being ufed at Sea, f though it hath lately been contrived 
to be made portable^ So it remait^ed^ find out fome o- 
thcr principle, wherein the pofition oi the Inftrument 
was not fo indifpenfably neceffary : For this, all chofe 
that ufe the Sea are obligld to ^he great facility Dr Hook 
has alvvays feevf'h; ill applyingPl^ofophica] Experiments 
to their proper ufes,..,^ . : -. 
It is about '40 years fince,tHat the Therrhof/teters oi: ^bt. 
de Fluciiks^ dQpQndmg on the dilataitiotl ^nd contraftion 
of included Air by Heat and Cold, have been d fbfed, 
upon difco very that the Airs preffure is unequal 3 that 
inequality mixing it felf v/ith thp*effe<9:s bt the warmth 
of the Air in that Inftrument. Arid inftead thereof was 
fubftituted the Seal'd Thermometer, mcluding Spirit of 
Wine ( firft brought into £^^/^^//^, out of i^^/)/, by Sir 
Robert SoHthmll )as a proper Standard of the temper of 
the Air in relation to* Heat and Cold ^ that aetherial Spirit 
being of all the known liquors the mofl: fufceptible of 
dilatatron and contrad:iofi,efpecrally'with a moderate de- 
gree of either Heat or Cold. '^Now this being allowed as 
a Standard, and the other Therhiom'eter that includes 
Air being graduated with the famedivifions,fo as at the 
time when the Air was included, to agree with the Spirit- 
Thermometer in all the degrees of Hekt and Cold, noting 
at the fame time the precife height of the Mercury in the 
common Barometers : It will readily be underftood that 
whenfoever thefe two Thermometers fhaH agree, the 
preffure of the Air is the fame it was, when the Air was 
included and the In (Irument graduated ; That if in the 
Air-Thermometer the liquor ftand higher than the divifion 
marked thereon, correfponding with that on the Spirit- 
Glafs, it is an indication that there is a greater preffure 
of the Air at that time, than when the Inflrument was 
graduated. And the contrary is to be concluded when 
the Air-glafs ftands lower than the Spirit, that then 
the Air is fo much lighter, and th^ Quick-finver in the 
or- 
