This article investigates how the eigenvalues of the Neumann problem for an
elliptic operator depend on the domain in the case when the domains involved
are of class C1. We consider the Laplacian and use results developed
previously for the corresponding Lipschitz case. In contrast with the Lipschitz
case however, in the C1-case we derive an asymptotic formula for the
eigenvalues when the domains are of class C1. Moreover, as an application we
consider the case of a C1-perturbation when the reference domain is of class
C1,α.Comment: arXiv admin note: text overlap with arXiv:1310.796