479 
1910-11.] On some Nuclei of Cloudy Condensation. 
The matter remained a mystery until last summer, when I was observing 
at Appin in connection with the work communicated to this Society on 
18 th July last. On the last day of my visit to Appin I was fortunate in 
stumbling on a clue to the cause of these abnormally high readings. There 
are a number of dwellings at Appin, and it was sometimes difficult to get 
clear of the products of their fires, as shown by the highness and the want 
of uniformity in the numbers of particles in each of the ten tests usually 
made to get a fair mean value. Generally it was possible to get out of 
these pollutions by moving cross-wind ways, but on this occasion it was 
not found possible ; showing that the nuclei were coming from some other 
source. And further, from the direction of the wind, it was evident there 
were no houses near which could have polluted the air; nor were there 
any steamers within sight on the loch to account for the high numbers. 
An investigation was at once begun as to the source of these nuclei. 
There did not seem to be any possible source of artificial pollution, and the 
question was, where and how was nature producing them ? The answer 
to this question was likely to explain the high readings at Kingairloch, as 
they were produced under similar conditions, namely, bright sunshine 
and clear air. 
In this investigation the dust-counter was used just as a dog uses its 
nose when quartering its ground in searching for game. The dog, after find- 
ing the scent, runs up the wind in the line of the scent towards the quarry ; 
with the dust-counter we usually go cross wind to get out of the scent, 
but in this case it was used to run up the scent and point to the source of 
the sun-made nuclei. 
The first thing to be done was to test the air cross-wind ways to try 
and strike the main stream of nuclei, but this gave no satisfactory result. 
Cross wind, the numbers varied but gave no clue, as they were everywhere 
high. On descending to the meadow near the shore, the numbers were 
found to be much higher, but a search over the meadow gave no result ; so, 
selecting the place where the numbers were highest, I walked up wind to 
seek the source of the nuclei. This led me to the shore, where the 
numbers continued to be very high. Walking still up wind over the fore- 
shore, I at last arrived at the water’s edge. On testing the air at this 
point I was at last rewarded with something definite to work on. At the 
water’s edge the numbers were much lower than back above high-water 
mark, showing that I had overrun the scent and had arrived at the purer air 
to the windward, and that therefore the source of the sun-made nuclei was 
something taking place on the foreshore behind me. The next two hours 
were spent in walking backward and forward over the foreshores, from high- 
