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.

190 MESSRS GLAZEBROOK AND LODGE, EXPERIMENTS ON THE OSCILLATORY
On the outer circle were taken 4 sparks, speed steady.
second,,,, 4,, fair.
third,. " 3,, steady.
fourth,,, 4,, fair.
fifth. ", 4,, fair.
sixth ",, 4,, quite steady.
seventh,,, 4, " steady.,, eighth,,,, 4,,, steady on average.
ninth - -,
(The number of sparks taken is not with perfect certainty correct, because there
was sometimes a difficulty in hearing them.)
The remarks as to the speed were noted at the time according as the stroboscopic
pattern had successfully been held still or not while the circle was being taken.
If attention is paid to these speed remarks it would seem that circles I., III., VI.,
VII. and VIII. should have most weight attached to them.
The averages for these circles are 16', 21', 18', 28', 19', for the middle swings, and
their mean is 14~ 20'.
The complete averages for these steadiest circles are 24', 27', 26', 31', 22', and the
mean of these is 14~ 26'.
It would thus appear that the best value for the wave length for this plate is
14 20'; while if all the sparks be included which lie on the circles retained, the
number is increased by 6'; if all the circles are included, each of these numbers is
reduced by 3'.
We may claim then to know the length of the oscillation on this plate to
about 5', i.e. to about 6 ~/,.
The frequency corresponding to 14~ 20' is 64 x 360/14-33 or
1608.
PLATE S.
Another series of wave lengths as recorded on plate S, in which coil A only was
used, is given in Table X.
The notes relating to this plate are as follows.
On this plate the sparks photographed were taken from the air condenser through
the A coil only. Machine charging via needle points.