/ 
C 419 ] 
39. The Introduction of the mercury is the nest 
operation. I firft roll a flip of paper three inches 
wide over the glafs tube, and tie it faff to the extre- 
mity which is neareft to the ivory pipe. I then in- 
troduce into the tube a horfe hair long enough to 
enter the cylinder by one end, and to have the other 
rife three or four inches beyond the orifice of the 
tube. I then raife the paper which has been fhaped 
round the tube, and ufe it as a funnel to pour the 
mercury into the inftrument, which I hold upright. 
The pureft quickfilver ought to be employed for 
that purpofe, and it will therefore be proper that it 
fliould be revivified from cinnabar. I poured it then 
into the paper funnel, from whence it eafily runs in- 
to the tube, with the affiftance of fome gentle fhakes. 
The air which it drives before it comes out along the 
horfe hair. Frefh mercury muft from time to time 
be fupplied, to prevent the entire emptying of the 
paper tube, and the running in of the mercurial pel- 
licle, which the contaCt cf air always produces upon 
the furface. 
40. Some air bubbles generally remain in the 
tubej they may be feen through the ivory pipe, 
which is thin enough to have fome tranfparency. 
Thefe being collected together by lhaking, muft be 
brought to the top of the tube, and expelled, by 
means of the horfe hair. To facilitate this opera- 
tion, fome part of the mercury muft be taken out of 
the tube, in order that the air may be lefs obftruCted 
in getting out, and the horfe hair have a freer motion 
to aflift it. 
41. Air, however, cannot be entirely driven out 
in this manner. It is the weight of the mercury, 
Vol. JLXIII. I i i with 
