrometer. The method adopted for insulating the 
terminals and connecting wires does not differ much from ordinary practice. The 
terminals are of corrugated ebonite, of slender section ; the wire passing into the 
terminal from the coils passes up the ebonite column without touching it, till it 
reaches the binding screw. The ebonite terminals themselves are screwed into the 
glass forming the front and back of the galvanometer, and the insulation is improved 
by drying and varnishing this glass. Where the wires pass from coil to coil inside, 
they are supported as little as possible ; but where supports can not be avoided, these 
are made of needles of fused quartz. All the connections are permanently soldered, 
and it is to be noted that we have carried out in insulating the coils what we consider 
to be an essential condition of success, viz., the use of a variety of insulating 
substances. 
There are 12,280 turns in each coil. 
Total turns, 98,240. 
Total resistance, 43,985 ohms, at 23° C. 
Screening from Electrostatic Effects.— We expected to have to interpose a film of 
mica silvered on one side, between the coils and magnetic system, but this has turned 
out to be unnecessary. The insulation would certainly suffer if the magnets have to 
be screened. 
Capacity of Coils. —The total capacity of the coils and terminals, the inner casing 
being put to earth, is 8 X 10 ~ 5 microfarad, by measurement. 
Avoidance of Thermo-electric Effects. —When the instrument was first set up, 
some small pieces of stiff German-silver wire were used to pass down inside the 
ebonite terminals. On short circuiting enormous thermo-electric effects were always 
noted even when all precautions to secure a constant temperature had been taken. 
These effects could only be removed by replacing the German-silver by copper, and 
by electroplating the brass binding screws with copper, and by soldering all joints 
(except the contact at the binding screws) right up to the galvanometer key. 
Screening from Air Currents and Convection Currents due to difference of Tem¬ 
perature. —It was found necessary to seal the coil cases with soft wax, so that the 
interior of the galvanometer becomes almost air-tight. The sealing is easily accom¬ 
plished, because, as has been mentioned, there are four glass sides, and the wax was 
run round the edges of the glass. Thermal effects were guarded against by enclosing 
the whole apparatus in a mill-board box, coated with tin-foil inside and out, and very 
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