496 Proceedings of the Royal Society of Edinburgh. [Sess. 
These experiments help us but little to an understanding of the con- 
ditions in nature, as we are not certain whether the nuclei formed by the 
sun on the foreshores are the product of any of the substances experimented 
with, and the study of the salt, iodine, and hydrochloric acid only suggests 
certain ways in which the sun may act as a nucleus-producer. The Kin- 
gairloch observations show that these sun-formed nuclei do not appear in 
the early morning though the sun be shining. It is generally about ten 
o’clock before they come in any numbers, but they remain till near sunset. 
This would seem to indicate that the foreshores require to be dried to a 
certain extent and heated by the sun, and this seems to support the supposi- 
tion that the nuclei may be due to the decomposition of the salt on the 
heated seaweed over which is passing damp air. 
Kingairloch Observations. 
Before concluding, I should like to call attention to the bearing of the 
results given in this paper on the conclusions previously arrived at. In a 
paper communicated to this Society on 19th February 1894 there is given a 
summary of the dust observations previous to that date. It is there shown 
that the haze in the atmosphere depends on the number of particles in the 
air and on the relative humidity. The higher the humidity, the smaller 
the number of particles required to produce a certain thickness of haze. It 
is shown that for the same humidity the transparency is inversely pro- 
portional to the number of dust particles in the air at the time. So that if 
the number of particles per c.c. be doubled, the limit of visibility is halved. 
The result of this is that if we multiply the number of particles by the 
limit of visibility in miles we get a constant for the wet-bulb depression 
at the time. By means of this constant, called C in the paper referred to, 
we can compare the different observations at the same and at different wet- 
bulb depressions. 
In the paper above referred to are given tables in which are shown for 
the different places of observation the number of particles and the limit 
of visibility in miles at the different wet-bulb depressions ; also the value 
of the constant C for each observation, as well as the mean value of all the 
observations taken at the same wet-bulb depression. In Table II. is here 
reproduced Table XXII. from the above paper. In this table are entered the 
names of the places where the observations were made, and in the three 
columns for the different wet-bulb depressions at the time the observations 
were made are entered the mean values of the constants of all the observa- 
tions. As these numbers are obtained by multiplying the limit of visibility 
in miles by the number of particles per c.c., it follows that if we multiply 
