( *°5 ) 
i(s upper fide being parallel with the Tame. The Qbj’ft 
is a Piece of white Paper, in form of a Crofs, parted 
on a black Board, and is fix’d at the end of the moving 
Limb, which is in length about 7 Feet from the Sight 5 
its Diameter is about 2 ~ Inches, which juft compre- 
hends the Sight through the Slit * fo that when the 
Objeft is wholly within view, we conclude the Obfer- 
vation to be exaft. With this Jppardtus the Experi- 
ments are made as well by Candle-light as Day-light, 
(the Prefence of the Sun Beams being no ways neceffaryj 
and I think they maybe depended on as pretty Accurate. 
I have taken the Specifick Gravity of the feveral Liquids, 
where I could obtain a fufficienc quantity, as appears 
by the Table : So that if any Perlon fhould have the 
Curiofity to repeat thefe Experiments, he muft expeft a 
different Angle of Obfervation, if the Specifick Gravity 
agree not with the Table $ for fometimes it happens, 
that Liquids of the fame Denomination are not always 
of an equal goodnefs, and confequently will have a dif- 
ferent Specifick Gravity and Refradion. 
The Chriftalline Humour of the Ox Eye I prefi; into 
the Angle of the Prifm, whereby it received tha form 
of it, and gave the Angle of Obfertvaion, as fpecify’d 
in the Table. I could not fee the common Objeft thro’ 
it, but was forc’d to make ufe of a Candle for that 
purpofe ; the Flame whereof appeared very broad, at 
leaft 5 or 6 Inches, nearly in the form of a Half Moon: 
But what fhould occafion fuch a Change of Figure, I 
cannot at prefent determine. Of all the Fluids I have 
try’d, t find nothing to Refratt a Ray of Light lefs 
thap Water 5 yet there are feveral other Liquids which 
make the fame Angle. I obferve Oil of Bees -Wax to 
be the lighted Fluid, and Butter of Antimony per Drti- 
quium to be much the heavieft : The difference of Spe- 
cifick Gravity between thefe two Bodies, is as 662 is 
to 1976, that is, nearly as one to three : And the Ratio 
Dd of 
