215 
1911-12.] The Sun as a Fog Producer. 
effects of the products of burning sulphur, but evidently there is a possi- 
bility of some of the other gases produced during combustion, other than 
those here referred to, playing some part in their formation, either alone or 
in combination with the sulphur compounds. 
It may be as well to call attention to the great difficulties met with in 
experiments of the kind here described. The extreme minuteness of the 
quantities of matter involved, the difficulty in getting purity of materials 
and vessels, and the many complicated influences at work, make experi- 
menting of this kind full of pitfalls ; so that much of what is here advanced 
is likely to have more than the average number of errors usual to physical 
investigations, and, though every care has been taken to make as many 
check experiments as possible, yet some of the conclusions may not be final. 
We can therefore only look on this communication as a first attempt to 
solve the relation between sunshine and a certain class of fogs. 
( Issued separately July 1 , 1912 .) 
