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Physics. — "''(hl llic ('iiniHlii'iiim Inlii^ri'ii a snl'it} IhhIi/ iiikI <i /////d 

 nhdsf, csjti'cuilhl in llic iit'itilihou rluHjd i>f' llic ci-ilicdl shih'." 



[W pai't). \\\ Prol'. J. 1). VAN DKK Waals. 



Ill iiiv loiMiicr coiiiiiiiniicalioii llic ciirxc of llic llircc-|(|i;is('-c(|iiili- 

 l)i'iiiiiis was considered as llic section ol" Iwo i //, 7'. ./■) snrrace^. \ i/,. 

 llial ol" llic Iwo lliiid cijiiiliUrinnis, and lliat of llic c(|inlil)riiiius 

 hclwccii solid and llnid phases. Foi- anllii'a((niiioiic and cllicr lliis 

 soclioii consists of Iwo sepai'ale paiis, one on llic side ol' llic ellicr. and 

 the ollici- on llic si(l(> of ilic anllira(|niiionc. For \aliics of ,r raii,iiiii,i!,' 

 Uetwccii Iwo delijiilc xalncs, llic Iwo nicnlioiied sniTaccs do not 

 iiitersecl. These \alnes of ,r ai'c nearer lo each oilier lliaii llioso of 

 the critical phases cocxistinu' with the solid hodv. 1 liax'c in<licale(l 

 thciu in niv preceding' coininimicalioii as a niaxiinimi \aliic oi" a 

 luiniunini \alne of ./•. We nii<i,hl also distinunish tliciu hv w |■iIi]i,^• 

 ./',.• JIJhI .I'a t"i" Ihcm. Then .i^ is the smallest \alne of ,/■ for which 

 the two ( /), 1\ ■!■) surfaces lia\e still a ])oiiit in coinino]i on the side 

 of the ether. In the same \\av ,/„ is the lai'gcst \aliie of ./' foi' the 

 coriespoiidiiiii' point on the siik' of the aiitlira(pnnone. 



In order to examine closer the pai'licnlaritics which take place in 

 the points in ^^ liich the l\\o ( />, 7', .r) surfaces separate, it is iisefid, 

 to di'aw Itesides the /y, ,/■ sections of the precedinu' coinmiinicalioii, 

 also the sections of the two ( ƒ>, 7', ,r) surtaces for constant \alne 

 of ,/•. x\s the particidai'ilics in the points, at >vhich the Iwo surfaces 

 se[)arale, dill'cr on the side of the clhci" from those on the sid(^ of 

 the aiithra(pnnone, I liaxi' drawn the two following' liunrcs, fii;-. 7 

 represenlinu' the particularities on the ctlici' side, and liti'. 'S those 

 on the other side. 



In tiu'. 7 we see first ti-aced the wcll-knowii loop for the Huid 

 e({uililiriums, (('out. 11, p. KkSi. It is lak'cii foi' the \alue of ,r 

 uf the critical phase on tlu^ side of the ether, which coexists with 

 the .solid body. Let /* represent that critical phase and so lie the 

 plaitpoint. This jilailpoinl has heen chosen left of llie maximum 

 |)ressure. in accordance with the circiimslaiicc thai the plaitpoint 

 pressure will most likclv increase with Hie leniperalure. In this 

 |)()inl the two />. T.r) surfaces would liaxc a common tan.ii'cnt, 

 which woiihl he normal l(» ihe plane of the liuiire. and so does 

 nol appear in llie liunre L!.i\('ii. This c(minion lamicnl is of c(mrse 

 a lan.Licnt to ihe section of the I wo surfaces, which section is projected 

 on the plane of the liuure as the ( y>, 7') cur\-e hn- the ihi'ce-phase- 

 etpiililiriimis. .\s in ihis (ƒ^7') curx'c the \aliie of p increases with 

 7'. il ma\' he traced in two wa\s; either as has been done in the 



