Motion of the Earth and Ether, suggested by the late Professor Pitz Gerald. 381 
As the condenser plates lay horizontally, the effect should have been a maxi- 
mum at twelve o’clock. The experiments were therefore carried out between the 
hours of eleven and one each day. In 
order to have the maximum turning 
effect the arm was placed north and 
south. 
Some preliminary experiments were 
made with a view of testing if a blow, 
whose kinetic energy was only 1 erg, 
could be competent to produce observa- 
ble effects. This was done by causing 
a small object to strike against the 
arrangement. 
These proving highly encouraging, 
apparatus was constructed with the 
object of enabling the condenser to be Conoenser 
charged and discharged continuously 
by means of clock-work at the intervals 
corresponding to the free period of Fic. I. 
swing of the apparatus. In this way any effect produced would cumulate and 
be made easier of observation. 
The complete period of swing was about 60 seconds, so that the charging and 
discharging followed each other at half these intervals or about 30 seconds. 
Coincidence between the rate of the clock which drove the commutator and that 
of the apparatus was most readily effected by increasing or diminishing the 
moment of inertia of the suspended apparatus, by means of small weights laid 
on it or removed as required. ‘This coincidence in period was made very perfect. 
The source of the current for charging the condenser was a continuous- 
current dynamo separately excited, capable of supplying a current of $ ampére 
at 1200 volts. Relays were employed for charging and discharging the 
condenser, as it was found undesirable, being likely to affect the rate of the clock, 
to allow such heavy sparking as necessarily took place to occur on the clock- 
driven commutator. 
BaLtaANce 
WEIGHT 
The leads for the charging current were provided by the suspending wire and 
by a wire which dipped centrally downwards into a mercury cup. A curved 
mirror was affixed to provide a spot of light on a mm. scale at the distance 
of 1860 mm. 
The method of experimenting was to charge and discharge at proper intervals 
by means of the synchronous commutator, and to observe if a swing was set up. 
Another plan sometimes used was to cause the apparatus to have a small swing to 
