C 675 ] 
The Air we live in, as it is" the moft rare 
and light Fluid, fo are its Alterations the moft fen- 
fible$ and indeed I know of no Experiments which 
determine how far it is capable of being expanded 
by Heat, or condenfed by Cold ; only we find that 
it will make its Way thro* any Fluid in which it lay 
dormant, when its elaftic Property is rouzed by the 
Approach offuch an Heat as will make the Fluid boil. 
On the other hand, when comprefs'd by a Fluid fo 
contracted by Cold, as to freeze, or become folid r 
its Elafticity will only bear a certain Degree of Com- 
preffion, till the Force wherewith it endeavours to 
reftore itfelf, exceeds the Force by which the Parts 
of the Solid, that confines it, adhere to each other, 
and fo burfts its Prifon 5 as we often fee during hard 
Frofts in Ice, and likewife Glafs, and other hard Bo- 
dies, whofe Parts cannot ftretch. 
Next to Air is Alcohol , or the higheft rectified 
Spirit of Wine : This, Water, and all other Liquids, 
are capable of receiving no greater Degree of Heat 
than what makes them boil, as was firlt demonftrated 
by Monfieur Amontons> a Member of the Royal 
Academy des Sciences at Baris*, but that ingenious 
Inventor of the Quickfilver Thermometer Mr. Fah- 
renheit hath difcover'd, that when the Barometer 
marks a greater Preffure of the Atmofphere, the 
fame Liquor will receive 8 or 9 Degrees more of 
Heat than when the Barometer is at the loweft. 
From hence the great Profeffor Boerhaave gives the 
^lint, that, from nice Experiments being made of 
the different Degrees of Heat mark'd by a Thermo* 
meter in boiling Water compared with the differ- 
ent Heights of the Barometer, and Tables formed 
upon 
