Now that such a constitution of the Air and Clouds, if such there be, may be sufficient to perform this effect, may be confirm’d by this Experiment.

Make as strong a Solution of Salt as you are able, then filling a Glass of some depth half full with it, fill the other half with fresh Water, and poyse a little Glass-bubble, so as that it may sink pretty quick in fresh Water, which take and put into the aforesaid Glass, and you shall find it to sink till it comes towards the middle, where it will remain fixt, without moving either upwards or downwards.  And by a second Experiment, of poising such a bubble in water, whose upper part is warmer, and consequently lighter, then the under, which is colder and heavier; the manner of which follows in this next Quaery, which is,

6.  Whether the rarifaction and condensation of Water be not made after the same manner, as those effects are produc’d in the Air by heat; for I once pois’d a seal’d up Glass-bubble so exactly, that never so small an addition would make it sink, and as small a detraction make it swim, which suffering to rest in that Vessel of Water for some time, I alwayes found it about noon to be at the bottom of the Water, and at night, and in the morning, at the top:  Imagining this to proceed from the Rarifaction of the Water, caus’d by the heat, I made tryal, and found most true; for I was able at any time, either to depress, or raise it, by heat and cold; for if I let the Pipe stand for some time in cold water, I could easily raise the Bubble from the bottom, whither I had a little afore detruded it, by putting the same Pipe into warm Water.  And this way I have been able, for a very considerable time, to keep a Bubble so poys’d in the Water, as that it should remain in the middle, and neither sink, nor swim:  For gently heating the upper part of the Pipe with a Candle, Coal, or hot Iron, till I perceived the Bubble begin to descend, then forbearing, I have observed it to descend to such or such a station, and there to remain suspended for some hours, till the heat by degrees were quite vanished, when it would again ascend to its former place.  This I have also often observed naturally performed by the heat of the Air, which being able to rarifie the upper parts of the Water sooner then the lower, by reason of its immediate contact, the heat of the Air has sometimes so slowly increased, that I have observed the Bubble to be some hours in passing between the top and bottom.

7.  Whether the appearance of the Pike of Tenerif, and several other high Mountains, at so much greater a distance then seems to agree with their respective heights, be not to be attributed to the Curvature of the visual Ray, that is made by its passing obliquely through so differingly Dense a Medium from the top to the eye very far distant in the Horizon:  For since we have already, I hope, made it very probable, that there is such an inflection of the Rays by the differing density of the parts of