This I should further proceed to hope, had any one been so inquisitive as to have found out the way of making any transparent body, either more dense or more rare, for then it might be possible to compose a Globule that should be more dense in the middle of it, then in any other part, and to compose the whole bulk, so as that there should be a continual gradual transition from one degree of density to another; such as should be found requisite for the desired inflection of the transmigrating Rays; but of this enough at present, because I may say more of it when I set down my own Trials concerning the melioration of Dioptricks, where I shall enumerate with how many several substances I have made both Microscopes, and Telescopes, and by what and how many, ways:  Let such as have leisure and opportunity farther consider it.

The next Quaery shall be, whether by the same collection of a more dense body then the other, or at least, of the denser part of the other, there might not be imagin’d a reason of the apparition of some new fix’d Stars, as those in the Swan, Cassiope’s Charr, Serpentarius, Piscis, Cetus, &c.

Thirdly, Whether it be possible to define the height of the Atmosphere from this inflection of the Rays, or from the Quicksilver Experiment of the rarifaction or extension of the Air.

Fourthly, Whether the disparity between the upper and under Air be not sometimes so great, as to make a reflecting superficies; I have had several Observations which seem to have proceeded from some such cause, but it would be too long to relate and examine them.  An Experiment, also somewhat analogous to this, I have made with Salt-water and Fresh, which two liquors, in most Positions, seem’d the same, and not to be separated by any determinate superficies, which separating surface yet in some other Positions did plainly appear.

And if so, Whether the reason of the equal bounding or terminus of the under parts of the clouds may not proceed from this cause; whether, secondly, the Reason of the apparition of many Suns may not be found out, by considering how the Rays of the Sun may so be reflected, as to describe a pretty true Image of the body, as we find them from any regular Superficies.  Whether also this may not be found to cause the apparition of some of those Parelii, of counterfeit Suns, which appear coloured, by refracting the Rays so, as to make the body of the Sun appear in quite another place then really it is.  But of this more elsewhere.

5.  Whether the Phaenomena of the Clouds may not be made out by this diversity of density in the upper and under parts of the Air, by supposing the Air above them to be much lighter then they themselves are, and they themselves to be yet lighter then that which is subjacent to them, many of them seeming to be the same substance with the Cobwebs that fly in the Air after a Fog.