( 5i6o ) 
An ExfraSl of Letters from Dr. John Wallis to the TuhUffHr^ 
1 672 .Sept.26.&c. concerning the Suf^enfton of g^uickfilver 
tPeU purged of Air^ much higher than the ordinary Standard 
in the Torricellian Experiment. 
S I R, 
I Am not forry to find , inborn tranfaUiom for the laft 
Month,( which I have newly received^) that M.Hugcnr^ 
ao Ingenious and Icquifitive perfon , doth endeavour to 
give a Reafon of that Odd phenomenon in the Torricellian 
~ Expcrimcnt(obferv'd by my Lord Bronncker^dinA Mr.BoyU^ 
many years fince^in purfuancc of an Order oitht R.Society 
to that purpoftj) of which I give an account in my Trcatifc 
De Motu €ap4i^>Schol,prop. 1 5. The Phasnomenoo is this : 
Whereas in the Torricellian Experimentjthe Quieknivcr 
contain'd 10 the Inverted Tubc, how long focver, whofe c* 
pen otifice G. is immcrged in ftagnant Quickfilver , does 
fet tk Ji£* ufually fall j^own to the height of about 29* inches above 
the furface of the ftagnant Quickfilver AB , and there re- 
mains fufpcnded,as at I : If the Quickfilver be well cleans'd 
from Air^it has beed found to ftand top-full, much higher, 
even to the height of 75. inches (and how much higher it 
may ftand;5 we cannot tell 5) but upon the admiffion of the 
left Air, or a concuflion of the Tube, it falls down to the 
ufual-ftandard. 
Two Reafons I did there hint ( though not perfeftly fa- 
tisfied in either:)The i^/^e^of my own^concerning the Spring 
pf the Air 5 neceflary to put Heavy bodies in motion, not 
impeird by any other force : The ^^^^fr^ofmy L^Brouncker^ 
that there might be in the Air yet a greater Weight or Pret 
fure than is neceflary for the height of 29 inches, in cafe 
thcrc benothiDg but thebare weight of Quickfilver to be 
fupported» 
I find, Monfiear Kvjje»/ to fall in with that of my Lord 
Brouncker^ fave that what we comprehend under the name 
o( Air^ he calls a more jubiile Matter : which alters not thtf 
Gafe at aU^ but ooly the Name. 
