(»3S) 
tagibus to rarify and drive out the Air as much as is poffib!e,be« 
eaufe in fucli feal’d Bubles the Air it felf ( as I have elfewhere 
fhewn ) hras a weight ; yet this advantage countervails not the 
inconvenience of being obliged to iucreafe the weight of the 
Glafs 3 which when it includes highly rarificd Air, if it be not 
fomewhat ftrong,will be broken by the prefTure of theExterna! 
Air, as I have Efficiently tryed. 
Thirdly, I would have tryed, whether the Drynefi and Moift- 
wre of the Air would in any meafure have alter'd tha weight of 
the Buble , as well as the Variation of Gravity produced in the 
jttmofphere by other caufes ; but the extraordinarily conftant ab- 
fence of Bogs, kept me from making Obfervations of this 
kindj fave that one morning early, being told of a mift, I'fent 
to fee (being my felf in bed) whether it made the Air fo heavy 
as to buoy up the Buble i but did not learn, that that mift* had 
any fenfible operation, on it. 
Fourthly, By reafon of the difficulties and cafualties, that may 
happen about the procuring and prefer ving fuch large and light 
Bubles, as 1 have been lately mentioning • it may in fome cafes- 
prove a convenience to be inform’d, That I have fome times,, 
inftead of one Efficiently large Buble, made ufe of two, that* 
werefmaller. And, though afingle Buble of competent big^ 
nesbemuch preferable, by reafon that a far lefs quantity and 
weight of Glafs is requisite to comprife an equafcapacity, when 
the Glafs is blown into a finglc Buble, than when it is divided 1 
into two; yet I found, that the employing of two inftead of 
one, did not fo ill anfwer my exfpedtations, but that they may 
for a need ferve the turn inftead of the other $ than which 
they are more eafier to be procured : And if the Ballance be' 
firrong enough to bear fomuch Glafs, without being injur’d 
by employing two or a greater number of large Bubles, the ef~ 
£e«ft may be more confpicuous, than if only a finglc Bub ! e- 
(though a very good one ) were employed. 
This inftrumeat may be much improved by divers Accom- 
modations. As 
Tirfl, There may be fitted to the Anfa (or Checks of the j 
Ballance) an Arch (of a Circle) divided into if. or 20. deg, 
( more or lefs, according to the.goodnefs of the Ballance ) that 
the Cock retting over againtt thefe Divifio.es , may readily 
andii 
