18 
Proceedings of the Royal Society 
that it is hopeless to expect that, adopting more perfect forms of 
combustion than those at present in use, we shall thereby diminish 
the frequency, persistency, or density of our town fogs. More perfect 
combustion will, however, remove the pea-soup character from the fogs 
and make them purer and whiter, by preventing the smoke which at 
present mixes with our town fogs and aggravates their character, and 
prevents them dissolving when they enter our rooms. Smoke de- 
scends during a fog, because the smoke particles are good radiators, 
and soon get cooled and form nuclei on which the water vapour 
condenses. The smoke thus becomes heavier and falls. This 
explains wh y it is falling smoke is often a sign of coming rain. It 
indicates a saturated condition of the atmosphere. 
Sulphur when burned has been shown to be an intensely active 
fog-producer. Calculation shows that there are more than 200 tons 
of sulphur burned with the coal every winter day in London, a 
quantity so enormous as quite to account for the density of the 
London fogs. It is suggested that some restriction ought to be put 
on the amount of sulphur in the coal used in towns. 
Before utterly condensing the smoke and the sulphur, it was 
pointed out that it would be necessary thoroughly to investigate, 
and fully to consider the value of smoke as a deodorizer, and also 
the powerful antiseptic properties of the sulphurous acid formed by 
the burning sulphur. The air during fogs is still and stagnant. 
There is no current to clear away the foul smells and deadly germs 
that float in the air, and which might be more deadly than they are 
were it not for the suspended soot and burned sulphur. We must 
therefore be on our guard lest we substitute a great and hidden 
danger for an evident but less evil. 
2. Solar Eclipse, 31st December 1880. By Mr E. Sang. 
The elements for the compution of eclipses are given in the 
“ Nautical Almanac ” with precision sufficient for all ordinary pur- 
poses ; but, when we wish to compare the lunar ephemeris with 
actual observation for the purpose of verifying or of improving our 
data, we must go somewhat more minutely into the investigation. 
Thus, in the List of Elements, p. 403, the changes in the right- 
ascension and declination of the sun and moon are supposed to be 
