  We use an effective field model (transverse Ising model) to describe the
dependence on the temperature of the energy gap of some two-dimensional $(2-D)$
superconducting systems. The order parameter of this model is put in a direct
correspondence with that of the Ising model. Then, we use the exact relations
for the spontaneous magnetization of the Ising model in some $2-D$ lattices as
a means to fit the experimental results of $Bi_2Sr_2CaCu_2O_8 $ films obtained
through reflectivity measurements by Brunel et al [Phys. Rev. Lett. 66, 1346
(1991)] and the argon-annealed $Bi_2Sr_2CaCu_2O_8$ samples investigated by
Staufer et al [Phys. Rev. Lett. 68, 1069 (1992)] through Raman scattering. The
zero temperature energy gap $E_g(0)$ relations were evaluated in various $2-D$
lattices and also in the $(3-D)$ simple cubic lattice, for comparison. In the
square lattice case we obtained $E_g(0)=3.52kT_c$, coincidentally the same
number as the BCS result, and in the triangular lattice case we get
$E_g(0)=3.30kT_c$ in agreement with the experimental findings of Brunel et al.
