362 
PROFESSOR A. M. WORTHINGTON ON THE 
suitable place 0 between E and F, 2 or 3 centims. from the extremity E of the 
uniform capillary tube. Then the liquid in the bulbs YB, CD is cooled by ice or cold 
water, so that the surface recedes towards, or even beyond F. Next the liquid in 
ELK is cooled so as to diminish the vapour-pressure and cause a draught of vapour 
from the surface of the warmer liquid in the tube, and while this draught continues, 
the tube EE is heated just between 0 and E, and allowed to close under atmospheric 
pressure. Gases formed or liberated in this operation are for the most part carried 
over into the large bulb GEIK by the draught of vapour. 
The length of tube which it is desirable to leave empty above the surface of the 
liquid at 0 when all is at the temperature of the room again, should be just, but not 
more than, sufficient to secure that the instrument shall not be in danger of bursting 
when left to itself and exposed to unavoidable changes of temperature in the room 
where it is placed. 
The trace of gas that is liberated in sealing is readily dissolved in the liquid, but 
on this account the liquid in the tube EF becomes unduly charged with gas, and does 
not, at first, adhere very well to the walls. It is well, therefore, by raising the tem¬ 
perature of the bulbs, to compress the residual vajDour into a bubble small enough to 
be floated along the tube into the bulbs, where any residual gas it may contain is 
dispersed through a large mass of liquid. 
The apparatus is now ready for experimenting. For this it is set in the erect 
position shown in fig. 1. A beaker of water of the temperature of the room is 
placed round the bulb containing the tonometer to secure it from temperature 
changes. A second beaker, containing warm water, is placed round the other 
bulb, while a third beaker, which can be quickly substituted for this, contains ice 
and ice-cold water. Plane mirrors are placed behind the two tubes to prevent 
parallactic errors. 
It is convenient now to have two observers, O x and 0 2 , one to watch the tonometer, 
and the other to manipulate the beakers of warm and of ice-cold water, and the wire 
terminals of the storage cell, and to observe the bubble. Let us suppose that this is 
lying in the tube with its upper end at the platinum wire. On setting the warm 
water Y in place, the bubble closes in, and, just before it disappears, will begin to 
float up the tube, disappearing, however, before it has risen more than 1 or 2 centims. 
At the moment of its disappearance, and not before , does the observer of the tonometer 
notice a sudden rise of the mercury ; this shows the freedom from residual undissolved 
gas. The warm liquid is quickly removed, and the ice-cold liquid substituted ; this 
causes the mercury in the tonometer to fall, and its observer 0 : calls aloud the 
divisions as it passes them ; when the tension is approached at which it is desired to 
observe the extension, the ice-cold water is removed, so that the cooling proceeds 
more slowly, and while 0! is carefully watching and calling the readings, 0 2 makes a 
momentary completion of the electric circuit, which results in the sudden reappearance 
