1892 - 93 .] Mr J. Aitken on Particles in Fogs and Clouds. 263 
burner, or in an open vessel without a wick, scarcely increases the 
number of condensing nuclei ; but if burned at a wick, and the flame 
shows the sodium yellow colour, the increase in nuclei is very 
great. A paraflin-lamp increases the number greatly, a candle gives 
but little increase, while a wax vesta or wooden match greatly 
increases the number. But in all these cases the particles have but 
little affinity for water vapour, and do not cause fogging unless the 
air tends to be supersaturated. The products of the combustion of 
coal from a perfectly clear fire, and from a stove burning char and 
glowing red to the top, both gave a large increase in the number of 
particles, and many of the particles had an affinity for water, causing 
fogging in moist air without supersaturation ; and if a little ammonia 
was present in the air, the fogging was very dense, and in both cases 
'persistent. 
The condition of fog particles when the temperature is below the 
freezing-point is shortly referred to. The lowest temperature at 
which observations have as yet been made with the fog-particle 
counter is 27° Fahr. after a night minimum of 24°. In this as well 
as in all the other cases the particles were unfrozen. The effect on 
certain meteorological phenomena of the particles being in a liquid 
condition at temperatures below the freezing-point is referred to. 
