754 



Mr. F. H. Newman on the 



It was thought, however, that a short account of the expe- 

 riment might be of interest, although the work of the above 

 investigators is very complete. The electrons were produced 

 by raising a lime-coated platinum wire to a state of incan- 

 descence, and by means of a potential difference applied 

 between two electrodes causing these electrons to acquire 

 such a velocity that they ionized the molecules of the vapour 

 with which they collided. The positive ions thereby pro- 

 duced were attracted to a negatively charged disk which was 

 in electrical connexion with a Dolezalek electrometer. 



§ 2. Apparatus. 



The apparatus employed is shown in the figure. The plati- 

 num wire producing the electrons was placed in a hole at the 



centre of the disk B, such that it was in the same horizontal 

 plane as the lower surface of the disk. C and D were two 

 other electrodes, C being of iron wire gauze, thus enabling 

 the moving electrons to pass through. D was connected to 

 one of the pairs of quadrants of a Dolezalek electrometer, and 

 charged to a negative potential of 8 volts. The other pair of 

 quadrants were charged and kept in electrical contact with 

 the same potential. In order to keep the electrometer under 

 control it was placed in a box lined with tinfoil — the latter 

 being connected to earth. E was a discharge-tube indicating 

 the gases present and their pressure. The vessel itself was 

 of glass and contained a pool of mercury. As glass conducts 

 considerably when heated, it was necessary to take special 

 precautions in the insulation of the electrode D, which was 

 accordingly introduced into the vessel by means of a quartz 

 tube, and the disk itself was prevented from coining into 

 contact with the glass sides by small beads of quartz inserted 

 round its circumference. It maybe mentioned that B and C 



