12 PROF. OSBORNE REYNOLDS ON THE 



Having extracted all the air, I found no difficulty in 

 making the gauge to stand up to the 35 inches without any 

 immediate tendency to fall. On applying the air-pump to 

 the open end the mercury several times remained up until 

 the exhaustion had proceeded so far that when it fell it fell 

 from 22 to 28 inches, and when the rupture took place it 

 was accompanied by a loud click. I could not on that 

 occasion get the mercury to withstand complete exhaustion; 

 but after leaving the gauge with the mercury suspended 

 for 24 hours at 35 inches, I was able to exhaust the open 

 end of the tube as far as the pump would draw, without 

 bringing the mercury down ; so that I had a column of 

 35 inches of mercury suspended by tbe cohesion of the 

 liquids. 



There was no reason to suppose that this was the limit 

 or anywhere near the limit. It was clearly possible to 

 suspend a longer column ; but as the length of the column 

 increased so would the difficulty of getting rid of the dis- 

 turbing causes, and I determined to rest satisfied with the 

 35 inches ; but in order to see if this could be maintained, 

 I obtained a gauge 60 inches long, which would leave 

 30 inches above the pressure of the atmosphere. 



The difficulty of getting rid of the air in this tube suffi- 

 ciently to allow of the mercury standing 60 inches was 

 very considerable. Before filling the tube it was rinsed 

 out with concentrated sulphuric acid, then twice washed 

 with distilled water, and then water put in and boiled in 

 the tube. Then sufficient mercury was introduced to fill 

 the long leg and the bend, so that the column, when com- 

 plete, was 59 inches long, the barometer being at 29*5. 



After the tube had been tilted several times so as to 

 allow the air to pass out, the mercury would be suspended 

 as the tube was slowly reerected, until it had attained an 

 elevation of 40, 50, or sometimes the full height of 60 inches 



