d'une charge punctiforme. 285 



c dt "^ rk " ^ ' c dt^ ri- 

 grad f =— r.']'- ^ 

 rot a -= [t)V|] 



c = — D -h r,^^ : f) = [t)r,] = [r,e] 

 [e()] = r, i'y — br'J.) + (']> — Ur) 



"^ ~ ?''^A-=* ' c rk' c 



u \ e \ 



' c c rk- c 



\ * cl rk^ \r c', 



c rk^ c 



