708 Proceedings of Royal Society of Edinburgh. [sess. 
It is shown by Mr Aitken’s dust-counters that the numbers of 
dust particles in the atmosphere are subject to extreme variation — 
the numbers varying from almost nil at the Ben Nevis Observatory 
in certain types of weather to 100,000 in a cubic inch. Under 
Mr Aitken’s direction the numbers of dust particles have been 
for some years observed regularly at this Observatory, and the 
importance of the results cannot be over-estimated in their bear- 
ings on the cyclones and anti-cyclones of North-Western Europe. 
This great discovery is leading the way in other important inquiries 
in meteorology, of which may be mentioned the formation of clear 
spaces in dusty air ( Transactions , vol. xxxii. p. 239) in connection 
with the sudden and frequent hygrometric changes in the atmos- 
phere, as shown by continuously self-recording hygrometers. 
His series of papers in the Proceedings on “ Thermometer 
Screens ” is a valuable contribution to practical meteorology. 
Meteorologists are enabled by the methods proposed to make the 
closest approximation yet possible to an observation of the true 
temperature of the air. 
Another very suggestive paper is the “Note on Hoar Frost” 
( Proceedings , vol. xiv. p. 121), in which such extraordinary accre- 
tions of ice as occur so frequently at the Ben Nevis Observatory on 
the windward side of posts and other objects exposed in the wind 
during certain types of weather are explained. 
The splendid researches, thus briefly alluded to, form only a 
small fraction of Mr Aitken’s work, — which includes valuable con- 
tributions to the physical explanation of dew ; the effects of oil on 
stormy seas ; of the moon on weather • sunsets ; chromomictors ; 
solar radiation ; breath figures, etc. etc. 
Professor James Edward Talmage and Mr Charles Tweedie 
were admitted Fellows of the Society. 
At the request of the Council , the Astronomer Royal for 
Scotland gave an Address on “The Total Solar Eclipse of 21st 
January 1898, with some account of Solar Observations generally.” 
( With illustrative Photographs.) 
The following Communications were then read : — 
1. On a new Species of Cephalaspis found by the Geological Survey of 
Scotland in the Old Red Sandstone of Oban. By Dr R. H. Traquair, 
F.R.S. T vans., xxxix. pp. 591-593. 
