239 
1916-17.] On some Nuclei of Cloudy Condensation. 
other surface, where they get discharged and repelled back again, and 
fall when passing from rod to side, the whole action resulting in a rapid 
flocculation of the dust, some of which falls and some adheres to the 
surfaces. These flocculated threads of dust projecting radially all round 
give us a new illustration of the so-called “tubes or lines of force/’ 
The amount of electricity involved in these movements is very small 
If in place of using an electrified rod in the centre of the enclosure we insert 
a glass tube 5 mm. in diameter and run a metal wire down the inside and 
electrify the wire, the induced charge on the glass is sufficient to show all 
the phenomena. And for the same reason it makes little difference whether 
we use the induced charge on the inside of the beaker to do the work, or 
provide a good conducting and earthed surface all round, or use metal plates, 
one electrified and one earthed. 
That this process of flocculation depends on the high electric density 
accumulating on the projecting dust particles on the surface seems to be 
proved by the fact that, though we can get similar flocculation from 
smoke, from burning naphtha, and from other sources, we do not get it if 
the particles form a wet surface. Further, if we cover the electrified rod 
with glycerine there is no flocculation in the magnesia dust till enough dust 
is deposited on the rod to neutralise the wetting and levelling power of the 
glycerine ; when this is effected, little specks of dry dust appear and the 
process goes on as before. Or if we coat the inside of the beaker we 
get little flocculation, though the rod gets a much denser coating of the 
dust under these conditions. Fumes produced by hydrochloric acid and 
ammonia, also smoke from brown paper, give no flocculation either with -f- 
or — electrification, owing to the attracted particles forming a wet deposit. 
Ion Nuclei. 
We shall now return to the point raised in the first paragraph of this 
paper, namely : Are the condensation nuclei in the atmosphere dust particles, 
or, as is now generally asserted, only aggregations of ions ? On what 
foundation the latter theory has been built it is difficult to see, unless it be 
the fact that there are a great number of particles in the air which move 
in the same way as ions in an electric field, though only at about T oV o of 
the velocity. To this point reference will be made later. In the meantime 
we will try to find if there is any evidence of ions ever combining to produce 
nuclei which are active with slight degrees of supersaturation such as we 
find in the atmosphere. 
To test this point some experiments were made with the new apparatus. 
First some radium salt was put on the top of the test-flask, where it 
