'( » 3 ° )

This Property is -not always Proportional to dic Denfiry (at leaH not tothe Gravity) or the RefracKng Meditim. For thc Refractive Power o fGlals to that of Water is as yy to 54, whereas «s Gravhy is as 87 to 34;that is, the Squarct of their Refractive Powers are (very near) as their re-fpectivc Gravides. And there are tome Fhrids, -which tho’ Lighter thanWater yct have a greak» Power of Refractian: Thus the Refractive Powerof Spirit of Winc, (according to Dr.Hool£$ Experiment, Microgr. Obs. lviii.Pag. i-io.) is tothat rif Water as 36 to 33 , and its Gravlty J{eciprocaIlpas 35 to 36, or 36,. But the Refractive Powers of Av and Water (eetnto oblerve the Simsh Proportion of their Gravides äircüly, as I have com-o pared them in the soüotviog Table. The Numbers there expreflir^ thcRefraction of Water are tak.cn from the Mean df Nine * * Experiments,made at <b many fevtTal Angles of Incidence Jan. ay. 1.64.!. hy Mr. GaJ-cmgncy fthe Ingmious ftrft Inventor of the Micromctcr, and thc Ways cfMeafurtng Angfes hy Telefcopes) and thofe of Air are prodnc’d by thct pttceding Experimerit.

VTnter.

An.

The faffum’d) Lines of the Angles of Incidence on

the Void from—----—-—

The-Sines of thc Coritfpondent-Angfcs of Emer-si on oiit o f - . 1 ’ ... -■*

The Refractive Power of---————

The •Specisick Gravity fis as 900 to 1 at thetime of the Experiment) «f» 1, Or i(is as 8jo -to t) o f" —

^ aoooooj

\ 1344»°:

- 34400’

| 344 ®°,

-

JOODOO

tsoszö

36

?8

4 °

From hence it seemc very. probable, That their Refpectivc Denfities and-Refractive Powers «re in aiust Simple Prpportion. And if this Ihould hcconhrmcd by tücceeding Experiments, made at different Angles of Inci-dence, and with Cylinders comintiing Exhttufted through leveral Changesof thc Air, it would be more than probable that thc Refractive Powersof the Atmofphcrt ure erery "Where, and at ali Hejghrs above the Eavth,-Proportional to its Dchsities and Expanfionsr And then it would be no diffi-cil It matter to trntse The.Cight fhrotigh it, lo as to terminate the Shadowof the Earth, and (together with proper Expedients sor-Meaiiiring the qusm-tity öf Light Ilhiftiinating an Öpaque Body) to Examine at what Distancesthc Moon must be from the Earth to -soffer EciipicS vf rite «brfcrvcdDuration.

* I-*m_ fir 'titfe Bxptrvinrtftt 10 ihr ~Rev#tnt 4 «i vtry Accurate Jfjlrdkomn

Mr. Fktmftecj, orbo ClfiM t}xn i, Oojrf/w rrtih tnufjy ethtr '6bjeruit1iblr »M fcveräl TPhffj&ftrtiotr^ to tksm, frbm Sir. Gascoigne’r Lotten to Mr. Crabtrce : Thty bopftly

i» Ikt IV»* of ank n*H IK«r, ’it) p* Urr Sir JöliaJ Möör, äri& Mr. 'Chr. Townkys auithffj

*rt noTt'in r tbr Htnit if ttU. Rieh. Townlty tf Tcnfltley W» ^LaiWejhitt-, ityVbomVyiyimiorlftt ftnt limr ajo tt Mr. FlamstfCa.

IX. Give