76 
Proceedings of Royal Society of Edinburgh. [sess. 
On some Observations made without a Dust Counter on 
the Hazing Effect of Atmospheric Dust. By John 
Aitken, Esq., F.R.S. (With a Plate.) 
(Read January 30, 1893.) 
There was corsiderable difficulty in selecting a proper title for 
this paper. It may appear to some, after reading it, that a shorter 
and better title would have been, “On the Hazing Effects of 
Smoke.” But as smoke particles generally reflect a reddish-brown 
light, they do not therefore seem to be the cause of the whitish 
light which we call haze ; and further, smoke particles generally 
condense into little masses of such a size that they fall to the 
ground before they are carried to any great distance. It was 
thought that as this paper is a continuation of previous work, and 
is founded on results already communicated to this Society, it would 
be better to keep to the use of the same terms, and as usual, under 
the name of “ dust particles,” to include all the solid and liquid 
products of combustion, of whatever size or colour they may be. 
Although the results obtained in the investigation have been 
arrived at without the use of a dust counter, yet the work pre- 
viously done by that instrument has been made use of. Indeed, 
without a knowledge of the relations which the dust counter has 
shown to exist between the .thickness of a haze and the dust and 
humidity existing at the time, this investigation would not have been 
possible. The results contained in this paper prove that, without 
counting the number of dust particles, we can show that the trans- 
parency of the atmosphere is very much destroyed by the impurities 
communicated to it while passing over the inhabited areas of the 
country. As we know, from observations made with the dust 
counter, that the number of dust particles is great in air coming from 
these areas, and that the transparency of the atmosphere varies with 
the amount of dust in it, it may be assumed that this thickness is 
due to the dusty impurity communicated to the air by the products 
of combustion and other causes. 
Shortly after beginning the observation of the number of dust 
particles in the atmosphere, I was discussing with a friend, who 
