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leaving the column at 29 inches. This operation having been 
repeated several times, it became quite evident that it was 
this small bubble which either by rising up the tube or 
being generated at the top had caused the mercury in the 
first instance to sink. As the bubble would not pass out 
by itself the tube was tilted so as to allow a larger bubble 
of air to enter, and having been left standing for about 12 
hours to allow the small bubble to unite with the larger one, 
it was again tipped so as to allow the air to pass out. When 
this was done the mercury again remained firmly against 
the end of the tube and did not descend when violently 
shaken. The open end of the tube was then connected with 
an air pump and exhausted until the pressure within it fell 
to about 4 inches of mercury. This operation occupied 
some seconds, but all this time the mercury did not move 
from the end of the tube, but eventually the column opened 
near the bottom of the tube and a large bubble appeared 
which rose up the tube, the mercury falling past through the 
opening. That the breaking of the column so near the 
bottom of the tube was owing to the presence at that point 
of a small bubble of air was almost proved by the fact that 
on readmitting the air to the open end of the tube and 
inclining the tube to see if it was free from air, there was 
found a minute bubble which played exactly the same part 
as the small bubble which had been previously examined. 
At the instant previous to the rupture of the column at 
the bottom of the tube there must at the top of the tube 
have been an unbalanced tension or negative pressure equal 
to 27 inches of mercury, and this tension did not break the 
continuity of the column. Hence I had a proof that the 
cohesion within the mercury and the sulphuric acid as well 
the adhesion of the sulphuric acid to the mercury and the 
glass is sufficient to resist this very considerable tension. 
Further Experiments 
In the hope of improving the experiments another gauge 
