130 Mr Rudge, On the Electrification given 
The exploring electrode was made in many forms such as small _ 
cylinders, discs of metal or wire gauze, or plain wires; a fine 
needle seemed however to be the most satisfactory form to use. 
This needle was attached to a rod of ebonite and mounted upon — 
the carriage of a travelling microscope, so that it might be moved 
in two directions at right angles and its position noted. The 
arrangement is shown in fig. 1. The tube projected about 20 cm. 
from the boiler, the orifice from which the steam escaped was — 
1mm. in diameter. The electroscope /, was connected to the 
needle and served to indicate the charge in the steam jet; whilst 
H, gave the charge at the same time upon the air. 
In starting an observation the needle was arranged at some 
ny 
distance from the end of the tube and the charges on the electro- _ 
scopes noted. By moving the screw the needle could be moved 
nearer or farther from the orifice from which the steam was 
escaping and any variations in the charge observed. If the 
Fig. 1. The steam escapes from the small orifice in the tube attached to the 
boiler. The charge upon the air is indicated by the radium collector R, and 
electroscope EH, and that upon the point by the electroscope #,. Hy, and Hz 
are at some distance, 2—3 metres, from the boiler. 
distance of the needle was a few centimetres from the orifice 
from which the steam was escaping a positive charge was shown 
by £, and also by #, but on gradually lessening the distance 
by turning the microscope screw the charge shown by &, 
diminished in strength, and then changed sign, whilst that shown 
by E, remained always positive. The point at which the inversion 
of sign occurred was fairly sharply defined, as is shown 1n Table II. 
The results there shown were obtained with an orifice 1 mm. in 
diameter, and a pressure of steam about 60cm. above that of the 
atmosphere. 
