A method is described for obtaining a velocity spectrum of a metallic vapor. The apparatus consists of a number of coaxial discs with radial slots which rotate at high speed and serve as a velocity filter for the molecules. The velocity can be measured directly somewhat as in the Fizeau experiment. The apparatus has been used to measure the distribution law of molecular velocities in cadmium vapor and it is found to agree with that of Maxwell within experimental error.

• Received 28 September 1927

DOI:https://doi.org/10.1103/PhysRev.30.931