Had some instruction from Wright this morning on the electrical
instruments.
Later went into our carbide expenditure with Day: am glad to find it
sufficient for two years, but am not making this generally known as
there are few things in which economy is less studied than light if
regulations allow of waste.
Electrical Instruments
For measuring the ordinary potential gradient we have two
self-recording quadrant electrometers. The principle of this instrument
is the same as that of the old Kelvin instrument; the clockwork
attached to it unrolls a strip of paper wound on a roller; at intervals
the needle of the instrument is depressed by an electromagnet and makes
a dot on the moving paper. The relative position of these dots forms
the record. One of our instruments is adjusted to give only 1/10th
the refinement of measurement of the other by means of reduction in
the length of the quartz fibre. The object of this is to continue the
record in snowstorms, &c., when the potential difference of air and
earth is very great. The instruments are kept charged with batteries
of small Daniels cells. The clocks are controlled by a master clock.
The instrument available for radio-activity measurements is a modified
type of the old gold-leaf electroscope. The measurement is made by the
mutual repulsion of quartz fibres acting against a spring--the extent
of the repulsion is very clearly shown against a scale magnified by
a telescope.
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