Gf tbe Atmofpbere. toF 
phenonieria and extent from the well-known ptoperties of 
elaftic fluids. For this purpofe we muft have before our eyes 
the following principles of aérometry, to be found in moft 
elementary books :=—— 
1. The elafticity of fluids is in the inverfe ratio of their 
denfity, and in the dire& ratio of their rarity. Thus air is 
more elaftic than water; light more elaftic than air; and 
ether than light. This is one of the principles ‘of New- 
ton *. 
2. The force of elafticity of the air expands and contracts 
itfelf in the direét ratio of the weight with which it 1s loaded, 
and diffufes itfelf in the inverfe ratio of the force by which it 
is comprefled ‘ie 
3. The air is rarefied, or diffufes itfelf, in the direct ratio of 
the quantity of heat which aéts upon it f. 
4. The air, as well as all fluids in general, has a tendency 
to put itfelf in equilibrium, and does not reft until it has 
obtained it §. 
It now follows, from thefe principles, that every thing 
_ which increafes the weight of the atmofphere, and preffes 
_ the air more in one place than another near it, muft occa- 
 fion the air to ruth from the former to the latter, where it is 
lighter: and, on the other hand, every thing that leffens the 
"gravity of the atmofphere, and increafes or rarefies the air, 
‘and makes it lighter than in the neighbouring parts, muft 
occafion the air to ruth in from all fides to thofe parts 5 and 
‘this continues in each cafe till the equilibrium is reftored, 
and reft again effetted. This is the principal caufe of the ‘ 
‘origin of wind. But, as a pendulum put in motion does not 
mediately reft when it has come to a perpendicular direc- 
n, but obtains reft after making fome {mall vibrations; in 
the fame manner, the currents of air, from the places where 
_ the air is more preffed to that where it is Jefs fo, will ruth be- 
yond the boundaries of the equilibrium, from which they 
will again fly back, and at length obtain reft after feveral 
“undulations. As this takes place in all ‘fluids, it is more 
i 
a 6 
» * Princip. in fine, p. 530, edit. 1726, et quaft. 21, 22, inf fine optices. — 
_ + Wolf Elem. Aérom. § 72—77- t Ibid, § 146. § Ibid, 
§36—44. Ad 
Pa, peculiarly 
