dy 

 dN 



d » 

 dNi 



dy 

 dNi 



d X 



dNi 



' d X 



de z - 

 on tire 



;>' = 



y = 





^ = 



DES Sciences. '421 



-dy-77 = ^4.-^7- -Y- Ni~ = P4.&C. 



-TT~d7 = ^5.-77- -»- ^^ -zr = ^5>&c- 

 = Mf:s 4- iV/':j -H Pf":s -f- -4- 6//« • : j 4- ÏT, 



-jyf'S -h Nif'is -H ..... + Uif'''.s 



dx J ' «/# * 



-^ /:J +: A^j/ :^ H- -H £/3/« " :f 



.^-^ /: j »H ;V4/ :j H- . . . . . -H i/ 4/« . : j 



dj dx-i- ■> ~r- ^^^^ : 



