AbstractsPhysics

The light sources chosen for special study were arc tubes through which a condenser was discharged. The discharge was initiated by an external control electrode. Tubes were made of Pyrex or quartz and had cathodes of mercury or nickel. Work was first done with mercury tubes at low pressures. Later, tubes were made having nickel cathodes and filled with argon. Tubes were tested to see at what voltage they discharged spontaneously one hence if they could be used with the 20,000 V power supply available. A 2500 V power supply was obtained for use with low voltage tubes. An integrating light output meter was constructed for measuring the light output of the tubes. Using this meter relative readings of the light output of tubes used under different conditions were obtained. Fine fibres were set up and illuminated in a manner reproducing conditions of cloud tracks in an expansion chamber. The fibres were then photographed to get an indication of whether the light sources would be practically useful, and of their effects on a photographic emulsion. Emperimental results indicate that low pressure arc tubes are not a practical means of obtaining high voltage operation, Mercury cathodes were shown to be little better than nickel ones in all types of tubes studied; and have the disadvantage of becoming dirty. In gas filled tubes having pressures of the order of a few centimeters of mercury, the light output is greatest when the bore of the tube is small.[...]