490 Proceedings of the Royal Society of Edinburgh. [Sess. 
Point Dischaege. 
In a previous part of this investigation it was found that the newly 
prepared hydrogen escaping from the small battery made it an active 
nucleus-producer when it met with salt and iodine. It was therefore 
thought that an electric discharge through the gases might have a similar 
effect. The first thing to be done was to ascertain the effect of the point 
discharge on normal air, and to see if the gases and vapours under test 
Fig. 2. 
in any way altered it. The apparatus used for this purpose is shown in 
fig. 2. S is an ordinary glass flask about four inches in diameter. The flask 
is fitted with a stopper, through which pass two tubes for letting the air 
in from the filter and out to the test flask ; when in use this flask takes the 
place of the flask S in fig. 1. Through the stopper also passes a glass tube 
inside of which is cemented a copper wire terminating inside the flask in a 
fine platinum point. Through the side of the flask passes, as shown, a metal 
wire for connecting the lower part of the flask with earth. An electrophorus 
or a small induction electrical machine was used for electrifying the point. 
It is long since it was shown by many investigators that the point 
discharge in dusty air rapidly clears the dust out of the air and deposits it 
