This Article Full Text (PDF) Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Search for Related Content

Rayleigh's "Radium Clock"

In a recent issue of Nature, Mr. J. S. Thompson, of the Armour Institute of Technology, Chicago, relates that 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 connection 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.