Memoirs presented to the Cambridge philosophical society on the occasion of the jubilee of Sir George Gabriel Stokes, bart., Hon. LL. D., Hon. SC. D., Lucasian professor.

DISCHARGE OF AN AIR CONDENSER, WITH A DETERMINATION OF "v." 173
The length of the circuit is 4 kilometres.
The wave length in the chief cases is either
3 x 1010 3 x 1010
80 or 1600- centms.
880 1600
and is always bigger than 100 kilometres, so no complication from different phases will
arise.
PART IV.
PRELIMINARY EXPERIMENTS.
IN the earlier stages of the work a large number of experiments were made with
various condensers; some of these had a small capacity. It was thought at the time
that it might be possible to use a guard-ring condenser of which the capacity could be
accurately determined and that thus a good value for " v" might have been obtained;
at this stage the importance of the correction for the capacity of the coil was not
fully realized and it was the discrepancy which was observed when the results of these
experiments were compared with a simple theory which led to the fuller consideration
of this correction which has been given in Part III.
The experiments therefore are chiefly of interest as a test of the theory and
as enabling us to see the consequences of the correction.
Several measurements were made with a small air condenser consisting of 7 concentric
brass cylinders each 45'4 cm. high and '75 mm, thick and of internal diameters 13'25,
9'90, 8-26, 6-92, 5-00, 3-40, and 1-60 cms. respectively. The capacity of this condenser
making some allowance for the edges and for connecting wires was calculated at 5'5
metres.
Another condenser consisted of eleven circular dises of brass of total capacity, as
calculated from the dimensions, of 5 metres. A list of these various condensers is given
below. (See p. 175.)
Two other condensers were used, one consisting of tinfoil plates on glass, the other
a paraffin paper condenser. The capacity of the former calculated from its dimensions
is 47'5 K metres, K being the specific inductive capacity of glass. Taking K as 5 this
comes to 237 metres. An attempt made however to determine by observation the capacity
of this condenser gave as the value 190 metres, corresponding to the value 4 for K
which is very low.
The capacity of the paraffin paper condenser was - microfarad or 3000 metres.
The capacities of these condensers were also determined by the ballistic method, but
it must be remembered that with such small capacities accuracy cannot be expected
and the values found are therefore only approximate.