171 
which it was poured into the tube, some acid passing in 
with the mercury. When first introduced into the tube a 
few small bubbles could be seen rising between the mercury 
and the tube and passing up through the sulphuric acid into 
the vacuum above ; but after it had stood for five or six 
hours no bubbles were perceived, the surface of the mercury 
against the tube being perfectly clear ; nevertheless, on erect- 
ing the tube the mercury would not rise above the height of 
the barometer, and air was always found to have collected 
above the mercury. Water was then introduced so as to 
dilute the acid. Then the mercury was suspended as before 
only for a few seconds. The tube was then placed in a posi- 
tion with the closed end lowest, so that the air and water 
might ascend towards the end and pass out, and after being 
in this position for some hours, when it was again erected, 
the column remained intact. 
It was thereupon again lowered, and left to drain for forty- 
eight hours. On being again erected the mercury was still 
suspended. The tube has since been carried in a more or 
less horizontal position some three miles to the Society’s 
rooms, in order that I might exhibit the phenomenon. If it 
has not been affected by the shaking you will see a column 
of mercury suspended some fifty-nine inches, or twenty-nine 
inches above the height due to the atmosphere.* 
Conclusion . 
The difficulty of obtaining a column of mercury 30 inches 
above the pressure of the atmosphere does not, I think, prove 
that the limit of the cohesive power of the liquid has been ar- 
rived at, or even the limit of the adhesive power of the water 
for glass and mercury; but simply shows that, although im- 
perceptible, there are still bubbles of air in the liquid between 
the mercury and the glass which will not readily pass out. 
It seems to me to be probable that with sufficient care, 
# At the meeting not only did the mercury remain suspended when the 
tube was erect, but on the pressure of the atmosphere being removed 
with an air pump it still remained suspended, although the tension at 
the top of the tube was nearly equal to two atmospheres. 
It 
