A-CC0Umr.JOFaTHEJtMDMETt:RS. filJ 



make out fo my fatisfaction, how the fpirit, by attracting glafs, 

 can prevent the other index from- ever rifmg out of its furface. 

 Perhaps this thing may be already explained in elementary 

 books ; but whether it be or no, lam i'ure that an account in 

 your clear and popular way cannot be thought fuperfluous. 



t c or 11 JMiPtoAaKi* •*** *«*k»1»»3 



I am relpectfully, ..; .., v 



OIT, 



Your, obliged 



F. A. 



REPLY.—W. N. 



urn 



•nt 



When the furface of the column of fpirit is viewed by a Explanation, 

 magnifier, it is (een to have the form of a concave hemifphere, . thefmall S^ 



° r . • piece were pro- 



which '(hews that the h'quid is' attracted by the glafs. The truded beyond 



glafs in that place is corifeduently attracted in the oppofite ^ fpirlt> the 

 i- *>i i r i • . i • i • /■ it- fluid would hang 



direction by a force equal to that which is to employed in to it and draw it 



maintaining that concave figure; and if it were at liberty to baclc » 



move, it would be drawn back till the flat furface Was re- 



ftored. Let us fuppofe a fmall flick or piece of glafs to be 



Joofe within the tube, and to protrude into the vacant fpace 



beyond the furface of the alcohol. The fluid will be attracted 



alfo by this glafs, and form a concave between its furface and 



that of the bore of the tube. But the fmall interior piece 



being quite at liberty to move, will be drawn towards the 



fpirit fo long as the attractive force poffeffes any activity ; that 



is, fo long as any additional fluid hangs round the glafs ; or in 



other words, until the end of the flick of glafs is even with 



the furface. Whence it is feen that the fmall piece of glafs 



will be refitted, in any action that may tend to protrude it 



beyond the furface of the fluid ; and if this refinance begreater 



than the force required to Aide it along in the tube (as in fact 



it is), the piece mult be Aided along as the alcohol contracts ; 



fo as always to keep the piece within the fluid. And this 



fact is accordingly obferved to take place. 



Abftraft 



