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Proceedings of the Royal Society of Edinburgh. [Sess. 
converting them into fine dust. No attempt has been made to determine 
what is the exact chemical composition of this sensitive gas. All that is 
shown is that it acts in every way like S0 2 . But, further, the sun acts not 
only on these gases, but also on the other constituents of the atmosphere, 
producing substances which act powerfully on the S0 2 , and not only make 
nuclei with it, but also that worst kind, the nuclei of spontaneous condensa- 
tion. Probably the worst of the gases produced by sunshine is the peroxide 
of hydrogen. This gas is generally admitted to be produced by the ultra- 
violet rays of the sun. It is found in dew and in rain, but not in dew 
formed during the night — only in that condensed after sunrise. These 
same ultra-violet rays are also credited with the production of ozone in the 
atmosphere. It would thus appear that during sunshine there are constantly 
being produced both peroxide of hydrogen and ozone, two powerful oxidis- 
ing agents ; and we have seen in a previous part of this communication that 
these gases act powerfully on S0 2 , making with it nuclei which cause 
condensation in unsaturated air, and at the same time increasing the 
number of the ordinary nuclei. The presence of the first form of nuclei 
will therefore add much to the thickness even of air which has some degree 
of dryness. To these influences acting on S0 2 we may possibly add the 
effect of any electric discharge taking place in the atmosphere should the 
sun’s action be shown to increase the current. 
Turning now briefly to the question of the amount of these sulphur 
products in our atmosphere. Is there sufficient of them to account for the 
results attributed to them ? No attempt has been made to ascertain their 
amount in the atmosphere ; but even if we knew, it would not help us 
much, as we do not know how many particles go to a gram. So we can 
here only fall back on what is taking place in our fires to see how much 
sulphur is burned there along with the coal. The consumption of coal in 
this country is something like 200,000,000 tons per annum ; and supposing 
we allow 1 per cent, as the amount of sulphur in them, which is not a high 
estimate, then there are burned something like 2,000,000 tons of sulphur 
every year, which gives an average consumption of over 5000 tons per day, 
more or less, according to the season, etc. The quantity seems enormous, 
one might almost say incredible, and it also represents a colossal waste, to 
say nothing of what might be its money value. From the quantity of 
sulphur burned in our fires, there are evidently enough sulphur products to 
pollute the atmosphere from Land’s End to John o’ Groat’s House. 
In connection with this question of the power of the products of our 
fires to produce sufficient haze after being acted on by sunshine to account 
for all the haze in the air, it may be as well here to recall the results of the 
