Jit my Barofiope , I have never found the Quickfilver higher 
than 50. inches, nor lower than 28. (at leaft, fcarcedifcernably, 
not ~ of an inch higher than that , or lower than this : ) which I 
mention 3 not only to (hew the limits, within which I have obfer- 
ved mine to keep,w/ 7 . full 2 inches, but likewife as an Eftimate 
of the Clearnefs of the Qaickfilver from Air. For, though 
my Quickfilver were with good care cleanfed from the Air; yet 
I find that which Mr, Boyle uf'eth, much better : for, comparing 
his with mine at the fame times, and both in Oxford, at no great 
diftance; I find his Quickfilver to Hand alwaies fomewhat high- 
er than mine (fomeiimes neer a quarter of an Inch ; ) which I 
know now how to give a more probable account off, than that 
my .Quickfilver is either heavier than his; orelfe, that his is 
better cleanfed from Air - (unlefs , peffibly, the difference of 
the Bore, or other circumftances of the Tube, may caufe the 
alteration } m lie being a taller Tube, apd a bigger Bore, than 
his.) And upon like reafon,as his Hards higher thanmioe,fo ano- 
ther, lefs cleanfed, from Air, may at the fame time be confidera- 
bly lower , and confequently under 28. Inches at the lowed:. 
' In thieJ^foggy weather, I find my Quickfilver to rife; which I 
adfcribe to the heavinefs of the Vapours in the Airr And I 
have never found it higher, than in the foggy weather above- 
mentioned. 
In Smfhiny weather,it rifeth alfo (and commonly the clearer, 
the more ; ) which, I think, may be imputed partly to the Va- 
pors railed by the Sun, and making the Air heavier ; and partly 
to the Heat, increafing the Elaftickor Springy power of the 
Air. Which latter I the rather add 3 becaufe I have fometimes ob* 
ferved in Sunfhiny weather, when there have come Clouds for 
fomeconfiderable time (fuppofe an hour or two) the Quick- 
filver has fallen ; and then, upon the Suns breaking out again, 
It has rifen as before. 
In 7 \ainy weather, it ufeth to fall (of which the reafon is obvi- 
ous, becaufe the Air is lightned, by fo much as falls : J In Snowy 
weather, likewife,but not fo much as in fyim. And fometimes I 
have obferved it, upon a Eoarfref^ falling in the night. 
For Windy weather, I find it generally to fall ; and that more 
oniverfally, and more difcernably, than upon Rain: (which I 
attribute to the Winds moving the Air collaterally , and thereby 
not fullering it to preis fo much direUly downwards ; the like of 
