240. New Form of Mountain or other Barometer. 
a piece of cast-iron, supposed to be uniform enough,—the tube 
being inverted and immersed in water of about 130°,—the ex- 
panded mercury, not able to escape by any of the joints, actually 
forced its way in two or three places through the metal itself; 
that is, through flaws in its texture, though they were so micro- 
scopic as not to be observable to the naked eye, except by the 
emission of the quicksilver. So comminuted was the stream, 
and so great the force of emission, that the metal ascended in 
graceful wreaths, like smoke, to a height not less than two feet. 
Having now explained the different parts of the instrument, I 
shall describe the various steps which were taken in the com- 
position of it. 
First, upon the open end of the tube was cemented the collar; 
and they were then ground to remove any irregularities, and 
make them fit evenly. Then the tube was clamped in a vice; 
and the disk was screwed on in cement, as far as possible. Clean 
mercury was then sifted into the tube, until it filled a part of the 
disk. 'The whole was then boiled over a spirit-lamp by suc- 
cessive portions; the flame being finally brought about as near 
to the end of the tube, as is shewn in fig. 2. ‘The whole was 
then replaced in the vice, the plate of Russia-iron laid in its place, 
and the ring screwed on in cement, as tightly as might be. ‘The 
tube was then removed, the side-screw taken out, while the in- 
strument was held in a position somewhat inclined, but not so 
far as by possibility to uncover the end of the tube by the mercu- 
ry now contained in the disk; and warm mercury was sifted down 
through the screw-hole, until it overflowed. The overflowing 
was regulated by the pressure of the finger against the elastic 
bottom, the tube being held nearly horizontal; and the screw 
was inserted and turned tight. I should have said that due care 
was taken, before inserting the screw, to disentangle and expel 
any air that might have been taken in with the mercury; and 
the proof of success in that regard was afforded, in giving the in- 
strument, held in proper position, some smart shocks in order 
to see if any air could be forced up the tube above the cylinder. 
None shewed itself; and I think because there was none there. 
This mode of terminating the tube, I regard as one of the most 
important modifications which it has been my aim to describe ; 
and the merit of its suggestion belongs to Mr. Green, the artist 
who constructed the various portions of the instrument. ‘The 
