( ) 
fore it returned into it : And though the Reflexion in 
that Cafe be not made by impinging on the folid Parts 
of the Glafs, yet it is owing to them that the Light 
(acted upon at a Diftance) is turned up again, as has 
been Ihewn by feveral of the Experiments abovemen- 
tioned. 
Now let us fee how Rizzetti’s Account of the new 
Immerfion agrees with Rhanomena. 
Let all above the Line P p {Fig. 19) be a denfe Medi- 
um, as Glafs ^ and all below it a rare Medium, as Air^ 
AB CD is a Beam of Light infenfible in Thicknefs,but 
of fome Breadth, whofe Rays cohere to one another, 
and whofe Se&ion or firft Line is B C. If the Medium in 
which B C is, did not change, B C would move parallel to 
it felf in the Lines B a and C d ; but as the End C of 
the Line B C comes out into a rare Medium, which be- 
ing of lefs Refinance to Light (for fo he fuppofes) the 
Point C moving with more Facility than the Point B 
defcribes the Curve C F H, whilft B moving in the 
denfe Medium with more Difficulty, defcribes the lef- 
fer Curve BEG ; then the Point C being got to H is 
re-iramerfed, and the Line B C being got to H G goes 
on in the Direction HK GL parallel to itfelf, draw- 
ing the Beam after it in a re&ilinear Direction, after 
Part of it has been bent within the Glafs and Part of 
it without. 
Now if this be true, and P p tt be a Prifm, I beg 
to know what becomes of the Line at E F which u- 
nites the Rays of the Beam about the Point of Inci- 
dence I, when Water is brought to touch the Surface 
Pp, as at A B Fig. 17 ? If it be faid that Water mak- 
ing a great Refiftance, though not fo great as Glafs, the 
Curve BE G deviates fo little from the Line B a that 
the 
