by Cathode and Canal Rays to Exciting Current. 183 
area. From this I concluded that nets of the first kind 
absorbed 35°33 per cent. of the rays, and those of. the second 
kind 51°6 per cent. In the tube, fig. 2, the net-electrodes 
were soldered to springy brass rings, 8 mms. wide, which 
pressed firmly against the walls of the tube. The distance 
apart of the rings amounted to 2°9 ems. By means of these 
tubes, the values given in Tables I. to VIII. were obtained. 
The collecting electrode consisted of a disk of aluminium 
which fitted the tube exactly. The thick iron connecting 
wire passed through the mercury of the barometer. Thus 
the collecting electrode could be pushed up and down inside 
the barometer-tube, and moved up to a distance of 11 cms. 
away from the nearest net-electrode. The amount of this 
displacement could be read off on a scale running along the 
tube. In the case of the electrode nearest the collecting 
electrode, it was necessary to observe that the ring fitted 
the wall of the tube closely, so as to leave no open space ; 
as otherwise with a high vacuum a secondary. discharge 
passed to the collecting electrode, causing considerable dis- 
turbance and rendering observations impossible. 
For exhausting the tubes, a Tépler mercury hand-pump 
was used, and in order to save labour arrangements were 
made for a preliminary exhaustion down to a pressure of a 
few millimetres by means of a water-jet pump. 
For measuring the pressure inside the tube, a Mcleod 
precision-gauge by Rich. Miiller Uri of Brunswick was at 
first used. As, however, this gave incorrect results with 
high pressures, and as I wished to avoid the use of all greased 
stoppers in the experiments with other gases, instead of the 
pressures the potential-differences were noted in this case. 
These were measured by a Thomson electrostatic volt- 
meter by Siemens & Halske, which enabled the potential- 
differences to be read off directly on a scale extending up to 
15,000 volts. 
For the measurement of the current as well as of the rate 
at which electric charges were picked up by the collecting 
electrode, a Kohlrausch galvanometer was at first employed. 
Later on, the current was measured with a Wiedemann’s 
galvanometer, and the radiated electricity with the Kohlrausch 
instrument. 
The Kohlrausch galvanometer had a resistance of 952°8 
ohms, and a sensitiveness of 8°7x10-° ampere per scale- 
division with a scale distance of 2 metres. 
The front coil of the Wiedemann’s galvanometer had a 
resistance of 3354°7 ohms, and the back coil a resistance of 
2933 ohms. 
