[ 439 ] 
“ conceive that when an elaflic fluid iflues from a 
“ body (as from the quickfilver in the bent tube) it 
“ willbedenfer at the furface from whence it iflues, 
“ than it is where it finds more liberty to expand 
“ itlelf. And therefore the furface near which 
“ the electric light is the brightefl, fhouldbe that 
“ fr °m whence the fluid iflues, which caufes thofe 
“ luminous appearances.” 
This reafoning appears intirely new to me, and 
I am at a lofs to comprehend why an elaflic fluid 
confined witnin a tube, whofe fides are fuppofed 
parallel, will be denfer at the furface of a body from 
whence it iflues, than in any other part; fince its 
expanfive force muft in that cafe be limitted by the 
fides thereof. As you have not given any particular 
experiment to prove what you afl'ert in this cafe, 
you will therefore give me leave to differ from you 
in opinion. If, as you fay, there is really more 
liberty^ for an elaflic fluid to expand in any other 
part or the exhaufted tube, than at the furface it- 
felf, you muft produce fome evidence in favour of 
that opinion, before it can be admitted. On the 
othei hand, I fhould have thought, if all rejijlance is 
fuppofed to be removed from within the tube, the 
liberty, for the fluid to expand itfelf, will be equal 
m every part; reckoning from the furface of one 
column of quickfilver through the whole void, 
to the furface of the other column of quick- 
filver. 
A.s I am for fupporting this opinion, let us exa- 
mine it more particularly, and attend only to the 
appearances which glafs affords in certain circum- 
ftances : becaufe when the direction of the fluid, 
fr 1 1 2 caufed 
5 
