194 Proceedings of Royal Society of Edinburgh. [sess. 
to be troublesome, frequent polishings being required to keep it in 
good working order. Other metals less easily tarnished than silver 
have been tried, but with no very satisfactory result as yet. Plati- 
num does very well, and keeps free from tarnish, but it is difficult to 
give it a very perfect polish. Platinoid, which owing to its property 
of keeping bright in impure air, promised to bridge this difficulty, 
but on trial it was found to be most unsuitable, as it soon got spotted 
all over. The little drops of rain seemed to eat into it, and not 
more than one test could be made without repolishing. Blackened 
glass had also been tried again, in the hope it might be got to work 
well, as it could be much more easily kept in order than silver. 
Unfortunately it does not act very satisfactorily, owing to the tendency 
of glass to get dewed. As this dewing is not easily observed in the 
instrument, it gives rise to difficulties, as the drops are not visible on 
the dewed surface. And when the surface is kept undewed the 
drops tend to evaporate, and the number counted is rather low. 
Further, owing to less light being reflected by the glass surface than 
by the silver, the drops are not so brilliantly illuminated and there- 
fore not so easily counted. On the other hand, silver has been 
found to require very little attention in pure air. The stage has 
frequently been used for weeks without once being taken out of 
the receiver for polishing, and it worked quite satisfactorily at the 
end of the time. 
The first place on the Continent at which regular observations 
were made with the dust-counter was Hyeres in the south of 
France. Hy&res is a small town on the shores of the Mediterranean, 
and is the westmost of the health resorts on the French Riviera. 
It is situated on the southern slopes of a hill, at rather more than 
two miles from the sea. A flat fertile plain extends for some dis- 
tance from the town seawards, and at some places the shore is 
fringed by marshy lands. Observations were occasionally made at an 
open window of the hotel, which is situated just on the outskirts of 
the town. The observations of most value, however, were made on 
the top of Finouillet, a hill situated at about two miles to the north 
of west of Hyeres. Finouillet has an elevation of slightly less than 
1000 feet. 
Along with this paper is given a table showing the results obtained 
at this situation, and also at a number of other places on the Conti- 
