P {zrddy - (ffdj) - Qfa rddx-dr(lx)-{- r {d?dj - dQ^dx) zro 

 cx qiiii colligitur 



djr :Q,ddx — i?d dy — d?d'')-t-dO_4 x 



r Q<Xx — fdy^ > 



fiiie commodiiis 



A_r z(lddx-\-dQdx — -.Tdiy — jP fTy 



r 0.1*^ — f<iy » 



qiiae eadem aeqiiatio etiam ex fecunda formula /Q^ds 

 eJicitur, Eodcm igitur modo ex reliquis obtincbiiur 



d p jRddy- i-iRd y — 2Q , ddz — d Q_d z 



"jr K d > — Q,d z » 



dj jPddz-t-dP az — zRddx — dRdx 



^ " Pdz — Rdx 



Qnoniam autcm vnica tantum aequatio, praeter Inucntam 

 P^-t-Q^-HRr-o, ad aeqiiilibrium dcterminandum re- 

 quiritur , ncccfle eft has tres aequationes modo inucntas ad 

 \nicam reduci ptJlTe, fi quidcm iii fubfidium vocetur for- 

 roula p d x ~\- q dy ^ r d z — o. 



f 23. Quo haec darius perfpiciantur in cakulum 

 introducamus tcnfionem fili T, quandoquidcm pcr eam ter- 

 nas nortras formulas intcgralcs concinnc expreffas inucni- 

 mus: erat autem 



Vnde differentiando clicimus 



p_ _d-X\x—lddx . r\ dTdy — T^rf \. -O dldr—TAi z. 



* — df^ J V.— dji ' ^ — ds» "» 



vnde colligimus pro prima noftra aequatione 



(^dx-?dy-Trds et Q^ddx-V ddy — - i.r d sdt\ 

 dcindc vcro hinc erit porro 



^p— _ ddTJx_-.dTddx— Td-x ^ JQ __ ddT a.^ — ; dTdd;r-Td^3> . 



vndc 



