Rayleigh's ‘Radium Clock.’

Abstract

Two years ago a ‘radium clock’ was constructed for the Chicago Radium Institute similar to the original one described by Strutt (Phil. Mag., 1903). Three milligrams of radium sulphate, contained in a thin-walled glass tube, was used as the activating source. A platinum wire sealed into the tube made metallic connexion with the gold leaf support. The containing tube was of pyrex glass and was fitted with a ground joint at the top to allow the removal and adjustment of the parts. A carefully cleaned glass rod was sealed into the upper half of the ground joint which served as a support for the source and gold leaves and provided sufficient insulation for the operation of the clock. A chemical deposit of silver made the inner walls of the tube conducting, with the exception of a small opening left for observation. Due to this silver coating, the tube was not baked out but was exhausted with mercury diffusion pumps.