(170) 
1.Y\mv Barofcope ^ I have never found the Quickfilver higher 
than 50. inches^nor lower than 28. (at leaft, fcarcedifcernably, 
not of an inch higher x\\2inihat, or lower than this : ) which I 
mentioojnotonlyto fliew the limits,within which I have-obfer- 
ved mine to keep,f full 2 inches,but likewife as an Eftimate 
of the Clearnefs of the Qtiickfilver from Air. For, though 
my Quickfilver were with good care clennfed from the Air; yet 
I fincl tliat which Mr. Boyle ufeth^ much better : for, comparing 
his withmine at the fame times, 2nd both in Oxford^ atno great 
diftancej I find his Quickfilver to flandalwaies fomewhat high- 
er than mine (fometimes neer a (juarter of an Inch ; ) which I 
know now how to give a more probable account off, than that 
my Qiiickfilver is either heavier than hij; orelfe, that his is 
better cleanfed from Air 3 (unlefs, poffibly, the difference of 
iheBore, or other circumflances of theTube, maycaufethe 
alteration ^ ra n - being a taller Tube, and a bigger Bore, than 
Ilis.)And upon like reaion,as his ftands higher thanmine^fo ano- 
ther, lefs cleanfed from Air, may at the fame time be confidera- 
bly lower, and confequently under 28. Inches at the loweft. 
In ^^'/Vy^/i?^^^^ weather, I find my Quickfilver to rife 5 which I 
adfcribe to the heavinefs of the Vapours in the Air^ And 
have never found it higher, thaa in the foggy weather above- 
mentioned. 
In SmiJloiny weather^it rifeth alfo (and Commonly the dcarerj. 
the more; ) which,,! think, may, be imputed^/ir//y to the Va- 
pors railed by the Sun,and making the Air heavier ; an-dpartty 
to the Heat, iijcreafing the Elaftickor Springy power of the 
Air, Which latter I the rather add,becaufe I have fometimes ob- 
ferved in Sunfhiny weather, when there have come Clouds forj 
fomeconfiderabk time (fuppofe an hour or two) tlieQuiclcrt. 
fitver has fatten ; and then, upon the Suns breakingout again^ . 
it has rifen as before. 
In 7{ainy weather,it ufeth to fall (of which thefreafon is obvi- 
ousjbecaufe the Air is lightned, by fo much as falls : J In Snmy 
weather,likewife,buc not fo much as in J^am. And fometimes I 
have obferved it, upon a Hoanfrefi^ falling in the night. 
For Windy weather, I find it generally to fall ; and that more 
univerfally, and more difcernably^ than upon Rain: (which I 
attribute to the Winds moving the Air collateraBy ^ and thereby 
not fufFering it to prefsi fo xmdidireBly downwards : the like of 
whicii ; 
