some Experiments with Rontgen's JRai/s. 163 



of a number of iron wires spread out from a centre, and the 

 antikathode, which also served as anode, was a spade-shaped 

 piece of iron or platinum. Another form of which many 

 bulbs were tried was provided with an external kathode of 

 foil, and an internal anode projecting to about the centre, 

 terminating in a small spade of platinum-foil as antikathode 

 (fig. 2) . This also gave good results, but was liable to be pierced 



Ffc. 2. 



at high stages of exhaustion. With this form various experi- 

 ments were tried as to the influence of the material of the 

 antikathodic surface. Glass was found to work quite well, 

 but to be more troublesome than metal. A phosphorescent 

 enamel made by fusing together two parts of a soft lead-glass 

 with one part of Balmain's luminous paint was also tried. 

 The result of these experiments was to show that, contrary to 

 the opinion then current that the presence of much phospho- 

 rescence or fluorescence was promotive of the production of 

 the #-rays, the #-rays were most freely emitted when the 

 conditions were such as to waste as little as possible of their 

 energy in internal fluorescent effects : that in fact a metal 

 surface was preferable to a surface of glass, enamel, or por- 

 celain for receiving the impact of the kathodic discharge. 



At about this time Mr. Jackson's perfected form of focus- 

 tube was brought out, a tube which for photographic purposes 

 was found superior to any other form, and has not yet been 

 surpassed. 



3. Observing in some of these experiments that the metal 

 spade used as antikathode became red-hot, a special tube was 

 constructed for me by Mr. Gardiner to test the question 

 * whether the high temperature of the antikathode was, or was 

 not, prejudicial to the emission of #-rays. This special tube 

 (fig. 3) was furnished with an antikathode of platinum-foil 

 mounted so that while serving both as antikathode and as 

 anode it could be heated by passing a current through it 

 from an auxiliary battery. Observing the activity of the 

 tube by means of a luminescent screen of platinocyanide of 

 potassium, it was found that the heating of the antikathode, 

 "so far from being disadvantageous, decidedly promoted the 



