[1013 j 
what we think to be done upon the open Air s is indeed' 
done upon the ^ick^Silver s or rather upon the Jir 
latent therein. 
My meaning is this. We find that in very hot weather, 
and alfo in frofty weather, the ^u^SHver in the tube 
Gommonly ftaads very high j from whence we are apt 
to conclude, that therefore the outward Air preffes 
very hard on the itagnant^/^/^-'&7i^^r, without the tube. 
Wherein I am not latistyed. 
For weare taconfider, that, in filling the Tube v/ith 
S^uic^-Silver before it be inverted, if great care be not 
uled to cleanfeit from^/^r, many aery particles will re* 
main mixed with it ; which, while their fpring is weak, 
areeafily prefTed by the weight of xhQ QjiicI^Siiver ciofe 
as hardly to be difcerned otherwife then by theefted:^ : 
but when^by the external heat^ their fprmg isftrengthen- 
ed, they expand themfelves,, and eaufe the ^uick^S'ilver, 
wherein they are, to fwell in bulk, without increaling its- 
weight; and confequently to ftand higher though not: 
to prefsheavyer.. 
Of this I liad manif eft experience, when (many years 
fince j I did for five or fix years together conftaatly ob- 
fervethe height of the §lui cJ^ Silver in tht xnhQy a nd kept 
a regifter of it, and of the weather withit:and did for two 
or three of the firft years obferve^that in very hot weather 
the G^cJ^Siher commonly flood very high. But;, for 
fome of the latter years, I found it much lower in hoc 
weather then in thofe former years. Of whichlfatisfyed 
J ^'^elfwith this account; that, in thofe former years^ . 
tlx )e having been but lately filled, the aery parts re- 
EialntUg in the ^ick^Silver, being by the heat expanded^ 
made the §^ick^Silver to fwell and iland higher: but, 
when xYi^ ^icJ^Silver^ by divers years ftandiog unmo- 
lefted, had by its own weight cleanfed it felf, and forced 
that Air (which had been in it into the upper part of the 
glafsi it now ceafed to make the ^ickcSilver fwell 
higher^ 
