1910-11.] On some Nuclei of Cloudy Condensation. 
495 
Hazing Effect of Sun-formed Nuclei. 
Some experiments were made to ascertain what was the nature of these 
sunshine nuclei. The observations made in nature show that they have 
hut little hazing effect. Air was observed at Kingairloch which was very 
clear yet had a great number of these nuclei. To explain this non -hazing 
effect of these nuclei three suppositions may be advanced. First, that they 
are not in the form of solid or liquid nuclei while in the atmosphere, but are 
in the gaseous state, and only form nuclei when mixed with air saturated 
with water vapour ; second, that they may be extremely small, so small as not 
to affect the transparency of the air ; or, third, that the number produced by 
the sun may not be sufficient to affect the transparency. It is true the 
number per c.c. was occasionally very high, but the depth of the stream of 
air charged with them can only be a few feet, and this stream when mixed 
with the higher air will not have much effect, and it will take long to get 
to the upper air in which the haze observations are made. That this stream 
of nuclei-laden air is very thin is probable from the fact that the nuclei are 
formed on the ground, and the wind cannot mix them up with the higher 
air till they have passed some distance over irregular surfaces. But that 
this mixing quickly takes place after the air has travelled over the rough 
ground on shore is shown by the observations taken at Appin on 10th 
July, the day referred to at the beginning of this communication, when the 
number of particles was from 50,000 to 150,000 per c.c. on the shore, while 
the ordinary records for that day already given * show that the number 
observed a few hundred yards back from the shore was only about 3000. 
The number was thus reduced to about one-thirtieth of what it was, showing 
that the nuclei-laden stream near the shore must have been thin to undergo 
so great a dilution in so short a flow. 
Experiments were made to test the nature of some of these sun-made 
nuclei. The method of testing was to see if they would pass through a 
filter. If they did, then we might conclude they were gases. Unfortunately, 
the converse is not true, namely, that if they do not pass through they are 
not gases, because all filters stop gases more or less, and it is only if there 
is enough of the gas to saturate the filter that any gets through. Tried by 
this test, only slight indications of the passage of some of them were obtained, 
the greater part of the condensation being stopped. The product of the 
ozone tube passed freely through after a time, but in that case we were 
dealing with a large quantity, and the first part of it was even then entirely 
stopped by the filter. 
* Proc. Roy. Soc. Edin vol. xxx., part vii., No. 39. 
