( r>io ) 



/9"„, A |>;nr in cnnimoji \\ hicli \ac sliall iiidicilc hy l*\,,. /^",„ and 

 also \)\ 7",„, 7"'-,;. ( )]i ilio coiiiicctijiü' line /' ot' lliese [toijils ure 

 also the points 7'\„, 7"',,,, 7""^,,. wiiicli can Jnst as well he indicated 

 Ity the synilxijs 7"",5,, P' -^i,. ]*" ■^^■. conse(|ne]itly r hcai'S also the pair 



which /'^,. and /•',„ iiave in coninion M)esides />',.. //'J. 



The iinohilions /-'^^ and /%,. Iia\(' hun- pair> in coninion anionu- 

 AA'hich ihc pair JJ' ,,, JJ'\: the reniainin.u' three lic on three coninion 



tan.uents of </^,, and «/r,^ : the foiirtli coninion taiiücnt i^ evidently the 

 ahove mentioned i'ioht line i\ 



5. Lei Si-i he Ihe point of intersection of (''' with the riiiht line 

 Dl ])i . From the preceding ensues thai tlic lines -Si.^ -Sg^, 'S\,, X_,^ and 

 ''^'i^ '^23 delermine with the lines /., /,, loiiclujig the conics 1>\.^:,^;, 



^'123 1« ill ^^5- IK. '■! collie </'.„ tonciiinu' C'" lixc times. 



2 3 



Besides the lifteen jiaii-s of fiindamenlal inxoliitions Fki , Fid we 

 sfill notice the H central fundamental ciihic in\'olntions intersected 

 Ity the ])encils of rays with vertices JJi-. Vnv tlie>e the directing 

 curve (heilig hir a general 7"' of class 8) breaks up into the vertex 

 to he counted three times and the remaining live point> ]). 



Physics. — ''Tlu' determination of the pre.s.iure with a closed air- 

 fiianometer. By C. H. Brixkmvn. (Cominnnicated hy Prof, J. D. 

 VAN Di'Ji Waals). 



For the determination of the presMire \vitli the aid of closed 

 airmanometers we may avail ourselves of Amagat's Avellkuowu deter- 

 tninations of isotherms^). In tahle 5 aud JO n.c.) four air isotherms 

 are given for pressures ranging between 1(10 a 8()()() ats. For pres- 

 sures, smaller than KM) ats. we ha\e to extrapolate. 1 have thoimht 

 that I could justly avail myself for this extrapolation of the eipiation 

 of slate of VAN dek Waals: 



, ^ (1 +a)(l-A, )(l + at) _ a 

 V — It ?•' 



if J) is taken here as a function of the \(ilnin(>. 



The variability of // \vith the volume has been interpreted in two 

 ways: 1'. as a (piasi change in consecpience of the partial coinci- 



1) Mémoires sur I'elasticite et la dilatahilili'' drs tliiid^s jusqu'aux tres hautes 

 piessioiis. Ann. Gh. Plus. Ge s. 1893. 



