an 'unproved Thermometer . 77 
attended with many difad vantages, and the motion of the Quids 
in the fpirit-ones perfectly agreeing with, and being as readily 
excited by change of heat and cold, as in the mercurial ther- 
mometers, I preferred the former as much more commodious. 
A perfon cannot approach near to the thermometer firft de- 
fended when the air is very cold (efpecially with a light which 
by night is neceffary) without caufing the fpirits prefently to 
expand, and confequently the mercury on the left fide imme- 
diately to defeend. This fenfibility is here attended with every 
advantage, without the inconvenience to which common ther- 
mometers in this cafe are liable * ; for the index will accurately 
fhew the greated: height to which the mercury had rifen, 
although, before the exadt degree can well be didinguilhed, it 
will appear feparated from the index, and defeending apace. 
As the fcale is fixteen inches long, and divided into ioo° only, 
which are more than fufficient for the temperature of the air, 
they are large enough to be fub-divided at plealure. The 
indexes, though of a tender and delicate nature, when once 
placed in the tube, are not liable to fuffer any alteration by 
time or accident ; and the thermometer may be expofed to rain 
at all times, without buffering the lead: injury in any refpedt. 
In condrudting the thermometer before mentioned, 1 at drd: 
hit on a plan by which the fame end was obtained by a dif- 
* The moft fenfible mercurial thermometers commonly have the column of 
mercury as well as the degrees very fmall, and a perfon aflifted with a light can 
hardly view them near enough, when the weather is very cold, without caufing 
the mercury to rife before the degrees where it flood can be well afeertained. 
Freezing fogs alfo, which with us ufually attend the greateft degrees of cold, 
by covering the glafs with froft, render the mercury invifible, and cannot well be 
mercury removed without caufing the to rife, or at leaft render the obfervation 
doubtful, which at iuch a time is very dilagreeable ; for, in proportion to the 
extraordinary degree of cold, fo is our curio flty likely to be excited. 
ferent 
