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The cooling temperatures of rectangular parallelepiped Bi arid Bi0.88Sb0.12 polycrystals with various widths W and thickness t were measured at 293 K as a function of electric current in the magnetic field B up to 2.17 T. where the magnetic field is aligned along the thickness of a sample and the current flows along its length L through the copper lead, soldered to both end whole surfaces of the cross section (W x t). Under such a configuration the temperatures were measured at both end surfaces. A thermoelement is not in contact with a heat sink. The cooling temperature at the cooled surface with increasing the magnetic field, and the rate of increase depended strongly on the cross-sectional area (W x t) of a sample, particularly in high magnetic fields. The highest cooling temperature was found to be achieved when a thermoelement has an optimum crosssectional area (fitted to its length) so that Joule heating and the thermal conduction energies become equal under the operating conditions. The cooling temperature of Bi0.88Sb0.12 with optimum dimensions increased from 3.1 K in B = 0T to 6.4 K In B = +/-2.17 T. so that it slightly exceeded a cooling temperature of 5.7 K which was obtained for a typical Bi2Te3 with a thermoelectric figure of merit of ZT = 0.87 at 298 K.