yet have a Greater ?ower of Refraftion 5 thu«thc Rcfraftlrtf^ 
Power of Spirit of Wine ( according to Dr. //o'^i^J Experiment!) 
Microg. p. 220) is to that of Water as 36 tn n ani it's Gra- 
vity reciprocally as 33 to36or 3^1 But the Refra(!l:ire Powers 
of Air and Water feem to obferve the Hm pie /Proportion of their 
Gravities, -firedlyj as I havecr.mpar'd them in the following 
Table. The Numbers there ExprcflTing the Refradion of Water 
arc taken from the mean of ^ . . , r f „ ci 
* 9 Obfervadons at (o many ./.r^w /^7,^';.!^'"^ 
feveral Angles of Incidence oyrr-.viA/o»/, and feveral pafages rela^ 
made f^n. ay. 164! by Mr. thig to thm , from his Utttrs to hir. 
Gakotone the Ingenious Fire In- Crahreer nhich were happily prcjcrv'4 
v.nJ,>f,he Micrometer, ..d ^/{:T 1^!' 
the ays of meafuring Angles Xou .ieky; and are. mw in tht Hands 
by Tclefcopes and thofe of o/^ir.RichardTowne]ey•/Townclcy 
Air are produced by theExpe- ;w Lancalhire, w^ow they^tre {m^ 
riment above related , &c. ^^'''"^ 
Water, Air. 
The (aflTum'd; fines of the Anglesof Z jootooo: looooo 
Incidence through ^ 
The fines of the correfpondenc Angles l , 
of Emerfion out of > ^W^^- i°^^3^ 
The Refradive power of 34^00 ..... j6 
The Spccifick Gravity Cif as 900 to i? 
at the time of- the Experiment ^ of> 34400, 
or ( if as 8 JO to i ) of j[ 
From hence it feems very probable that their Refpedtive Den- 
fities and Refraftrve Powers are in a juft fimple proportion: 
And if this (hould be confirm'd by fucceedihg Experiments 
made at different Angles of Incidence and with Cylinders con- 
tinuing Exhaufted through TeveraJ Changes of the Air it would 
be more than probable that the Refradive Powers of the 
Atmofpherc are every where, at all heights above the Earth, 
proportional to it'^ Denfities and Expanfions» And here it 
would be no difficult matter to trace the Light through it, 
thereby to terminate the (hadow of the Earth 5 and ( together, 
with proper Expedients for meafuring the Gtyantity of Light 
IHuminating an Opaque Body) to Examin at what diftances 
the Moon muft be from the Earth tofufFtr Eclipfcs of the Ob. 
ferv'd Duration. This Limitation is confiderable enough in. 
Aftronomy, abundantly to recompenfe the trouble of Pfofc- 
eutkig fuch a New Experiment. 
