taglous to f arify and drive out the Air as much as is poffib!e,be^ 
caufc in fuch feald Bubles the Airit (elf (asl have elfewhere 
fliewn ) has a weight > yet this advantage countervails not the 
inconvenience of being obh'ged to increafe the weight of the 
Glafs 3 which when it includes, highly rarificd Air,if it be not 
fomewhat ftrongjwill be broken by the prefliire of theExterna! 
Air, as I have lufBciently tryed. 
Thirdly, I would have tryed,whether the Drynefs2iVid Moifl^ 
ure of the Air would in any meafure have altered the weight of 
the Buble ^ as well as the Variation of Gravity produced in the 
Atmofphereby other caufes ; but the extraordinarily conftanr ab- 
fence of Fogs, kept me from making Obfervations of this 
kind 5 fave that one morning^arly, being told of a raift, I fent 
to fee (being my felf in bed) v/hetheritmadethe Air fo heavy 
as to buoy up the Buble s but did not learn, that that mift had 
any fenfible operation on it. 
Fourthly, By reafon of the difficulties and cafuakies, that may 
happen about the procuring and prefervmg fuch large and light 
Bubles^ as I have been lately mentioning- itmay in fome cafes 
prove a convenience to be infornVd, That I have fometimes^ 
inftead of one fufficiently large Buble^ made ufe of twoj that 
were fmaller. And, though a fingle Buble of competent big- - 
nes be much preferable, by reafon that a far lefs quantity and 
weight of Glafs is requifite to comprife an equal capacity, when 
the Glafs is blown into a fingle Buble, than when it is divided 
into two ; yet I found3 that the employing of two inftead of 
one, did not fo ill anfwer my exfpedationsj but that they may 
for a need ferve the turn inftead of the other 5 than which 
they are more eafier to be procured: And if the Baljance be 
ftrongenough to bear fomuch Glafs, without being injur'd: 
by employing two or a greater number of large Bubles, the ef- 
fect: may be more confpicuous, than ifonly a fingle Buble 
(though a very good one ) were employed. 
This inftrument may be much improved by divers Accom- 
modations. As 
Firjlj There aiay be fitted toihcJnfa (or Checks of the 
Ballance ) an Arch (of a Circle) divided into i f. or 20. dcg, 
( aiore or lefs, according to the goodnefs of the Ballance) that 
the Cock refting over againft thcfc Divifions, may readily 
and 
