271. The _Wind_ would more frequently be perceived to _descend_ and _rebound upwards_, (Trials of which might be made by holding an Umbrella, extended at right Angles with its Axis, upright in the Hand;) if the same Opportunity offered, of opposing as great a Surface to it in a perpendicular, as is every Day done, in an horizontal Direction: for in walking, the whole Height of the Body, and half its Surface, is opposed horizontally to the Wind: but the Head only, which is covered, is opposed to the perpendicular Pressure. 272. As every Circumstance in the Order of Nature is so admirably contrived that each apparent Inconvenience rectifies itself; in _heavy_ Winds continuing to blow from a +cold+ Point; the Construction of the Atmosphere is such, that the _warm light_ Air from the opposite Points will necessarily rise up and flow over the cold Stratum, and by their Tendency to an Equilibrium, will produce an Air _less cold_, before the _same_ Wind is exhausted. 273. On the one Hand; it is probable, that, as cold Winds are heavy; the Eknèfiai Winds are covered with frequent Waves of the Apogay, or light warm Air rolling over them, frequently from the opposite Points. 274. On the other Hand, as the _Apogay_ Winds are naturally light and warm, it is _improbable_ that they shoud be _frequently_ covered with Waves of _cold heavy Air_, rolling over them from Eknèfiai Points. It may therefore be reasonably concluded, that the Eknèfiai Winds, when approaching or opposed to the Apogay, shoud be considered as _Ground Winds_, (i.e. Winds blowing next the Surface of the Earth, tho’ they be supposed at the same Time to descend) which receive the Apogay above them: and that the Apogay being warm light and +moist+, (which last will have the same Effect, as if they were more elastic;)[81] being also more turbulent, and endued with greater Velocity, press back the Eknèfiai from the Surface of the Earth, and upwards; and at the same Time flow above them. By which means the Eknèfiai partake of their Qualities;—become less _cold_, less _heavy_, and less _dry_.[82] CHAPTER LI. Section 275. If then this Reasoning be allowed; aërial Travellers will not be subject, when, at a considerable Height, even in Winter, to great Degrees of Cold, supposing that the Air does not actually freeze the Waters below; and the Apogay or Southerly Winds have continued for a few Days. On the Contrary; Aironauts may expect Cold, encreasing with their Ascent, even in Summer, tho’ _warm_ below; supposing the Eknèfiai or Northerly Winds to have continued but for a Day before the Ascent: they may possibly, indeed by soaring higher, rise into the regular Stratum of the warm Apogay floating above them. 276. From what has been said, there seems a Degree of Probability, that the Air for a Number of Miles, _above warm cultivated Plains_ shoud differ materially in its Temperature, from Air above Mountains, or _even on a Level_ with their Summits.