( 785 ) 
'Whereas t intimated in the Preamble to thefe Notes, Exp.xii. 
that Confining Fluids may have di/Hnft Surfaces , withouc 
haviog,at leaft in many Pofitions, refraftions differing enough, 
©rrefledionsftrong enough, to make the Plain, that difter- 
minates them, obvious to the Eye ; I fliall here obferve, thac 
when the Qil of tartar, or Nitrom Alcali , that 1 employed, 
happened to be very dear and colourlefs , I have more than 
once made highly reflified Sfirif of Wine float upon it fo, 
thac in moft Pofitions the Vial feem'd to have in it but one 
Uniform Liquor ; the Plain that divided the two Fluids being 
unapt tobedifcerned, but in a Pofirion, wherein the Rays of 
Lighc pafling thenceto the Eye, fell very obliquely on it ; 
and indeed, when there was no little Duft or other Fecalency, 
fwimminguponthe/»r/i^eof the Oil of tartar; I had fome- 
times much ado to convince ordinary Spe6tators , that the 
Vial, in two diftinft Regions of it, contain'd two unfociable 
Liquors. 
Onthisoccafion,! (hall add an Experiment, which, Ehp.xul 
though it does not fo direftly belong to our Subjeft , as to 
make its Omiflion a fault, is not yet perhaps fo Impertinent 
as to beunwelcom. 
We took a deliquated Alcali^ made of Niter tartar^ 
and deeply ting*d with Cochaneel ; and, that the Liquors 
might not only be heterogeneous , but as differing in gravity 
anddenfityas we could make them, we poured on it a pe- 
culiar kind of Oil lighter than Spirit 0/ Wine , and holding 
the Plain where the two Liquors were contiguous in a con* 
venient Poficion , in refpeft of the Light and the Eye , , I 
obfcrv'd it to make a ftrangely vivid Refledion of rhe inci- 
dent beams of Light: fothat this Phyfical Surface, which was 
fiat, look't almoft, for/cwas not fo fpecular, like that of 
mickfilver\ and when I kept it till Night , and confidered 
it by the Light of a Candle , the bright Figure of the flame 
was ftrongly reflefted almoft as from a clofe Specular body; 
whichrcmptedmetofufpeft, that there might be fouiething 
elfe than the bare finoothnefs of the fur face of the J/calizat 
Liquor to produce fo brisk a Refleftion ; and the rather, 
5 K 2 becaufe 
