Peano on definition of surface area
  In this paper we investigate the evolution of the concept of area in Peano's works, taking into account the main role played by Grassmann's geometric-vector calculus and Peano's theory on derivative of measures. Geometric (1887) and bi-vectorial (1888) Peano's approaches to surface area mark the development of this topic during the first half of the last century. In the sequel we will present some significative contributions on surface area that are inspired and/or closely related to Peano's definition. 
Gabriele H. Greco, Sonia Mazzucchi and Enrico M. Pagani
math.HO