ON FOG. 
37 
Times, that the electric light hardly penetrated further than the 
ordinary gas flame : an observation which can be easily sub- 
stantiated on any foggy night from the parapet of Westminster 
Bridge. The gas flame is notoriously rich in yellow vibra- 
tions ; whereas those that give to the electric arc its dazzling 
and somewhat ghastly brilliancy belong to the violet, and 
even the ultra-violet end of the spectrum. Such vibrations 
would he entirely cancelled by an absorbent medium of mono- 
chromatic vapour, whose wave-length lay in the neighbourhood 
of the D. Sodium lines. It would he an interesting and com- 
plementary experiment to determine whether a strong Sodium 
flame would prove to he exceptionally transmissible through fog : 
certainly the red and flaring 4 links/ made of rope-yarn, plen- 
tifully served with pitch, which used to be brought out on such 
occasions, and which were in the last century carried by foot- 
men behind private carriages, seem to point in this direction. 
The causes, then, of Fog, may he fairly divided into those 
which are climatic, and others which are due to the use of 
mineral coal. Besides these two, locality and geological struc- 
ture must not be overlooked. It is not only unnecessary, hut 
unscientific, to refer points needing investigation of this cha- 
racter to ‘ some magnetical changes/ the nature of which is not 
apparent. This absurd proposition was actually sustained 1 ?y 
Dr. Carpenter at the Society of Arts, and fairly deserves the 
comment of a scientific contemporary, ‘We fancy that Dr. 
Carpenter has written without taking time to think, for it is 
certain that his letter contains some fallacious reasoning based 
on a want of knowledge of the facts.’ 
Very different as specimens of patient induction, free from 
hasty jumping at irrelevant conclusions, are the views of Dr. 
Frankland given above : probably they approach more nearly 
to a scientific solution of the enigma than any others. 
But when the question of practically remedying an acknow- 
ledged evil is raised, the matter becomes more complicated and 
difficult : indeed, different minds seem to have approached the 
topic by various avenues of thought. Captain Gfalton, in his 
lecture, lays especial stress on the climatic and geological 
element. 
‘ The London basin/ he says, ‘ may be described generally 
as formed of clay, which retains the moisture from rainfall ; 
deposits of gravel rest in many places in the clay. These 
deposits are not usually of great depth. The river Thames runs 
through the centre of London. The surface of the metropolitan 
area when built over, is generally well drained, and all mois- 
ture which falls is rapidly removed ; but there are numerous 
spaces not built over, where the rain sinks into the soil, as, for 
instance, the parks, squares, gardens, &c., and there are also 
