244 
POPULAR SCIENCE REYIETV. 
that the fall of the barometer at the centre is itself, in great 
measure, due to the centrifugal force of the revolving mass of 
air. 
Of the various theories which have been propounded to 
account for storms, which are generally more or less cyclonic in 
their character, I shall only mention four. 
1. Some authorities, and amongst them our own countryman 
the Rev. Clement Ley, attribute the formation and subsequent 
progress of a storm to the condensation of moisture, but they 
apparently ignore the fact that many of our very heaviest rains 
do not give rise to cyclonic disturbances of serious character. 
For instance, when on April 10 and 11, 1878, 4*6 inches of 
rain fell at Haverstock Hill, we had no storm of wind at all. 
In partial confirmation of this view, Professor Mohn, of Christi- 
ania, points to the accidental condensation of moisture caused 
by the contact of a mass of damp air with the surface of an 
extensive snowfield as a possible cause of a storm. About the 
61st parallel of latitude the glacier region of Justedal stretches 
for several miles along the coast of Norway, and this has occa- 
sionally been known to exert an influence in increasing the 
intensity of an existing cyclone, and even in some instances has 
appeared as the centre of a newly-formed depression. 
These gentlemen, moreover, rely greatly on the fact that the 
rain area which accompanies every cyclonic system is roughly 
oval in shape, with its longer axis extending in the direction in 
which the system is advancing, and that by far the greatest 
amount of rain falls in front of the storm. They do not, how- 
ever, explain the fact that very heavy rain frequently occurs on 
the northern side of a depression, where the wind is easterly, 
and that this circumstance does not indicate a northward motion 
of the system. 
The most serious objection to this theory is, however, that 
first stated, that not only do the heaviest rains not come with 
the severest storms, but that frequently they are observed in 
times of nearly absolute calm. 
2. The second theory to which I shall refer is the mechanical 
one, most strongly urged by Mr. Meldrum, of the Mauritius, 
whose investigations into the weather over the Indian Ocean 
have led him to the belief that every cyclone is generated in 
the intervening space between two oppositely flowing currents 
of air, of which the easterly moving stream, speaking in the 
most general terms, lies on the polar side of the westerly wind. 
Such a disposition of the currrents would be that which would 
naturally arise were the cyclone once formed. 
This view is called seriously in question by Messrs. Blanford 
and Eliot in their discussion of recent cyclones in the Bay of 
Bengal, which they have been able to study from very early 
