22 
Fig. 3. 
MrcrocrRarHi a. 
. breaking off the fmal! feal’d neck of the Bubble ( without at all ftirring 
the fights, obje@, or glafs!) and admitting the external Air, you wil] 
find yourdelf unable to fee the utmoft ends of the obje& 5 but the termi- 
nating rayes' AE’ and A D (which were before refracted to G and F 
by the rarified Air) will proceed almoft directly tol and H's which al- 
teration of the ah (feeing there is no other alteration made in the 
t 
Organ by which the Experiment istryed, fave only the admiffion,’ or ex- 
_ ¢lufionof the condens'd Air’) muft neceflarily be caufed by the variation 
of the medium contain’d in the GlafsB; the greateft difficulty in the ma- 
king of which Experiment, is from the uneven furfaces of the bubble, 
which will 'reprefent an uneven image of the objet. . 
_ > Now,that there is fuch a difference of the upper and under parts of the 
Air,is:clear enough evinc'd from the late improvement of the Torriceliian 
Experiment, which has been tryed at the ee and ‘feet of Mountains; 
and may be further illuftrated , and inquired into, byameans, which 
fome whilesfince Ithought of, and us'd, for the finding by what degrees 
the Air pafles from fuch a degree of Denfity to fuch a degree of Rarity. 
And another, for the finding what preflure was requifite to make it pafs 
from fuch’a degree of Rarefaction to a determinate Denfity :, Which 
Experiments, becaufe they may be ufeful to illuftrate the prefent Inqui- 
ry, ifhall briefly defcribe. i} eof | 
Itook then a {mall Glafs-pipe A B, about the bignef of a Swans quill, 
and about four foot long, which was very equally drawn, fothat, as far 
as I could. perceive ,:no one part was bigger thenanother: This Tube 
being‘open at both ends) I fitted into another {mall Tube DE, that 
id‘a {mall bore juft big enough to contain the {mall Pipe, and this was 
feal'd up at one, and open at the other, end; about which open end I 
faftned:a {mall wooden box C with cement, {6 that wie the bigger . 
Tube, and part of the box, with Quickfilver, T could thruft the {maller 
Tube intoit, till it were all covered with the Quickfilver : Having thus 
done, I faftned my bigger Tube againft the fide of awall, thatit might 
ftand the fteadier , ‘ed plunging the {mall Tube cleer under the Afercy- 
ry in the box, I ftopt the upper end of it very fat with cement, then 
lifting up the {mall Tube, I'drewit up by a {mall pully, and a ftring that 
Thad faftned tothe top of the Room, and found the height of the Afer- 
curial Cylinder to be about twenty nine inches. 
Then letting down the Tube again, I opened thetop, and then thruft 
down the {mall Tube, till I perceived the Quickfilver to rife withinit to 
a mark that I had plac’d juft an inch from the top;and immediately clap- 
ping on a {mall peice of cement that Ihad kept warm, I witha hot Iron 
feald up the top very fait, then lettingit cool (that both the cement - 
might growhard , and more efpecially, that the Air might come to its 
temper, natural for the Day I try’d the Experiment in) I obferv'd dili- 
gently, and found the included Air to be exaétly an Inch. 
__ Here you are to take'notice.. that after the Air is feal’d up, thetop of 
the Tubeis not to be elevated above the fuperficies ef the Quickfilver 
: in 
ee ee ee eee — ee cee —pP i 
