■ f ^^ig ) 
whofe parts are llike fo many fragments of fach Plates. 
Thefe feem to be the moft plain^ genuine and jDeceffary 
conditions oithi$ Mypotbefj: And they agree fo juftly withmy 
T^hcoryj^ ih^t if thz J mmadver for think tit to apply rhem, he 
need not, on thataccoiint , apprehend a divorce froniir^ Buc 
yet how he will defend it from other difficulties, 1 know not. 
For, to me, the Fundamental Suppofition it felf feems impof- 
fible • nameJyjThac the Wave/ or Vibrations of any Fluid.cai?^. 
l.ke the Rays of Light^ be propagated in Stf eight hnes^withoiiE 
a continual and very extravagant fpreading and ben^ug every 
way into the quielcent Medium^ where they are terminated 
by it. I miftake, if there be not both Experiment and De- 
monflration to the contrary^ And as to the other two or three 
Hypqthefes^ which he mentions, I had rather believe them fub- 
jett to the like difEcultieSjthan fufpe^the^^/p^it'^^^r fliould 
iele(3: the worft for his owe. 
What I have faid of thiSj may be eafily applied to all other 
Mephankal Hypothsfesy in which Light is fuppofed to be canfed 
by any Preffion or Motion whatfoeverj excited in the £ther by 
the agitated parts of Luminous bod ies^For^itfeems impoffible^ 
that any of thofe Motions or Preffidns can be propagared io 
6Yr^ig/;^ lines without the Hke fpreading every way into the 
fhadow'd Medium^ on which they boraen . But yet, if any 
man can think it poffible^ he muft at leaft alloWythat thofe Mo-- 
tions or Endeavors to motion, caufed in the <^^^er by the feve- 
ral parts of any Lucid body that differ in fize,, figure^ and agi* 
ration^ muft neceifarily be unequal Which is enough to oe- 
nominate Light an Aggr^gat of ^/j^f??? rays^ accofdiog to any 
ofthof;^ Hypothefes, And if thofe Originai inequalities may 
fuflSlce to difference the Rays in Colour and Rcfrangibiiity^ I 
fee no reafon, why they^ that adhere td any of thofe 
ftiouid feek for other Caules of thefe EffeQ-s^ unlefs (to iife the 
Objectors argument ) they will multiply entities without oe- 
ceffity^ 
The jf^jrW thing to be confidered i^ the Condition of the 
'Animadver[t^rs Conceffions, which 
is, that I would.explicate my Iheo- ^- 0fth^^p^xm^vtv{axy^m^ 
nesby m% Hypotbe/isikna III coma tkp, 
comply with him in that pointy 
■ •there 
