In this article, natural convection and surface radiation from a vertical plate to air have been measured for vertical plates with several total emissivities of the vertical plate surface. The experiments were conducted under a variety of pressures, ranging from atmospheric pressure at 760 mmHg to a very low 4 x 10-5 mmHg. It has been demonstrated that at the lowest possible pressure, the mechanism of natural convection vanishes, and the mechanism of surface radiation predominates, depending on the value of the total emissivity.