HYDRODYNAMICS. 



465 



l!y sustineriqne potest majui pondus, quam habet pu-illa 

 Attrition a q ua particula insinuate, et ideo graduspncdicte virtutis 

 6 rf snspensivsf et adhiwionis exercetur in aqua subjecta, et 

 proinde ea reddetur aliquo pacto levis seu, minus pon- 

 -y-^ derosa, quam sit aqua collateralis^iibere premens. Et, 

 quia minima; aquar particulae porositatibus et asperita- 

 tibus internis fistula? innLxae eSiciuntur operanturque 

 ut totidem tectet, qua? flecti possunt et interne rotari, 

 necesse est, ut partes aqua?, collaterales magis compres- 

 ase a total i energia sui, ponderis vim faciant, impellen- 

 do sursum particulas aquae, quae minus oomprimuntur 

 a vectibus supra dictis ; et ideo rotando excurrere pos- 

 sunt inferius efibrmando tumorem, vel monticulum 

 aqueum, qui excurrendo lateraliter altioribus fistulz po- 

 rocitatibus insinuabitur adharrebitque et ideo denuo 

 imminuetur ejus vis compresaiva, renovabiturque cau- 

 sa ulterioris tuspensionis et proinde altius aqua intra 

 fistuUm impelletur, et sic de novo eminentioribus latcri- 

 bus adbsrrendo successive altius impelletur quousque 

 ad supremam et maximum illara altitudinem aqua per- 

 ducta, in qua equilibrium, cum aqua collateral! libere 

 premente efficiatur : tune quidcm quies ejus subse- 

 quetur nee altius elevari poterit ;" and in another 

 place, prop, clxxxviii. p. 243, he accounts for the ele- 

 vation of water to a greater height in small tubes: 

 " Quia adtuerentia et connexio aqua; parietibus inter- 

 nis canalium majorem proportionem ad molem aqu 

 insinuate ettennoe et nlentne in canaliculis subtiliasi. 

 mis habet quam in araplis et capacioribus. Extea- 

 tire quia vis adharsionis mensuratur a contactibus, et 

 ideo a superficie interna canaliculorum ; e contra re- 

 sistentia mensuratur a pondere cylindri aquei contenti 

 in iudem canaliculis ; estque nroportio cylindrorum 

 aqueorum ejusdem altitudinis uuplicata ejus rationis 

 quam habent eorum perimetri intenue, &c. I* trustee 

 quoniam facultas et energia adhsctionis minus efficax 

 est quanto magis a parietibus retnovctur." 



lytti. Similarexperiments made by our countryman Sinclair, 



tsof are described in his work, entitled An Aora et Magna 

 s*Utf. Gravilatit et Lrritalii, which was published at Rotter- 

 '' '' dam in 1669; and the experiments were repeated by 



Johannes Christopher Stunnius, who adopts the hypo- 

 thesis of Fabri, and gives a full account of the* opinion* 

 of Hooke, Boyle, Fabri, and Vostius, in the first part 

 of his Collegium Kxperimenlale live Cttriotum, which 

 was published at Nuremberg in 1 



-.-..-, The suspension of mercury in Toricellian tube*, far 

 Jwini, above the height of 28 inches, liad been observed by 

 several philosophers, ami which was owing to the at- 

 traction of cohesion, and Huygens and Wallu at- 

 tempted in vain to explain it. The former of these 

 philosophers ascribes it to the pressure of a matter more 

 thu subtle thin air, which penetrates glass, water, quick- 

 * i silver, and all other bodies, and which, added to the 

 """ pressure of the air, enables it to sustain 75 inches of 

 mercury. Wallis is equally unsuccessful in his expla- 

 nation of the phenomena, which he ascribes to a parti- 

 cular spring of the air, which does not exist in the 

 quicksilver. 



The celebrated James Bernoulli appears to have paid 

 some attention to the subject of capillary attraction. In 

 his Dinrrialia de Gravitate I'.theris, which was publish- 

 ed in ltiS3, he has endeavoured to explain the ascent of 

 water, upon the supposition that the particles of air 

 have a greater magnitude than those of water. In or- 

 der to ilo thi'. he employs the diagram in Fig. I. where 

 A BCD is a capillary tube plunged in the vessel MS, 

 and F.FGH what he calls a similar atmospherical ty- 

 vou xi. PART n. 



Its' 



MuCi. 

 't*TT 



.'. I. 



linder. He then supposes that the diameter of each OnCipUUry 

 tube will only receive a certain number of spherical 

 particles of air, viz. seven for example, so that seven 

 such particles placed in a straight line will exhaust the 

 breadth of the tubes, as shewn at i / ; but according to 

 our author, it will always happen that the Jlrtt and 

 eighth globules will rest upon the margin of the tube, 

 as shewn at AB, and therefore only the six- intermediate 

 ones will re*t upon the surface of the fluid, as seen at 

 q r. Hence it will happen that the size of the globules of 

 the air which occupies the circumference of the upper 

 orifice of the tubes, with the superincumbent rows A m, 

 B n, which rest upon that ring, will press upon the mar- 

 gin of the tubes, and will not produce the smallest 

 pressure upon the surface q r of the fluid. In the ima- 

 ginary atmospherical cylinder or tube EFGH, nothing 

 prevents the seven particles from acting freely upon 

 the surface of the fluid EF. Hence Bernoulli concludes, 

 that as the water without the tube is affected with a 

 greater pressure than the water within the tube, it must 

 n ace as inly rise to a height proportional to the excess of 

 pressure. He then concludes from this hypothesis, 

 that the water should not rise in wide tubes, as the 

 portion of air prevented from acting by the margin 

 bean a small proportion to the whole column ; th.it 

 tluids specifically lighter than water ought to rise to a 

 greater height ; that the water cannot flow over the 

 top of a capillary tube however short ; and that the 

 surface of mercury ought to stand below its level in 

 tubes of glass, if its particles are larger than those of wa- 

 ter ; (this effect he explains by Fig. 2. where the row Fi _ t 

 of particles of mercury / / is more pressed down by the 

 weight of the air above than it is by the pressure of the 

 mercury from below ;) and finally, that the surface of 

 water in capillary tubes ought to be concave, nnd that 

 of mercury convex. Bernoulli next proceeds to de- 

 duce from this hypothesis the magnitude of a globule 

 of air, and by assuming, from his own experiment*, 

 that water rises half an inch in a tube J of an inch 

 in diameter, he concludes that the magnitude of a 

 particle of air, or rather the distance between the 

 centres of two adjacent particles, is -rtfrTr f *n inch. 

 Hut having convinced himself by other means, that 

 four particles of a very subtle matter is interposed be- 

 tween every two particles of air, he determines the 

 real magnitude of a panicle of air to be virTV of an 

 inch! 



A very interesting memoir on capillary attraction was Rxprri- 

 published by M. Louis Carre in tin- .MthcAca- *'' 



demy of Sciences for 1705, entitled Experience* tur let !, ^\ 



-, ... . ._ Hum 



tuyauxt.afitlUiirei. lie ascribes the ascent ol the water to 

 its adhesion to the sides of the tubes, and to the mutu.il 

 attraction of the particles of water. The portion of 

 water contiguous to the sides of the tube is first i 

 and supported, and therefore presses less upon the lt- 

 tom of the vessel than the collateral column. He at- 

 tributes the higher elevation of the wntcr within than 

 without the tube to the mutual adhesion of the aqu< 

 particles which contributes to their elevation ; and l.r 

 says that water rise* higher in small tubes, since t IIP 

 force of adhesion is measured by the internal surface 

 of the tubes, and the resistance by the supported co- 

 lumn of fluid ; and he supposes that water has a great- 

 er contact with glass than alcohol, and therefore rises 

 higher. These views are supported by tome new and 

 curious facts : he found that when the same surface* 

 were anointed with grease, the water would not rise 

 above it* level ; that if only part of the surface w* 

 3 N 



I 



