The penetration into the sea of light of various wave-lengths as measured by emission or rectifier photo-electric cells

This subject has engaged our attention since 1924, and papers dealing with it have been published already. The object of the present communication is to describe our latest methods of work with range increased one hundredfold, to discuss some sources of error and the precautions taken to minimize them, and to present further results, comprising eight spectral regions. The latter relate to a few series made with emission cells since the publication of our last communication (Atkins and Poole 1933) and other series carried out with rectifier cells and a modified method of measurement. The Photo-eletric Cells(a) Emission Cells These were vacuum thin film caesium cells, which were used both under water and on deck with colour filters and a gas-filled sensitized potassium cell which was used for work under water at an anode potential of 12V, a value below that at which an increase in sensitivity occurs owing to ionization by collision; it thus behaved like a vacuum cell as regards the rectilinear character of its light/current relation. The corresponding measurements on deck were made with a vacuum potassium cell.