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Proceedings of the Royal Society of Edinburgh. [Sess. 
Parliament to make its use compulsory. I think that if the country were 
thoroughly awake to the deleterious effects of the sulphur products, the 
concentration of many minds on the subject would be likely to result in 
some remedy being found. 
Other Considerations. 
Though this investigation clearly points to the great power of sulphur 
products in forming both haze and fog, yet it is evident we have not 
brought sufficient evidence to prove that these products alone, along with 
sunshine, are the cause of morning sunshine fogs. We have, so to speak, 
detected the products leaving their home by the fireside, or furnace, fully 
armed for harm ; but something more is required to show that they really 
bring about the fogging in the manner here suggested. A burglar may 
leave his home fully supplied with the implements of his profession, but 
that is no proof that he has really done any damage ; and though the law 
may punish him, yet in science we must be sure the offence has been 
committed, as it is quite possible the accused may have left his home with 
the power of doing harm, but may with the passage of time lose this power. 
Some change may come over the sulphur products which may alter them 
and make them insensitive to the action of sunshine. In order to complete 
the evidence against them we must find them prowling at night with all 
their powers for evil. We can hardly look for them during the day, as 
the sun will be acting on them and making them into nuclei ; but at night, 
when there is nothing which we know of to change them, we ought to 
be able to detect their presence in the air ; since we have here assumed that 
it is the impurities that have been collecting during the quiet nights that 
the sun acts on, causing the formation of thick haze and fog. 
The detection of these impurities in the air is a very difficult matter. 
In the experiments described the quantities of matter are exceedingly 
small, but in the free atmosphere they are very much less. If we use 
the test for the presence of nuclei of spontaneous condensation — that is, 
by adding peroxide of hydrogen and exposing to light — then the particles 
are too few to form a cone of light in the test-flask, and the individual 
particles are frequently too small to be seen with a lens. Then if we test 
the air for sulphur products by first filtering it, and then adding the per- 
oxide and acting on them with light to see if they are capable of producing 
cloudy condensation on supersaturation by expansion, we are at once met 
with a difficulty in the action of the filter. All filters absorb some of the 
gas, and the air coming through at any particular time is not in the same 
