THE THICKNESS OF M31

This Letter gives the results of a determination of the thickness and the optimum inclination (i.e., the angle between the galactic plane an d the tangent plane) of M31, which are 1.01 kpc and 77.degrees 5, resp ectively. The method for determining the thickness of spiral galaxies is proposed by Peng, on the basis of the solution of Poisson's equatio n for a logarithmic disturbance of density. The optimum inclination is determined by assuming that the pattern of spiral structure is a loga rithmic spiral form. We find that the thickness and optimum inclinatio n of M31 are in good agreement with previously published results.