MrerocRaPHiaAg 
~ Sun and Moon have both been feen above the Horizon, whil'ft the Mooti 
hasbeen in an Eclipfe. I thall not here inftance in the great refractions, 
have; all which feem’ to argue the Horizontal refraction, much greater 
then it is hitherto generally beliév'd: t aimee leis $d4 40 caahss' 
- [have further taken notice, that not onely the Sun, Moon and Starrs; 
and high tops of mountains have fuffer'd thefe kinds of refraGtion, but 
Trees, and feveral bright Obje&ts on the ground : I have often taken no- 
tice of the twinkling of the reflections of the Sun from a Glaf-window 
at a good diftance, and ofa Candle in the night, but that is not focon- 
{picuous.and in obferving the fetting Sun,I have-often taken notice: of the 
tremulation of the Trees and Buthes, as wellas ofthe edges of the Sun. 
Divers of thefe Phenomena have been taken notice of by feveral, who 
have given feveral reafons of them; but I have not yet met with any, alto- 
gether fatisfactory, though fome ef their conjectures have been partly 
true,but parly alfo falfe.setting my felf therfore upon the inquity of thefe 
Phenomena, \ firtt endeavour'd to be very diligent in taking notice of 
the feveral particulars and circumftances obfervable in thems, and next; 
in making divers particular Experiments, that might cleer fome doubts, 
and ferve to determine, confirm, and illuftrate the true and adequate 
caufe of each 3 and upon the whole, I find much reafon to think, that 
the true caufe of all thefe Pherxomena is from the inflection, or multi- 
and that it does not proceed froma refradion caus'd by any terminating 
fuperficies of the Air above, nor from any fuch exactly defin'd faperficies 
within the body of the Atwo/phere. : +s 
- This Conclufion is grounded upon thefe two Propofitions: 
Firft, that a wedmm, whole parts are unequally dexfe, and mov'd by 
various motions and tranfpofitions as to one another, will produce all 
thefe vifible effects upon the Rays of light, without any other coefficient 
caufe. peril 7 vain 5 cael de 
Secondly, that there is in the Air or Atmofphere, fuch a variety in the 
conftituent parts of it, both as to their denfity and rarity, and as to. their 
divers mutations and pofitions one to another. | 
__ By Denfity and Rarity, Lunderftand a property of a tranfparent body; 
that does either more or lefs refrat a Ray of light (coming obliquely 
upon its fuperficies out ofa third #edixm) toward its perpendicular : As 
Icall Glafs a more denfe body then Water; and Water a more rare body 
then Glafs, becaufe of the refractions (more or lefs deflecting rowardsthe 
perpendicular) that are made in;them, of a Ray of light out of the Air 
that has the fame inclination upon either of their fuperficies. 
Soas to the bufinefs of Refraction, fpirit of Wineis a more denfé body 
then Water, it having been found by an accurate Inftrument that meafures 
_ theangles of Refractions to Minutesthat for the fame refraéted angle of 
30700! in both thofe Avedinms, the angle of incidence in Water was 
but 41°. 35. but the angle of the incidence in the trial with {pirit of 
Wine was 42°: 45'. But astogravity, Water is amore denfé body then 
a - Gg2 {pirit 
that the tops of high mountains, feen at a diftance, ‘have been found to _ 
plicate refraction of thofe Rays of light within the body of the Ataiofpheres — 
a 
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