268 
MR. C. T. R. WILSON ON CONDENSATION OF WRITER VAPOUR 
fixed like a diving-bell below the surface of the water, which nearly fills the outer 
vessel B, 
The latter is a bell-jar of the form shown in the figure, resting on a ground-glass 
plate, to which it is wired down, and having a wide neck, closed by an indiarubber 
cork through which pass two glass tubes, the one, C, serving to regulate the quantity 
of water in B, and provided with a pinch-cock ; through the other, D, the ah’ 
occupying the upper part of B can be suddenly removed by opening communication 
with a large exhausted stoneware bottle F. 
The water is prevented from following the air by means of the valve E, 
Fi^. 1. 
The result is a sudden expansion of the air in A. The increase in volume is equal 
to the volume of the space in the upper part of B occupied by air before the 
expansion, and can therefore be made more or less by running a little water out, or 
drawing some more in through the tube C. 
By opening the tap T, which communicates with the atmosphere, air is admitted 
through the tube D, and the air in A contracts to its original volume. 
To bring about very sudden communication with the exhausted vessel F, the 
arrangement shown in the upper part of the figure was used. A short glass tube, 
H, is closed at both ends by indiarubber corks, each bored to receive two glass tubes. 
Of these, D and T have already been referred to. The tube G, which leads to the 
vacuum vessel F, has its upper end ground smooth, and upon this rests the flat 
