[ M] 
higher ; or, by the Approach of Cold, the Air eon : 
trading, the Water will fall lower in the Stem. This 
Inftrument may be of IJfe in fmall Degrees of Heat, 
and in Cold, till the Water begins |o freeze, when 
it becomes ufelefs. 
The next in Order of Senfibility is that firft in- 
vented by Cornelius \ Drebbelius of Alcmar, and 
improved by Boerhaave . ( See hi sChemiftry, Tom. I. 
p, 152, & 1 53.) It conftfts of an hollow glafs Lens 
joined to a Stem of a larger Size than in the pre- 
ceding, and a Bafon into which the End of the 
Stem is inverted. The Air in the Lens muff be fo 
much rarefied, that the Stem being inverted into a 
tinged Liquor in the Bafon, the Liquor will rife up 
fome way in the Stem; then, by the Application 
of Heat to the Lens, the Liquor in the Stem will be 
pufh'd down, and by Cold the Liquor will rife up- 
This Inftrument will give Notice of the fmalleft; 
Changes in the Air; but it cannot be immerfed 
into any Liquid for chemical Experiments, unlefs 
the Stem were made much longer, and bent down 
in Form of a Syphon: But even then it would be 
very unhandy, and, like the preceding, it would 
never lerve for any Degree below what would 
freeze the Liquor made ufe of, nor for any above 
what would force out the confin'd Air through the 
Liquor in the Bafon. Befides, both thefe Inftru- 
ments, being fubjeft to the Preflure of the Atmo- 
fphere, are not proper, without comparing the Ba- 
rometer at the fame time, to determine the Degrees 
of Heat at a great Diftance of Time between each 
Experiment. 
The 
