544 PROFESSOR DANIELL ON THE WATER-BAROMETER ERECTED 
inches, but the column was perfectly unbroken and clear. On this occasion 
it was found impossible to raise it higher than thirteen feet, owing to the stuf- 
fing-box and cover not being sufficiently close. The cock upon the boiler was 
therefore gradually opened, and the column of water slowly subsided, the steam 
rushing out with considerable violence. Several practical points were deter- 
mined by this experiment, which it was of importance to be acquainted with. 
The apparatus was found perfectly manageable ; the pressure could be regu- 
lated with great precision by the cock, and the elasticity of the steam increased 
by very slow degrees, even when quite shut off. The temperature of the rising 
column was very moderate, and felt but just warm to the hand at the upper 
part. 
Several little alterations were made in the fire-place, and the part ( v , w) 
which was immediately under the tube was bricked up, so that the flame was 
cut off from the front of the boiler, that the steam might be raised from the 
back part only, and the possibility of any bubble passing up into the tube pre- 
cluded. The stuffing-box was repacked, and the top screwed down with 
greater care. The water was drawn off, and fresh distilled water poured in. 
It was now determined to prove the apparatus, by raising the column of 
water by condensed air ; and for this purpose the pump of a soda-water ma- 
chine was connected, by means of a flexible pipe and screw, with a collar ( x ) 
fixed for the purpose upon the arch of the boiler. As the condensation pro- 
ceeded, the column of water rose steadily, till it issued with considerable force 
from the aperture of a small glass tube fixed into the stop-cock on the summit, 
and bent to an angle to prevent the waste water trickling down the apparatus. 
When the force of the jet began to decrease, the stop-cock was closed, and the 
cock on the boiler at the same moment opened. After a short interval the 
column of water began slowly to decline, and appeared to boil violently from 
the extrication of air from its surface. This effervescence continued for more 
than an hour, with decreasing force ; and the formation of air bubbles could 
be perceived nearly half way down the column. After eighteen hours, the 
water stood in the tube at about thirty feet eight inches from the level of the 
water in the cistern. 
Advantage was taken of this opportunity to ascertain the relative capacities 
of the tube and cistern ; and it was found, by careful measurement, that the 
