@Book{pp,
  author ={W.~Panofsky and M.~Phillips},
  title ={Classical Electricity and Magnetism},
  publisher ={Addison-Wesley},
  address ={New York},
  year={1965},
}
@Book{helix,
  author ={W.~Smythe},
  title ={Static and Dynamic Electricity, pp.~276},
  publisher ={McGraw-Hill Book Co.},
  address ={New York},
  year={1950},
}		  
@Book{bleta,
  author ={I.S.~Gradshteyn and I.~Ryzhik},
  title ={Tables of integrals, Series and Products, pp. 712},
  publisher ={Academic Press},
  address ={New York},
  year={1980},
}