39 
The most noticeable circumstance was that as time went 
on the difficulty of getting rid of the air and getting the 
tube into such a condition that its contents would sustain 
themselves diminished. In the first instance it had been 
only after a fortnight’s attempts that suspension was obtained. 
The first successful suspension was obtained in the following 
manner : a little of the water was allowed to pass up by the 
side of the mercury when the tube was in an inclined po- 
sition, the tube was then brought gently down so that the 
water reached the top or closed end of the tube as nearly as 
the air, generally a small bubble, would admit ; then further 
inclined until the closed end was so low that the air bubble 
and water would float up to the open end and pass out, leaving 
the straight portion of the tube and part of the bend full of 
mercury. The tube was then left in this position for 24 hours, 
when on being erected the mercury sustained itself. It was 
then again reversed and left for some days, when on being 
erected not only was the mercury sustained for the 30 inches 
above the barometer, but it remained suspended when the 
pressure of the air on the lower end was reduced by the air 
pump to one or two inches of mercury. 
No other method ever proved successful with this tube. 
It was always necessary to leave the tube reversed for a 
longer or shorter interval. 
As to what went on in this interval I changed my opinion. 
At first I thought it must be that time was necessary to bring 
the mercury or water into more intimate contact with the 
tube, but subsequent observation convinced me that the 
interval was necessary to allow the water with such air as 
it contained to drain up between the mercury and the 
glass — that in this way the surface of the glass was freed 
from air. After arriving at this view I observed the tube 
carefully to see if after it had remained some days in the 
reversed position any trace of water was left. I could find 
none either while the tube was full or after the mercury 
