  In 1996, J. Pendry, an English theoretical physicist put forward an idea
about the dependence of the effective electron mass on the magnetic field,
while interpreting the dielectric response of metal wire mesh structures. The
idea was based on the well-known relation between the kinematic and canonical
momenta of a charged particle moving in the magnetic field. In this paper,
proceeding from the universal character of that relation, the applicability of
Pendry's effective electron mass $m_{\text{eff}}$ to the problem of electrons
in metal mesh structures, as well as to a wide class of problems for charges
moving in the magnetic field, has been examined. The general properties of
$m_{\text{eff}}$ following directly from its definition were found, and an
analogy between the effective electron mass $m_{\text{eff}}$ and $m^{\ast}$
known in the solid-state theory was established. A physical interpretation of
$m_{\text{eff}}$ was proposed. It was demonstrated in several examples that,
despite the generality of the defining relation for the effective mass
$m_{\text{eff}}$, the use of $m_{\text{eff}}$ beyond the problem of the
dielectric response of metal wire mesh structures leads to incorrect results.
