A Direct Measurement of Molecular Velocities

A method is described for the direct measurement of the velocities of neutral molecules. The molecules condense on a glass plate fastened to a cylinder which rotates at a high speed, 241 r.p.s. The molecules having velocities from 168 m/sec to 673 m/sec were spread over a band 3 cm wide. A stream of bismuth molecules is studied and the vapor found to be composed of 40 percent Bi and 60 percent Bi₂ at a temperature of 851^∘{}C.