Letter from [Joseph John] Thomson, FRS, Golmleigh, West Road, Cambridge, to James Mackenzie Davidson Writes of his enquiries into the production of cathode rays outside vacuum tubes. Notes that while there is no great difficulty in making aluminium windows to allow the rays to get through, the pencil of rays which comes through is very diffuse. Disscuses the advantages of ebonite tubes in relation to this. 23 November 1913