ON A CHAIi(4ED EI.ECTRIC CONDENSER MOVING THROUGH SPACE. 
d;7 
potential only fell from 8000 to 2000 volts in about 5 minutes, although the 
outside terminal or protecting coating was wrapped round the condenser to 
within 1 centim. of the other terminal. 
The lower contact was made by a wire dipping into a liquid, which also served the 
purpose of damper to the oscillations. Water was first tried, hut the air m the case 
soon became saturated with water ^'apour, to the detriment of the insulation. Hie 
water was then replaced by sulphuric acid, hut it was found that the acid contioiled 
the motion of the condenser to a large extent, although thin platinum wires weie 
used, and all damping ari'angements detached. The acid was then diluted as far as 
was compatible with good insulation, the thin platinum wire (6 mils.) dijiping into it. 
This has been found satisfactory, even for small controlling couples. 
The last difficulty ’was with convection 
currents oi' draughts. 
Owing to 
the 
unsynimetrical sliape of the suspended 
condenser — a fiat vertical disc-—-air 
currents had powerful distiirhing effects. 
The condenser was then fitted into a 
smooth .spherical celluloid hall, upon 
which tlie draughts had less effect. The 
hall was covered with gilt paint, and 
earthed by means of the lower contact. 
A cylindrical vessel of zinc plate, just 
wide enough to hold tlie hall, was made, 
inside which the conden.ser was liung. 
We thus further dimini.shed the possibility 
of convection currents by limiting tlie 
space around the condenser. Around 
the inner zinc vessel was })laced another, 
concentric witli the first, the inters}jace 
being packed v’ith cotton-wool. Hie 
whole of the apparatus except the 
suspending wire was earthed. 
The final form of the apjiaratus is as 
follows (fig. 1) :—PA, the suspension, is a 
phos})hor bronze strip 87 centims. long, 
the finest that could he obtained. Tliis 
was soldered at its lowei’ end A to a copper cap, fixed to the condenser protecting the 
projecting tin foil tags, and making contact witli tliem by means of fusible metal. 
The upper end of the suspension, P, was wound on a small wundlass, which was 
insulated by a mica plate fixed to an annular wooden ring MN, forming the lid to 
the inner zinc ves.sel. 
