Southern 07i the Elasticity of Steam. 



121 



The experiments for ascertaining the temperature of steam 

 below the atmospheric pressure were made with an apparatus 

 essentially similar to that which you originally used, and with 

 scrupulous care and attention ; and I met with the same inci- 

 dents as you had done; such as the production of a bubble 

 of air whenever, after any experiment, the tube was inclined 

 to refill the ball; and also the extraordinary suspension of a 

 column of mercury of 35 inches vertical height, and of 7 inches 

 of water above that, although the counterpoise was only that 

 of the atmosphere, then under 30 inches. I found also that 

 the tube required a considerable degree of labouring or sha- 

 king to make the column subside and leave a space in the 

 ball. This phaenomenon was not produced till after much 

 pains taken in inverting and re-inverting the tube again and 

 again, nor till it had been suffered, after these operations, to 

 stand for three or four days undisturbed in the exhausting 

 position, and then discharging the air that had been accumu- 

 lating in the interval. 



The results, to be found in the table below, wei'e deduced 

 from the observations as you had done, viz. by adding to the 

 height of the column of mercury in the tube (ascertained by 

 a gauge floating on the surface of the mercury in the basin), 

 that of the water above it, or rather of an equivalent column 

 of mercury, and subtracting their sum from the height of the 

 common barometer at the time. All these results were taken 

 from observations made after the apparatus had been so per- 

 fectly exhausted of air as to produce the phaenomenon just 

 mentioned. 



Phil, Mag. S. 3. Vol. 30. No. 199. Feb. 1817. 



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