THOSE who will take the Trouble of calling, will be able to form a more distinct Idea of the Construction and Use of this Machine, than can be conveyed by Writing: But as many People have neither the Curiosity or Opportunity for occular Inspection, I shall give a particular Description of it, as well as of all the other Machines, that have been contrived for the like Purposes; and it will appear, by a fair and impartial Comparison, that this is attended with greater Advantages, and fewer Inconveniences, than any that has ever yet been offered to the Publick. BUT, for the better understanding of what follows, it will be necessary to explain some of the Properties of Air and Fire. THE chief Properties of Air, are Fluidity, Gravity, and Elasticity. _First_, THE Air is a Fluid, consisting of Parts which have not any sensible Attraction or Cohesion betwixt themselves; but of such a Shape or Form, as to glide one over another, and yield to the slightest Impression: Of this we need no other Proof, than the Ease and Freedom with which Animals breathe this Element, and pass through it, without any sensible Resistance. _Secondly_, THAT the Air does gravitate, or act upon inferior Bodies by its Weight, is demonstrable by a great many Experiments, and particularly the Barometer, which by the rising and falling of the Mercury, shews the greater or lesser Weight of the Column of Air incumbent upon it. _Thirdly_, NOR is the Elasticity of the Air less demonstrable than either its Fluidity or Gravity. AIR is an elastick Body, for if it be confined or compressed within a less Space than its natural State requires, it will, the Moment the Restraint is removed, dilate and expand itself so as to fill the same Space as before; and that too with such Force, as to break in Pieces the Glass or Earthen Vessel that contained it; as may be seen by the common Experiment of a Bottle full of common Air, strongly cork’d, and put under the Receiver on the Air-Pump, when the Air surrounding the Bottle is pump’d out. But what is particularly remarkable with reference to the Subject we are treating of, is, That Air is rarified by Heat, and condensed by Cold; First, Air rarified and expanded by Heat, becomes specifically lighter than it was before, and will ascend in Air of greater Density: As Matter specifically lighter than Water, Cork for Instance, if placed at the bottom of an empty Vessel, will, if Water be poured into the Vessel, ascend above the Surface of the Water; so rarified Air will rise in common Air till it comes to Air of equal Weight, or is by Cold reduced to its former Density.