1911-12.] 
The Sun as a Fog Producer. 
203 
Electricity. 
The last of the outside influences to which I shall refer is electricity. The 
apparatus used for testing the effect of the electric discharge is the same as 
that represented in fig. 2 in the paper previously referred to,* and consists 
simply of an arrangement of wires for making a point discharge, in the flask 
S. The other arrangements are all as before. It is found that if an electric 
discharge be made in air containing S0 2 , an enormous number of nuclei are 
produced, which give a very dense fog on expansion ; and, further, many of 
the nuclei cause condensation in unsaturated air. One cannot help wondering 
to what extent the high-tension electricity now so much used for stimulating 
plant life, and high-tension transmission for other purposes, may affect the 
air in causing the formation of fine dust out of the impurities in the 
atmosphere of inhabited areas. 
Gases which Act on S0 2 . 
Turning now to the effect of the presence of other gases on S0 2 . As 
previously stated, neither oxygen, nitrogen, nor water vapour has any effect 
on it ; but there are a number of other gases in the atmosphere, especially of 
polluted districts, about which some information is desirable, as these gases 
act on the S0 2 without the aid of light or other outside influence. Along 
with the S0 2 the combustion of coal throws into the atmosphere a 
number of other gases. Amongst these there is 
Ammonia. 
When ammonia and air are tested in the apparatus they are found to 
form no nuclei after being acted on by light, or radio-activity. But if we 
put a little weak solution of S0 2 in the flask S, and some weak ammonia in E, 
we get constant condensation on expansion, and also some spontaneous con- 
densation. As this action, however, can take place in the dark, it is probable 
that any nuclei produced in this way will have already been formed before 
sunrise, so that ammonia does not seem to have anything to do with the 
formation of these morning fogs, though they will add to the early morning 
haze. Another important gas given off during combustion is 
Hydrogen Peroxide. 
If we put a little of the ordinary peroxide solution in the flask E in place 
of the ammonia, and test it alone with filtered air, it will be found to give 
* Proc. Roy. Soc. Edin., vol. xxxi., Part IV., No. 31. 
