244 Proceedings of the Royal Society of Edinburgh. [Sess. 
particles are found in the air of polluted districts, the results of chemical 
or heat action ; and the air containing the greatest number of particles or 
the so-called large ions is also found in polluted districts, in the centres 
of manufacturing industries where great amounts of coal are burned. In 
these areas the air has many thousands of particles per c.c , while the air 
of uncontaminated areas has only hundreds, which represent the pollution 
not got rid of, added to the natural supplies from volcanoes, meteoric 
matter, dried water spray, and other sources. 
Some of those who have investigated the large ions by means of the 
electric field seem to admit the necessity of a nucleus to which an ion is 
attached and which gives it its charge ; and, so far as can be judged from 
the results of this investigation, this seems to be correct, because in the ex- 
periments described, when nuclei are formed by chemical or heat action 
there is always something thrown off which forms a nucleus to which the 
ions naturally attach themselves. If, then, this be the correct explanation, 
why call charged particles ions ? In suspensoid colloidal solution there 
are just such similar small particles of matter ; in both cases they are in 
brownian movement, they have electric charges, and they move in an electric 
field. But the small particles in liquids are not called ions; then why 
call similar particles in gases ions ? The movement of the particles in 
air corresponds to cataphoresis in liquids, with slight differences. In 
liquids the particles have a repulsive action on each other, and do not tend 
to coagulate unless their charge be destroyed ; while in gases there seems 
to be no repulsive action, and the particles tend to come into contact and 
adhere to each other and to the sides of the vessel. In cataphoresis the 
particles adhere to the electrodes, while in air they may adhere to the 
plates or be charged by them and repelled. In this manner it seems 
possible they may become carriers of electricity from one plate to the 
other, and so come to be counted more than once. This action, however, 
can be checked, as we have shown, by the field plates being covered with 
glycerine or a similar substance. 
No doubt the electricity which escapes at high temperatures plays 
some part in the behaviour of the nuclei, as it was found that when both 
were given off at the same time the life of the particles was short, 
owing to their charges causing combination and deposition on the sides 
of the vessel. But all particles, whether electrified or not, tend to disappear. 
So far as these tests go, there has not been found anything in gases cor- 
responding to suspensoid colloidal solution in liquids. The very smallest 
particles all disappeared in a short time, owing probably to there being 
no repulsive zone surrounding the small particles in air correspond- 
