4c4 On Capillary Aclmt, 



dence of rivulets, foclofely aflbciatecl in our minds with luxu- 

 rious eafe and the calm pleafures of padoral life. 



If we examine carefully the afcent of mercury in a fine 

 thermometer, we fhall find that it mounts by a fucceffion of 

 flarts. It feems to force itfelf along by a fort of vermicular 

 motion. Nor does the refiftance depend much on the fric- 

 tion experienced airainll the fides of the tube ; it is owing 

 chiefly to the wafte of force in imprefling a narrow thread of 

 liquid with thofe concatenated contractions and dihitations 

 indifpenfable to progreflive motion. I mult obferve that the 

 term fluidity itfelf is merely of relative impcrt. A folid body 

 may foften by infenfible gradations, and pafs into the ftate of 

 a fluid. In this new condition the particles are indifferent to 

 polition, and therefore eafily admit of intcftine motion. But 

 fuch a property implies an exteniion of the fphere of mutual 

 conne6lion. In a large fyftem of molecules, the flightefi al- 

 teration in the fitualion of each is fufficient to produce a total 

 change of arrangement. It is othcrwife when the group is 

 very limited. 1 he compofition of a fluid may thus be con- 

 ceived to refemble a long fpring, which bends eafily and 

 without rifle under the fmalleft preOTure; while the ftrufture 

 of a folid may be compared to a fliort fpring, which yields 

 only to the application of a great force, and is then liable to 

 break. But the aftion of heat extends this imaginary fpring, 

 and promotes foftnefs and fluidity. Thus a bit of fealing- 

 wax, held near the flame of a candle, gradually lofes its angles 

 and protuberances ; an evident proof that the fphere of mu- 

 tual cohefion is enlarged. And evcrv perfon mufi; have re- 

 marked that oil, during the heat of fummer, becomes appa- 

 rently thin, and flows with facility. Nay, water itfelf under- 

 goes a fimilar change of confiitution, though it eludes ordi- 

 nary obfervation. I bend a thermometer tube, with rather 

 a wide bore, into a fiplinn, which I inlert into a tumbler of 

 cold water, and count how many drops fall in a minute. I 

 then empty the tumbler, and fill it to the fame height with 

 hot water; anil, replacing the fiplion, I find that the drops, 

 which are fiill of the fame fize, fucceed each other much 

 •more rapidly than before, infomurh as fometimcs to form <a 

 continual ftreamlet. I conclude, from leveral trials, that the 

 velocity of the floA' is at lead fix times greater near the boil- 

 ing point than on the verge of congelation. But the dif- 

 ference may be rendered much more flriking in another 

 way. The height to which liquids are projrftcd is pro- 

 portional to the fquare of their initial velocity. Provide, 

 therefore, a glafs tube three or four feet long and more 

 than half an inch wide: by the help of a blow-pipe, draw 

 5 «"t 



