241 
1916-17.] On some Nuclei of Cloudy Condensation. 
make them active. Further, Table II shows that in the pure air of Loch 
Awe there were few requiring more than a 4 per cent, expansion, and that 
in a locality where the ions in the atmosphere were free to act, and where 
also the particles were few, thus reducing the possibility of any very 
small particles being lost in the testing. It will also be seen from the 
table that the smallest particles were found in the newly polluted air of 
inhabited districts. 
A great amount of research has been directed to the observation of the 
electricity discharged by heated bodies. The discharge of the electricity is 
supposed by some to cause the formation of the nuclei, due to heat. Now, 
in the experiments here described it has been shown that enormous quan- 
tities of nuclei are given off from all kinds of matter when heated to 
temperatures far below that at which either + or — electricity escapes — that 
is, at temperatures a long way below a visible red in a dark room. Further, 
it has been shown that, when the temperature is raised high enough to 
cause the escape of electricity, some chemical or disintegrating action is 
also at the same time taking place, as is shown by the spectroscopic 
examination of the flame after it has passed over the heated body. This 
seems to point to these two influences being the cause of the nuclei given 
off by bodies when heated. 
All particles produced by heat, and also those produced by other causes, 
are very small when the temperature is just high enough to cause some 
action, and as the temperature is increased the particles become larger; but 
it is difficult to say whether the greater size is due to the higher tempera- 
ture or to the greater crowding of the particles, since all particles have a 
tendency to grow by aggregating, while at the same time, of course, diminish- 
ing in numbers. There is also an important condition which greatly affects 
the aggregation and also the disappearance of the particles, and that is 
their electric charge. It was noticed that the nuclei produced by the 
electric discharge and those produced by heat while electricity is escaping 
are all short-lived. This will be seen from Table III. In tests 1 to 5, while 
the temperature was under red there were always plenty of very small 
particles produced by the cleansing process which were capable of an 
independent existence, as many did not aggregate though densely crowded. 
These particles were also very stable, and remained in the air for a long 
time. But when the temperature was high enough to allow of the escape 
of electricity, all the very small particles disappeared (see test No. 6). As 
already stated, it is probably the charge given by the ions in burning gas 
that causes the aggregation and disappearance of all the very small nuclei 
in room air. 
VOL. XXXVII. 
16 
