1916-17.] On some Nuclei of Cloudy Condensation. 221 
of the number of expansions at 8 per cent, and the number at 2 per cent, 
required to clear them out. It is, of course, only a rough indication, as 
the numbers brought down in the different showers will probably vary 
a good deal. 
The sample of air being now free of all the large particles — that is, those 
capable of becoming nuclei with a 2 per cent, expansion, — w T e next proceed to 
test for any smaller particles that may be in the air. For this purpose the 
slide on the expander is now moved to, say, 4 per cent., when the handle of 
the expander is quickly drawn to the stop and the test-flask examined to 
see if any cloud particles are formed. If a shower falls, the treatment is 
repeated till condensation ceases, the number of showers observed being 
entered in the notebook. When the showers stop, the slide on the 
expander is moved up to, say, 6 per cent., and the process is repeated 
till the showers stop, the result being entered in the notebook. Higher 
and higher expansions are continued till all condensation ceases, showing 
that all nuclei, large and small, have been brought down. 
Table I. — Nuclei from Different Sources. 
-4-^ 
tn 
Density 
Number of Showers at 
o> 
E h 
Source of 
of First 
Condensa- 
Higher Expansions. 
Remarks. 
o 
Nuclei. 
16 
o 
tion at 
4 
6 
8 
10 
12 
14 
18 
fc 
2 p.c. 
p.c. 
p.c. 
p.c. 
p.c. 
p.c. 
p.c. 
p.c. 
p.c. 
1 
Outside air 
Dense 
9 
3 
1 
2 
55 
5? 
3 
2 
3 
Room air 
Very dense 
0 
4 
Electricity 
0 
1 
• . . 
• . . 
1 
• . . 
• . . 
1 
i 
4 
Electrophorus, two elec- 
trodes. 
5 
55 
0 
0 
... 
i 
4 
1 
1 
One electrode. 
6 
55 
Slight 
10 
7 
4 
1 
2 
1 
10 
Small spark. 
7 
55 
Very dense 
1 
• . . 
With condenser and spark. 
8 
Sun and S0 2 
5 
2 
i 
4 
. . . 
Short exposure. 
9 
5) 
Dense fog 
0 
. . . 
Longer exposure. 
10 
El and S0 2 
... 
3 
6 
1 
... 
Very little S0 2 . 
11 
5 J 
Dense fog 
0 
... 
... 
... 
More S0 2 added. 
The results of the first tests with outside air and with the air in the 
room where gas was burning are entered in Table I. The outside air was 
always found to contain some small nuclei requiring more than a 2 percent, 
expansion to make them active. Their number and size were variable. 
The table contains the results of two tests of outside air. In the first 
column is entered the number of the test ; in the second, the source from 
which the air was drawn ; in the third, the density of the first con- 
densation at 2 per cent, expansion. In the next series of columns are 
entered the numbers of showers given at the different expansions above 
