134 Mr Rudge, On the Electrification given to the Air, ete. 
Origin of the charge given to the air. 
The experiments do not throw much light on the origin of ie } 
charge given to the air, but two or three possible causes suggest. 
themselves as being at least contributory. ) 
(1) The charge might be thought to be due to the condensed | 
water being atomised by the outrushing steam, but in that case, | 
reasoning by analogy with the electrification near a waterfall, it 
should be negative, whilst it is actually positive. 
(2) Friction of the escaping jet at the orifice. Undoubtedly ' 
some charge originates here if the steam passing through the/ 
orifice is not dry, but this will account for only a part of the | 
charge, for the interposition of a fine needle in the path of the | 
steam will considerably increase the charge given to the air, and | 
at the same time the colour of the steam cloud changes, the | 
strongest charges being produced when the colour appears blue; 
even a partial stoppage of the orifice which causes the cloud to | 
become blue is accompanied by an increase of the charge. 
(3) The charge may be due to the friction of the drops of | 
condensed water against each other, much in the same fashion as | 
is the charge produced during the raising of a dust-cloud*. This | 
suggestion is put forward tentatively, but the fact that the finer) 
the water particles—as shown by the colour of the cloud—the | 
stronger the charge, seems to substantiate it, for here by analogy | 
the finer the particles of dust the greater is the charge given to | 
the air. 
SUMMARY. 
(1) Some experiments have been made with steam jets which | 
show that a positive charge is given to the air by the action of the | 
jet, and this charge persists for some time after the condensation | 
of the steam. | 
(2) The charge given to the air by the steam from pure water 
is always positive, and the presence of non-volatile substances | 
dissolved in the water has no influence on the charge. | 
(3) Volatile bodies mixed with the water may give a negative ; 
charge to the air. 
(4) The charge acquired by the air appears to be due to some- 
thing which occurs in the cloud of condensed vapour. i 
(5) Positive and negative charges can be obtained cate 
taneously from the same jet, by ‘suitably placing exploring | 
electrodes in the path of the steam. | 
My thanks are due to Professor Sir J. J. Thomson for the use 
of the Cavendish Laboratory where the greater part of the work 
was carried out. 
* Roy. Soc. Proc. A. Vol. 90, 1914. 
