IMPROVED THERMOMETER. 249 
placed horizontally, though the ivory will be equally pufhed 
forwards by the mercury, while this is expanded by an increafe 
of temperature, yet fhould the mercury again contract, the 
ivory will not follow it, but remain {tationary, and confe- 
quently the point at which it refts will mark the highett degree 
to which the thermometer had rifen. An inftrument of this 
kind is rectified by bringing the ftem into a vertical fituation 
with the bulb undermoft, then cautioufly reftoring it to a hori- 
zontal fituation. 
Two thermometers fuch as thofe above defcribed, one filled 
with {pirit of wine, and the other with mercury, may conve- 
niently be difpofed upon one frame. If their bulbs be fituated 
at the oppofite ends of the frame, or as reprefented by the fi- 
gure, then both may be reétified by the fame movement, and 
we fhall have an opportunity of afcertaining, by the fituation 
of the conical pieces in the different {tems, both the higheft 
and the loweft point which the fluids of the thermometers have 
- reached during any interval of our obfervations. 
Vou. III. Ti XIII. 
