-MicrocRapnia, 
geneous medinm by direthor firaight lines extended:every waylike Rays 
from thé center of a Sphere. Fifthly, in'an Homogencous wedinue this mos 
tion'is propagated every way withegwil velocity, whence neceflarily eve: 
y pulleor witration of the luminous body will'generate a Sphere; which 
will continually increafe, and grow bigger, juftafter théfame manner 
(thoughindefinitely fwifter) as the waves or rings.dn the furface ef the 
waterdo fwellinto bigger and bigger circles about-a pointof it; where} 
by theifinking of 2 Stone the motion was begun, whiencé it neceflarily fols 
lows) thatiall the parts:of thefe Spheres undulated through an,Homogene- 
ous medium cut the Raysiat right angless © © 4) 0 fey tor) ey 
I8Q Tony ey Wis IE 
_ But becaufe all tranfparent medinms are not Homogeneous, toyond ; an- 
other,therefore we willnext examine how this pulfe or. motion willbe 
propagated ‘through differingly tranfparent mediums: -, And (here, ac 
cording to the moftacute and excellent Philofopher Des Cartes, I fap? 
pofe the fign of the angle of inclination in the: fir ,wedinm to ibe to 
the fign of refraction:in’ the fecond;, As: the denfity, of the. firlt; to the 
denfity‘of the fecond. »By denfity, I mean not thé-denfity in refpect of 
gravity’ (with which therefrations or tranfparency of #ediuws hold no 
roportion) but in refpectonely to the trajeFion of the Rays-ofjight, in _ 
P 
which refpeé they only differ in this; that the one/propagates the pulfe 
more eafily and weakly, the other more flowly, but more {trongly. ~ But 
as for the pulfes cheaelites they will by the refraction acquire another 
pope which we hall now endeavour to-explicate,. of) oini ey on 
e will fuppofe therefore in the. firft'Figure AG ED to bela:phyfical 
Ray, or ABC and D EF to be two Mathematical Rays, trajetted fron 
a very remote point of a luminous bedy throughan Homogeneous tran{pa- 
rent medium LLL; and DA, EB,FC, to be {mall portions of the or- 
bicular impulfes which muft therefore! cut the Raysat right anglessthefe 
Rays meeting with the plain furface NO of a wedinw; that. yields-an 
eafier tranfitus to the propagation of light, and falling obliquelj.on ity 
they will in the medium MMM be refratted; towards the,perpendicular 
of the furface, And becaufe this medzum is mote: cafily. trajeded then 
the former by a third, therefore the point C of theorbicular-pulfe FC 
will be mov'd to H four {paces in the fame time that F the other end of 
it is mov d to G three fpaces, therefore the whole refracted pulfe GH 
fhall be oblique to the refracted RaysC HK and Gi;and the angle GHC 
fhall be an acute, and fo: much the more-acute by how much the greater 
the refraction be, then which nothing ismore evident, for the fign of the 
inclination is to be the fign of refraction as'GF to T € the diftance be- 
tween the point C and the perpendicular from G on CK, which being as 
four to three, HC being longer then GF is longer alfothen T C, there- 
fore the angle GHC is lefsthan G T G. So that henceforth the parts of 
the — H and IK are movd afcew, or cut the Rays at oblique 
It is not my bufinefs in this place to fet down the reafons:why this or 
that body fhould impede the Rays mote, others lef : as why Water fhould 
tranfmit the Raysmore eafily, though ae weakly than air. Onely thus 
much 
